bridge/go-llvm-bfunction.cpp - gollvm - Git at Google

 //===-- go-llvm-bfunction.cpp - implementation of 'Bfunction' class ---===//
 //
 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 //
 //===----------------------------------------------------------------------===//
 //
 // Methods for class Bfunction.
 //
 //===----------------------------------------------------------------------===//

 #include "go-llvm-bfunction.h"

 #include "go-llvm-btype.h"
 #include "go-llvm-bstatement.h"
 #include "go-llvm-bexpression.h"
 #include "go-llvm-bvariable.h"
 #include "go-llvm-cabi-oracle.h"
 #include "go-llvm-typemanager.h"
 #include "go-llvm-irbuilders.h"
 #include "go-system.h"

 #include "llvm/IR/Argument.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Value.h"

 Bfunction::Bfunction(llvm::Constant *fcnValue,
                      BFunctionType *fcnType,
                      const std::string &name,
                      const std::string &asmName,
                      Location location,
                      TypeManager *tm)

     : fcnType_(fcnType), fcnValue_(fcnValue),
       abiOracle_(new CABIOracle(fcnType, tm)),
       rtnValueMem_(nullptr), chainVal_(nullptr),
       paramsRegistered_(0), name_(name), asmName_(asmName),
       location_(location), splitStack_(YesSplit),
       prologGenerated_(false), abiSetupComplete_(false),
       errorSeen_(false)
 {
   if (! fcnType->followsCabi())
     abiSetupComplete_ = true;
 }

 Bfunction::~Bfunction()
 {
   if (! prologGenerated_) {
     for (auto ais : allocas_)
       ais->deleteValue();
   }
   for (auto &lab : labels_)
     delete lab;
   for (auto &v : localVariables_) {
     // only delete declvars here, others are in valueVarMap_
     // and will be deleted below.
     if (v->isDeclVar())
       delete v;
   }
   for (auto &kv : valueVarMap_)
     delete kv.second;
   assert(labelAddressPlaceholders_.empty());
 }

 llvm::Function *Bfunction::function() const
 {
   return llvm::cast<llvm::Function>(fcnValue());
 }

 std::string Bfunction::namegen(const std::string &tag)
 {
   return abiOracle_->tm()->tnamegen(tag);
 }

 llvm::Instruction *Bfunction::addAlloca(llvm::Type *typ,
                                         const std::string &name)
 {
   llvm::Instruction *insBefore = nullptr;
   TypeManager *tm = abiOracle_->tm();
   llvm::Align aaAlign = tm->datalayout()->getABITypeAlign(typ);
   llvm::Value *aaSize = nullptr;
   llvm::Instruction *inst = new llvm::AllocaInst(typ, 0, aaSize, aaAlign,
                                                  name, insBefore);
   if (! name.empty())
     inst->setName(name);
   allocas_.push_back(inst);
   return inst;
 }

 void Bfunction::lazyAbiSetup()
 {
   if (abiSetupComplete_)
     return;
   abiSetupComplete_ = true;

   // Populate argument list
   if (arguments_.empty())
     for (auto argit = function()->arg_begin(), argen = function()->arg_end(); argit != argen; ++argit)
       arguments_.push_back(&(*argit));

   // If the return value is going to be passed via memory, make a note
   // of the argument in question, and set up the arg.
   unsigned argIdx = 0;
   if (abiOracle_->returnInfo().disp() == ParmIndirect) {
     std::string sretname(namegen("sret.formal"));
     arguments_[argIdx]->setName(sretname);
     llvm::AttrBuilder SRETAttrs(function()->getContext());
     SRETAttrs.addStructRetAttr(fcnType_->resultType()->type());
     arguments_[argIdx]->addAttrs(SRETAttrs);
     rtnValueMem_ = arguments_[argIdx];
     argIdx += 1;
   }

   // Handle static chain param.  In contrast with real / explicit
   // function params, we don't create the spill slot eagerly.
   assert(abiOracle_->chainInfo().disp() == ParmDirect);
   std::string nestname(namegen("nest"));
   arguments_[argIdx]->setName(nestname);
   arguments_[argIdx]->addAttr(llvm::Attribute::Nest);
   chainVal_ = arguments_[argIdx];
   argIdx += 1;

   // Sort out what to do with each of the parameters.
   const std::vector<Btype *> &paramTypes = fcnType()->paramTypes();
   for (unsigned idx = 0; idx < paramTypes.size(); ++idx) {
     const CABIParamInfo &paramInfo = abiOracle_->paramInfo(idx);
     switch(paramInfo.disp()) {
       case ParmIgnore: {
         // Seems weird to create a zero-sized alloca(), but it should
         // simplify things in that we can avoid having a Bvariable with a
         // null value.
         llvm::Type *llpt = paramTypes[idx]->type();
         llvm::Instruction *inst = addAlloca(llpt, "");
         paramValues_.push_back(inst);
         break;
       }
       case ParmIndirect: {
         paramValues_.push_back(arguments_[argIdx]);
         assert(paramInfo.numArgSlots() == 1);
         if (paramInfo.attr() == AttrByVal) {
           llvm::AttrBuilder BVAttrs(function()->getContext());
           BVAttrs.addByValAttr(paramTypes[idx]->type());
           arguments_[argIdx]->addAttrs(BVAttrs);
         }
         argIdx += 1;
         break;
       }
       case ParmDirect: {
         llvm::Type *llpt = paramTypes[idx]->type();
         llvm::Instruction *inst = addAlloca(llpt, "");
         paramValues_.push_back(inst);
         if (paramInfo.attr() == AttrSext)
           arguments_[argIdx]->addAttr(llvm::Attribute::SExt);
         else if (paramInfo.attr() == AttrZext)
           arguments_[argIdx]->addAttr(llvm::Attribute::ZExt);
         else
           assert(paramInfo.attr() == AttrNone);
         argIdx += paramInfo.numArgSlots();
         break;
       }
     }
   }
 }

 Bvariable *Bfunction::parameterVariable(const std::string &name,
                                         Btype *btype,
                                         bool is_address_taken,
                                         Location location)
 {
   lazyAbiSetup();
   unsigned argIdx = paramsRegistered_++;

   // Create Bvariable and install in value->var map.
   llvm::Value *argVal = paramValues_[argIdx];
   assert(valueVarMap_.find(argVal) == valueVarMap_.end());
   Bvariable *bv =
       new Bvariable(btype, location, name, ParamVar, is_address_taken, argVal);
   valueVarMap_[argVal] = bv;

   // Set parameter name or names.
   const CABIParamInfo &paramInfo = abiOracle_->paramInfo(argIdx);
   switch(paramInfo.disp()) {
     case ParmIgnore: {
       std::string iname(name);
       iname += ".ignore";
       paramValues_[argIdx]->setName(name);
       break;
     }
     case ParmIndirect: {
       unsigned soff = paramInfo.sigOffset();
       arguments_[soff]->setName(name);
       break;
     }
     case ParmDirect: {
       unsigned soff = paramInfo.sigOffset();
       if (paramInfo.abiTypes().size() == 1) {
         arguments_[soff]->setName(name);
       } else {
         assert(paramInfo.abiTypes().size() <= CABIParamInfo::ABI_TYPES_MAX_SIZE);
         for (unsigned i = 0; i < paramInfo.abiTypes().size(); ++i) {
           std::string argp = name + ".chunk" + std::to_string(i);
           arguments_[soff+i]->setName(argp);
         }
       }
       std::string aname(name);
       aname += ".addr";
       paramValues_[argIdx]->setName(aname);
     }
   }

   // All done.
   return bv;
 }

 Bvariable *Bfunction::staticChainVariable(const std::string &name,
                                           Btype *btype,
                                           Location location)
 {
   lazyAbiSetup();
   const CABIParamInfo &chainInfo = abiOracle_->chainInfo();
   assert(chainInfo.disp() == ParmDirect);

   // Set name of function parameter
   unsigned soff = chainInfo.sigOffset();
   arguments_[soff]->setName(name);

   // Create the spill slot for the param.
   std::string spname(name);
   spname += ".addr";
   llvm::Instruction *inst = addAlloca(btype->type(), spname);
   assert(chainVal_);
   assert(llvm::isa<llvm::Argument>(chainVal_));
   chainVal_ = inst;

   // Create backend variable to encapsulate the above.
   Bvariable *bv =
       new Bvariable(btype, location, name, ParamVar, false, inst);
   assert(valueVarMap_.find(bv->value()) == valueVarMap_.end());
   valueVarMap_[bv->value()] = bv;

   return bv;
 }

 Bvariable *Bfunction::localVariable(const std::string &name,
                                     Btype *btype,
                                     Bvariable *declVar,
                                     bool is_address_taken,
                                     Location location)
 {
   lazyAbiSetup();
   llvm::Instruction *inst = nullptr;
   if (declVar != nullptr) {
     // If provided, declVar must be an existing local variable in
     // the same function (presumably at an outer scope).
     assert(valueVarMap_.find(declVar->value()) != valueVarMap_.end());

     // For the correct semantics, we need the two variables in question
     // to share the same alloca instruction.
     inst = llvm::cast<llvm::Instruction>(declVar->value());
   } else {
     inst = addAlloca(btype->type(), name);
   }
   if (is_address_taken) {
     llvm::Instruction *alloca = inst;
     if (auto *ascast = llvm::dyn_cast<llvm::AddrSpaceCastInst>(alloca))
       alloca = llvm::cast<llvm::Instruction>(ascast->getPointerOperand());
     alloca->setMetadata("go_addrtaken", llvm::MDNode::get(inst->getContext(), {}));
   }
   Bvariable *bv =
       new Bvariable(btype, location, name, LocalVar, is_address_taken, inst);
   localVariables_.push_back(bv);
   if (declVar != nullptr) {
     // Don't add the variable in question to the value var map.
     // Mark it so that it can be handled properly during creation
     // of lifetime annotations.
     bv->markAsDeclVar();
   } else {
     assert(valueVarMap_.find(bv->value()) == valueVarMap_.end());
     valueVarMap_[bv->value()] = bv;
   }
   return bv;
 }

 llvm::Value *Bfunction::createTemporary(Btype *btype, const std::string &tag)
 {
   return createTemporary(btype->type(), tag);
 }

 llvm::Value *Bfunction::createTemporary(llvm::Type *typ, const std::string &tag)
 {
   return addAlloca(typ, tag);
 }

 // This implementation uses an alloca instruction as a placeholder
 // for a block address.

 llvm::Instruction *
 Bfunction::createLabelAddressPlaceholder(Btype *btype)
 {
   std::string name(namegen("labeladdrplaceholder"));
   TypeManager *tm = abiOracle_->tm();
   llvm::Type *lltype = btype->type();
   llvm::Instruction *insBefore = nullptr;
   llvm::Align aaAlign = tm->datalayout()->getABITypeAlign(lltype);
   llvm::Value *aaSize = nullptr;
   llvm::Instruction *inst = new llvm::AllocaInst(lltype, 0, aaSize, aaAlign,
                                                  name, insBefore);
   labelAddressPlaceholders_.insert(inst);
   return inst;
 }

 // Called at the point where we have a concrete basic block for
 // a Blabel that has had its address taken. Replaces uses of the
 // placeholder instruction with the real thing.

 void Bfunction::replaceLabelAddressPlaceholder(llvm::Value *placeholder,
                                                llvm::BasicBlock *bbForLabel)
 {
   // Locate the PH inst and remove it from the tracking set.
   llvm::Instruction *phinst = llvm::cast<llvm::Instruction>(placeholder);
   auto it = labelAddressPlaceholders_.find(phinst);
   assert(it != labelAddressPlaceholders_.end());
   labelAddressPlaceholders_.erase(it);

   // Create real block address and replace uses of the PH inst with it.
   llvm::BlockAddress *blockad =
       llvm::BlockAddress::get(function(), bbForLabel);
   phinst->replaceAllUsesWith(blockad);

   // Placeholder inst no longer needed.
   phinst->deleteValue();
 }

 std::vector<Bvariable*> Bfunction::getParameterVars()
 {
   std::vector<Bvariable*> res;
   for (auto &argval : paramValues_) {
     auto it = valueVarMap_.find(argval);
     assert(it != valueVarMap_.end());
     Bvariable *v = it->second;
     res.push_back(v);
   }
   return res;
 }

 std::vector<Bvariable*> Bfunction::getFunctionLocalVars()
 {
   return localVariables_;
 }

 Bvariable *Bfunction::getBvarForValue(llvm::Value *val)
 {
   auto it = valueVarMap_.find(val);
   return (it != valueVarMap_.end() ? it->second : nullptr);
 }

 Bvariable *Bfunction::getNthParamVar(unsigned argIdx)
 {
   assert(argIdx < paramValues_.size());
   llvm::Value *pval = paramValues_[argIdx];
   return getBvarForValue(pval);
 }

 unsigned Bfunction::genArgSpill(Bvariable *paramVar,
                                 const CABIParamInfo &paramInfo,
                                 Binstructions *spillInstructions,
                                 llvm::Value *sploc)
 {
   lazyAbiSetup();
   assert(paramInfo.disp() == ParmDirect);
   TypeManager *tm = abiOracle_->tm();
   BlockLIRBuilder builder(function(), this);

   // Simple case: param arrived in single register.
   if (paramInfo.abiTypes().size() == 1) {
     llvm::Argument *arg = arguments_[paramInfo.sigOffset()];
     assert(sploc->getType()->isPointerTy());
     llvm::PointerType *llpt = llvm::cast<llvm::PointerType>(sploc->getType());
     if (paramInfo.abiType()->isVectorTy() ||
         arg->getType() != llpt->getElementType()) {
       std::string tag(namegen("cast"));
       llvm::Type *ptv = llvm::PointerType::get(paramInfo.abiType(), 0);
       llvm::Value *bitcast = builder.CreateBitCast(sploc, ptv, tag);
       sploc = bitcast;
     }
     llvm::Instruction *si = builder.CreateStore(arg, sploc);
     paramVar->setInitializer(si);
     spillInstructions->appendInstructions(builder.instructions());
     return 1;
   }

   assert(paramInfo.abiTypes().size() <= CABIParamInfo::ABI_TYPES_MAX_SIZE);
   // More complex case: param arrives in multiple registers.

   // Create struct type corresponding to multiple params.
   llvm::Type *llst = paramInfo.computeABIStructType(tm);
   llvm::Type *ptst = llvm::PointerType::get(llst, 0);

   // Cast the spill location to a pointer to the struct created above.
   std::string tag(namegen("cast"));
   llvm::Value *bitcast = builder.CreateBitCast(sploc, ptst, tag);
   llvm::Instruction *stinst = nullptr;

   // Generate a store to each field.
   for (unsigned i = 0; i < paramInfo.abiTypes().size(); ++i) {
     std::string tag(namegen("field" + std::to_string(i)));
     llvm::Value *fieldgep =
         builder.CreateConstInBoundsGEP2_32(llst, bitcast, 0, i, tag);
     llvm::Value *argChunk = arguments_[paramInfo.sigOffset() + i];
     stinst = builder.CreateStore(argChunk, fieldgep);
   }
   paramVar->setInitializer(stinst);
   spillInstructions->appendInstructions(builder.instructions());

   // All done.
   return paramInfo.abiTypes().size();
 }

 void Bfunction::genProlog(llvm::BasicBlock *entry)
 {
   lazyAbiSetup();
   unsigned argIdx = (abiOracle_->returnInfo().disp() == ParmIndirect ? 1 : 0);
   Binstructions spills;

   // Spill the static chain param if needed. We only want to do this
   // if a chain variable was explicitly requested.
   const CABIParamInfo &chainInfo = abiOracle_->chainInfo();
   assert(chainInfo.disp() == ParmDirect);
   unsigned soff = chainInfo.sigOffset();
   if (arguments_[soff] != chainVal_) {
     auto it = valueVarMap_.find(chainVal_);
     assert(it != valueVarMap_.end());
     Bvariable *chainVar = it->second;
     genArgSpill(chainVar, chainInfo, &spills, chainVal_);
   }
   argIdx += 1;

   // Spill any directly-passed function arguments into their previous
   // created spill areas.
   const std::vector<Btype *> &paramTypes = fcnType()->paramTypes();
   unsigned nParms = paramTypes.size();
   for (unsigned pidx = 0; pidx < nParms; ++pidx) {
     const CABIParamInfo &paramInfo = abiOracle_->paramInfo(pidx);
     if (paramInfo.disp() != ParmDirect)
       continue;
     Bvariable *v = getNthParamVar(pidx);
     if (!v) {
       assert(errorSeen());
       continue;
     }
     llvm::Value *sploc = llvm::cast<llvm::Instruction>(paramValues_[pidx]);
     argIdx += genArgSpill(v, paramInfo, &spills, sploc);
   }

   // Append allocas for local variables
   // FIXME: create lifetime annotations
   for (auto aa : allocas_)
     entry->getInstList().push_back(aa);

   // Param spills
   for (auto sp : spills.instructions())
     entry->getInstList().push_back(sp);

   // Debug meta-data generation needs to know the position at which a
   // parameter variable is available for inspection -- this is
   // typically either A) the start of the function for by-address
   // params, or B) the spill instruction that copies a direct param to
   // the stack. If the entry block is not empty, then use the last
   // inst in it as an initializer for by-address params. If the block
   // is still empty at this point we'll take care of things later.
   if (! entry->empty()) {
     for (unsigned pidx = 0; pidx < nParms; ++pidx) {
       Bvariable *v = getNthParamVar(pidx);
       if (!v) {
         assert(errorSeen());
         continue;
       }
       if (v->initializer() == nullptr)
         v->setInitializer(&entry->front());
     }
   }

   prologGenerated_ = true;
 }

 void Bfunction::fixupProlog(llvm::BasicBlock *entry,
                             const std::vector<llvm::Instruction *> &temps)
 {
   lazyAbiSetup();
   // If there are any "new" temporaries discovered during the control
   // flow generation walk, incorporate them into the entry block. At this
   // stage in the game the entry block is already fully populated, including
   // (potentially) references to the alloca instructions themselves, so
   // we insert any new temps into the start of the block.
   if (! temps.empty())
     for (auto ai : temps) {
       entry->getInstList().push_front(ai);
       if (auto *ascast = llvm::dyn_cast<llvm::AddrSpaceCastInst>(ai)) {
         llvm::Value *op = ascast->getPointerOperand();
         assert(llvm::isa<llvm::AllocaInst>(op));
         entry->getInstList().push_front(llvm::cast<llvm::Instruction>(op));
       }
     }
 }

 llvm::Value *Bfunction::genReturnSequence(Bexpression *toRet,
                                           Binstructions *retInstrs,
                                           NameGen *inamegen)
 {
   lazyAbiSetup();
   const CABIParamInfo &returnInfo = abiOracle_->returnInfo();

   // If we're returning an empty struct, or if the function has void
   // type, then return a null ptr (return "void").
   TypeManager *tm = abiOracle_->tm();
   if (returnInfo.disp() == ParmIgnore ||
       fcnType()->resultType()->type() == tm->llvmVoidType()) {
     llvm::Value *rval = nullptr;
     return rval;
   }

   // Indirect return: emit memcpy into sret
   if (returnInfo.disp() == ParmIndirect) {
     BlockLIRBuilder bbuilder(function(), inamegen);
     uint64_t sz = tm->typeSize(fcnType_->resultType());
     uint64_t algn = tm->typeAlignment(fcnType_->resultType());
     llvm::MaybeAlign malgn(algn);
     bbuilder.CreateMemCpy(rtnValueMem_, malgn, toRet->value(), malgn, sz);
     retInstrs->appendInstructions(bbuilder.instructions());
     llvm::Value *rval = nullptr;
     return rval;
   }

   // Direct return: single value
   if (! returnInfo.abiType()->isAggregateType() &&
       ! toRet->btype()->type()->isAggregateType())
     return toRet->value();

   // Direct return: either the ABI type is a structure or the
   // return value type is a structure. In this case we bitcast
   // the return location address to the ABI type and then issue a load
   // from the bitcast.
   llvm::Type *llrt = (returnInfo.abiType()->isAggregateType() ?
                       returnInfo.computeABIStructType(tm) :
                       returnInfo.abiType());
   llvm::Type *ptst = llvm::PointerType::get(llrt, 0);
   BlockLIRBuilder builder(function(), inamegen);
   std::string castname(namegen("cast"));
   llvm::Value *bitcast = builder.CreateBitCast(toRet->value(), ptst, castname);
   std::string loadname(namegen("ld"));
   llvm::Instruction *ldinst = builder.CreateLoad(llrt, bitcast, loadname);
   retInstrs->appendInstructions(builder.instructions());
   return ldinst;
 }

 Blabel *Bfunction::newLabel(Location loc) {
   unsigned labelCount = labels_.size();
   Blabel *lb = new Blabel(this, labelCount, loc);
   labelmap_.push_back(nullptr);
   labels_.push_back(lb);
   return lb;
 }

 void Bfunction::registerLabelDefStatement(Bstatement *st, Blabel *label)
 {
   assert(st && st->flavor() == N_LabelStmt);
   assert(label);
   assert(labelmap_[label->label()] == nullptr);
   labelmap_[label->label()] = st;
 }
	//===-- go-llvm-bfunction.cpp - implementation of 'Bfunction' class ---===//
	//
	// Copyright 2018 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.
	//
	//===----------------------------------------------------------------------===//
	//
	// Methods for class Bfunction.
	//
	//===----------------------------------------------------------------------===//

	#include "go-llvm-bfunction.h"

	#include "go-llvm-btype.h"
	#include "go-llvm-bstatement.h"
	#include "go-llvm-bexpression.h"
	#include "go-llvm-bvariable.h"
	#include "go-llvm-cabi-oracle.h"
	#include "go-llvm-typemanager.h"
	#include "go-llvm-irbuilders.h"
	#include "go-system.h"

	#include "llvm/IR/Argument.h"
	#include "llvm/IR/Instructions.h"
	#include "llvm/IR/Constants.h"
	#include "llvm/IR/Value.h"

	Bfunction::Bfunction(llvm::Constant *fcnValue,
	BFunctionType *fcnType,
	const std::string &name,
	const std::string &asmName,
	Location location,
	TypeManager *tm)

	: fcnType_(fcnType), fcnValue_(fcnValue),
	abiOracle_(new CABIOracle(fcnType, tm)),
	rtnValueMem_(nullptr), chainVal_(nullptr),
	paramsRegistered_(0), name_(name), asmName_(asmName),
	location_(location), splitStack_(YesSplit),
	prologGenerated_(false), abiSetupComplete_(false),
	errorSeen_(false)
	{
	if (! fcnType->followsCabi())
	abiSetupComplete_ = true;
	}

	Bfunction::~Bfunction()
	{
	if (! prologGenerated_) {
	for (auto ais : allocas_)
	ais->deleteValue();
	}
	for (auto &lab : labels_)
	delete lab;
	for (auto &v : localVariables_) {
	// only delete declvars here, others are in valueVarMap_
	// and will be deleted below.
	if (v->isDeclVar())
	delete v;
	}
	for (auto &kv : valueVarMap_)
	delete kv.second;
	assert(labelAddressPlaceholders_.empty());
	}

	llvm::Function *Bfunction::function() const
	{
	return llvm::cast<llvm::Function>(fcnValue());
	}

	std::string Bfunction::namegen(const std::string &tag)
	{
	return abiOracle_->tm()->tnamegen(tag);
	}

	llvm::Instruction Bfunction::addAlloca(llvm::Type typ,
	const std::string &name)
	{
	llvm::Instruction *insBefore = nullptr;
	TypeManager *tm = abiOracle_->tm();
	llvm::Align aaAlign = tm->datalayout()->getABITypeAlign(typ);
	llvm::Value *aaSize = nullptr;
	llvm::Instruction *inst = new llvm::AllocaInst(typ, 0, aaSize, aaAlign,
	name, insBefore);
	if (! name.empty())
	inst->setName(name);
	allocas_.push_back(inst);
	return inst;
	}

	void Bfunction::lazyAbiSetup()
	{
	if (abiSetupComplete_)
	return;
	abiSetupComplete_ = true;

	// Populate argument list
	if (arguments_.empty())
	for (auto argit = function()->arg_begin(), argen = function()->arg_end(); argit != argen; ++argit)
	arguments_.push_back(&(*argit));

	// If the return value is going to be passed via memory, make a note
	// of the argument in question, and set up the arg.
	unsigned argIdx = 0;
	if (abiOracle_->returnInfo().disp() == ParmIndirect) {
	std::string sretname(namegen("sret.formal"));
	arguments_[argIdx]->setName(sretname);
	llvm::AttrBuilder SRETAttrs(function()->getContext());
	SRETAttrs.addStructRetAttr(fcnType_->resultType()->type());
	arguments_[argIdx]->addAttrs(SRETAttrs);
	rtnValueMem_ = arguments_[argIdx];
	argIdx += 1;
	}

	// Handle static chain param. In contrast with real / explicit
	// function params, we don't create the spill slot eagerly.
	assert(abiOracle_->chainInfo().disp() == ParmDirect);
	std::string nestname(namegen("nest"));
	arguments_[argIdx]->setName(nestname);
	arguments_[argIdx]->addAttr(llvm::Attribute::Nest);
	chainVal_ = arguments_[argIdx];
	argIdx += 1;

	// Sort out what to do with each of the parameters.
	const std::vector<Btype *> &paramTypes = fcnType()->paramTypes();
	for (unsigned idx = 0; idx < paramTypes.size(); ++idx) {
	const CABIParamInfo &paramInfo = abiOracle_->paramInfo(idx);
	switch(paramInfo.disp()) {
	case ParmIgnore: {
	// Seems weird to create a zero-sized alloca(), but it should
	// simplify things in that we can avoid having a Bvariable with a
	// null value.
	llvm::Type *llpt = paramTypes[idx]->type();
	llvm::Instruction *inst = addAlloca(llpt, "");
	paramValues_.push_back(inst);
	break;
	}
	case ParmIndirect: {
	paramValues_.push_back(arguments_[argIdx]);
	assert(paramInfo.numArgSlots() == 1);
	if (paramInfo.attr() == AttrByVal) {
	llvm::AttrBuilder BVAttrs(function()->getContext());
	BVAttrs.addByValAttr(paramTypes[idx]->type());
	arguments_[argIdx]->addAttrs(BVAttrs);
	}
	argIdx += 1;
	break;
	}
	case ParmDirect: {
	llvm::Type *llpt = paramTypes[idx]->type();
	llvm::Instruction *inst = addAlloca(llpt, "");
	paramValues_.push_back(inst);
	if (paramInfo.attr() == AttrSext)
	arguments_[argIdx]->addAttr(llvm::Attribute::SExt);
	else if (paramInfo.attr() == AttrZext)
	arguments_[argIdx]->addAttr(llvm::Attribute::ZExt);
	else
	assert(paramInfo.attr() == AttrNone);
	argIdx += paramInfo.numArgSlots();
	break;
	}
	}
	}
	}

	Bvariable *Bfunction::parameterVariable(const std::string &name,
	Btype *btype,
	bool is_address_taken,
	Location location)
	{
	lazyAbiSetup();
	unsigned argIdx = paramsRegistered_++;

	// Create Bvariable and install in value->var map.
	llvm::Value *argVal = paramValues_[argIdx];
	assert(valueVarMap_.find(argVal) == valueVarMap_.end());
	Bvariable *bv =
	new Bvariable(btype, location, name, ParamVar, is_address_taken, argVal);
	valueVarMap_[argVal] = bv;

	// Set parameter name or names.
	const CABIParamInfo &paramInfo = abiOracle_->paramInfo(argIdx);
	switch(paramInfo.disp()) {
	case ParmIgnore: {
	std::string iname(name);
	iname += ".ignore";
	paramValues_[argIdx]->setName(name);
	break;
	}
	case ParmIndirect: {
	unsigned soff = paramInfo.sigOffset();
	arguments_[soff]->setName(name);
	break;
	}
	case ParmDirect: {
	unsigned soff = paramInfo.sigOffset();
	if (paramInfo.abiTypes().size() == 1) {
	arguments_[soff]->setName(name);
	} else {
	assert(paramInfo.abiTypes().size() <= CABIParamInfo::ABI_TYPES_MAX_SIZE);
	for (unsigned i = 0; i < paramInfo.abiTypes().size(); ++i) {
	std::string argp = name + ".chunk" + std::to_string(i);
	arguments_[soff+i]->setName(argp);
	}
	}
	std::string aname(name);
	aname += ".addr";
	paramValues_[argIdx]->setName(aname);
	}
	}

	// All done.
	return bv;
	}

	Bvariable *Bfunction::staticChainVariable(const std::string &name,
	Btype *btype,
	Location location)
	{
	lazyAbiSetup();
	const CABIParamInfo &chainInfo = abiOracle_->chainInfo();
	assert(chainInfo.disp() == ParmDirect);

	// Set name of function parameter
	unsigned soff = chainInfo.sigOffset();
	arguments_[soff]->setName(name);

	// Create the spill slot for the param.
	std::string spname(name);
	spname += ".addr";
	llvm::Instruction *inst = addAlloca(btype->type(), spname);
	assert(chainVal_);
	assert(llvm::isa<llvm::Argument>(chainVal_));
	chainVal_ = inst;

	// Create backend variable to encapsulate the above.
	Bvariable *bv =
	new Bvariable(btype, location, name, ParamVar, false, inst);
	assert(valueVarMap_.find(bv->value()) == valueVarMap_.end());
	valueVarMap_[bv->value()] = bv;

	return bv;
	}

	Bvariable *Bfunction::localVariable(const std::string &name,
	Btype *btype,
	Bvariable *declVar,
	bool is_address_taken,
	Location location)
	{
	lazyAbiSetup();
	llvm::Instruction *inst = nullptr;
	if (declVar != nullptr) {
	// If provided, declVar must be an existing local variable in
	// the same function (presumably at an outer scope).
	assert(valueVarMap_.find(declVar->value()) != valueVarMap_.end());

	// For the correct semantics, we need the two variables in question
	// to share the same alloca instruction.
	inst = llvm::cast<llvm::Instruction>(declVar->value());
	} else {
	inst = addAlloca(btype->type(), name);
	}
	if (is_address_taken) {
	llvm::Instruction *alloca = inst;
	if (auto *ascast = llvm::dyn_cast<llvm::AddrSpaceCastInst>(alloca))
	alloca = llvm::cast<llvm::Instruction>(ascast->getPointerOperand());
	alloca->setMetadata("go_addrtaken", llvm::MDNode::get(inst->getContext(), {}));
	}
	Bvariable *bv =
	new Bvariable(btype, location, name, LocalVar, is_address_taken, inst);
	localVariables_.push_back(bv);
	if (declVar != nullptr) {
	// Don't add the variable in question to the value var map.
	// Mark it so that it can be handled properly during creation
	// of lifetime annotations.
	bv->markAsDeclVar();
	} else {
	assert(valueVarMap_.find(bv->value()) == valueVarMap_.end());
	valueVarMap_[bv->value()] = bv;
	}
	return bv;
	}

	llvm::Value Bfunction::createTemporary(Btype btype, const std::string &tag)
	{
	return createTemporary(btype->type(), tag);
	}

	llvm::Value Bfunction::createTemporary(llvm::Type typ, const std::string &tag)
	{
	return addAlloca(typ, tag);
	}

	// This implementation uses an alloca instruction as a placeholder
	// for a block address.

	llvm::Instruction *
	Bfunction::createLabelAddressPlaceholder(Btype *btype)
	{
	std::string name(namegen("labeladdrplaceholder"));
	TypeManager *tm = abiOracle_->tm();
	llvm::Type *lltype = btype->type();
	llvm::Instruction *insBefore = nullptr;
	llvm::Align aaAlign = tm->datalayout()->getABITypeAlign(lltype);
	llvm::Value *aaSize = nullptr;
	llvm::Instruction *inst = new llvm::AllocaInst(lltype, 0, aaSize, aaAlign,
	name, insBefore);
	labelAddressPlaceholders_.insert(inst);
	return inst;
	}

	// Called at the point where we have a concrete basic block for
	// a Blabel that has had its address taken. Replaces uses of the
	// placeholder instruction with the real thing.

	void Bfunction::replaceLabelAddressPlaceholder(llvm::Value *placeholder,
	llvm::BasicBlock *bbForLabel)
	{
	// Locate the PH inst and remove it from the tracking set.
	llvm::Instruction *phinst = llvm::cast<llvm::Instruction>(placeholder);
	auto it = labelAddressPlaceholders_.find(phinst);
	assert(it != labelAddressPlaceholders_.end());
	labelAddressPlaceholders_.erase(it);

	// Create real block address and replace uses of the PH inst with it.
	llvm::BlockAddress *blockad =
	llvm::BlockAddress::get(function(), bbForLabel);
	phinst->replaceAllUsesWith(blockad);

	// Placeholder inst no longer needed.
	phinst->deleteValue();
	}

	std::vector<Bvariable*> Bfunction::getParameterVars()
	{
	std::vector<Bvariable*> res;
	for (auto &argval : paramValues_) {
	auto it = valueVarMap_.find(argval);
	assert(it != valueVarMap_.end());
	Bvariable *v = it->second;
	res.push_back(v);
	}
	return res;
	}

	std::vector<Bvariable*> Bfunction::getFunctionLocalVars()
	{
	return localVariables_;
	}

	Bvariable Bfunction::getBvarForValue(llvm::Value val)
	{
	auto it = valueVarMap_.find(val);
	return (it != valueVarMap_.end() ? it->second : nullptr);
	}

	Bvariable *Bfunction::getNthParamVar(unsigned argIdx)
	{
	assert(argIdx < paramValues_.size());
	llvm::Value *pval = paramValues_[argIdx];
	return getBvarForValue(pval);
	}

	unsigned Bfunction::genArgSpill(Bvariable *paramVar,
	const CABIParamInfo &paramInfo,
	Binstructions *spillInstructions,
	llvm::Value *sploc)
	{
	lazyAbiSetup();
	assert(paramInfo.disp() == ParmDirect);
	TypeManager *tm = abiOracle_->tm();
	BlockLIRBuilder builder(function(), this);

	// Simple case: param arrived in single register.
	if (paramInfo.abiTypes().size() == 1) {
	llvm::Argument *arg = arguments_[paramInfo.sigOffset()];
	assert(sploc->getType()->isPointerTy());
	llvm::PointerType *llpt = llvm::cast<llvm::PointerType>(sploc->getType());
	if (paramInfo.abiType()->isVectorTy() \|\|
	arg->getType() != llpt->getElementType()) {
	std::string tag(namegen("cast"));
	llvm::Type *ptv = llvm::PointerType::get(paramInfo.abiType(), 0);
	llvm::Value *bitcast = builder.CreateBitCast(sploc, ptv, tag);
	sploc = bitcast;
	}
	llvm::Instruction *si = builder.CreateStore(arg, sploc);
	paramVar->setInitializer(si);
	spillInstructions->appendInstructions(builder.instructions());
	return 1;
	}

	assert(paramInfo.abiTypes().size() <= CABIParamInfo::ABI_TYPES_MAX_SIZE);
	// More complex case: param arrives in multiple registers.

	// Create struct type corresponding to multiple params.
	llvm::Type *llst = paramInfo.computeABIStructType(tm);
	llvm::Type *ptst = llvm::PointerType::get(llst, 0);

	// Cast the spill location to a pointer to the struct created above.
	std::string tag(namegen("cast"));
	llvm::Value *bitcast = builder.CreateBitCast(sploc, ptst, tag);
	llvm::Instruction *stinst = nullptr;

	// Generate a store to each field.
	for (unsigned i = 0; i < paramInfo.abiTypes().size(); ++i) {
	std::string tag(namegen("field" + std::to_string(i)));
	llvm::Value *fieldgep =
	builder.CreateConstInBoundsGEP2_32(llst, bitcast, 0, i, tag);
	llvm::Value *argChunk = arguments_[paramInfo.sigOffset() + i];
	stinst = builder.CreateStore(argChunk, fieldgep);
	}
	paramVar->setInitializer(stinst);
	spillInstructions->appendInstructions(builder.instructions());

	// All done.
	return paramInfo.abiTypes().size();
	}

	void Bfunction::genProlog(llvm::BasicBlock *entry)
	{
	lazyAbiSetup();
	unsigned argIdx = (abiOracle_->returnInfo().disp() == ParmIndirect ? 1 : 0);
	Binstructions spills;

	// Spill the static chain param if needed. We only want to do this
	// if a chain variable was explicitly requested.
	const CABIParamInfo &chainInfo = abiOracle_->chainInfo();
	assert(chainInfo.disp() == ParmDirect);
	unsigned soff = chainInfo.sigOffset();
	if (arguments_[soff] != chainVal_) {
	auto it = valueVarMap_.find(chainVal_);
	assert(it != valueVarMap_.end());
	Bvariable *chainVar = it->second;
	genArgSpill(chainVar, chainInfo, &spills, chainVal_);
	}
	argIdx += 1;

	// Spill any directly-passed function arguments into their previous
	// created spill areas.
	const std::vector<Btype *> &paramTypes = fcnType()->paramTypes();
	unsigned nParms = paramTypes.size();
	for (unsigned pidx = 0; pidx < nParms; ++pidx) {
	const CABIParamInfo &paramInfo = abiOracle_->paramInfo(pidx);
	if (paramInfo.disp() != ParmDirect)
	continue;
	Bvariable *v = getNthParamVar(pidx);
	if (!v) {
	assert(errorSeen());
	continue;
	}
	llvm::Value *sploc = llvm::cast<llvm::Instruction>(paramValues_[pidx]);
	argIdx += genArgSpill(v, paramInfo, &spills, sploc);
	}

	// Append allocas for local variables
	// FIXME: create lifetime annotations
	for (auto aa : allocas_)
	entry->getInstList().push_back(aa);

	// Param spills
	for (auto sp : spills.instructions())
	entry->getInstList().push_back(sp);

	// Debug meta-data generation needs to know the position at which a
	// parameter variable is available for inspection -- this is
	// typically either A) the start of the function for by-address
	// params, or B) the spill instruction that copies a direct param to
	// the stack. If the entry block is not empty, then use the last
	// inst in it as an initializer for by-address params. If the block
	// is still empty at this point we'll take care of things later.
	if (! entry->empty()) {
	for (unsigned pidx = 0; pidx < nParms; ++pidx) {
	Bvariable *v = getNthParamVar(pidx);
	if (!v) {
	assert(errorSeen());
	continue;
	}
	if (v->initializer() == nullptr)
	v->setInitializer(&entry->front());
	}
	}

	prologGenerated_ = true;
	}

	void Bfunction::fixupProlog(llvm::BasicBlock *entry,
	const std::vector<llvm::Instruction *> &temps)
	{
	lazyAbiSetup();
	// If there are any "new" temporaries discovered during the control
	// flow generation walk, incorporate them into the entry block. At this
	// stage in the game the entry block is already fully populated, including
	// (potentially) references to the alloca instructions themselves, so
	// we insert any new temps into the start of the block.
	if (! temps.empty())
	for (auto ai : temps) {
	entry->getInstList().push_front(ai);
	if (auto *ascast = llvm::dyn_cast<llvm::AddrSpaceCastInst>(ai)) {
	llvm::Value *op = ascast->getPointerOperand();
	assert(llvm::isa<llvm::AllocaInst>(op));
	entry->getInstList().push_front(llvm::cast<llvm::Instruction>(op));
	}
	}
	}

	llvm::Value Bfunction::genReturnSequence(Bexpression toRet,
	Binstructions *retInstrs,
	NameGen *inamegen)
	{
	lazyAbiSetup();
	const CABIParamInfo &returnInfo = abiOracle_->returnInfo();

	// If we're returning an empty struct, or if the function has void
	// type, then return a null ptr (return "void").
	TypeManager *tm = abiOracle_->tm();
	if (returnInfo.disp() == ParmIgnore \|\|
	fcnType()->resultType()->type() == tm->llvmVoidType()) {
	llvm::Value *rval = nullptr;
	return rval;
	}

	// Indirect return: emit memcpy into sret
	if (returnInfo.disp() == ParmIndirect) {
	BlockLIRBuilder bbuilder(function(), inamegen);
	uint64_t sz = tm->typeSize(fcnType_->resultType());
	uint64_t algn = tm->typeAlignment(fcnType_->resultType());
	llvm::MaybeAlign malgn(algn);
	bbuilder.CreateMemCpy(rtnValueMem_, malgn, toRet->value(), malgn, sz);
	retInstrs->appendInstructions(bbuilder.instructions());
	llvm::Value *rval = nullptr;
	return rval;
	}

	// Direct return: single value
	if (! returnInfo.abiType()->isAggregateType() &&
	! toRet->btype()->type()->isAggregateType())
	return toRet->value();

	// Direct return: either the ABI type is a structure or the
	// return value type is a structure. In this case we bitcast
	// the return location address to the ABI type and then issue a load
	// from the bitcast.
	llvm::Type *llrt = (returnInfo.abiType()->isAggregateType() ?
	returnInfo.computeABIStructType(tm) :
	returnInfo.abiType());
	llvm::Type *ptst = llvm::PointerType::get(llrt, 0);
	BlockLIRBuilder builder(function(), inamegen);
	std::string castname(namegen("cast"));
	llvm::Value *bitcast = builder.CreateBitCast(toRet->value(), ptst, castname);
	std::string loadname(namegen("ld"));
	llvm::Instruction *ldinst = builder.CreateLoad(llrt, bitcast, loadname);
	retInstrs->appendInstructions(builder.instructions());
	return ldinst;
	}

	Blabel *Bfunction::newLabel(Location loc) {
	unsigned labelCount = labels_.size();
	Blabel *lb = new Blabel(this, labelCount, loc);
	labelmap_.push_back(nullptr);
	labels_.push_back(lb);
	return lb;
	}

	void Bfunction::registerLabelDefStatement(Bstatement st, Blabel label)
	{
	assert(st && st->flavor() == N_LabelStmt);
	assert(label);
	assert(labelmap_[label->label()] == nullptr);
	labelmap_[label->label()] = st;
	}