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//===- 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 "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/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/CallSite.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DomTreeUpdater.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/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,
// Print the liveset only for the specified function.
static cl::opt<std::string> PrintFunc("gogc-print-func", cl::Hidden,
// 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,
ConstantInt::get(Int64Ty, GO_FUNC_SENTINEL),
bool Changed = false;
auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
for (Function &F : M) {
// Nothing to do for declarations.
if (F.isDeclaration() || F.empty())
// Policy choice says not to rewrite - the most common reason is that we're
// compiling code without a GCStrategy.
if (!shouldRewriteStatepointsIn(F))
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.
PreservedAnalyses PA;
return PA;
namespace {
class GoStatepointsLegacyPass : public ModulePass {
GoStatepoints Impl;
static char ID; // Pass identification, replacement for typeid
GoStatepointsLegacyPass() : ModulePass(ID), Impl() {
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,
ConstantInt::get(Int64Ty, GO_FUNC_SENTINEL),
bool Changed = false;
const TargetLibraryInfo &TLI =
for (Function &F : M) {
// Nothing to do for declarations.
if (F.isDeclaration() || F.empty())
// Policy choice says not to rewrite - the most common reason is that
// we're compiling code without a GCStrategy.
if (!shouldRewriteStatepointsIn(F))
TargetTransformInfo &TTI =
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.
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.
} // end anonymous namespace
char GoStatepointsLegacyPass::ID = 0;
ModulePass *llvm::createGoStatepointsLegacyPass() {
return new GoStatepointsLegacyPass();
"Insert statepoints for Go GC", false, false)
"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.
Instruction *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);
// 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, CallSite CS,
PartiallyConstructedSafepointRecord &Result,
SetVector<Value *> &AllAllocas,
DefiningValueMapTy &DVCache) {
Instruction *Inst = CS.getInstruction();
StatepointLiveSetTy LiveSet;
findLiveSetAtInst(Inst, OriginalLivenessData, AddrTakenAllocas,
LiveSet, AllAllocas, DVCache);
if (PrintLiveSet) {
dbgs() << "Live Variables at " << *Inst << ":\n";
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);
} // 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()),
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()) {
// fall through to general call handling
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.
"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 {
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); }
void dump() const {
dbgs() << '\n';
void print(raw_ostream &OS) const {
switch (getStatus()) {
case Unknown:
OS << "U";
case Base:
OS << "B";
case Conflict:
OS << "C";
OS << " (" << getBaseValue() << " - "
<< (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): ";
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) {
return OS;
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:
// b1 b2 b3 b4
// 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) ||
// 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;
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
assert(isExpectedBDVType(Base) && "the only non-base values "
"we see should be base defining values");
if (States.insert(std::make_pair(Base, BDVState())).second)
if (PHINode *PN = dyn_cast<PHINode>(Current)) {
for (Value *InVal : PN->incoming_values())
} else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) {
} else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
} 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)) {
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");
// 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();
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");
// 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())
/// 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,
} 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.
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())
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!");
// 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?");
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;
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) ||
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,
CallSite CS,
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
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;
// Create new attribute set containing only attributes which can be transferred
// from original call to the safepoint.
static AttributeList legalizeCallAttributes(AttributeList AL) {
if (AL.isEmpty())
return AL;
// Remove the readonly, readnone, and statepoint function attributes.
AttrBuilder FnAttrs = AL.getFnAttributes();
for (Attribute A : AL.getFnAttributes()) {
if (isStatepointDirectiveAttr(A))
LLVMContext &Ctx = AL.getContext();
AttributeList Ret = AttributeList::get(Ctx, AttributeList::FunctionIndex,
AttributeSet::get(Ctx, FnAttrs));
// Add parameter attrs.
// TODO: use AttrBuilder?
for (unsigned i = AttributeList::FirstArgIndex, e = AL.getNumAttrSets(); i < e; ++i)
Ret = Ret.addAttributes(Ctx, i+5, AL.getAttributes(i));
// Skip return attributes
return Ret;
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;
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");
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)
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);
} // 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; }),
// 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())
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();
for (unsigned i = 0, e = T->getStructNumElements(); i < e; ++i) {
Type *ElemT = T->getStructElementType(i);
if (ElemT->isPointerTy()) {
Value *Field = Builder.CreateExtractValue(V, {i});
} else
assert(!hasPointer(ElemT) && "nested FCA is not supported");
static void
makeStatepointExplicitImpl(const CallSite CS, /* 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.
Instruction *InsertBefore = CS.getInstruction();
const DataLayout &DL = InsertBefore->getModule()->getDataLayout();
IRBuilder<> Builder(InsertBefore);
// 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))
if (Phi->hasConstantValue())
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)) {
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
ArrayRef<Value *> GCArgs(PtrFields);
uint64_t StatepointID = ID;
uint32_t NumPatchBytes = 0;
uint32_t Flags = uint32_t(StatepointFlags::None);
ArrayRef<Use> CallArgs(CS.arg_begin(), CS.arg_end());
ArrayRef<Use> TransitionArgs;
if (auto TransitionBundle =
CS.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 =
if (SD.NumPatchBytes)
NumPatchBytes = *SD.NumPatchBytes;
if (SD.StatepointID)
StatepointID = *SD.StatepointID;
Value *CallTarget = CS.getCalledValue();
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)
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);
IsDeoptimize = true;
// Create the statepoint given all the arguments
Instruction *Token = nullptr;
if (CS.isCall()) {
// We should have converted all statepoints to invoke.
assert(false && "statepoint is not an invoke");
} else {
InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction());
// 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).
InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(),
ToReplace->getUnwindDest(), CallArgs, GCArgs, ArrayRef<Value*>(),
// 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.
Token = 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!");
// 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!");
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.
} else {
if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) {
StringRef Name =
CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : "";
CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name);
AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex,
// 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.
DeferredReplacement::createRAUW(CS.getInstruction(), GCResult));
} else {
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, CallSite CS,
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;
for (Value *L : LiveSet) {
Value *Base = PointerToBase.find(L)->second;
assert(LiveVec.size() == BaseVec.size());
// Do the actual rewriting and delete the old statepoint
makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements);
static void findLiveReferences(
Function &F, DominatorTree &DT, ArrayRef<CallSite> 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()))
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;
while (!Phis.empty()) {
PHINode *Phi = *Phis.begin();
for (Value *Operand : Phi->incoming_values()) {
if (PHINode *P = dyn_cast<PHINode>(Operand)) {
if (!Visited.count(P))
Value *Base = Operand->stripPointerCasts();
if (ToZero.count(Base) != 0 && AddrTakenAllocas.count(Base) != 0)
return true;
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).
} 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.
} 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, 0);
for (Instruction *I : InstToDelete)
if (ToZero.empty())
// 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);
// 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)
return V;
// 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;
while (!Phis.empty()) {
PHINode *Phi = *Phis.begin();
for (Value *Operand : Phi->incoming_values()) {
if (PHINode *P = dyn_cast<PHINode>(Operand)) {
if (!Visited.count(P))
if (isa<Constant>(Operand)) {
if (V && V != Operand)
return nullptr; // operands not same
V = Operand;
} else
return nullptr; // has non-constant input
return V;
static void
fixBadPhiOperands(Function &F, SetVector<Value *> &BadLoads,
SetVector<Instruction *> &ToDel) {
for (auto *I : BadLoads) {
// 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.
// Don't delete them yet -- they may be referenced in the liveness
// map. We'll delete them at the end.
bool Changed = true;
while (Changed) {
Changed = false;
for (Instruction &I : instructions(F))
if (auto *Phi = dyn_cast<PHINode>(&I))
if (!ToDel.count(Phi))
if (Value *V = phiHasConstantValue(Phi)) {
Changed = true;
static void fixStackWriteBarriers(Function &F, DefiningValueMapTy &DVCache);
static bool insertParsePoints(Function &F, DominatorTree &DT,
TargetTransformInfo &TTI,
SmallVectorImpl<CallSite> &ToUpdate) {
#ifndef NDEBUG
// sanity check the input
std::set<CallSite> Uniqued;
Uniqued.insert(ToUpdate.begin(), ToUpdate.end());
assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!");
for (CallSite CS : ToUpdate)
assert(CS.getInstruction()->getFunction() == &F);
// 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 (CallSite CS : ToUpdate) {
if (!CS.isInvoke())
auto *II = cast<InvokeInst>(CS.getInstruction());
normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT);
normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT);
SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size());
SetVector<Value *> AddrTakenAllocas, ToZero, 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);
SetVector<Instruction *> ToDel;
fixBadPhiOperands(F, BadLoads, ToDel);
// 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.
for (auto &Info : Records)
for (auto &BasePair : Info.PointerToBase)
if (isa<Constant>(BasePair.second))
// 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 CallSites
for (auto &PR : Replacements)
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.
// 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.
Statepoint Statepoint(Info.StatepointToken);
Live.insert(Live.end(), Statepoint.gc_args_begin(),
#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 : Statepoint.gc_args()) {
if (!isa<Instruction>(V))
// Non-instruction values trivial dominate all possible uses
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");
#ifndef NDEBUG
// sanity check
for (auto *Ptr : Live)
assert(isHandledGCPointerType(Ptr->getType()) &&
"must be a gc pointer type");
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)
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)
// Delete dead Phis.
for (Instruction *I : ToDel)
return !Records.empty();
// Handles both return values and arguments for Functions and CallSites.
template <typename AttrHolder>
static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
unsigned Index) {
AttrBuilder R;
if (AH.getDereferenceableBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
if (AH.getDereferenceableOrNullBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
if (AH.getAttributes().hasAttribute(Index, Attribute::NoAlias))
if (!R.empty())
AH.setAttributes(AH.getAttributes().removeAttributes(Ctx, Index, R));
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);
/// 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))
// 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 metadata, which applies
// to loads within a group.
unsigned ValidMetadata[] = {LLVMContext::MD_tbaa,
// Drops all metadata on the instruction other than ValidMetadata.
static void stripNonValidDataFromBody(Function &F) {
if (F.empty())
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) {
if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) {
MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag);
I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
if (CallSite CS = CallSite(&I)) {
for (int i = 0, e = CS.arg_size(); i != e; i++)
if (isa<PointerType>(CS.getArgument(i)->getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, i + AttributeList::FirstArgIndex);
if (isa<PointerType>(CS.getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, AttributeList::ReturnIndex);
// Delete the invariant.start instructions and RAUW undef.
for (auto *II : InvariantStartInstructions) {
/// 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!");
for (Function &F : M)
for (Function &F : M)
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 (ImmutableCallSite CS = ImmutableCallSite(&I))
return !callsGCLeafFunction(CS, TLI) && !isStatepoint(CS);
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, nullptr, &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))
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);
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.
// 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<CallSite, 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");
// 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;
// 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;
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 &&
return Base;
return nullptr;
/// 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
// Don't consider *uses* in PHI nodes, we handle their contribution to
// predecessor blocks when we seed the LiveOut sets
if (isa<PHINode>(I))
// 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))
// For non-address-taken alloca, record its use.
if (isa<DbgInfoIntrinsic>(I) || isa<BitCastInst>(I) ||
isa<GetElementPtrInst>(I) || isa<ICmpInst>(I) ||
// Not real use.
if (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<InvokeInst>(I)) {
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.
// We know it is not address-taken, other operation should not happen.
assert(false && "illegal operation on non-address-taken alloca");
// Compute the def and kill of allocas.
static void
computeAllocaDefs(BasicBlock::iterator Begin,
BasicBlock::iterator End,
SetVector<Value *> &AllocaDefs,
SetVector<Value *> &AllocaKills,
DefiningValueMapTy &DVCache) {
for (auto &I : make_range(Begin, End)) {
// skip Phi ?
if (isa<PHINode>(I))
if (StoreInst *SI = dyn_cast<StoreInst>(&I)){
Value *V = SI->getPointerOperand();
if (Value *Base = isTrackedAlloca(V, DVCache))
if (CallInst *CI = dyn_cast<CallInst>(&I)){
if (CI->hasStructRetAttr()) {
Value *V = CI->getOperand(0);
if (Value *Base = isTrackedAlloca(V, DVCache))
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))
case Intrinsic::lifetime_end: {
Value *V = CI->getOperand(1);
if (Value *Base = isTrackedAlloca(V, DVCache)) {
// We 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.
if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
if (II->hasStructRetAttr()) {
Value *V = II->getOperand(0);
if (Value *Base = isTrackedAlloca(V, DVCache))
// 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") &&
// 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()))
if (Value *Base = isTrackedAlloca(V, DVCache)) {
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)) {
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)
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.)
static SetVector<Value *> computeKillSet(BasicBlock *BB, DefiningValueMapTy &DVCache) {
SetVector<Value *> KillSet;
for (Instruction &I : *BB) {
if (isHandledGCPointerType(I.getType()))
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)
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());
// 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)
// 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 (CI->hasStructRetAttr()) {
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 =
if (Len)
StoreSize += Len->getZExtValue();
} else if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
if (II->hasStructRetAttr()) {
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
// 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)
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";
// Seed the liveness for each individual block
for (BasicBlock &BB : F) {
Data.KillSet[&BB] = computeKillSet(&BB, DVCache);
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.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");
// Propagate Alloca def any until stable.
bool changed = true;
while (changed) {
changed = false;
for (BasicBlock &BB : F) {
unsigned OldSize = Data.AllocaDefAny[&BB].size();
for (BasicBlock *Pred : predecessors(&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) {
for (Value *V : AllocaAddrUse[&BB])
if (!Data.AllocaDefAny[&BB].count(V)) {
changed = true;
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;
if (!Init)
if (!AddrTakenAllocas.count(V)) { // addr-taken alloca is tracked separately
// If it is incomplete initialization, it needs zeroing.
checkStoreSize(V, BB, DL, ToZero, DVCache);
SmallSetVector<BasicBlock *, 32> Worklist;
for (BasicBlock &BB : F) {
Data.LiveIn[&BB] = Data.LiveSet[&BB];
if (!Data.LiveIn[&BB].empty())
Worklist.insert(pred_begin(&BB), pred_end(&BB));
// Propagate liveness until stable
while (!Worklist.empty()) {
BasicBlock *BB = Worklist.pop_back_val();
// Compute our new liveout set, then exit early if it hasn't changed despite
// the contribution of our successor.
SetVector<Value *> LiveOut = Data.LiveOut[BB];
const auto OldLiveOutSize = LiveOut.size();
for (BasicBlock *Succ : successors(BB)) {
// assert OutLiveOut is a subset of LiveOut
if (OldLiveOutSize == LiveOut.size()) {
// If the sets are the same size, then we didn't actually add anything
// when unioning our successors LiveIn. Thus, the LiveIn of this block
// hasn't changed.
Data.LiveOut[BB] = LiveOut;
// Apply the effects of this basic block
SetVector<Value *> LiveTmp = LiveOut;
const SetVector<Value *> &OldLiveIn = Data.LiveIn[BB];
// assert: OldLiveIn is a subset of LiveTmp
if (OldLiveIn.size() != LiveTmp.size()) {
Data.LiveIn[BB] = LiveTmp;
Worklist.insert(pred_begin(BB), pred_end(BB));
} // while (!Worklist.empty())
// 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 heppend before