forked from OSchip/llvm-project
347 lines
12 KiB
C++
347 lines
12 KiB
C++
//===-- StructRetPromotion.cpp - Promote sret arguments ------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass finds functions that return a struct (using a pointer to the struct
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// as the first argument of the function, marked with the 'sret' attribute) and
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// replaces them with a new function that simply returns each of the elements of
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// that struct (using multiple return values).
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//
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// This pass works under a number of conditions:
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// 1. The returned struct must not contain other structs
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// 2. The returned struct must only be used to load values from
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// 3. The placeholder struct passed in is the result of an alloca
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "sretpromotion"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Module.h"
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#include "llvm/CallGraphSCCPass.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Compiler.h"
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using namespace llvm;
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STATISTIC(NumRejectedSRETUses , "Number of sret rejected due to unexpected uses");
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STATISTIC(NumSRET , "Number of sret promoted");
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namespace {
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/// SRETPromotion - This pass removes sret parameter and updates
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/// function to use multiple return value.
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///
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struct VISIBILITY_HIDDEN SRETPromotion : public CallGraphSCCPass {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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CallGraphSCCPass::getAnalysisUsage(AU);
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}
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virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
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static char ID; // Pass identification, replacement for typeid
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SRETPromotion() : CallGraphSCCPass((intptr_t)&ID) {}
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private:
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bool PromoteReturn(CallGraphNode *CGN);
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bool isSafeToUpdateAllCallers(Function *F);
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Function *cloneFunctionBody(Function *F, const StructType *STy);
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void updateCallSites(Function *F, Function *NF);
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bool nestedStructType(const StructType *STy);
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};
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}
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char SRETPromotion::ID = 0;
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static RegisterPass<SRETPromotion>
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X("sretpromotion", "Promote sret arguments to multiple ret values");
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Pass *llvm::createStructRetPromotionPass() {
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return new SRETPromotion();
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}
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bool SRETPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
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bool Changed = false;
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for (unsigned i = 0, e = SCC.size(); i != e; ++i)
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Changed |= PromoteReturn(SCC[i]);
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return Changed;
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}
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/// PromoteReturn - This method promotes function that uses StructRet paramater
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/// into a function that uses mulitple return value.
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bool SRETPromotion::PromoteReturn(CallGraphNode *CGN) {
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Function *F = CGN->getFunction();
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if (!F || F->isDeclaration() || !F->hasInternalLinkage())
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return false;
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// Make sure that function returns struct.
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if (F->arg_size() == 0 || !F->hasStructRetAttr() || F->doesNotReturn())
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return false;
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assert (F->getReturnType() == Type::VoidTy && "Invalid function return type");
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Function::arg_iterator AI = F->arg_begin();
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const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
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assert (FArgType && "Invalid sret parameter type");
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const llvm::StructType *STy =
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dyn_cast<StructType>(FArgType->getElementType());
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assert (STy && "Invalid sret parameter element type");
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if (nestedStructType(STy))
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return false;
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// Check if it is ok to perform this promotion.
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if (isSafeToUpdateAllCallers(F) == false) {
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NumRejectedSRETUses++;
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return false;
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}
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NumSRET++;
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// [1] Replace use of sret parameter
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AllocaInst *TheAlloca = new AllocaInst (STy, NULL, "mrv",
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F->getEntryBlock().begin());
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Value *NFirstArg = F->arg_begin();
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NFirstArg->replaceAllUsesWith(TheAlloca);
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// [2] Find and replace ret instructions
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SmallVector<Value *,4> RetVals;
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for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
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for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
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Instruction *I = BI;
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++BI;
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if (isa<ReturnInst>(I)) {
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RetVals.clear();
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for (unsigned idx = 0; idx < STy->getNumElements(); ++idx) {
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SmallVector<Value*, 2> GEPIdx;
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GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, 0));
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GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, idx));
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Value *NGEPI = GetElementPtrInst::Create(TheAlloca, GEPIdx.begin(),
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GEPIdx.end(),
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"mrv.gep", I);
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Value *NV = new LoadInst(NGEPI, "mrv.ld", I);
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RetVals.push_back(NV);
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}
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ReturnInst *NR = ReturnInst::Create(&RetVals[0], RetVals.size(), I);
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I->replaceAllUsesWith(NR);
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I->eraseFromParent();
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}
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}
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// [3] Create the new function body and insert it into the module.
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Function *NF = cloneFunctionBody(F, STy);
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// [4] Update all call sites to use new function
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updateCallSites(F, NF);
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F->eraseFromParent();
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getAnalysis<CallGraph>().changeFunction(F, NF);
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return true;
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}
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// Check if it is ok to perform this promotion.
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bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {
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if (F->use_empty())
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// No users. OK to modify signature.
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return true;
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for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
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FnUseI != FnUseE; ++FnUseI) {
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CallSite CS = CallSite::get(*FnUseI);
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Instruction *Call = CS.getInstruction();
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CallSite::arg_iterator AI = CS.arg_begin();
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Value *FirstArg = *AI;
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if (!isa<AllocaInst>(FirstArg))
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return false;
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// Check FirstArg's users.
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for (Value::use_iterator ArgI = FirstArg->use_begin(),
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ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {
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// If FirstArg user is a CallInst that does not correspond to current
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// call site then this function F is not suitable for sret promotion.
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if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
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if (CI != Call)
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return false;
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}
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// If FirstArg user is a GEP whose all users are not LoadInst then
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// this function F is not suitable for sret promotion.
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else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
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// TODO : Use dom info and insert PHINodes to collect get results
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// from multiple call sites for this GEP.
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if (GEP->getParent() != Call->getParent())
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return false;
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for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
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GEPI != GEPE; ++GEPI)
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if (!isa<LoadInst>(GEPI))
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return false;
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}
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// Any other FirstArg users make this function unsuitable for sret
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// promotion.
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else
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return false;
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}
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}
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return true;
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}
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/// cloneFunctionBody - Create a new function based on F and
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/// insert it into module. Remove first argument. Use STy as
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/// the return type for new function.
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Function *SRETPromotion::cloneFunctionBody(Function *F,
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const StructType *STy) {
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const FunctionType *FTy = F->getFunctionType();
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std::vector<const Type*> Params;
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// ParamAttrs - Keep track of the parameter attributes for the arguments.
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SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
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const PAListPtr &PAL = F->getParamAttrs();
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// Add any return attributes.
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if (ParameterAttributes attrs = PAL.getParamAttrs(0))
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ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));
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// Skip first argument.
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Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
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++I;
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// 0th parameter attribute is reserved for return type.
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// 1th parameter attribute is for first 1st sret argument.
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unsigned ParamIndex = 2;
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while (I != E) {
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Params.push_back(I->getType());
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if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
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ParamAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
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++I;
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++ParamIndex;
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}
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FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
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Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
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NF->copyAttributesFrom(F);
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NF->setParamAttrs(PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()));
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F->getParent()->getFunctionList().insert(F, NF);
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NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
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// Replace arguments
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I = F->arg_begin();
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E = F->arg_end();
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Function::arg_iterator NI = NF->arg_begin();
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++I;
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while (I != E) {
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I->replaceAllUsesWith(NI);
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NI->takeName(I);
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++I;
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++NI;
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}
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return NF;
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}
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/// updateCallSites - Update all sites that call F to use NF.
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void SRETPromotion::updateCallSites(Function *F, Function *NF) {
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SmallVector<Value*, 16> Args;
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// ParamAttrs - Keep track of the parameter attributes for the arguments.
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SmallVector<ParamAttrsWithIndex, 8> ArgAttrsVec;
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for (Value::use_iterator FUI = F->use_begin(), FUE = F->use_end();
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FUI != FUE;) {
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CallSite CS = CallSite::get(*FUI);
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++FUI;
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Instruction *Call = CS.getInstruction();
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const PAListPtr &PAL = F->getParamAttrs();
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// Add any return attributes.
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if (ParameterAttributes attrs = PAL.getParamAttrs(0))
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ArgAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));
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// Copy arguments, however skip first one.
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CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
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Value *FirstCArg = *AI;
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++AI;
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// 0th parameter attribute is reserved for return type.
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// 1th parameter attribute is for first 1st sret argument.
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unsigned ParamIndex = 2;
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while (AI != AE) {
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Args.push_back(*AI);
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if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
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ArgAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
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++ParamIndex;
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++AI;
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}
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PAListPtr NewPAL = PAListPtr::get(ArgAttrsVec.begin(), ArgAttrsVec.end());
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// Build new call instruction.
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Instruction *New;
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if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
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New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
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Args.begin(), Args.end(), "", Call);
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cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
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cast<InvokeInst>(New)->setParamAttrs(NewPAL);
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} else {
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New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
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cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
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cast<CallInst>(New)->setParamAttrs(NewPAL);
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if (cast<CallInst>(Call)->isTailCall())
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cast<CallInst>(New)->setTailCall();
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}
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Args.clear();
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ArgAttrsVec.clear();
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New->takeName(Call);
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// Update all users of sret parameter to extract value using getresult.
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for (Value::use_iterator UI = FirstCArg->use_begin(),
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UE = FirstCArg->use_end(); UI != UE; ) {
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User *U2 = *UI++;
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CallInst *C2 = dyn_cast<CallInst>(U2);
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if (C2 && (C2 == Call))
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continue;
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else if (GetElementPtrInst *UGEP = dyn_cast<GetElementPtrInst>(U2)) {
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ConstantInt *Idx = dyn_cast<ConstantInt>(UGEP->getOperand(2));
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assert (Idx && "Unexpected getelementptr index!");
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Value *GR = new GetResultInst(New, Idx->getZExtValue(), "gr", UGEP);
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for (Value::use_iterator GI = UGEP->use_begin(),
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GE = UGEP->use_end(); GI != GE; ++GI) {
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if (LoadInst *L = dyn_cast<LoadInst>(*GI)) {
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L->replaceAllUsesWith(GR);
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L->eraseFromParent();
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}
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}
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UGEP->eraseFromParent();
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}
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else assert( 0 && "Unexpected sret parameter use");
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}
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Call->eraseFromParent();
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}
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}
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/// nestedStructType - Return true if STy includes any
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/// other aggregate types
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bool SRETPromotion::nestedStructType(const StructType *STy) {
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unsigned Num = STy->getNumElements();
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for (unsigned i = 0; i < Num; i++) {
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const Type *Ty = STy->getElementType(i);
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if (!Ty->isSingleValueType() && Ty != Type::VoidTy)
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return true;
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}
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return false;
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}
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