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llvm-project/llvm/lib/Transforms/IPO/StructRetPromotion.cpp

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//===-- StructRetPromotion.cpp - Promote sret arguments -000000------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// TODO : Describe this pass.
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sretpromotion"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Module.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/Instructions.h"
#include "llvm/ParamAttrsList.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;
STATISTIC(NumRejectedSRETUses , "Number of sret rejected due to unexpected uses");
STATISTIC(NumSRET , "Number of sret promoted");
namespace {
/// SRETPromotion - This pass removes sret parameter and updates
/// function to use multiple return value.
///
struct VISIBILITY_HIDDEN SRETPromotion : public CallGraphSCCPass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
CallGraphSCCPass::getAnalysisUsage(AU);
}
virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
static char ID; // Pass identification, replacement for typeid
SRETPromotion() : CallGraphSCCPass((intptr_t)&ID) {}
private:
bool PromoteReturn(CallGraphNode *CGN);
bool isSafeToUpdateAllCallers(Function *F);
Function *cloneFunctionBody(Function *F, const StructType *STy);
void updateCallSites(Function *F, Function *NF);
};
char SRETPromotion::ID = 0;
RegisterPass<SRETPromotion> X("sretpromotion",
"Promote sret arguments to multiple ret values");
}
Pass *llvm::createStructRetPromotionPass() {
return new SRETPromotion();
}
bool SRETPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
bool Changed = false;
for (unsigned i = 0, e = SCC.size(); i != e; ++i)
Changed |= PromoteReturn(SCC[i]);
return Changed;
}
/// PromoteReturn - This method promotes function that uses StructRet paramater
/// into a function that uses mulitple return value.
bool SRETPromotion::PromoteReturn(CallGraphNode *CGN) {
Function *F = CGN->getFunction();
if (!F || F->isDeclaration())
return false;
// Make sure that function returns struct.
if (F->arg_size() == 0 || !F->hasStructRetAttr() || F->doesNotReturn())
return false;
assert (F->getReturnType() == Type::VoidTy && "Invalid function return type");
Function::arg_iterator AI = F->arg_begin();
const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
assert (FArgType && "Invalid sret paramater type");
const llvm::StructType *STy =
dyn_cast<StructType>(FArgType->getElementType());
assert (STy && "Invalid sret parameter element type");
// Check if it is ok to perform this promotion.
if (isSafeToUpdateAllCallers(F) == false) {
NumRejectedSRETUses++;
return false;
}
// [1] Replace use of sret parameter
AllocaInst *TheAlloca = new AllocaInst (STy, NULL, "mrv",
F->getEntryBlock().begin());
Value *NFirstArg = F->arg_begin();
NFirstArg->replaceAllUsesWith(TheAlloca);
// [2] Find and replace ret instructions
SmallVector<Value *,4> RetVals;
for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
Instruction *I = BI;
++BI;
if (isa<ReturnInst>(I)) {
RetVals.clear();
for (unsigned idx = 0; idx < STy->getNumElements(); ++idx) {
SmallVector<Value*, 2> GEPIdx;
GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, 0));
GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, idx));
Value *NGEPI = new GetElementPtrInst(TheAlloca, GEPIdx.begin(), GEPIdx.end(),
"mrv.gep", I);
Value *NV = new LoadInst(NGEPI, "mrv.ld", I);
RetVals.push_back(NV);
}
ReturnInst *NR = new ReturnInst(&RetVals[0], RetVals.size(), I);
I->replaceAllUsesWith(NR);
I->eraseFromParent();
}
}
// [3] Create the new function body and insert it into the module.
Function *NF = cloneFunctionBody(F, STy);
// [4] Update all call sites to use new function
updateCallSites(F, NF);
F->eraseFromParent();
getAnalysis<CallGraph>().changeFunction(F, NF);
return true;
}
// Check if it is ok to perform this promotion.
bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {
if (F->use_empty())
// No users. OK to modify signature.
return true;
for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
FnUseI != FnUseE; ++FnUseI) {
CallSite CS = CallSite::get(*FnUseI);
Instruction *Call = CS.getInstruction();
CallSite::arg_iterator AI = CS.arg_begin();
Value *FirstArg = *AI;
if (!isa<AllocaInst>(FirstArg))
return false;
// Check FirstArg's users.
for (Value::use_iterator ArgI = FirstArg->use_begin(),
ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {
// If FirstArg user is a CallInst that does not correspond to current
// call site then this function F is not suitable for sret promotion.
if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
if (CI != Call)
return false;
}
// If FirstArg user is a GEP whose all users are not LoadInst then
// this function F is not suitable for sret promotion.
else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
GEPI != GEPE; ++GEPI)
if (!isa<LoadInst>(GEPI))
return false;
}
// Any other FirstArg users make this function unsuitable for sret
// promotion.
else
return false;
}
}
return true;
}
/// cloneFunctionBody - Create a new function based on F and
/// insert it into module. Remove first argument. Use STy as
/// the return type for new function.
Function *SRETPromotion::cloneFunctionBody(Function *F,
const StructType *STy) {
const FunctionType *FTy = F->getFunctionType();
std::vector<const Type*> Params;
// ParamAttrs - Keep track of the parameter attributes for the arguments.
ParamAttrsVector ParamAttrsVec;
const ParamAttrsList *PAL = F->getParamAttrs();
// Add any return attributes.
if (ParameterAttributes attrs = PAL ? PAL->getParamAttrs(0) : ParamAttr::None)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));
// Skip first argument.
Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
++I;
unsigned ParamIndex = 1; // 0th parameter attribute is reserved for return type.
while (I != E) {
Params.push_back(I->getType());
if (ParameterAttributes attrs = PAL ? PAL->getParamAttrs(ParamIndex) :
ParamAttr::None)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), attrs));
++I;
++ParamIndex;
}
FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
NF->setCallingConv(F->getCallingConv());
NF->setParamAttrs(ParamAttrsList::get(ParamAttrsVec));
F->getParent()->getFunctionList().insert(F, NF);
NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
// Replace arguments
I = F->arg_begin();
E = F->arg_end();
Function::arg_iterator NI = NF->arg_begin();
++I;
while (I != E) {
I->replaceAllUsesWith(NI);
NI->takeName(I);
++I;
++NI;
}
return NF;
}
/// updateCallSites - Update all sites that call F to use NF.
void SRETPromotion::updateCallSites(Function *F, Function *NF) {
SmallVector<Value*, 16> Args;
// ParamAttrs - Keep track of the parameter attributes for the arguments.
ParamAttrsVector ParamAttrsVec;
for (Value::use_iterator FUI = F->use_begin(), FUE = F->use_end(); FUI != FUE;) {
CallSite CS = CallSite::get(*FUI);
++FUI;
Instruction *Call = CS.getInstruction();
const ParamAttrsList *PAL = F->getParamAttrs();
// Add any return attributes.
if (ParameterAttributes attrs = PAL ? PAL->getParamAttrs(0) : ParamAttr::None)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));
// Copy arguments, however skip first one.
CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
Value *FirstCArg = *AI;
++AI;
unsigned ParamIndex = 1; // 0th parameter attribute is reserved for return type.
while (AI != AE) {
Args.push_back(*AI);
if (ParameterAttributes Attrs = PAL ? PAL->getParamAttrs(ParamIndex) :
ParamAttr::None)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
++ParamIndex;
++AI;
}
// Build new call instruction.
Instruction *New;
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
Args.begin(), Args.end(), "", Call);
cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
cast<InvokeInst>(New)->setParamAttrs(ParamAttrsList::get(ParamAttrsVec));
} else {
New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
cast<CallInst>(New)->setParamAttrs(ParamAttrsList::get(ParamAttrsVec));
if (cast<CallInst>(Call)->isTailCall())
cast<CallInst>(New)->setTailCall();
}
Args.clear();
ParamAttrsVec.clear();
New->takeName(Call);
// Update all users of sret parameter to extract value using getresult.
for (Value::use_iterator UI = FirstCArg->use_begin(),
UE = FirstCArg->use_end(); UI != UE; ) {
User *U2 = *UI++;
CallInst *C2 = dyn_cast<CallInst>(U2);
if (C2 && (C2 == Call))
continue;
else if (GetElementPtrInst *UGEP = dyn_cast<GetElementPtrInst>(U2)) {
Value *GR = new GetResultInst(New, 5, "xxx", UGEP);
for (Value::use_iterator GI = UGEP->use_begin(),
GE = UGEP->use_end(); GI != GE; ++GI) {
if (LoadInst *L = dyn_cast<LoadInst>(*GI)) {
L->replaceAllUsesWith(GR);
L->eraseFromParent();
}
}
UGEP->eraseFromParent();
}
else assert( 0 && "Unexpected sret parameter use");
}
Call->eraseFromParent();
}
}
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