| //===- GoStatepoints.cpp - Insert statepoints for Go GC -------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // Rewrite call/invoke instructions so as to record live variables on |
| // stack for the use of garbage collector. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "CallingConv.h" |
| #include "GoStatepoints.h" |
| #include "GoStackMap.h" |
| #include "GollvmPasses.h" |
| |
| #include "llvm/ADT/ArrayRef.h" |
| #include "llvm/ADT/BitVector.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DenseSet.h" |
| #include "llvm/ADT/MapVector.h" |
| #include "llvm/ADT/None.h" |
| #include "llvm/ADT/Optional.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/StringRef.h" |
| #include "llvm/ADT/iterator_range.h" |
| #include "llvm/Analysis/DomTreeUpdater.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/IR/Argument.h" |
| #include "llvm/IR/Attributes.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/Constant.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/IRBuilder.h" |
| #include "llvm/IR/InstIterator.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/MDBuilder.h" |
| #include "llvm/IR/Metadata.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Statepoint.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/IR/ValueHandle.h" |
| #include "llvm/Pass.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/PromoteMemToReg.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <cstddef> |
| #include <cstdint> |
| #include <iterator> |
| #include <set> |
| #include <string> |
| #include <utility> |
| #include <vector> |
| |
| #define DEBUG_TYPE "go-statepoints" |
| |
| using namespace llvm; |
| using namespace gollvm::passes; |
| |
| // Print the liveset found at the insert location |
| static cl::opt<bool> PrintLiveSet("gogc-print-liveset", cl::Hidden, |
| cl::init(false)); |
| |
| // Print the liveset only for the specified function. |
| static cl::opt<std::string> PrintFunc("gogc-print-func", cl::Hidden, |
| cl::init("")); |
| |
| // At each statepoint, clobber all the stack slots that are considered |
| // dead, for debugging purposes. |
| static cl::opt<bool> ClobberNonLive("gogc-clobber-non-live", |
| cl::Hidden, cl::init(false)); |
| |
| // Statepoint ID. TODO: this is not thread safe. |
| static uint64_t ID = 0; |
| |
| /// The IR fed into this pass may have had attributes and |
| /// metadata implying dereferenceability that are no longer valid/correct after |
| /// this pass has run. This is because semantically, after |
| /// this pass runs, all calls to gc.statepoint "free" the entire |
| /// heap. stripNonValidData (conservatively) restores |
| /// correctness by erasing all attributes in the module that externally imply |
| /// dereferenceability. Similar reasoning also applies to the noalias |
| /// attributes and metadata. gc.statepoint can touch the entire heap including |
| /// noalias objects. |
| /// Apart from attributes and metadata, we also remove instructions that imply |
| /// constant physical memory: llvm.invariant.start. |
| // |
| // TODO: revisit this. For a non-moving GC some attributes may still be valid. |
| // It probably doesn't really matter, as we run this pass at the end of |
| // optimization pipeline. |
| static void stripNonValidData(Module &M); |
| |
| static bool shouldRewriteStatepointsIn(Function &F); |
| |
| PreservedAnalyses GoStatepoints::run(Module &M, |
| ModuleAnalysisManager &AM) { |
| // Create a sentinel global variable for stack maps. |
| Type *Int64Ty = Type::getInt64Ty(M.getContext()); |
| new GlobalVariable(M, Int64Ty, /* isConstant */ true, |
| GlobalValue::InternalLinkage, |
| ConstantInt::get(Int64Ty, GO_FUNC_SENTINEL), |
| GO_FUNC_SYM); |
| |
| bool Changed = false; |
| auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); |
| for (Function &F : M) { |
| // Nothing to do for declarations. |
| if (F.isDeclaration() || F.empty()) |
| continue; |
| |
| // Policy choice says not to rewrite - the most common reason is that we're |
| // compiling code without a GCStrategy. |
| if (!shouldRewriteStatepointsIn(F)) |
| continue; |
| |
| auto &DT = FAM.getResult<DominatorTreeAnalysis>(F); |
| auto &TTI = FAM.getResult<TargetIRAnalysis>(F); |
| auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F); |
| Changed |= runOnFunction(F, DT, TTI, TLI); |
| } |
| if (!Changed) |
| return PreservedAnalyses::all(); |
| |
| // stripNonValidData asserts that shouldRewriteStatepointsIn |
| // returns true for at least one function in the module. Since at least |
| // one function changed, we know that the precondition is satisfied. |
| stripNonValidData(M); |
| |
| PreservedAnalyses PA; |
| PA.preserve<TargetIRAnalysis>(); |
| PA.preserve<TargetLibraryAnalysis>(); |
| return PA; |
| } |
| |
| namespace { |
| |
| class GoStatepointsLegacyPass : public ModulePass { |
| GoStatepoints Impl; |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| |
| GoStatepointsLegacyPass() : ModulePass(ID), Impl() { |
| initializeGoStatepointsLegacyPassPass( |
| *PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnModule(Module &M) override { |
| // Create a sentinel global variable for stack maps. |
| Type *Int64Ty = Type::getInt64Ty(M.getContext()); |
| new GlobalVariable(M, Int64Ty, /* isConstant */ true, |
| GlobalValue::InternalLinkage, |
| ConstantInt::get(Int64Ty, GO_FUNC_SENTINEL), |
| GO_FUNC_SYM); |
| |
| bool Changed = false; |
| for (Function &F : M) { |
| // Nothing to do for declarations. |
| if (F.isDeclaration() || F.empty()) |
| continue; |
| |
| // Policy choice says not to rewrite - the most common reason is that |
| // we're compiling code without a GCStrategy. |
| if (!shouldRewriteStatepointsIn(F)) |
| continue; |
| |
| const TargetLibraryInfo &TLI = |
| getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); |
| |
| TargetTransformInfo &TTI = |
| getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); |
| auto &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree(); |
| |
| Changed |= Impl.runOnFunction(F, DT, TTI, TLI); |
| } |
| |
| if (!Changed) |
| return false; |
| |
| // stripNonValidData asserts that shouldRewriteStatepointsIn |
| // returns true for at least one function in the module. Since at least |
| // one function changed, we know that the precondition is satisfied. |
| stripNonValidData(M); |
| return true; |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| // We add and rewrite a bunch of instructions, but don't really do much |
| // else. We could in theory preserve a lot more analyses here. |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| AU.addRequired<TargetLibraryInfoWrapperPass>(); |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| char GoStatepointsLegacyPass::ID = 0; |
| |
| ModulePass *llvm::createGoStatepointsLegacyPass() { |
| return new GoStatepointsLegacyPass(); |
| } |
| |
| INITIALIZE_PASS_BEGIN(GoStatepointsLegacyPass, |
| "go-statepoints", |
| "Insert statepoints for Go GC", false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) |
| INITIALIZE_PASS_END(GoStatepointsLegacyPass, |
| "go-statepoints", |
| "Insert statepoints for Go GC", false, false) |
| |
| namespace { |
| |
| // Liveness tracking has three parts: in-register values, non-address-taken |
| // allocas (stack slots), and address-taken allocas. |
| // |
| // In-register values are live since it is defined, until it has no more |
| // use. At statepoints they are spilled so the runtime can find them on |
| // the stack. |
| // |
| // Non-address-taken allocas are live since it is initialized, until it |
| // has no more use. At statepoints they are not spilled but its stack |
| // location is recorded. |
| // |
| // Address-taken allocas are live since it is initialized and remain live |
| // thereafter, unless an explicit lifetime.end is seen. As above, they |
| // are not spilled at statepoints but has its stack location recorded. |
| // |
| // In the data structure, there are some overlap. The live sets are used |
| // for both in-register values and non-address-taken allocas, but not |
| // for address-taken allocas. The alloca def/kill sets are used for both |
| // kinds of allocas. |
| struct GCPtrLivenessData { |
| // In-register value and non-address-taken alloca. |
| |
| /// Values defined in this block. |
| MapVector<BasicBlock *, SetVector<Value *>> KillSet; |
| /// Values used in this block (and thus live); does not included values |
| /// killed within this block. |
| MapVector<BasicBlock *, SetVector<Value *>> LiveSet; |
| /// Values live into this basic block (i.e. used by any |
| /// instruction in this basic block or ones reachable from here) |
| MapVector<BasicBlock *, SetVector<Value *>> LiveIn; |
| /// Values live out of this basic block (i.e. live into |
| /// any successor block) |
| MapVector<BasicBlock *, SetVector<Value *>> LiveOut; |
| |
| // Alloca liveness. |
| |
| MapVector<BasicBlock *, SetVector<Value *>> AllocaDefSet; // initialized in BB |
| MapVector<BasicBlock *, SetVector<Value *>> AllocaKillSet; // killed (lifetime.end) in BB |
| |
| // Unlike above, these are propagated forwards, instead of backwards. |
| MapVector<BasicBlock *, SetVector<Value *>> AllocaDefAny; // initialized at any path reaching the end of BB |
| MapVector<BasicBlock *, SetVector<Value *>> AllocaDefAll; // initialized at all paths reaching the end of BB |
| }; |
| |
| // The type of the internal cache used inside the findBasePointers family |
| // of functions. From the callers perspective, this is an opaque type and |
| // should not be inspected. |
| // |
| // In the actual implementation this caches two relations: |
| // - The base relation itself (i.e. this pointer is based on that one) |
| // - The base defining value relation (i.e. before base_phi insertion) |
| // Generally, after the execution of a full findBasePointer call, only the |
| // base relation will remain. Internally, we add a mixture of the two |
| // types, then update all the second type to the first type |
| using DefiningValueMapTy = MapVector<Value *, Value *>; |
| using StatepointLiveSetTy = SetVector<Value *>; |
| using RematerializedValueMapTy = |
| MapVector<AssertingVH<Instruction>, AssertingVH<Value>>; |
| |
| struct PartiallyConstructedSafepointRecord { |
| /// The set of values known to be live across this safepoint |
| StatepointLiveSetTy LiveSet; |
| |
| /// Mapping from live pointers to a base-defining-value |
| MapVector<Value *, Value *> PointerToBase; |
| |
| /// The *new* gc.statepoint instruction itself. This produces the token |
| /// that normal path gc.relocates and the gc.result are tied to. |
| GCStatepointInst *StatepointToken; |
| |
| /// Instruction to which exceptional gc relocates are attached |
| /// Makes it easier to iterate through them during relocationViaAlloca. |
| Instruction *UnwindToken; |
| |
| /// Record live values we are rematerialized instead of relocating. |
| /// They are not included into 'LiveSet' field. |
| /// Maps rematerialized copy to it's original value. |
| RematerializedValueMapTy RematerializedValues; |
| }; |
| |
| } // end anonymous namespace |
| |
| /// Compute the live-in set for every basic block in the function |
| static void computeLiveInValues(DominatorTree &DT, Function &F, |
| GCPtrLivenessData &Data, |
| SetVector<Value *> &AddrTakenAllocas, |
| SetVector<Value *> &ToZero, |
| SetVector<Value *> &BadLoads, |
| DefiningValueMapTy &DVCache); |
| |
| /// Given results from the dataflow liveness computation, find the set of live |
| /// Values at a particular instruction. |
| static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data, |
| SetVector<Value *> &AddrTakenAllocas, |
| StatepointLiveSetTy &out, |
| SetVector<Value *> &AllAllocas, |
| DefiningValueMapTy &DVCache); |
| |
| // TODO: Once we can get to the GCStrategy, this becomes |
| // Optional<bool> isGCManagedPointer(const Type *Ty) const override { |
| |
| static bool isGCPointerType(Type *T) { |
| return isa<PointerType>(T); |
| } |
| |
| // Return true if this type is one which a) is a gc pointer or contains a GC |
| // pointer and b) is of a type this code expects to encounter as a live value. |
| // (The insertion code will assert that a type which matches (a) and not (b) |
| // is not encountered.) |
| static bool isHandledGCPointerType(Type *T) { |
| // We fully support gc pointers |
| if (isGCPointerType(T)) |
| return true; |
| // We partially support vectors of gc pointers. The code will assert if it |
| // can't handle something. |
| if (auto VT = dyn_cast<VectorType>(T)) |
| if (isGCPointerType(VT->getElementType())) |
| return true; |
| // FCA is supported. |
| if (T->isStructTy()) |
| return hasPointer(T); |
| return false; |
| } |
| |
| #ifndef NDEBUG |
| /// Returns true if this type contains a gc pointer whether we know how to |
| /// handle that type or not. |
| static bool containsGCPtrType(Type *Ty) { |
| if (isGCPointerType(Ty)) |
| return true; |
| if (VectorType *VT = dyn_cast<VectorType>(Ty)) |
| return isGCPointerType(VT->getScalarType()); |
| if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) |
| return containsGCPtrType(AT->getElementType()); |
| if (StructType *ST = dyn_cast<StructType>(Ty)) |
| return llvm::any_of(ST->subtypes(), containsGCPtrType); |
| return false; |
| } |
| |
| // Returns true if this is a type which a) is a gc pointer or contains a GC |
| // pointer and b) is of a type which the code doesn't expect (i.e. first class |
| // aggregates). Used to trip assertions. |
| static bool isUnhandledGCPointerType(Type *Ty) { |
| return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty); |
| } |
| #endif |
| |
| // Return the name of the value suffixed with the provided value, or if the |
| // value didn't have a name, the default value specified. |
| static std::string suffixed_name_or(Value *V, StringRef Suffix, |
| StringRef DefaultName) { |
| return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str(); |
| } |
| |
| // Helper function to print a live set, for debugging. |
| static void |
| printLiveSet(SetVector<Value *> &LiveSet) { |
| for (Value *V : LiveSet) |
| dbgs() << "\t" << *V << "\n"; |
| } |
| |
| // Conservatively identifies any definitions which might be live at the |
| // given instruction. The analysis is performed immediately before the |
| // given instruction. Values defined by that instruction are not considered |
| // live. Values used by that instruction are considered live. |
| static void |
| analyzeParsePointLiveness(DominatorTree &DT, |
| GCPtrLivenessData &OriginalLivenessData, |
| SetVector<Value *> &AddrTakenAllocas, CallBase *Call, |
| PartiallyConstructedSafepointRecord &Result, |
| SetVector<Value *> &AllAllocas, |
| DefiningValueMapTy &DVCache) { |
| StatepointLiveSetTy LiveSet; |
| findLiveSetAtInst(Call, OriginalLivenessData, AddrTakenAllocas, |
| LiveSet, AllAllocas, DVCache); |
| |
| if (PrintLiveSet) { |
| dbgs() << "Live Variables at " << *Call << ":\n"; |
| printLiveSet(LiveSet); |
| } |
| Result.LiveSet = LiveSet; |
| } |
| |
| static bool isKnownBaseResult(Value *V); |
| |
| namespace { |
| |
| /// A single base defining value - An immediate base defining value for an |
| /// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'. |
| /// For instructions which have multiple pointer [vector] inputs or that |
| /// transition between vector and scalar types, there is no immediate base |
| /// defining value. The 'base defining value' for 'Def' is the transitive |
| /// closure of this relation stopping at the first instruction which has no |
| /// immediate base defining value. The b.d.v. might itself be a base pointer, |
| /// but it can also be an arbitrary derived pointer. |
| struct BaseDefiningValueResult { |
| /// Contains the value which is the base defining value. |
| Value * const BDV; |
| |
| /// True if the base defining value is also known to be an actual base |
| /// pointer. |
| const bool IsKnownBase; |
| |
| BaseDefiningValueResult(Value *BDV, bool IsKnownBase) |
| : BDV(BDV), IsKnownBase(IsKnownBase) { |
| #ifndef NDEBUG |
| // Check consistency between new and old means of checking whether a BDV is |
| // a base. |
| bool MustBeBase = isKnownBaseResult(BDV); |
| assert(!MustBeBase || MustBeBase == IsKnownBase); |
| #endif |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| static BaseDefiningValueResult findBaseDefiningValue(Value *I); |
| |
| /// Return a base defining value for the 'Index' element of the given vector |
| /// instruction 'I'. If Index is null, returns a BDV for the entire vector |
| /// 'I'. As an optimization, this method will try to determine when the |
| /// element is known to already be a base pointer. If this can be established, |
| /// the second value in the returned pair will be true. Note that either a |
| /// vector or a pointer typed value can be returned. For the former, the |
| /// vector returned is a BDV (and possibly a base) of the entire vector 'I'. |
| /// If the later, the return pointer is a BDV (or possibly a base) for the |
| /// particular element in 'I'. |
| static BaseDefiningValueResult |
| findBaseDefiningValueOfVector(Value *I) { |
| // Each case parallels findBaseDefiningValue below, see that code for |
| // detailed motivation. |
| |
| if (isa<Argument>(I)) |
| // An incoming argument to the function is a base pointer |
| return BaseDefiningValueResult(I, true); |
| |
| if (isa<Constant>(I)) |
| // Base of constant vector consists only of constant null pointers. |
| // For reasoning see similar case inside 'findBaseDefiningValue' function. |
| return BaseDefiningValueResult(ConstantAggregateZero::get(I->getType()), |
| true); |
| |
| if (isa<LoadInst>(I)) |
| return BaseDefiningValueResult(I, true); |
| |
| if (isa<InsertElementInst>(I)) |
| // We don't know whether this vector contains entirely base pointers or |
| // not. To be conservatively correct, we treat it as a BDV and will |
| // duplicate code as needed to construct a parallel vector of bases. |
| return BaseDefiningValueResult(I, false); |
| |
| if (isa<ShuffleVectorInst>(I)) |
| // We don't know whether this vector contains entirely base pointers or |
| // not. To be conservatively correct, we treat it as a BDV and will |
| // duplicate code as needed to construct a parallel vector of bases. |
| // TODO: There a number of local optimizations which could be applied here |
| // for particular sufflevector patterns. |
| return BaseDefiningValueResult(I, false); |
| |
| // The behavior of getelementptr instructions is the same for vector and |
| // non-vector data types. |
| if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) |
| return findBaseDefiningValue(GEP->getPointerOperand()); |
| |
| // If the pointer comes through a bitcast of a vector of pointers to |
| // a vector of another type of pointer, then look through the bitcast |
| if (auto *BC = dyn_cast<BitCastInst>(I)) |
| return findBaseDefiningValue(BC->getOperand(0)); |
| |
| // We assume that functions in the source language only return base |
| // pointers. This should probably be generalized via attributes to support |
| // both source language and internal functions. |
| if (isa<CallInst>(I) || isa<InvokeInst>(I)) |
| return BaseDefiningValueResult(I, true); |
| |
| // A PHI or Select is a base defining value. The outer findBasePointer |
| // algorithm is responsible for constructing a base value for this BDV. |
| assert((isa<SelectInst>(I) || isa<PHINode>(I)) && |
| "unknown vector instruction - no base found for vector element"); |
| return BaseDefiningValueResult(I, false); |
| } |
| |
| /// Helper function for findBasePointer - Will return a value which either a) |
| /// defines the base pointer for the input, b) blocks the simple search |
| /// (i.e. a PHI or Select of two derived pointers), or c) involves a change |
| /// from pointer to vector type or back. |
| static BaseDefiningValueResult findBaseDefiningValue(Value *I) { |
| if (I->getType()->isStructTy()) |
| // Assuming FCA is always base. |
| // FCAs appear mostly in the call sequnce where we pass/return multiple |
| // values in registers, e.g. { i8*, i64 }. If it contains the address of |
| // an alloca, the alloca should already be address taken (at least when |
| // creating the FCA), so we don't need to link the FCA back to the alloca. |
| // It is also unlikely to contain past-the-end pointer (we cannot do |
| // pointer arithmetic directly with FCA). So it is safe to treat FCA as |
| // base. |
| return BaseDefiningValueResult(I, true); |
| |
| assert(I->getType()->isPtrOrPtrVectorTy() && |
| "Illegal to ask for the base pointer of a non-pointer type"); |
| |
| if (I->getType()->isVectorTy()) |
| return findBaseDefiningValueOfVector(I); |
| |
| if (isa<Argument>(I)) |
| // An incoming argument to the function is a base pointer |
| // We should have never reached here if this argument isn't an gc value |
| return BaseDefiningValueResult(I, true); |
| |
| if (isa<Constant>(I)) { |
| // We assume that objects with a constant base (e.g. a global) can't move |
| // and don't need to be reported to the collector because they are always |
| // live. Besides global references, all kinds of constants (e.g. undef, |
| // constant expressions, null pointers) can be introduced by the inliner or |
| // the optimizer, especially on dynamically dead paths. |
| // Here we treat all of them as having single null base. By doing this we |
| // trying to avoid problems reporting various conflicts in a form of |
| // "phi (const1, const2)" or "phi (const, regular gc ptr)". |
| // See constant.ll file for relevant test cases. |
| |
| return BaseDefiningValueResult( |
| ConstantPointerNull::get(cast<PointerType>(I->getType())), true); |
| } |
| |
| if (CastInst *CI = dyn_cast<CastInst>(I)) { |
| Value *Def = CI->stripPointerCasts(); |
| if (isa<IntToPtrInst>(Def)) |
| // Pointer converted from integer is a base. |
| return BaseDefiningValueResult(Def, true); |
| |
| // Pointer-to-pointer and int-to-pointer casts are handled above. |
| // We don't know how to handle other type of casts. |
| assert(!isa<CastInst>(Def) && "shouldn't find another cast here"); |
| return findBaseDefiningValue(Def); |
| } |
| |
| if (isa<AllocaInst>(I)) |
| // alloca is a gc base |
| return BaseDefiningValueResult(I, true); |
| |
| if (isa<LoadInst>(I)) |
| // The value loaded is a gc base itself |
| return BaseDefiningValueResult(I, true); |
| |
| if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) |
| // The base of this GEP is the base |
| return findBaseDefiningValue(GEP->getPointerOperand()); |
| |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { |
| switch (II->getIntrinsicID()) { |
| default: |
| // fall through to general call handling |
| break; |
| case Intrinsic::experimental_gc_statepoint: |
| llvm_unreachable("statepoints don't produce pointers"); |
| case Intrinsic::experimental_gc_relocate: |
| // Rerunning safepoint insertion after safepoints are already |
| // inserted is not supported. It could probably be made to work, |
| // but why are you doing this? There's no good reason. |
| llvm_unreachable("repeat safepoint insertion is not supported"); |
| case Intrinsic::gcroot: |
| // Currently, this mechanism hasn't been extended to work with gcroot. |
| // There's no reason it couldn't be, but I haven't thought about the |
| // implications much. |
| llvm_unreachable( |
| "interaction with the gcroot mechanism is not supported"); |
| } |
| } |
| // We assume that functions in the source language only return base |
| // pointers. This should probably be generalized via attributes to support |
| // both source language and internal functions. |
| if (isa<CallInst>(I) || isa<InvokeInst>(I)) |
| return BaseDefiningValueResult(I, true); |
| |
| // TODO: I have absolutely no idea how to implement this part yet. It's not |
| // necessarily hard, I just haven't really looked at it yet. |
| assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented"); |
| |
| if (isa<AtomicCmpXchgInst>(I)) |
| // A CAS is effectively a atomic store and load combined under a |
| // predicate. From the perspective of base pointers, we just treat it |
| // like a load. |
| return BaseDefiningValueResult(I, true); |
| |
| assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are " |
| "binary ops which don't apply to pointers"); |
| |
| // The aggregate ops. Aggregates can either be in the heap or on the |
| // stack, but in either case, this is simply a field load. As a result, |
| // this is a defining definition of the base just like a load is. |
| if (isa<ExtractValueInst>(I)) |
| return BaseDefiningValueResult(I, true); |
| |
| // We should never see an insert vector since that would require we be |
| // tracing back a struct value not a pointer value. |
| assert(!isa<InsertValueInst>(I) && |
| "Base pointer for a struct is meaningless"); |
| |
| // An extractelement produces a base result exactly when it's input does. |
| // We may need to insert a parallel instruction to extract the appropriate |
| // element out of the base vector corresponding to the input. Given this, |
| // it's analogous to the phi and select case even though it's not a merge. |
| if (isa<ExtractElementInst>(I)) |
| // Note: There a lot of obvious peephole cases here. This are deliberately |
| // handled after the main base pointer inference algorithm to make writing |
| // test cases to exercise that code easier. |
| return BaseDefiningValueResult(I, false); |
| |
| // The last two cases here don't return a base pointer. Instead, they |
| // return a value which dynamically selects from among several base |
| // derived pointers (each with it's own base potentially). It's the job of |
| // the caller to resolve these. |
| assert((isa<SelectInst>(I) || isa<PHINode>(I)) && |
| "missing instruction case in findBaseDefiningValing"); |
| return BaseDefiningValueResult(I, false); |
| } |
| |
| /// Returns the base defining value for this value. |
| static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) { |
| Value *&Cached = Cache[I]; |
| if (!Cached) { |
| Cached = findBaseDefiningValue(I).BDV; |
| LLVM_DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> " |
| << Cached->getName() << "\n"); |
| } |
| assert(Cache[I] != nullptr); |
| return Cached; |
| } |
| |
| /// Return a base pointer for this value if known. Otherwise, return it's |
| /// base defining value. |
| static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) { |
| Value *Def = findBaseDefiningValueCached(I, Cache); |
| auto Found = Cache.find(Def); |
| if (Found != Cache.end()) { |
| // Either a base-of relation, or a self reference. Caller must check. |
| return Found->second; |
| } |
| // Only a BDV available |
| return Def; |
| } |
| |
| /// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV, |
| /// is it known to be a base pointer? Or do we need to continue searching. |
| static bool isKnownBaseResult(Value *V) { |
| if (!isa<PHINode>(V) && !isa<SelectInst>(V) && |
| !isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) && |
| !isa<ShuffleVectorInst>(V)) { |
| // no recursion possible |
| return true; |
| } |
| if (isa<Instruction>(V) && |
| cast<Instruction>(V)->getMetadata("is_base_value")) { |
| // This is a previously inserted base phi or select. We know |
| // that this is a base value. |
| return true; |
| } |
| |
| // We need to keep searching |
| return false; |
| } |
| |
| namespace { |
| |
| /// Models the state of a single base defining value in the findBasePointer |
| /// algorithm for determining where a new instruction is needed to propagate |
| /// the base of this BDV. |
| class BDVState { |
| public: |
| enum Status { Unknown, Base, Conflict }; |
| |
| BDVState() : BaseValue(nullptr) {} |
| |
| explicit BDVState(Status Status, Value *BaseValue = nullptr) |
| : Status(Status), BaseValue(BaseValue) { |
| assert(Status != Base || BaseValue); |
| } |
| |
| explicit BDVState(Value *BaseValue) : Status(Base), BaseValue(BaseValue) {} |
| |
| Status getStatus() const { return Status; } |
| Value *getBaseValue() const { return BaseValue; } |
| |
| bool isBase() const { return getStatus() == Base; } |
| bool isUnknown() const { return getStatus() == Unknown; } |
| bool isConflict() const { return getStatus() == Conflict; } |
| |
| bool operator==(const BDVState &Other) const { |
| return BaseValue == Other.BaseValue && Status == Other.Status; |
| } |
| |
| bool operator!=(const BDVState &other) const { return !(*this == other); } |
| |
| LLVM_DUMP_METHOD |
| void dump() const { |
| print(dbgs()); |
| dbgs() << '\n'; |
| } |
| |
| void print(raw_ostream &OS) const { |
| switch (getStatus()) { |
| case Unknown: |
| OS << "U"; |
| break; |
| case Base: |
| OS << "B"; |
| break; |
| case Conflict: |
| OS << "C"; |
| break; |
| } |
| OS << " (" << getBaseValue() << " - " |
| << (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): "; |
| } |
| |
| private: |
| Status Status = Unknown; |
| AssertingVH<Value> BaseValue; // Non-null only if Status == Base. |
| }; |
| |
| } // end anonymous namespace |
| |
| #ifndef NDEBUG |
| static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) { |
| State.print(OS); |
| return OS; |
| } |
| #endif |
| |
| static BDVState meetBDVStateImpl(const BDVState &LHS, const BDVState &RHS) { |
| switch (LHS.getStatus()) { |
| case BDVState::Unknown: |
| return RHS; |
| |
| case BDVState::Base: |
| assert(LHS.getBaseValue() && "can't be null"); |
| if (RHS.isUnknown()) |
| return LHS; |
| |
| if (RHS.isBase()) { |
| if (LHS.getBaseValue() == RHS.getBaseValue()) { |
| assert(LHS == RHS && "equality broken!"); |
| return LHS; |
| } |
| return BDVState(BDVState::Conflict); |
| } |
| assert(RHS.isConflict() && "only three states!"); |
| return BDVState(BDVState::Conflict); |
| |
| case BDVState::Conflict: |
| return LHS; |
| } |
| llvm_unreachable("only three states!"); |
| } |
| |
| // Values of type BDVState form a lattice, and this function implements the meet |
| // operation. |
| static BDVState meetBDVState(const BDVState &LHS, const BDVState &RHS) { |
| BDVState Result = meetBDVStateImpl(LHS, RHS); |
| assert(Result == meetBDVStateImpl(RHS, LHS) && |
| "Math is wrong: meet does not commute!"); |
| return Result; |
| } |
| |
| /// For a given value or instruction, figure out what base ptr its derived from. |
| /// For gc objects, this is simply itself. On success, returns a value which is |
| /// the base pointer. (This is reliable and can be used for relocation.) On |
| /// failure, returns nullptr. |
| static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache) { |
| Value *Def = findBaseOrBDV(I, Cache); |
| |
| if (isKnownBaseResult(Def)) |
| return Def; |
| |
| // Here's the rough algorithm: |
| // - For every SSA value, construct a mapping to either an actual base |
| // pointer or a PHI which obscures the base pointer. |
| // - Construct a mapping from PHI to unknown TOP state. Use an |
| // optimistic algorithm to propagate base pointer information. Lattice |
| // looks like: |
| // UNKNOWN |
| // b1 b2 b3 b4 |
| // CONFLICT |
| // When algorithm terminates, all PHIs will either have a single concrete |
| // base or be in a conflict state. |
| // - For every conflict, insert a dummy PHI node without arguments. Add |
| // these to the base[Instruction] = BasePtr mapping. For every |
| // non-conflict, add the actual base. |
| // - For every conflict, add arguments for the base[a] of each input |
| // arguments. |
| // |
| // Note: A simpler form of this would be to add the conflict form of all |
| // PHIs without running the optimistic algorithm. This would be |
| // analogous to pessimistic data flow and would likely lead to an |
| // overall worse solution. |
| |
| #ifndef NDEBUG |
| auto isExpectedBDVType = [](Value *BDV) { |
| return isa<PHINode>(BDV) || isa<SelectInst>(BDV) || |
| isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV) || |
| isa<ShuffleVectorInst>(BDV); |
| }; |
| #endif |
| |
| // Once populated, will contain a mapping from each potentially non-base BDV |
| // to a lattice value (described above) which corresponds to that BDV. |
| // We use the order of insertion (DFS over the def/use graph) to provide a |
| // stable deterministic ordering for visiting DenseMaps (which are unordered) |
| // below. This is important for deterministic compilation. |
| MapVector<Value *, BDVState> States; |
| |
| // Recursively fill in all base defining values reachable from the initial |
| // one for which we don't already know a definite base value for |
| /* scope */ { |
| SmallVector<Value*, 16> Worklist; |
| Worklist.push_back(Def); |
| States.insert({Def, BDVState()}); |
| while (!Worklist.empty()) { |
| Value *Current = Worklist.pop_back_val(); |
| assert(!isKnownBaseResult(Current) && "why did it get added?"); |
| |
| auto visitIncomingValue = [&](Value *InVal) { |
| Value *Base = findBaseOrBDV(InVal, Cache); |
| if (isKnownBaseResult(Base)) |
| // Known bases won't need new instructions introduced and can be |
| // ignored safely |
| return; |
| assert(isExpectedBDVType(Base) && "the only non-base values " |
| "we see should be base defining values"); |
| if (States.insert(std::make_pair(Base, BDVState())).second) |
| Worklist.push_back(Base); |
| }; |
| if (PHINode *PN = dyn_cast<PHINode>(Current)) { |
| for (Value *InVal : PN->incoming_values()) |
| visitIncomingValue(InVal); |
| } else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) { |
| visitIncomingValue(SI->getTrueValue()); |
| visitIncomingValue(SI->getFalseValue()); |
| } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) { |
| visitIncomingValue(EE->getVectorOperand()); |
| } else if (auto *IE = dyn_cast<InsertElementInst>(Current)) { |
| visitIncomingValue(IE->getOperand(0)); // vector operand |
| visitIncomingValue(IE->getOperand(1)); // scalar operand |
| } else if (auto *SV = dyn_cast<ShuffleVectorInst>(Current)) { |
| visitIncomingValue(SV->getOperand(0)); |
| visitIncomingValue(SV->getOperand(1)); |
| } |
| else { |
| llvm_unreachable("Unimplemented instruction case"); |
| } |
| } |
| } |
| |
| #ifndef NDEBUG |
| LLVM_DEBUG(dbgs() << "States after initialization:\n"); |
| for (auto Pair : States) { |
| LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); |
| } |
| #endif |
| |
| // Return a phi state for a base defining value. We'll generate a new |
| // base state for known bases and expect to find a cached state otherwise. |
| auto getStateForBDV = [&](Value *baseValue) { |
| if (isKnownBaseResult(baseValue)) |
| return BDVState(baseValue); |
| auto I = States.find(baseValue); |
| assert(I != States.end() && "lookup failed!"); |
| return I->second; |
| }; |
| |
| bool Progress = true; |
| while (Progress) { |
| #ifndef NDEBUG |
| const size_t OldSize = States.size(); |
| #endif |
| Progress = false; |
| // We're only changing values in this loop, thus safe to keep iterators. |
| // Since this is computing a fixed point, the order of visit does not |
| // effect the result. TODO: We could use a worklist here and make this run |
| // much faster. |
| for (auto Pair : States) { |
| Value *BDV = Pair.first; |
| assert(!isKnownBaseResult(BDV) && "why did it get added?"); |
| |
| // Given an input value for the current instruction, return a BDVState |
| // instance which represents the BDV of that value. |
| auto getStateForInput = [&](Value *V) mutable { |
| Value *BDV = findBaseOrBDV(V, Cache); |
| return getStateForBDV(BDV); |
| }; |
| |
| BDVState NewState; |
| if (SelectInst *SI = dyn_cast<SelectInst>(BDV)) { |
| NewState = meetBDVState(NewState, getStateForInput(SI->getTrueValue())); |
| NewState = |
| meetBDVState(NewState, getStateForInput(SI->getFalseValue())); |
| } else if (PHINode *PN = dyn_cast<PHINode>(BDV)) { |
| for (Value *Val : PN->incoming_values()) |
| NewState = meetBDVState(NewState, getStateForInput(Val)); |
| } else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) { |
| // The 'meet' for an extractelement is slightly trivial, but it's still |
| // useful in that it drives us to conflict if our input is. |
| NewState = |
| meetBDVState(NewState, getStateForInput(EE->getVectorOperand())); |
| } else if (auto *IE = dyn_cast<InsertElementInst>(BDV)){ |
| // Given there's a inherent type mismatch between the operands, will |
| // *always* produce Conflict. |
| NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(0))); |
| NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(1))); |
| } else { |
| // The only instance this does not return a Conflict is when both the |
| // vector operands are the same vector. |
| auto *SV = cast<ShuffleVectorInst>(BDV); |
| NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(0))); |
| NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(1))); |
| } |
| |
| BDVState OldState = States[BDV]; |
| if (OldState != NewState) { |
| Progress = true; |
| States[BDV] = NewState; |
| } |
| } |
| |
| assert(OldSize == States.size() && |
| "fixed point shouldn't be adding any new nodes to state"); |
| } |
| |
| #ifndef NDEBUG |
| LLVM_DEBUG(dbgs() << "States after meet iteration:\n"); |
| for (auto Pair : States) { |
| LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); |
| } |
| #endif |
| |
| // Insert Phis for all conflicts |
| // TODO: adjust naming patterns to avoid this order of iteration dependency |
| for (auto Pair : States) { |
| Instruction *I = cast<Instruction>(Pair.first); |
| BDVState State = Pair.second; |
| assert(!isKnownBaseResult(I) && "why did it get added?"); |
| assert(!State.isUnknown() && "Optimistic algorithm didn't complete!"); |
| |
| // extractelement instructions are a bit special in that we may need to |
| // insert an extract even when we know an exact base for the instruction. |
| // The problem is that we need to convert from a vector base to a scalar |
| // base for the particular indice we're interested in. |
| if (State.isBase() && isa<ExtractElementInst>(I) && |
| isa<VectorType>(State.getBaseValue()->getType())) { |
| auto *EE = cast<ExtractElementInst>(I); |
| // TODO: In many cases, the new instruction is just EE itself. We should |
| // exploit this, but can't do it here since it would break the invariant |
| // about the BDV not being known to be a base. |
| auto *BaseInst = ExtractElementInst::Create( |
| State.getBaseValue(), EE->getIndexOperand(), "base_ee", EE); |
| BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); |
| States[I] = BDVState(BDVState::Base, BaseInst); |
| } |
| |
| // Since we're joining a vector and scalar base, they can never be the |
| // same. As a result, we should always see insert element having reached |
| // the conflict state. |
| assert(!isa<InsertElementInst>(I) || State.isConflict()); |
| |
| if (!State.isConflict()) |
| continue; |
| |
| /// Create and insert a new instruction which will represent the base of |
| /// the given instruction 'I'. |
| auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* { |
| if (isa<PHINode>(I)) { |
| BasicBlock *BB = I->getParent(); |
| int NumPreds = pred_size(BB); |
| assert(NumPreds > 0 && "how did we reach here"); |
| std::string Name = suffixed_name_or(I, ".base", "base_phi"); |
| return PHINode::Create(I->getType(), NumPreds, Name, I); |
| } else if (SelectInst *SI = dyn_cast<SelectInst>(I)) { |
| // The undef will be replaced later |
| UndefValue *Undef = UndefValue::get(SI->getType()); |
| std::string Name = suffixed_name_or(I, ".base", "base_select"); |
| return SelectInst::Create(SI->getCondition(), Undef, Undef, Name, SI); |
| } else if (auto *EE = dyn_cast<ExtractElementInst>(I)) { |
| UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType()); |
| std::string Name = suffixed_name_or(I, ".base", "base_ee"); |
| return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name, |
| EE); |
| } else if (auto *IE = dyn_cast<InsertElementInst>(I)) { |
| UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType()); |
| UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType()); |
| std::string Name = suffixed_name_or(I, ".base", "base_ie"); |
| return InsertElementInst::Create(VecUndef, ScalarUndef, |
| IE->getOperand(2), Name, IE); |
| } else { |
| auto *SV = cast<ShuffleVectorInst>(I); |
| UndefValue *VecUndef = UndefValue::get(SV->getOperand(0)->getType()); |
| std::string Name = suffixed_name_or(I, ".base", "base_sv"); |
| return new ShuffleVectorInst(VecUndef, VecUndef, SV->getOperand(2), |
| Name, SV); |
| } |
| }; |
| Instruction *BaseInst = MakeBaseInstPlaceholder(I); |
| // Add metadata marking this as a base value |
| BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); |
| States[I] = BDVState(BDVState::Conflict, BaseInst); |
| } |
| |
| // Returns a instruction which produces the base pointer for a given |
| // instruction. The instruction is assumed to be an input to one of the BDVs |
| // seen in the inference algorithm above. As such, we must either already |
| // know it's base defining value is a base, or have inserted a new |
| // instruction to propagate the base of it's BDV and have entered that newly |
| // introduced instruction into the state table. In either case, we are |
| // assured to be able to determine an instruction which produces it's base |
| // pointer. |
| auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) { |
| Value *BDV = findBaseOrBDV(Input, Cache); |
| Value *Base = nullptr; |
| if (isKnownBaseResult(BDV)) { |
| Base = BDV; |
| } else { |
| // Either conflict or base. |
| assert(States.count(BDV)); |
| Base = States[BDV].getBaseValue(); |
| } |
| assert(Base && "Can't be null"); |
| // The cast is needed since base traversal may strip away bitcasts |
| if (Base->getType() != Input->getType() && InsertPt) |
| Base = CastInst::CreatePointerBitCastOrAddrSpaceCast(Base, Input->getType(), "cast", InsertPt); |
| return Base; |
| }; |
| |
| // Fixup all the inputs of the new PHIs. Visit order needs to be |
| // deterministic and predictable because we're naming newly created |
| // instructions. |
| for (auto Pair : States) { |
| Instruction *BDV = cast<Instruction>(Pair.first); |
| BDVState State = Pair.second; |
| |
| assert(!isKnownBaseResult(BDV) && "why did it get added?"); |
| assert(!State.isUnknown() && "Optimistic algorithm didn't complete!"); |
| if (!State.isConflict()) |
| continue; |
| |
| if (PHINode *BasePHI = dyn_cast<PHINode>(State.getBaseValue())) { |
| PHINode *PN = cast<PHINode>(BDV); |
| unsigned NumPHIValues = PN->getNumIncomingValues(); |
| for (unsigned i = 0; i < NumPHIValues; i++) { |
| Value *InVal = PN->getIncomingValue(i); |
| BasicBlock *InBB = PN->getIncomingBlock(i); |
| |
| // If we've already seen InBB, add the same incoming value |
| // we added for it earlier. The IR verifier requires phi |
| // nodes with multiple entries from the same basic block |
| // to have the same incoming value for each of those |
| // entries. If we don't do this check here and basephi |
| // has a different type than base, we'll end up adding two |
| // bitcasts (and hence two distinct values) as incoming |
| // values for the same basic block. |
| |
| int BlockIndex = BasePHI->getBasicBlockIndex(InBB); |
| if (BlockIndex != -1) { |
| Value *OldBase = BasePHI->getIncomingValue(BlockIndex); |
| BasePHI->addIncoming(OldBase, InBB); |
| |
| #ifndef NDEBUG |
| Value *Base = getBaseForInput(InVal, nullptr); |
| // In essence this assert states: the only way two values |
| // incoming from the same basic block may be different is by |
| // being different bitcasts of the same value. A cleanup |
| // that remains TODO is changing findBaseOrBDV to return an |
| // llvm::Value of the correct type (and still remain pure). |
| // This will remove the need to add bitcasts. |
| assert(Base->stripPointerCasts() == OldBase->stripPointerCasts() && |
| "Sanity -- findBaseOrBDV should be pure!"); |
| #endif |
| continue; |
| } |
| |
| // Find the instruction which produces the base for each input. We may |
| // need to insert a bitcast in the incoming block. |
| // TODO: Need to split critical edges if insertion is needed |
| Value *Base = getBaseForInput(InVal, InBB->getTerminator()); |
| BasePHI->addIncoming(Base, InBB); |
| } |
| assert(BasePHI->getNumIncomingValues() == NumPHIValues); |
| } else if (SelectInst *BaseSI = |
| dyn_cast<SelectInst>(State.getBaseValue())) { |
| SelectInst *SI = cast<SelectInst>(BDV); |
| |
| // Find the instruction which produces the base for each input. |
| // We may need to insert a bitcast. |
| BaseSI->setTrueValue(getBaseForInput(SI->getTrueValue(), BaseSI)); |
| BaseSI->setFalseValue(getBaseForInput(SI->getFalseValue(), BaseSI)); |
| } else if (auto *BaseEE = |
| dyn_cast<ExtractElementInst>(State.getBaseValue())) { |
| Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand(); |
| // Find the instruction which produces the base for each input. We may |
| // need to insert a bitcast. |
| BaseEE->setOperand(0, getBaseForInput(InVal, BaseEE)); |
| } else if (auto *BaseIE = dyn_cast<InsertElementInst>(State.getBaseValue())){ |
| auto *BdvIE = cast<InsertElementInst>(BDV); |
| auto UpdateOperand = [&](int OperandIdx) { |
| Value *InVal = BdvIE->getOperand(OperandIdx); |
| Value *Base = getBaseForInput(InVal, BaseIE); |
| BaseIE->setOperand(OperandIdx, Base); |
| }; |
| UpdateOperand(0); // vector operand |
| UpdateOperand(1); // scalar operand |
| } else { |
| auto *BaseSV = cast<ShuffleVectorInst>(State.getBaseValue()); |
| auto *BdvSV = cast<ShuffleVectorInst>(BDV); |
| auto UpdateOperand = [&](int OperandIdx) { |
| Value *InVal = BdvSV->getOperand(OperandIdx); |
| Value *Base = getBaseForInput(InVal, BaseSV); |
| BaseSV->setOperand(OperandIdx, Base); |
| }; |
| UpdateOperand(0); // vector operand |
| UpdateOperand(1); // vector operand |
| } |
| } |
| |
| // Cache all of our results so we can cheaply reuse them |
| // NOTE: This is actually two caches: one of the base defining value |
| // relation and one of the base pointer relation! FIXME |
| for (auto Pair : States) { |
| auto *BDV = Pair.first; |
| Value *Base = Pair.second.getBaseValue(); |
| assert(BDV && Base); |
| assert(!isKnownBaseResult(BDV) && "why did it get added?"); |
| |
| LLVM_DEBUG( |
| dbgs() << "Updating base value cache" |
| << " for: " << BDV->getName() << " from: " |
| << (Cache.count(BDV) ? Cache[BDV]->getName().str() : "none") |
| << " to: " << Base->getName() << "\n"); |
| |
| if (Cache.count(BDV)) { |
| assert(isKnownBaseResult(Base) && |
| "must be something we 'know' is a base pointer"); |
| // Once we transition from the BDV relation being store in the Cache to |
| // the base relation being stored, it must be stable |
| assert((!isKnownBaseResult(Cache[BDV]) || Cache[BDV] == Base) && |
| "base relation should be stable"); |
| } |
| Cache[BDV] = Base; |
| } |
| assert(Cache.count(Def)); |
| return Cache[Def]; |
| } |
| |
| // For a set of live pointers (base and/or derived), identify the base |
| // pointer of the object which they are derived from. This routine will |
| // mutate the IR graph as needed to make the 'base' pointer live at the |
| // definition site of 'derived'. This ensures that any use of 'derived' can |
| // also use 'base'. This may involve the insertion of a number of |
| // additional PHI nodes. |
| // |
| // preconditions: live is a set of pointer type Values |
| // |
| // side effects: may insert PHI nodes into the existing CFG, will preserve |
| // CFG, will not remove or mutate any existing nodes |
| // |
| // post condition: PointerToBase contains one (derived, base) pair for every |
| // pointer in live. Note that derived can be equal to base if the original |
| // pointer was a base pointer. |
| static void |
| findBasePointers(const StatepointLiveSetTy &live, |
| MapVector<Value *, Value *> &PointerToBase, |
| DominatorTree *DT, DefiningValueMapTy &DVCache) { |
| for (Value *ptr : live) { |
| Value *base = findBasePointer(ptr, DVCache); |
| assert(base && "failed to find base pointer"); |
| PointerToBase[ptr] = base; |
| assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) || |
| DT->dominates(cast<Instruction>(base)->getParent(), |
| cast<Instruction>(ptr)->getParent())) && |
| "The base we found better dominate the derived pointer"); |
| } |
| } |
| |
| /// Find the required based pointers (and adjust the live set) for the given |
| /// parse point. |
| static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, |
| CallBase *Call, |
| PartiallyConstructedSafepointRecord &result) { |
| MapVector<Value *, Value *> PointerToBase; |
| findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache); |
| |
| result.PointerToBase = PointerToBase; |
| } |
| |
| // When inserting gc.relocate and gc.result calls, we need to ensure there are |
| // no uses of the original value / return value between the gc.statepoint and |
| // the gc.relocate / gc.result call. One case which can arise is a phi node |
| // starting one of the successor blocks. We also need to be able to insert the |
| // gc.relocates only on the path which goes through the statepoint. We might |
| // need to split an edge to make this possible. |
| static BasicBlock * |
| normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent, |
| DominatorTree &DT) { |
| BasicBlock *Ret = BB; |
| if (!BB->getUniquePredecessor()) |
| Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT); |
| |
| // Now that 'Ret' has unique predecessor we can safely remove all phi nodes |
| // from it |
| FoldSingleEntryPHINodes(Ret); |
| assert(!isa<PHINode>(Ret->begin()) && |
| "All PHI nodes should have been removed!"); |
| |
| // At this point, we can safely insert a gc.relocate or gc.result as the first |
| // instruction in Ret if needed. |
| return Ret; |
| } |
| |
| // List of all function attributes which must be stripped when lowering from |
| // abstract machine model to physical machine model. Essentially, these are |
| // all the effects a safepoint might have which we ignored in the abstract |
| // machine model for purposes of optimization. We have to strip these on |
| // both function declarations and call sites. |
| static constexpr Attribute::AttrKind FnAttrsToStrip[] = |
| {Attribute::ReadNone, Attribute::ReadOnly, Attribute::WriteOnly, |
| Attribute::ArgMemOnly, Attribute::InaccessibleMemOnly, |
| Attribute::InaccessibleMemOrArgMemOnly, |
| Attribute::NoSync, Attribute::NoFree}; |
| |
| // List of all parameter and return attributes which must be stripped when |
| // lowering from the abstract machine model. Note that we list attributes |
| // here which aren't valid as return attributes, that is okay. There are |
| // also some additional attributes with arguments which are handled |
| // explicitly and are not in this list. |
| static constexpr Attribute::AttrKind ParamAttrsToStrip[] = |
| {Attribute::ReadNone, Attribute::ReadOnly, Attribute::WriteOnly, |
| Attribute::NoAlias, Attribute::NoFree}; |
| |
| // Create new attribute set containing only attributes which can be transferred |
| // from original call to the safepoint. |
| static AttributeList legalizeCallAttributes(LLVMContext &Ctx, |
| AttributeList AL) { |
| if (AL.isEmpty()) |
| return AL; |
| |
| // Remove the readonly, readnone, and statepoint function attributes. |
| AttrBuilder FnAttrs(Ctx, AL.getFnAttrs()); |
| for (auto Attr : FnAttrsToStrip) |
| FnAttrs.removeAttribute(Attr); |
| |
| for (Attribute A : AL.getFnAttrs()) { |
| if (isStatepointDirectiveAttr(A)) |
| FnAttrs.removeAttribute(A); |
| } |
| |
| // Just skip parameter and return attributes for now |
| return AttributeList::get(Ctx, AttributeList::FunctionIndex, |
| AttributeSet::get(Ctx, FnAttrs)); |
| } |
| |
| namespace { |
| |
| /// This struct is used to defer RAUWs and `eraseFromParent` s. Using this |
| /// avoids having to worry about keeping around dangling pointers to Values. |
| class DeferredReplacement { |
| AssertingVH<Instruction> Old; |
| AssertingVH<Instruction> New; |
| bool IsDeoptimize = false; |
| |
| DeferredReplacement() = default; |
| |
| public: |
| static DeferredReplacement createRAUW(Instruction *Old, Instruction *New) { |
| assert(Old != New && Old && New && |
| "Cannot RAUW equal values or to / from null!"); |
| |
| DeferredReplacement D; |
| D.Old = Old; |
| D.New = New; |
| return D; |
| } |
| |
| static DeferredReplacement createDelete(Instruction *ToErase) { |
| DeferredReplacement D; |
| D.Old = ToErase; |
| return D; |
| } |
| |
| static DeferredReplacement createDeoptimizeReplacement(Instruction *Old) { |
| #ifndef NDEBUG |
| auto *F = cast<CallInst>(Old)->getCalledFunction(); |
| assert(F && F->getIntrinsicID() == Intrinsic::experimental_deoptimize && |
| "Only way to construct a deoptimize deferred replacement"); |
| #endif |
| DeferredReplacement D; |
| D.Old = Old; |
| D.IsDeoptimize = true; |
| return D; |
| } |
| |
| /// Does the task represented by this instance. |
| void doReplacement() { |
| Instruction *OldI = Old; |
| Instruction *NewI = New; |
| |
| assert(OldI != NewI && "Disallowed at construction?!"); |
| assert((!IsDeoptimize || !New) && |
| "Deoptimize intrinsics are not replaced!"); |
| |
| Old = nullptr; |
| New = nullptr; |
| |
| if (NewI) |
| OldI->replaceAllUsesWith(NewI); |
| |
| if (IsDeoptimize) { |
| // Note: we've inserted instructions, so the call to llvm.deoptimize may |
| // not necessarily be followed by the matching return. |
| auto *RI = cast<ReturnInst>(OldI->getParent()->getTerminator()); |
| new UnreachableInst(RI->getContext(), RI); |
| RI->eraseFromParent(); |
| } |
| |
| OldI->eraseFromParent(); |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| /// A unique function which doesn't require we sort the input vector. |
| template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) { |
| SmallSet<T, 8> Seen; |
| Vec.erase(remove_if(Vec, [&](const T &V) { return !Seen.insert(V).second; }), |
| Vec.end()); |
| } |
| |
| // Attach the stack map to the statepoint. The statepoint is an invoke |
| // with the given landing pad. The stack map (pointer) is attached as |
| // the type info of the landing pad. |
| static void |
| attachStackMap(uint64_t StatepointID, Instruction *LandingPad) { |
| if (cast<LandingPadInst>(LandingPad)->isCleanup()) |
| return; |
| Module *M = LandingPad->getModule(); |
| std::string Name = (Twine(GO_STACKMAP_SYM_PREFIX) + Twine(StatepointID)).str(); |
| Constant *C = M->getOrInsertGlobal(Name, Type::getInt64Ty(M->getContext())); |
| LandingPad->setOperand(0, C); |
| } |
| |
| // Extract pointer fields from an FCA. |
| static void |
| extractPointerFromFCA(Value *V, IRBuilder<> &Builder, |
| SmallVectorImpl<Value *> &PtrFields) { |
| Type *T = V->getType(); |
| assert(T->isStructTy()); |
| for (unsigned i = 0, e = T->getStructNumElements(); i < e; ++i) { |
| Type *ElemT = T->getStructElementType(i); |
| if (ElemT->isPointerTy()) { |
| Value *Field = Builder.CreateExtractValue(V, {i}); |
| PtrFields.push_back(Field); |
| } else |
| assert(!hasPointer(ElemT) && "nested FCA is not supported"); |
| } |
| } |
| |
| static Value *phiHasConstantValue(PHINode *Phi0); |
| |
| static void |
| makeStatepointExplicitImpl(CallBase *Call, /* to replace */ |
| SmallVectorImpl<Value *> &BasePtrs, |
| SmallVectorImpl<Value *> &LiveVariables, |
| PartiallyConstructedSafepointRecord &Result, |
| std::vector<DeferredReplacement> &Replacements) { |
| assert(BasePtrs.size() == LiveVariables.size()); |
| |
| // Then go ahead and use the builder do actually do the inserts. We insert |
| // immediately before the previous instruction under the assumption that all |
| // arguments will be available here. We can't insert afterwards since we may |
| // be replacing a terminator. |
| const DataLayout &DL = Call->getModule()->getDataLayout(); |
| IRBuilder<> Builder(Call); |
| |
| unique_unsorted(BasePtrs); |
| |
| // For aggregate typed stack slots, attach a bitmap identifying its |
| // pointer fields. |
| SmallVector<Value *, 64> PtrFields; |
| for (Value *V : BasePtrs) { |
| if (auto *Phi = dyn_cast<PHINode>(V)) |
| assert(!phiHasConstantValue(Phi) && "constant phi should not be in liveset"); |
| if (isa<AllocaInst>(V) || |
| (isa<Argument>(V) && cast<Argument>(V)->hasByValAttr())) { |
| // Byval argument is at a fixed frame offset. Treat it the same as alloca. |
| Type *T = cast<PointerType>(V->getType())->getElementType(); |
| if (hasPointer(T)) { |
| PtrFields.push_back(V); |
| getPtrBitmapForType(T, DL, PtrFields); |
| } |
| } else if (V->getType()->isStructTy()) { |
| // Statepoint lowering doesn't handle FCA. So we do it ourselves by |
| // extracting all the pointer fields and letting the statepoint lowering |
| // spill them. |
| extractPointerFromFCA(V, Builder, PtrFields); |
| } else |
| PtrFields.push_back(V); |
| } |
| |
| ArrayRef<Value *> GCArgs(PtrFields); |
| uint64_t StatepointID = ID; |
| ID++; |
| uint32_t NumPatchBytes = 0; |
| uint32_t Flags = uint32_t(StatepointFlags::None); |
| |
| ArrayRef<Use> CallArgs(Call->arg_begin(), Call->arg_end()); |
| ArrayRef<Use> TransitionArgs; |
| if (auto TransitionBundle = |
| Call->getOperandBundle(LLVMContext::OB_gc_transition)) { |
| Flags |= uint32_t(StatepointFlags::GCTransition); |
| TransitionArgs = TransitionBundle->Inputs; |
| } |
| |
| // Instead of lowering calls to @llvm.experimental.deoptimize as normal calls |
| // with a return value, we lower then as never returning calls to |
| // __llvm_deoptimize that are followed by unreachable to get better codegen. |
| bool IsDeoptimize = false; |
| |
| StatepointDirectives SD = |
| parseStatepointDirectivesFromAttrs(Call->getAttributes()); |
| if (SD.NumPatchBytes) |
| NumPatchBytes = *SD.NumPatchBytes; |
| if (SD.StatepointID) |
| StatepointID = *SD.StatepointID; |
| |
| Value *CallTarget = Call->getCalledOperand(); |
| if (Function *F = dyn_cast<Function>(CallTarget)) { |
| if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize) { |
| // Calls to llvm.experimental.deoptimize are lowered to calls to the |
| // __llvm_deoptimize symbol. We want to resolve this now, since the |
| // verifier does not allow taking the address of an intrinsic function. |
| |
| SmallVector<Type *, 8> DomainTy; |
| for (Value *Arg : CallArgs) |
| DomainTy.push_back(Arg->getType()); |
| auto *FTy = FunctionType::get(Type::getVoidTy(F->getContext()), DomainTy, |
| /* isVarArg = */ false); |
| |
| // Note: CallTarget can be a bitcast instruction of a symbol if there are |
| // calls to @llvm.experimental.deoptimize with different argument types in |
| // the same module. This is fine -- we assume the frontend knew what it |
| // was doing when generating this kind of IR. |
| CallTarget = F->getParent() |
| ->getOrInsertFunction("__llvm_deoptimize", FTy).getCallee(); |
| |
| IsDeoptimize = true; |
| } |
| } |
| |
| // Create the statepoint given all the arguments |
| GCStatepointInst *Token = nullptr; |
| if (isa<CallInst>(Call)) { |
| // We should have converted all statepoints to invoke. |
| assert(false && "statepoint is not an invoke"); |
| } else { |
| InvokeInst *ToReplace = cast<InvokeInst>(Call); |
| |
| // Insert the new invoke into the old block. We'll remove the old one in a |
| // moment at which point this will become the new terminator for the |
| // original block. |
| |
| // Note (Go specific): |
| // Here we attach GCArgs actually to the "deopt arg" slots, instead of |
| // the "gc arg" slots, of the statepoint. Both are recorded in the stack |
| // map the same way. The difference is that "deopt arg" doesn't need |
| // relocation. We're implementing non-moving GC (for now). |
| FunctionCallee FCallTarget(Call->getFunctionType(), |
| Call->getCalledOperand()); |
| InvokeInst *Invoke = Builder.CreateGCStatepointInvoke( |
| StatepointID, NumPatchBytes, FCallTarget, ToReplace->getNormalDest(), |
| ToReplace->getUnwindDest(), CallArgs, GCArgs, ArrayRef<Value*>(), |
| "statepoint_token"); |
| |
| Invoke->setCallingConv(ToReplace->getCallingConv()); |
| |
| // Currently we will fail on parameter attributes and on certain |
| // function attributes. In case if we can handle this set of attributes - |
| // set up function attrs directly on statepoint and return attrs later for |
| // gc_result intrinsic. |
| Invoke->setAttributes( |
| legalizeCallAttributes(Invoke->getContext(), ToReplace->getAttributes())); |
| |
| Token = cast<GCStatepointInst>(Invoke); |
| |
| // Generate gc relocates in exceptional path |
| BasicBlock *UnwindBlock = ToReplace->getUnwindDest(); |
| assert(!isa<PHINode>(UnwindBlock->begin()) && |
| UnwindBlock->getUniquePredecessor() && |
| "can't safely insert in this block!"); |
| |
| Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt()); |
| Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc()); |
| |
| // Attach exceptional gc relocates to the landingpad. |
| Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst(); |
| Result.UnwindToken = ExceptionalToken; |
| |
| attachStackMap(StatepointID, ExceptionalToken); |
| |
| BasicBlock *NormalDest = ToReplace->getNormalDest(); |
| assert(!isa<PHINode>(NormalDest->begin()) && |
| NormalDest->getUniquePredecessor() && |
| "can't safely insert in this block!"); |
| |
| Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt()); |
| } |
| assert(Token && "Should be set in one of the above branches!"); |
| |
| if (IsDeoptimize) { |
| // If we're wrapping an @llvm.experimental.deoptimize in a statepoint, we |
| // transform the tail-call like structure to a call to a void function |
| // followed by unreachable to get better codegen. |
| Replacements.push_back( |
| DeferredReplacement::createDeoptimizeReplacement(Call)); |
| } else { |
| Token->setName("statepoint_token"); |
| if (!Call->getType()->isVoidTy() && !Call->use_empty()) { |
| StringRef Name = |
| Call->hasName() ? Call->getName() : ""; |
| CallInst *GCResult = Builder.CreateGCResult(Token, Call->getType(), Name); |
| GCResult->setAttributes( |
| AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex, |
| Call->getAttributes().getRetAttrs())); |
| |
| // We cannot RAUW or delete CS.getInstruction() because it could be in the |
| // live set of some other safepoint, in which case that safepoint's |
| // PartiallyConstructedSafepointRecord will hold a raw pointer to this |
| // llvm::Instruction. Instead, we defer the replacement and deletion to |
| // after the live sets have been made explicit in the IR, and we no longer |
| // have raw pointers to worry about. |
| Replacements.emplace_back( |
| DeferredReplacement::createRAUW(Call, GCResult)); |
| } else { |
| Replacements.emplace_back( |
| DeferredReplacement::createDelete(Call)); |
| } |
| } |
| |
| Result.StatepointToken = Token; |
| } |
| |
| // Replace an existing gc.statepoint with a new one and a set of gc.relocates |
| // which make the relocations happening at this safepoint explicit. |
| // |
| // WARNING: Does not do any fixup to adjust users of the original live |
| // values. That's the callers responsibility. |
| static void |
| makeStatepointExplicit(DominatorTree &DT, CallBase *Call, |
| PartiallyConstructedSafepointRecord &Result, |
| std::vector<DeferredReplacement> &Replacements) { |
| const auto &LiveSet = Result.LiveSet; |
| const auto &PointerToBase = Result.PointerToBase; |
| |
| // Convert to vector for efficient cross referencing. |
| SmallVector<Value *, 64> BaseVec, LiveVec; |
| LiveVec.reserve(LiveSet.size()); |
| BaseVec.reserve(LiveSet.size()); |
| for (Value *L : LiveSet) { |
| LiveVec.push_back(L); |
| assert(PointerToBase.count(L)); |
| Value *Base = PointerToBase.find(L)->second; |
| BaseVec.push_back(Base); |
| } |
| assert(LiveVec.size() == BaseVec.size()); |
| |
| // Do the actual rewriting and delete the old statepoint |
| makeStatepointExplicitImpl(Call, BaseVec, LiveVec, Result, Replacements); |
| } |
| |
| static void findLiveReferences( |
| Function &F, DominatorTree &DT, ArrayRef<CallBase *> toUpdate, |
| MutableArrayRef<struct PartiallyConstructedSafepointRecord> records, |
| SetVector<Value *> &AddrTakenAllocas, |
| SetVector<Value *> &ToZero, |
| SetVector<Value *> &BadLoads, |
| DefiningValueMapTy &DVCache) { |
| GCPtrLivenessData OriginalLivenessData; |
| |
| // Find all allocas. |
| SetVector<Value *> AllAllocas; |
| if (ClobberNonLive) |
| for (Instruction &I : F.getEntryBlock()) |
| if (isa<AllocaInst>(I) && hasPointer(I.getType()->getPointerElementType())) |
| AllAllocas.insert(&I); |
| |
| computeLiveInValues(DT, F, OriginalLivenessData, AddrTakenAllocas, |
| ToZero, BadLoads, DVCache); |
| for (size_t i = 0; i < records.size(); i++) { |
| struct PartiallyConstructedSafepointRecord &info = records[i]; |
| analyzeParsePointLiveness(DT, OriginalLivenessData, AddrTakenAllocas, |
| toUpdate[i], info, AllAllocas, DVCache); |
| } |
| } |
| |
| // A helper function that reports whether V is a Phi that contains an |
| // ambiguously live alloca as input. |
| static bool |
| phiContainsAlloca(Value *V, SetVector<Value *> &ToZero, |
| SetVector<Value *> &AddrTakenAllocas) { |
| PHINode *Phi0 = dyn_cast<PHINode>(V); |
| if (!Phi0) |
| return false; |
| |
| // Visit all the Phi inputs. Discover new Phis on the go, and visit them. |
| SmallSet<PHINode *, 4> Phis, Visited; |
| Phis.insert(Phi0); |
| while (!Phis.empty()) { |
| PHINode *Phi = *Phis.begin(); |
| Visited.insert(Phi); |
| for (Value *Operand : Phi->incoming_values()) { |
| if (PHINode *P = dyn_cast<PHINode>(Operand)) { |
| if (!Visited.count(P)) |
| Phis.insert(P); |
| continue; |
| } |
| Value *Base = Operand->stripPointerCasts(); |
| if (ToZero.count(Base) != 0 && AddrTakenAllocas.count(Base) != 0) |
| return true; |
| } |
| Phis.erase(Phi); |
| } |
| return false; |
| } |
| |
| // Zero ambigously lived stack slots. We insert zeroing at lifetime |
| // start (or the entry block), so the GC won't see uninitialized |
| // content. We also insert zeroing at kill sites, to ensure the GC |
| // won't see a dead slot come back to life. |
| // We also conservatively extend the lifetime of address-taken slots, |
| // to prevent the slot being reused while it is still recorded live. |
| static void |
| zeroAmbiguouslyLiveSlots(Function &F, SetVector<Value *> &ToZero, |
| SetVector<Value *> &AddrTakenAllocas) { |
| SmallVector<Instruction *, 16> InstToDelete; |
| SetVector<Value *> Done; |
| const DataLayout &DL = F.getParent()->getDataLayout(); |
| IntegerType *Int64Ty = Type::getInt64Ty(F.getParent()->getContext()); |
| IntegerType *Int8Ty = Type::getInt8Ty(F.getParent()->getContext()); |
| |
| // If a slot has lifetime.start, place the zeroing right after it. |
| for (Instruction &I : instructions(F)) { |
| if (CallInst *CI = dyn_cast<CallInst>(&I)) |
| if (Function *Fn = CI->getCalledFunction()) { |
| if (Fn->getIntrinsicID() == Intrinsic::lifetime_start) { |
| Value *V = I.getOperand(1)->stripPointerCasts(); |
| if ((ToZero.count(V) != 0 && AddrTakenAllocas.count(V) != 0) || |
| phiContainsAlloca(V, ToZero, AddrTakenAllocas)) { |
| // For addrtaken alloca, the lifetime start may not dominate all |
| // safepoints where the slot can be live. |
| // For now, zero it in the entry block and remove the lifetime |
| // marker. |
| // Also remove lifetime markers on Phis that contain interesting |
| // allocas (which must be address-taken). |
| InstToDelete.push_back(&I); |
| } else if (ToZero.count(V) != 0) { |
| // Non-addrtaken alloca. Just insert zeroing, keep the lifetime marker. |
| IRBuilder<> Builder(I.getNextNode()); |
| Value *Zero = Constant::getNullValue(V->getType()->getPointerElementType()); |
| Builder.CreateStore(Zero, V); |
| // Don't remove V from ToZero for now, as there may be multiple |
| // lifetime start markers, where we need to insert zeroing. |
| Done.insert(V); |
| } |
| } else if (Fn->getIntrinsicID() == Intrinsic::lifetime_end) { |
| Value *V = I.getOperand(1)->stripPointerCasts(); |
| if ((ToZero.count(V) != 0 && AddrTakenAllocas.count(V) != 0) || |
| phiContainsAlloca(V, ToZero, AddrTakenAllocas)) { |
| if (!succ_empty(I.getParent())) { // no need to zero at exit block |
| // What to zero in the Phi case? |
| // We just zero whatever the Phi points to, using the size on the |
| // lifetime marker. This also works in the alloca case. |
| IRBuilder<> Builder(&I); |
| Value *Zero = Constant::getNullValue(Int8Ty); |
| Value *Siz = I.getOperand(0); |
| Builder.CreateMemSet(V, Zero, Siz, MaybeAlign(0)); |
| } |
| InstToDelete.push_back(&I); |
| } |
| } |
| } |
| } |
| |
| for (Instruction *I : InstToDelete) |
| I->eraseFromParent(); |
| ToZero.set_subtract(Done); |
| if (ToZero.empty()) |
| return; |
| |
| // Otherwise, place the zeroing in the entry block after the alloca. |
| for (Instruction &I : F.getEntryBlock()) |
| if (ToZero.count(&I) != 0) { |
| IRBuilder<> Builder(I.getNextNode()); |
| Type *ElemTyp = I.getType()->getPointerElementType(); |
| if (AddrTakenAllocas.count(&I) != 0) { |
| // For addrtaken alloca, we removed the lifetime marker above. |
| // Insert a new one at the entry block. |
| unsigned Size = DL.getTypeStoreSize(ElemTyp); |
| Builder.CreateLifetimeStart(&I, ConstantInt::get(Int64Ty, Size)); |
| } |
| Value *Zero = Constant::getNullValue(ElemTyp); |
| Builder.CreateStore(Zero, &I); |
| ToZero.remove(&I); |
| } |
| |
| assert(ToZero.empty()); |
| } |
| |
| // Detect degenerate Phi. |
| // Try harder to handle mutually dependent case, like |
| // a = phi(null, b) |
| // (in a different block) |
| // b = phi(a, null) |
| static Value * |
| phiHasConstantValue(PHINode *Phi0) { |
| Value *V = Phi0->hasConstantValue(); |
| if (V && isa<Constant>(V)) |
| return V; |
| |
| V = nullptr; |
| |
| // Visit all the Phi inputs. Discover new Phis on the go, and visit them. |
| // Early exit if we see a non-constant or two different constants. |
| SmallSet<PHINode *, 4> Phis, Visited; |
| Phis.insert(Phi0); |
| while (!Phis.empty()) { |
| PHINode *Phi = *Phis.begin(); |
| Visited.insert(Phi); |
| for (Value *Operand : Phi->incoming_values()) { |
| if (PHINode *P = dyn_cast<PHINode>(Operand)) { |
| if (!Visited.count(P)) |
| Phis.insert(P); |
| continue; |
| } |
| if (isa<Constant>(Operand)) { |
| if (V && V != Operand) |
| return nullptr; // operands not same |
| V = Operand; |
| } else |
| return nullptr; // has non-constant input |
| } |
| Phis.erase(Phi); |
| } |
| |
| return V; |
| } |
| |
| static void |
| fixBadPhiOperands(Function &F, SetVector<Value *> &BadLoads) { |
| // Don't delete instructions yet -- they may be referenced in the liveness |
| // map. We'll delete them at the end. |
| |
| for (auto *I : BadLoads) |
| I->replaceAllUsesWith(Constant::getNullValue(I->getType())); |
| |
| // The replacement above may lead to degenerate Phis, which, if live, |
| // will be encoded as constants in the stack map, which is bad |
| // (confusing with pointer bitmaps). Clean them up. |
| bool Changed = true; |
| while (Changed) { |
| Changed = false; |
| for (Instruction &I : instructions(F)) |
| if (auto *Phi = dyn_cast<PHINode>(&I)) |
| if (!BadLoads.count(Phi)) |
| if (Value *V = phiHasConstantValue(Phi)) { |
| Phi->replaceAllUsesWith(V); |
| BadLoads.insert(Phi); |
| Changed = true; |
| } |
| } |
| } |
| |
| static void fixStackWriteBarriers(Function &F, DefiningValueMapTy &DVCache); |
| |
| static bool insertParsePoints(Function &F, DominatorTree &DT, |
| TargetTransformInfo &TTI, |
| SmallVectorImpl<CallBase *> &ToUpdate) { |
| #ifndef NDEBUG |
| // sanity check the input |
| std::set<CallBase *> Uniqued; |
| Uniqued.insert(ToUpdate.begin(), ToUpdate.end()); |
| assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!"); |
| |
| for (CallBase *Call : ToUpdate) |
| assert(Call->getFunction() == &F); |
| #endif |
| |
| // When inserting gc.relocates for invokes, we need to be able to insert at |
| // the top of the successor blocks. See the comment on |
| // normalForInvokeSafepoint on exactly what is needed. Note that this step |
| // may restructure the CFG. |
| for (CallBase *Call : ToUpdate) { |
| auto *II = dyn_cast<InvokeInst>(Call); |
| if (!II) |
| continue; |
| normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT); |
| normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT); |
| } |
| |
| SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size()); |
| |
| SetVector<Value *> AddrTakenAllocas, ToZero; |
| |
| // In some rare cases, the optimizer may generate a load |
| // from an uninitialized slot. I saw this happens with LICM's |
| // load promotion. A load is moved out of the loop, and its |
| // only used in Phis. In the actual execution when the value |
| // is used, the Phi is always holding other incoming values, |
| // which are valid. The problem is that the load or the Phi |
| // may be recorded live, and the stack scan may heppen before |
| // it holding valid data, which is bad. We'll record those bad |
| // loads and remove them from the live sets. |
| SetVector<Value *> BadLoads; |
| |
| // Cache the 'defining value' relation used in the computation and |
| // insertion of base phis and selects. This ensures that we don't insert |
| // large numbers of duplicate base_phis. |
| DefiningValueMapTy DVCache; |
| |
| fixStackWriteBarriers(F, DVCache); |
| |
| // A) Identify all gc pointers which are statically live at the given call |
| // site. |
| findLiveReferences(F, DT, ToUpdate, Records, AddrTakenAllocas, ToZero, |
| BadLoads, DVCache); |
| |
| // B) Find the base pointers for each live pointer |
| for (size_t i = 0; i < Records.size(); i++) { |
| PartiallyConstructedSafepointRecord &info = Records[i]; |
| findBasePointers(DT, DVCache, ToUpdate[i], info); |
| } |
| |
| fixBadPhiOperands(F, BadLoads); |
| |
| // It is possible that non-constant live variables have a constant base. For |
| // example, a GEP with a variable offset from a global. In this case we can |
| // remove it from the liveset. We already don't add constants to the liveset |
| // because we assume they won't move at runtime and the GC doesn't need to be |
| // informed about them. The same reasoning applies if the base is constant. |
| // Note that the relocation placement code relies on this filtering for |
| // correctness as it expects the base to be in the liveset, which isn't true |
| // if the base is constant. |
| // Also make sure bad loads are not included in the liveset. |
| for (auto &Info : Records) |
| for (auto &BasePair : Info.PointerToBase) |
| if (isa<Constant>(BasePair.second) || BadLoads.count(BasePair.second)) |
| Info.LiveSet.remove(BasePair.first); |
| |
| // We need this to safely RAUW and delete call or invoke return values that |
| // may themselves be live over a statepoint. For details, please see usage in |
| // makeStatepointExplicitImpl. |
| std::vector<DeferredReplacement> Replacements; |
| |
| // Now run through and replace the existing statepoints with new ones with |
| // the live variables listed. We do not yet update uses of the values being |
| // relocated. We have references to live variables that need to |
| // survive to the last iteration of this loop. (By construction, the |
| // previous statepoint can not be a live variable, thus we can and remove |
| // the old statepoint calls as we go.) |
| for (size_t i = 0; i < Records.size(); i++) |
| makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements); |
| |
| ToUpdate.clear(); // prevent accident use of invalid calls |
| |
| for (auto &PR : Replacements) |
| PR.doReplacement(); |
| |
| Replacements.clear(); |
| |
| // At this point we should be able to delete all the bad loads and Phis. |
| // There should be no reference to them. If there are, it will assert, |
| // since the liveness args are already linked into the IR. |
| for (Value *V : BadLoads) |
| cast<Instruction>(V)->eraseFromParent(); |
| |
| for (auto &Info : Records) { |
| // These live sets may contain state Value pointers, since we replaced calls |
| // with operand bundles with calls wrapped in gc.statepoint, and some of |
| // those calls may have been def'ing live gc pointers. Clear these out to |
| // avoid accidentally using them. |
| // |
| // TODO: We should create a separate data structure that does not contain |
| // these live sets, and migrate to using that data structure from this point |
| // onward. |
| Info.LiveSet.clear(); |
| Info.PointerToBase.clear(); |
| } |
| |
| // Do all the fixups of the original live variables to their relocated selves |
| SmallVector<Value *, 128> Live; |
| for (size_t i = 0; i < Records.size(); i++) { |
| PartiallyConstructedSafepointRecord &Info = Records[i]; |
| |
| // We can't simply save the live set from the original insertion. One of |
| // the live values might be the result of a call which needs a safepoint. |
| // That Value* no longer exists and we need to use the new gc_result. |
| // Thankfully, the live set is embedded in the statepoint (and updated), so |
| // we just grab that. |
| Live.insert(Live.end(), Info.StatepointToken->gc_args_begin(), |
| Info.StatepointToken->gc_args_end()); |
| #ifndef NDEBUG |
| // Do some basic sanity checks on our liveness results before performing |
| // relocation. Relocation can and will turn mistakes in liveness results |
| // into non-sensical code which is must harder to debug. |
| // TODO: It would be nice to test consistency as well |
| assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) && |
| "statepoint must be reachable or liveness is meaningless"); |
| for (Value *V : Info.StatepointToken->gc_args()) { |
| if (!isa<Instruction>(V)) |
| // Non-instruction values trivial dominate all possible uses |
| continue; |
| auto *LiveInst = cast<Instruction>(V); |
| assert(DT.isReachableFromEntry(LiveInst->getParent()) && |
| "unreachable values should never be live"); |
| assert(DT.dominates(LiveInst, Info.StatepointToken) && |
| "basic SSA liveness expectation violated by liveness analysis"); |
| } |
| #endif |
| } |
| |
| #ifndef NDEBUG |
| // sanity check |
| for (auto *Ptr : Live) |
| assert(isHandledGCPointerType(Ptr->getType()) && |
| "must be a gc pointer type"); |
| #endif |
| |
| zeroAmbiguouslyLiveSlots(F, ToZero, AddrTakenAllocas); |
| |
| // In clobber-non-live mode, delete all lifetime markers, as the |
| // inserted clobbering may be beyond the original lifetime. |
| if (ClobberNonLive) { |
| SetVector<Instruction *> ToDel; |
| |
| for (Instruction &I : instructions(F)) |
| if (CallInst *CI = dyn_cast<CallInst>(&I)) |
| if (Function *Fn = CI->getCalledFunction()) |
| if (Fn->getIntrinsicID() == Intrinsic::lifetime_start || |
| Fn->getIntrinsicID() == Intrinsic::lifetime_end) |
| ToDel.insert(&I); |
| |
| for (Instruction *I : ToDel) |
| I->eraseFromParent(); |
| } |
| |
| return !Records.empty(); |
| } |
| |
| // Handles both return values and arguments for Functions and calls. |
| template <typename AttrHolder> |
| static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH, |
| unsigned Index) { |
| AttrBuilder R(Ctx); |
| AttributeSet AS = AH.getAttributes().getAttributes(Index); |
| if (AS.getDereferenceableBytes()) |
| R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable, |
| AS.getDereferenceableBytes())); |
| if (AS.getDereferenceableOrNullBytes()) |
| R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull, |
| AS.getDereferenceableOrNullBytes())); |
| for (auto Attr : ParamAttrsToStrip) |
| if (AS.hasAttribute(Attr)) |
| R.addAttribute(Attr); |
| |
| AttributeSet AS2 = AttributeSet::get(Ctx,R); |
| if (AS2.getNumAttributes() > 0) |
| AH.setAttributes(AH.getAttributes().removeAttributesAtIndex(Ctx, Index, AttributeMask(AS2))); |
| } |
| |
| static void stripNonValidAttributesFromPrototype(Function &F) { |
| LLVMContext &Ctx = F.getContext(); |
| |
| for (Argument &A : F.args()) |
| if (isa<PointerType>(A.getType())) |
| RemoveNonValidAttrAtIndex(Ctx, F, |
| A.getArgNo() + AttributeList::FirstArgIndex); |
| |
| if (isa<PointerType>(F.getReturnType())) |
| RemoveNonValidAttrAtIndex(Ctx, F, AttributeList::ReturnIndex); |
| |
| for (auto Attr : FnAttrsToStrip) |
| F.removeFnAttr(Attr); |
| } |
| |
| /// Certain metadata on instructions are invalid after running this pass. |
| /// Optimizations that run after this can incorrectly use this metadata to |
| /// optimize functions. We drop such metadata on the instruction. |
| static void stripInvalidMetadataFromInstruction(Instruction &I) { |
| if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) |
| return; |
| // These are the attributes that are still valid on loads and stores after |
| // this pass. |
| // The metadata implying dereferenceability and noalias are (conservatively) |
| // dropped. This is because semantically, after this pass runs, |
| // all calls to gc.statepoint "free" the entire heap. Also, gc.statepoint can |
| // touch the entire heap including noalias objects. Note: The reasoning is |
| // same as stripping the dereferenceability and noalias attributes that are |
| // analogous to the metadata counterparts. |
| // We also drop the invariant.load metadata on the load because that metadata |
| // implies the address operand to the load points to memory that is never |
| // changed once it became dereferenceable. This is no longer true after this |
| // pass. Similar reasoning applies to invariant.group metadata, which applies |
| // to loads within a group. |
| unsigned ValidMetadata[] = {LLVMContext::MD_tbaa, |
| LLVMContext::MD_range, |
| LLVMContext::MD_alias_scope, |
| LLVMContext::MD_nontemporal, |
| LLVMContext::MD_nonnull, |
| LLVMContext::MD_align, |
| LLVMContext::MD_type}; |
| |
| // Drops all metadata on the instruction other than ValidMetadata. |
| I.dropUnknownNonDebugMetadata(ValidMetadata); |
| } |
| |
| static void stripNonValidDataFromBody(Function &F) { |
| if (F.empty()) |
| return; |
| |
| LLVMContext &Ctx = F.getContext(); |
| MDBuilder Builder(Ctx); |
| |
| // Set of invariantstart instructions that we need to remove. |
| // Use this to avoid invalidating the instruction iterator. |
| SmallVector<IntrinsicInst*, 12> InvariantStartInstructions; |
| |
| for (Instruction &I : instructions(F)) { |
| // invariant.start on memory location implies that the referenced memory |
| // location is constant and unchanging. This is no longer true after |
| // this pass runs because there can be calls to gc.statepoint |
| // which frees the entire heap and the presence of invariant.start allows |
| // the optimizer to sink the load of a memory location past a statepoint, |
| // which is incorrect. |
| if (auto *II = dyn_cast<IntrinsicInst>(&I)) |
| if (II->getIntrinsicID() == Intrinsic::invariant_start) { |
| InvariantStartInstructions.push_back(II); |
| continue; |
| } |
| |
| if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) { |
| MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag); |
| I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA); |
| } |
| |
| stripInvalidMetadataFromInstruction(I); |
| |
| if (auto *Call = dyn_cast<CallBase>(&I)) { |
| for (int i = 0, e = Call->arg_size(); i != e; i++) |
| if (isa<PointerType>(Call->getArgOperand(i)->getType())) |
| RemoveNonValidAttrAtIndex(Ctx, *Call, i + AttributeList::FirstArgIndex); |
| if (isa<PointerType>(Call->getType())) |
| RemoveNonValidAttrAtIndex(Ctx, *Call, AttributeList::ReturnIndex); |
| } |
| } |
| |
| // Delete the invariant.start instructions and RAUW undef. |
| for (auto *II : InvariantStartInstructions) { |
| II->replaceAllUsesWith(UndefValue::get(II->getType())); |
| II->eraseFromParent(); |
| } |
| } |
| |
| /// Returns true if this function should be rewritten by this pass. |
| static bool shouldRewriteStatepointsIn(Function &F) { |
| return F.hasGC(); |
| } |
| |
| static void stripNonValidData(Module &M) { |
| #ifndef NDEBUG |
| assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!"); |
| #endif |
| |
| for (Function &F : M) |
| stripNonValidAttributesFromPrototype(F); |
| |
| for (Function &F : M) |
| stripNonValidDataFromBody(F); |
| } |
| |
| bool GoStatepoints::runOnFunction(Function &F, DominatorTree &DT, |
| TargetTransformInfo &TTI, |
| const TargetLibraryInfo &TLI) { |
| assert(!F.isDeclaration() && !F.empty() && |
| "need function body to rewrite statepoints in"); |
| assert(shouldRewriteStatepointsIn(F) && "mismatch in rewrite decision"); |
| |
| if (!PrintFunc.empty()) |
| PrintLiveSet = F.getName() == PrintFunc; |
| if (PrintLiveSet) |
| dbgs() << "\n********** Liveness of function " << F.getName() << " **********\n"; |
| |
| auto NeedsRewrite = [&TLI](Instruction &I) { |
| if (const auto *Call = dyn_cast<CallBase>(&I)) |
| return !callsGCLeafFunction(Call, TLI) && !isa<GCStatepointInst>(Call); |
| return false; |
| }; |
| |
| // Delete any unreachable statepoints so that we don't have unrewritten |
| // statepoints surviving this pass. This makes testing easier and the |
| // resulting IR less confusing to human readers. |
| DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); |
| bool MadeChange = removeUnreachableBlocks(F, &DTU); |
| |
| // Rewrite all the calls that need statepoints to invokes, so we can |
| // attach a stack map through its landing pad. |
| SmallVector<CallInst *, 64> Calls; |
| for (Instruction &I : instructions(F)) |
| if (NeedsRewrite(I) && isa<CallInst>(I)) |
| Calls.push_back(cast<CallInst>(&I)); |
| |
| if (!Calls.empty()) { |
| MadeChange = true; |
| |
| for (CallInst *CI : Calls) { |
| // Create a dummy landing pad block. |
| LLVMContext &C = F.getContext(); |
| BasicBlock *PadBB = BasicBlock::Create(C, "dummy", &F); |
| Type *ExnTy = StructType::get(Type::getInt8PtrTy(C), Type::getInt32Ty(C)); |
| |
| LandingPadInst *LPad = |
| LandingPadInst::Create(ExnTy, 1, "dummy.ex", PadBB); |
| LPad->addClause(Constant::getNullValue(Type::getInt8PtrTy(C))); |
| new UnreachableInst(PadBB->getContext(), PadBB); |
| |
| BasicBlock *Old = CI->getParent(); |
| BasicBlock *New = changeToInvokeAndSplitBasicBlock(CI, PadBB); |
| |
| // Old dominates New. New node dominates all other nodes dominated by Old. |
| DomTreeNode *OldNode = DT.getNode(Old); |
| std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end()); |
| |
| DomTreeNode *NewNode = DT.addNewBlock(New, Old); |
| for (DomTreeNode *I : Children) |
| DT.changeImmediateDominator(I, NewNode); |
| |
| DTU.insertEdge(Old, PadBB); |
| } |
| } |
| |
| // We should not run removeUnreachableBlocks at this point, as it |
| // will remove the dummy landing pads. |
| |
| // Flush the Dominator Tree. |
| DTU.getDomTree(); |
| |
| // Gather all the statepoints which need rewritten. Be careful to only |
| // consider those in reachable code since we need to ask dominance queries |
| // when rewriting. We'll delete the unreachable ones in a moment. |
| SmallVector<CallBase *, 64> ParsePointNeeded; |
| for (Instruction &I : instructions(F)) { |
| // TODO: only the ones with the flag set! |
| if (NeedsRewrite(I)) { |
| // NOTE removeUnreachableBlocks() is stronger than |
| // DominatorTree::isReachableFromEntry(). In other words |
| // removeUnreachableBlocks can remove some blocks for which |
| // isReachableFromEntry() returns true. |
| assert(DT.isReachableFromEntry(I.getParent()) && |
| "no unreachable blocks expected"); |
| ParsePointNeeded.push_back(cast<CallBase>(&I)); |
| } |
| } |
| |
| // Return early if no work to do. |
| if (ParsePointNeeded.empty()) |
| return MadeChange; |
| |
| // As a prepass, go ahead and aggressively destroy single entry phi nodes. |
| // These are created by LCSSA. They have the effect of increasing the size |
| // of liveness sets for no good reason. It may be harder to do this post |
| // insertion since relocations and base phis can confuse things. |
| for (BasicBlock &BB : F) |
| if (BB.getUniquePredecessor()) { |
| MadeChange = true; |
| FoldSingleEntryPHINodes(&BB); |
| } |
| |
| // Before we start introducing relocations, we want to tweak the IR a bit to |
| // avoid unfortunate code generation effects. The main example is that we |
| // want to try to make sure the comparison feeding a branch is after any |
| // safepoints. Otherwise, we end up with a comparison of pre-relocation |
| // values feeding a branch after relocation. This is semantically correct, |
| // but results in extra register pressure since both the pre-relocation and |
| // post-relocation copies must be available in registers. For code without |
| // relocations this is handled elsewhere, but teaching the scheduler to |
| // reverse the transform we're about to do would be slightly complex. |
| // Note: This may extend the live range of the inputs to the icmp and thus |
| // increase the liveset of any statepoint we move over. This is profitable |
| // as long as all statepoints are in rare blocks. If we had in-register |
| // lowering for live values this would be a much safer transform. |
| auto getConditionInst = [](Instruction *TI) -> Instruction* { |
| if (auto *BI = dyn_cast<BranchInst>(TI)) |
| if (BI->isConditional()) |
| return dyn_cast<Instruction>(BI->getCondition()); |
| // TODO: Extend this to handle switches |
| return nullptr; |
| }; |
| for (BasicBlock &BB : F) { |
| Instruction *TI = BB.getTerminator(); |
| if (auto *Cond = getConditionInst(TI)) |
| // TODO: Handle more than just ICmps here. We should be able to move |
| // most instructions without side effects or memory access. |
| if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) { |
| MadeChange = true; |
| Cond->moveBefore(TI); |
| } |
| } |
| |
| MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded); |
| return MadeChange; |
| } |
| |
| // liveness computation via standard dataflow |
| // ------------------------------------------------------------------- |
| |
| // TODO: Consider using bitvectors for liveness, the set of potentially |
| // interesting values should be small and easy to pre-compute. |
| |
| static Value* |
| isAlloca(Value *V, DefiningValueMapTy &DVCache) { |
| Value *Base = findBaseOrBDV(V, DVCache); |
| return isa<AllocaInst>(Base) ? Base : nullptr; |
| } |
| |
| static Value* |
| isTrackedAlloca(Value *V, DefiningValueMapTy &DVCache) { |
| Value *Base = isAlloca(V, DVCache); |
| if (Base && |
| hasPointer(Base->getType()->getPointerElementType())) |
| return Base; |
| return nullptr; |
| } |
| |
| static bool |
| hasStructRetAttr(CallBase *Call) { |
| return Call->hasStructRetAttr() || |
| (Call->getNumOperands() > 0 && |
| Call->getParamAttr(0, "go_sret") != Attribute()); |
| } |
| |
| /// Compute the live-in set for the location rbegin starting from |
| /// the live-out set of the basic block |
| static void computeLiveInValues(BasicBlock::reverse_iterator Begin, |
| BasicBlock::reverse_iterator End, |
| SetVector<Value *> &LiveTmp, |
| SetVector<Value *> &AddrTakenAllocas, |
| DefiningValueMapTy &DVCache) { |
| for (auto &I : make_range(Begin, End)) { |
| // KILL/Def - Remove this definition from LiveIn |
| LiveTmp.remove(&I); |
| |
| // Don't consider *uses* in PHI nodes, we handle their contribution to |
| // predecessor blocks when we seed the LiveOut sets |
| if (isa<PHINode>(I)) |
| continue; |
| |
| // USE - Add to the LiveIn set for this instruction |
| for (Value *V : I.operands()) { |
| assert(!isUnhandledGCPointerType(V->getType()) && |
| "unexpected value type"); |
| if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) { |
| // The choice to exclude all things constant here is slightly subtle. |
| // There are two independent reasons: |
| // - We assume that things which are constant (from LLVM's definition) |
| // do not move at runtime. For example, the address of a global |
| // variable is fixed, even though it's contents may not be. |
| // - Second, we can't disallow arbitrary inttoptr constants even |
| // if the language frontend does. Optimization passes are free to |
| // locally exploit facts without respect to global reachability. This |
| // can create sections of code which are dynamically unreachable and |
| // contain just about anything. (see constants.ll in tests) |
| |
| if (isAlloca(V, DVCache)) { |
| Value *Base = isTrackedAlloca(V, DVCache); |
| if (!Base || AddrTakenAllocas.count(Base)) |
| continue; |
| |
| // For non-address-taken alloca, record its use. |
| if (isa<DbgInfoIntrinsic>(I) || isa<BitCastInst>(I) || |
| isa<GetElementPtrInst>(I) || isa<ICmpInst>(I) || |
| isa<AddrSpaceCastInst>(I)) |
| // Not real use. |
| continue; |
| if (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<InvokeInst>(I)) { |
| LiveTmp.insert(Base); |
| continue; |
| } |
| |
| if (CallInst *CI = dyn_cast<CallInst>(&I)) { |
| if (Function *Fn = CI->getCalledFunction()) |
| switch (Fn->getIntrinsicID()) { |
| case Intrinsic::lifetime_start: |
| case Intrinsic::lifetime_end: |
| case Intrinsic::assume: |
| // Not real use. |
| continue; |
| default: |
| break; |
| } |
| LiveTmp.insert(Base); |
| continue; |
| } |
| |
| // We know it is not address-taken, other operation should not happen. |
| assert(false && "illegal operation on non-address-taken alloca"); |
| } |
| |
| LiveTmp.insert(V); |
| } |
| } |
| } |
| } |
| |
| // Compute the def and kill of allocas. |
| static void |
| computeAllocaDefs(BasicBlock::iterator Begin, |
| BasicBlock::iterator End, |
| SetVector<Value *> &AllocaDefs, |
| SetVector<Value *> &AllocaKills, |
| DefiningValueMapTy &DVCache) { |
| // Iterate forwards over the instructions, record the defs and kills |
| // of allocas. |
| // Notes on the special cases about def and kill appearing in the same |
| // block: |
| // - kill after def: |
| // Record the kill but don't remove it from def set, since we will |
| // subtract the kill set anyway. And when a slot is initialized and |
| // then killed in the same block, we don't lose information. |
| // - def after kill: |
| // The def overrides the kill, i.e. remove it from the kill set |
| // (unless we see a kill again later). So we have the information |
| // that the slot is initialized at the end of the block, even after |
| // we subtract the kill set. |
| for (auto &I : make_range(Begin, End)) { |
| // skip Phi ? |
| if (isa<PHINode>(I)) |
| continue; |
| |
| if (StoreInst *SI = dyn_cast<StoreInst>(&I)){ |
| Value *V = SI->getPointerOperand(); |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AllocaDefs.insert(Base); |
| AllocaKills.remove(Base); |
| } |
| continue; |
| } |
| |
| if (CallInst *CI = dyn_cast<CallInst>(&I)){ |
| if (hasStructRetAttr(CI)) { |
| Value *V = CI->getOperand(0); |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AllocaDefs.insert(Base); |
| AllocaKills.remove(Base); |
| } |
| } |
| if (Function *Fn = CI->getCalledFunction()) |
| switch (Fn->getIntrinsicID()) { |
| case Intrinsic::memmove: |
| case Intrinsic::memcpy: |
| case Intrinsic::memset: { |
| // We're writing to the first arg. |
| Value *V = CI->getOperand(0); |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AllocaDefs.insert(Base); |
| AllocaKills.remove(Base); |
| } |
| break; |
| } |
| case Intrinsic::lifetime_end: { |
| Value *V = CI->getOperand(1); |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AllocaKills.insert(Base); |
| } |
| break; |
| } |
| default: |
| break; |
| } |
| continue; |
| } |
| |
| if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) { |
| if (hasStructRetAttr(II)) { |
| Value *V = II->getOperand(0); |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AllocaDefs.insert(Base); |
| AllocaKills.remove(Base); |
| } |
| } |
| continue; |
| } |
| } |
| } |
| |
| // Determine whether an alloca has its address taken. |
| // We use different mechanisms to track the liveness of |
| // address-taken and non-address-taken allocas. |
| // Also keep track the location where the address is used. |
| // The alloca needs to be live where its address is taken. |
| static void |
| determineAllocaAddrTaken(Function &F, |
| SetVector<Value *> &AddrTakenAllocas, |
| MapVector<BasicBlock *, SetVector<Value *>> &AllocaAddrUse, |
| DefiningValueMapTy &DVCache) { |
| // Use the metadata inserted by the FE. |
| for (Instruction &I : F.getEntryBlock()) |
| if (isa<AllocaInst>(I) && I.getMetadata("go_addrtaken") && |
| hasPointer(I.getType()->getPointerElementType())) |
| AddrTakenAllocas.insert(&I); |
| |
| // The FE's addrtaken mark may be imprecise. Look for certain |
| // operations in the IR to mark as addrtaken. |
| // The address may be passed as argument to functions. We trust |
| // the FE that if it is not marked as addrtaken, the function |
| // won't hold its address. (for example, the equality function |
| // of aggregate types.) |
| for (Instruction &I : instructions(F)) { |
| if (isa<PHINode>(I) || isa<SelectInst>(I)) |
| // Phi/select could happen even it is not really addrtaken: |
| // for example, an IR transformation like |
| // if (cond) { x = a } else { x = b } |
| // ==> |
| // if (cond) { tmp = &a } else { tmp = &b }; x = *tmp |
| // Things get complicated with them. For now, treat them as |
| // address taken. |
| for (Value *V : I.operands()) { |
| if (!isHandledGCPointerType(V->getType())) |
| continue; |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AddrTakenAllocas.insert(Base); |
| AllocaAddrUse[I.getParent()].insert(Base); |
| } |
| } |
| else if (StoreInst *SI = dyn_cast<StoreInst>(&I)) { |
| // If the address of a slot is stored, it must be addrtaken. |
| // In most cases the FE marks it. One exception is the array |
| // holding the ... args. |
| // TODO: maybe we should fix the FE? |
| Value *V = SI->getValueOperand(); |
| if (isHandledGCPointerType(V->getType())) |
| if (Value *Base = isTrackedAlloca(V, DVCache)) { |
| AddrTakenAllocas.insert(Base); |
| AllocaAddrUse[I.getParent()].insert(Base); |
| } |
| } |
| } |
| } |
| |
| static void computeLiveOutSeed(BasicBlock *BB, SetVector<Value *> &LiveTmp, |
| DefiningValueMapTy &DVCache) { |
| for (BasicBlock *Succ : successors(BB)) { |
| for (auto &I : *Succ) { |
| PHINode *PN = dyn_cast<PHINode>(&I); |
| if (!PN) |
| break; |
| |
| Value *V = PN->getIncomingValueForBlock(BB); |
| assert(!isUnhandledGCPointerType(V->getType()) && |
| "unexpected value type"); |
| if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) { |
| if (isAlloca(V, DVCache)) |
| // Alloca is tracked separately. (It is a Phi arg so it |
| // must be address-taken.) |
| continue; |
| LiveTmp.insert(V); |
| } |
| } |
| } |
| } |
| |
| static SetVector<Value *> computeKillSet(BasicBlock *BB, DefiningValueMapTy &DVCache) { |
| SetVector<Value *> KillSet; |
| for (Instruction &I : *BB) { |
| if (isHandledGCPointerType(I.getType())) |
| KillSet.insert(&I); |
| } |
| return KillSet; |
| } |
| |
| #ifndef NDEBUG |
| /// Check that the items in 'Live' dominate 'TI'. This is used as a basic |
| /// sanity check for the liveness computation. |
| static void checkBasicSSA(DominatorTree &DT, SetVector<Value *> &Live, |
| Instruction *TI, bool TermOkay = false) { |
| for (Value *V : Live) { |
| if (auto *I = dyn_cast<Instruction>(V)) { |
| // The terminator can be a member of the LiveOut set. LLVM's definition |
| // of instruction dominance states that V does not dominate itself. As |
| // such, we need to special case this to allow it. |
| if (TermOkay && TI == I) |
| continue; |
| assert(DT.dominates(I, TI) && |
| "basic SSA liveness expectation violated by liveness analysis"); |
| } |
| } |
| } |
| |
| /// Check that all the liveness sets used during the computation of liveness |
| /// obey basic SSA properties. This is useful for finding cases where we miss |
| /// a def. |
| static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data, |
| BasicBlock &BB) { |
| checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator()); |
| checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true); |
| checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator()); |
| } |
| #endif |
| |
| // For initialization of an aggregate-typed slot, check whether the |
| // whole storage is initialized before we reach a statepoint, and |
| // insert zeroing if not. |
| // Normally the FE has lifted calls out of the initialization sequence. |
| // But they may occur due to optimizations, for example, |
| // type A struct { ...; b B; ... } |
| // type B struct { ... } |
| // a := A{ ..., b: SomeB(), ... } |
| // The FE generates something like |
| // %a = alloca A |
| // %tmp = alloca B |
| // call SomeB(%tmp) // as outgoing arg |
| // initialize part of a |
| // call memmove(gep %a, %tmp) |
| // initialize the rest of a |
| // The memmove may be optimized out, with direct store to A, as |
| // %a = alloca A |
| // initialize part of a |
| // call SomeB(gep %a) |
| // initialize the rest of a |
| // a is live at the call site, but not fully initialized. |
| // We need to make sure a doesn't contain bad pointers. |
| // TODO: this function is a little too conservative (see below). |
| // TODO: instead of zeroing, maybe we can record only the part |
| // of A that is live? |
| static void |
| checkStoreSize(Value *V, BasicBlock &BB, const DataLayout &DL, |
| SetVector<Value *> &ToZero, |
| DefiningValueMapTy &DVCache) { |
| unsigned PtrSize = DL.getPointerSize(); |
| unsigned Size = DL.getTypeStoreSize(V->getType()->getPointerElementType()); |
| if (Size <= PtrSize) |
| return; |
| |
| // We simply add the sizes of all stores in the block, assuming |
| // no overlapping stores (which are silly). |
| unsigned StoreSize = 0; |
| for (Instruction &I : BB) { |
| if (StoreInst *SI = dyn_cast<StoreInst>(&I)) { |
| Value *Ptr = SI->getPointerOperand(); |
| if (isTrackedAlloca(Ptr, DVCache) == V) |
| StoreSize += DL.getTypeStoreSize(SI->getValueOperand()->getType()); |
| } else if (CallInst *CI = dyn_cast<CallInst>(&I)) { |
| if (hasStructRetAttr(CI)) { |
| Value *Ptr = CI->getOperand(0); |
| if (isTrackedAlloca(Ptr, DVCache) == V) |
| StoreSize += DL.getTypeStoreSize(Ptr->getType()->getPointerElementType()); |
| } |
| if (Function *Fn = CI->getCalledFunction()) |
| switch (Fn->getIntrinsicID()) { |
| case Intrinsic::memmove: |
| case Intrinsic::memcpy: |
| case Intrinsic::memset: { |
| // We're writing to the first arg. The third arg is size. |
| Value *Ptr = CI->getOperand(0); |
| if (isTrackedAlloca(Ptr, DVCache) == V) { |
| ConstantInt *Len = |
| dyn_cast<ConstantInt>(cast<MemIntrinsic>(CI)->getLength()); |
| if (Len) |
| StoreSize += Len->getZExtValue(); |
| } |
| break; |
| } |
| default: |
| break; |
| } |
| } else if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) { |
| if (hasStructRetAttr(II)) { |
| Value *Ptr = II->getOperand(0); |
| if (isTrackedAlloca(Ptr, DVCache) == V) |
| if (DL.getTypeStoreSize(Ptr->getType()->getPointerElementType()) + PtrSize - 1 >= Size) |
| // We are storing the whole type |
| return; |
| |
| // Othersize we may have stored pointers into the alloca, which |
| // need to be live, but it is not completely initialized. We need |
| // to zero it. |
| // TODO: no need to zero if all previous stores are scalars. |
| } |
| } |
| |
| // We only care about pointers, so it's safe to round up to a pointer size. |
| // TODO: things with more than a simple padding may still be false positive. |
| // TODO: if the missing fields are all scalars, no need to zero. |
| if (StoreSize + PtrSize - 1 >= Size) |
| return; // early return if we have stored enough. |
| } |
| |
| // Incomplete initialization, needs zeroing. |
| if (StoreSize + PtrSize - 1 < Size) |
| ToZero.insert(V); |
| } |
| |
| static void computeLiveInValues(DominatorTree &DT, Function &F, |
| GCPtrLivenessData &Data, |
| SetVector<Value *> &AddrTakenAllocas, |
| SetVector<Value *> &ToZero, |
| SetVector<Value *> &BadLoads, |
| DefiningValueMapTy &DVCache) { |
| MapVector<BasicBlock *, SetVector<Value *>> AllocaAddrUse; |
| determineAllocaAddrTaken(F, AddrTakenAllocas, AllocaAddrUse, DVCache); |
| if (PrintLiveSet) { |
| dbgs() << "AddrTakenAllocas:\n"; |
| printLiveSet(AddrTakenAllocas); |
| } |
| |
| // Seed the liveness for each individual block |
| for (BasicBlock &BB : F) { |
| Data.KillSet[&BB] = computeKillSet(&BB, DVCache); |
| Data.LiveSet[&BB].clear(); |
| computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB], AddrTakenAllocas, DVCache); |
| computeAllocaDefs(BB.begin(), BB.end(), Data.AllocaDefSet[&BB], Data.AllocaKillSet[&BB], DVCache); |
| Data.AllocaDefAny[&BB] = Data.AllocaDefSet[&BB]; |
| Data.AllocaDefAny[&BB].set_subtract(Data.AllocaKillSet[&BB]); |
| Data.LiveOut[&BB] = SetVector<Value *>(); |
| computeLiveOutSeed(&BB, Data.LiveOut[&BB], DVCache); |
| |
| #ifndef NDEBUG |
| for (Value *Kill : Data.KillSet[&BB]) |
| assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill"); |
| #endif |
| } |
| |
| // Propagate Alloca def any until stable. |
| bool changed = true; |
| again: |
| while (changed) { |
| changed = false; |
| for (BasicBlock &BB : F) { |
| unsigned OldSize = Data.AllocaDefAny[&BB].size(); |
| for (BasicBlock *Pred : predecessors(&BB)) |
| Data.AllocaDefAny[&BB].set_union(Data.AllocaDefAny[Pred]); |
| Data.AllocaDefAny[&BB].set_subtract(Data.AllocaKillSet[&BB]); |
| if (Data.AllocaDefAny[&BB].size() != OldSize) |
| changed = true; |
| } |
| } |
| |
| // When a slot's address is taken, it can be live any point after it. |
| // It can also be initialized "indirectly", like |
| // tmp = phi(&a, &b) |
| // *tmp = ... |
| // computeAllocaDefs doesn't see this initialization. |
| // It can be initialized some time later, or never. We don't know for |
| // sure. The slot needs to be live. And we need to pre-zero it, if we |
| // don't otherwise know it is initialized. |
| if (!AllocaAddrUse.empty()) { |
| for (BasicBlock &BB : F) { |
| AllocaAddrUse[&BB].set_subtract(Data.AllocaKillSet[&BB]); |
| for (Value *V : AllocaAddrUse[&BB]) |
| if (!Data.AllocaDefAny[&BB].count(V)) { |
| Data.AllocaDefAny[&BB].insert(V); |
| ToZero.insert(V); |
| changed = true; |
| } |
| } |
| AllocaAddrUse.clear(); |
| if (changed) |
| goto again; // re-propagate alloca def any |
| } |
| |
| // Propagate Alloca def all until stable. |
| for (BasicBlock &BB : F) |
| Data.AllocaDefAll[&BB] = Data.AllocaDefAny[&BB]; |
| changed = true; |
| while (changed) { |
| changed = false; |
| for (BasicBlock &BB : F) { |
| auto NotDefAll = [&](Value *V){ |
| if (Data.AllocaDefSet[&BB].count(V) != 0) |
| return false; |
| for (BasicBlock *Pred : predecessors(&BB)) |
| if (Data.AllocaDefAll[Pred].count(V) == 0) { |
| if (PrintLiveSet) |
| dbgs() << ">>> removing " << V->getName() << " from " << |
| BB.getName() << " DefAll; pred = " << |
| Pred->getName() << "\n"; |
| return true; |
| } |
| return false; |
| }; |
| if (Data.AllocaDefAll[&BB].remove_if(NotDefAll)) |
| changed = true; |
| } |
| } |
| |
| const DataLayout &DL = F.getParent()->getDataLayout(); |
| |
| // An alloca is live only after it is initialized. |
| // It is initialized in a block if it is defined there and not defined |
| // in all of the predecessors (or there is no predecessors). |
| for (BasicBlock &BB : F) { |
| for (Value *V : Data.AllocaDefSet[&BB]) { |
| bool Init = false; |
| if (&BB == &F.getEntryBlock()) |
| Init = true; |
| for (BasicBlock *Pred : predecessors(&BB)) |
| if (!Data.AllocaDefAll[Pred].count(V)) { |
| Init = true; |
| break; |
| } |
| if (!Init) |
| continue; |
| if (!AddrTakenAllocas.count(V)) { // addr-taken alloca is tracked separately |
| Data.KillSet[&BB].insert(V); |
| Data.LiveSet[&BB].remove(V); |
| } |
| |
|