1 //===-- StructRetPromotion.cpp - Promote sret arguments ------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass finds functions that return a struct (using a pointer to the struct
11 // as the first argument of the function, marked with the 'sret' attribute) and
12 // replaces them with a new function that simply returns each of the elements of
13 // that struct (using multiple return values).
15 // This pass works under a number of conditions:
16 // 1. The returned struct must not contain other structs
17 // 2. The returned struct must only be used to load values from
18 // 3. The placeholder struct passed in is the result of an alloca
20 //===----------------------------------------------------------------------===//
22 #define DEBUG_TYPE "sretpromotion"
23 #include "llvm/Transforms/IPO.h"
24 #include "llvm/Constants.h"
25 #include "llvm/DerivedTypes.h"
26 #include "llvm/LLVMContext.h"
27 #include "llvm/Module.h"
28 #include "llvm/CallGraphSCCPass.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Analysis/CallGraph.h"
31 #include "llvm/Support/CallSite.h"
32 #include "llvm/Support/CFG.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/ADT/SmallVector.h"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/Support/raw_ostream.h"
40 STATISTIC(NumRejectedSRETUses , "Number of sret rejected due to unexpected uses");
41 STATISTIC(NumSRET , "Number of sret promoted");
43 /// SRETPromotion - This pass removes sret parameter and updates
44 /// function to use multiple return value.
46 struct SRETPromotion : public CallGraphSCCPass {
47 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
48 CallGraphSCCPass::getAnalysisUsage(AU);
51 virtual bool runOnSCC(std::vector<CallGraphNode *> &SCC);
52 static char ID; // Pass identification, replacement for typeid
53 SRETPromotion() : CallGraphSCCPass(&ID) {}
56 CallGraphNode *PromoteReturn(CallGraphNode *CGN);
57 bool isSafeToUpdateAllCallers(Function *F);
58 Function *cloneFunctionBody(Function *F, const StructType *STy);
59 CallGraphNode *updateCallSites(Function *F, Function *NF);
60 bool nestedStructType(const StructType *STy);
64 char SRETPromotion::ID = 0;
65 static RegisterPass<SRETPromotion>
66 X("sretpromotion", "Promote sret arguments to multiple ret values");
68 Pass *llvm::createStructRetPromotionPass() {
69 return new SRETPromotion();
72 bool SRETPromotion::runOnSCC(std::vector<CallGraphNode *> &SCC) {
75 for (unsigned i = 0, e = SCC.size(); i != e; ++i)
76 if (CallGraphNode *NewNode = PromoteReturn(SCC[i])) {
84 /// PromoteReturn - This method promotes function that uses StructRet paramater
85 /// into a function that uses multiple return values.
86 CallGraphNode *SRETPromotion::PromoteReturn(CallGraphNode *CGN) {
87 Function *F = CGN->getFunction();
89 if (!F || F->isDeclaration() || !F->hasLocalLinkage())
92 // Make sure that function returns struct.
93 if (F->arg_size() == 0 || !F->hasStructRetAttr() || F->doesNotReturn())
96 DEBUG(dbgs() << "SretPromotion: Looking at sret function "
97 << F->getName() << "\n");
99 assert(F->getReturnType()->isVoidTy() && "Invalid function return type");
100 Function::arg_iterator AI = F->arg_begin();
101 const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
102 assert(FArgType && "Invalid sret parameter type");
103 const llvm::StructType *STy =
104 dyn_cast<StructType>(FArgType->getElementType());
105 assert(STy && "Invalid sret parameter element type");
107 // Check if it is ok to perform this promotion.
108 if (isSafeToUpdateAllCallers(F) == false) {
109 DEBUG(dbgs() << "SretPromotion: Not all callers can be updated\n");
110 NumRejectedSRETUses++;
114 DEBUG(dbgs() << "SretPromotion: sret argument will be promoted\n");
116 // [1] Replace use of sret parameter
117 AllocaInst *TheAlloca = new AllocaInst(STy, NULL, "mrv",
118 F->getEntryBlock().begin());
119 Value *NFirstArg = F->arg_begin();
120 NFirstArg->replaceAllUsesWith(TheAlloca);
122 // [2] Find and replace ret instructions
123 for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
124 for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
127 if (isa<ReturnInst>(I)) {
128 Value *NV = new LoadInst(TheAlloca, "mrv.ld", I);
129 ReturnInst *NR = ReturnInst::Create(F->getContext(), NV, I);
130 I->replaceAllUsesWith(NR);
131 I->eraseFromParent();
135 // [3] Create the new function body and insert it into the module.
136 Function *NF = cloneFunctionBody(F, STy);
138 // [4] Update all call sites to use new function
139 CallGraphNode *NF_CFN = updateCallSites(F, NF);
141 CallGraph &CG = getAnalysis<CallGraph>();
142 NF_CFN->stealCalledFunctionsFrom(CG[F]);
144 delete CG.removeFunctionFromModule(F);
148 // Check if it is ok to perform this promotion.
149 bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {
152 // No users. OK to modify signature.
155 for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
156 FnUseI != FnUseE; ++FnUseI) {
157 // The function is passed in as an argument to (possibly) another function,
158 // we can't change it!
159 CallSite CS = CallSite::get(*FnUseI);
160 Instruction *Call = CS.getInstruction();
161 // The function is used by something else than a call or invoke instruction,
162 // we can't change it!
163 if (!Call || !CS.isCallee(FnUseI))
165 CallSite::arg_iterator AI = CS.arg_begin();
166 Value *FirstArg = *AI;
168 if (!isa<AllocaInst>(FirstArg))
171 // Check FirstArg's users.
172 for (Value::use_iterator ArgI = FirstArg->use_begin(),
173 ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {
175 // If FirstArg user is a CallInst that does not correspond to current
176 // call site then this function F is not suitable for sret promotion.
177 if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
181 // If FirstArg user is a GEP whose all users are not LoadInst then
182 // this function F is not suitable for sret promotion.
183 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
184 // TODO : Use dom info and insert PHINodes to collect get results
185 // from multiple call sites for this GEP.
186 if (GEP->getParent() != Call->getParent())
188 for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
189 GEPI != GEPE; ++GEPI)
190 if (!isa<LoadInst>(GEPI))
193 // Any other FirstArg users make this function unsuitable for sret
203 /// cloneFunctionBody - Create a new function based on F and
204 /// insert it into module. Remove first argument. Use STy as
205 /// the return type for new function.
206 Function *SRETPromotion::cloneFunctionBody(Function *F,
207 const StructType *STy) {
209 const FunctionType *FTy = F->getFunctionType();
210 std::vector<const Type*> Params;
212 // Attributes - Keep track of the parameter attributes for the arguments.
213 SmallVector<AttributeWithIndex, 8> AttributesVec;
214 const AttrListPtr &PAL = F->getAttributes();
216 // Add any return attributes.
217 if (Attributes attrs = PAL.getRetAttributes())
218 AttributesVec.push_back(AttributeWithIndex::get(0, attrs));
220 // Skip first argument.
221 Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
223 // 0th parameter attribute is reserved for return type.
224 // 1th parameter attribute is for first 1st sret argument.
225 unsigned ParamIndex = 2;
227 Params.push_back(I->getType());
228 if (Attributes Attrs = PAL.getParamAttributes(ParamIndex))
229 AttributesVec.push_back(AttributeWithIndex::get(ParamIndex - 1, Attrs));
234 // Add any fn attributes.
235 if (Attributes attrs = PAL.getFnAttributes())
236 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs));
239 FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
240 Function *NF = Function::Create(NFTy, F->getLinkage());
242 NF->copyAttributesFrom(F);
243 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()));
244 F->getParent()->getFunctionList().insert(F, NF);
245 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
250 Function::arg_iterator NI = NF->arg_begin();
253 I->replaceAllUsesWith(NI);
262 /// updateCallSites - Update all sites that call F to use NF.
263 CallGraphNode *SRETPromotion::updateCallSites(Function *F, Function *NF) {
264 CallGraph &CG = getAnalysis<CallGraph>();
265 SmallVector<Value*, 16> Args;
267 // Attributes - Keep track of the parameter attributes for the arguments.
268 SmallVector<AttributeWithIndex, 8> ArgAttrsVec;
270 // Get a new callgraph node for NF.
271 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
273 while (!F->use_empty()) {
274 CallSite CS = CallSite::get(*F->use_begin());
275 Instruction *Call = CS.getInstruction();
277 const AttrListPtr &PAL = F->getAttributes();
278 // Add any return attributes.
279 if (Attributes attrs = PAL.getRetAttributes())
280 ArgAttrsVec.push_back(AttributeWithIndex::get(0, attrs));
282 // Copy arguments, however skip first one.
283 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
284 Value *FirstCArg = *AI;
286 // 0th parameter attribute is reserved for return type.
287 // 1th parameter attribute is for first 1st sret argument.
288 unsigned ParamIndex = 2;
291 if (Attributes Attrs = PAL.getParamAttributes(ParamIndex))
292 ArgAttrsVec.push_back(AttributeWithIndex::get(ParamIndex - 1, Attrs));
297 // Add any function attributes.
298 if (Attributes attrs = PAL.getFnAttributes())
299 ArgAttrsVec.push_back(AttributeWithIndex::get(~0, attrs));
301 AttrListPtr NewPAL = AttrListPtr::get(ArgAttrsVec.begin(), ArgAttrsVec.end());
303 // Build new call instruction.
305 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
306 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
307 Args.begin(), Args.end(), "", Call);
308 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
309 cast<InvokeInst>(New)->setAttributes(NewPAL);
311 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
312 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
313 cast<CallInst>(New)->setAttributes(NewPAL);
314 if (cast<CallInst>(Call)->isTailCall())
315 cast<CallInst>(New)->setTailCall();
321 // Update the callgraph to know that the callsite has been transformed.
322 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
323 CalleeNode->removeCallEdgeFor(Call);
324 CalleeNode->addCalledFunction(New, NF_CGN);
326 // Update all users of sret parameter to extract value using extractvalue.
327 for (Value::use_iterator UI = FirstCArg->use_begin(),
328 UE = FirstCArg->use_end(); UI != UE; ) {
330 CallInst *C2 = dyn_cast<CallInst>(U2);
331 if (C2 && (C2 == Call))
334 GetElementPtrInst *UGEP = cast<GetElementPtrInst>(U2);
335 ConstantInt *Idx = cast<ConstantInt>(UGEP->getOperand(2));
336 Value *GR = ExtractValueInst::Create(New, Idx->getZExtValue(),
338 while(!UGEP->use_empty()) {
339 // isSafeToUpdateAllCallers has checked that all GEP uses are
341 LoadInst *L = cast<LoadInst>(*UGEP->use_begin());
342 L->replaceAllUsesWith(GR);
343 L->eraseFromParent();
345 UGEP->eraseFromParent();
348 Call->eraseFromParent();
354 /// nestedStructType - Return true if STy includes any
355 /// other aggregate types
356 bool SRETPromotion::nestedStructType(const StructType *STy) {
357 unsigned Num = STy->getNumElements();
358 for (unsigned i = 0; i < Num; i++) {
359 const Type *Ty = STy->getElementType(i);
360 if (!Ty->isSingleValueType() && !Ty->isVoidTy())