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(errs() << "SretPromotion: Looking at sret function "
97 << F->getName() << "\n");
99 assert(F->getReturnType() == Type::getVoidTy(F->getContext()) &&
100 "Invalid function return type");
101 Function::arg_iterator AI = F->arg_begin();
102 const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
103 assert(FArgType && "Invalid sret parameter type");
104 const llvm::StructType *STy =
105 dyn_cast<StructType>(FArgType->getElementType());
106 assert(STy && "Invalid sret parameter element type");
108 // Check if it is ok to perform this promotion.
109 if (isSafeToUpdateAllCallers(F) == false) {
110 DEBUG(errs() << "SretPromotion: Not all callers can be updated\n");
111 NumRejectedSRETUses++;
115 DEBUG(errs() << "SretPromotion: sret argument will be promoted\n");
117 // [1] Replace use of sret parameter
118 AllocaInst *TheAlloca = new AllocaInst(STy, NULL, "mrv",
119 F->getEntryBlock().begin());
120 Value *NFirstArg = F->arg_begin();
121 NFirstArg->replaceAllUsesWith(TheAlloca);
123 // [2] Find and replace ret instructions
124 for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
125 for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
128 if (isa<ReturnInst>(I)) {
129 Value *NV = new LoadInst(TheAlloca, "mrv.ld", I);
130 ReturnInst *NR = ReturnInst::Create(F->getContext(), NV, I);
131 I->replaceAllUsesWith(NR);
132 I->eraseFromParent();
136 // [3] Create the new function body and insert it into the module.
137 Function *NF = cloneFunctionBody(F, STy);
139 // [4] Update all call sites to use new function
140 CallGraphNode *NF_CFN = updateCallSites(F, NF);
142 CallGraph &CG = getAnalysis<CallGraph>();
143 NF_CFN->stealCalledFunctionsFrom(CG[F]);
145 delete CG.removeFunctionFromModule(F);
149 // Check if it is ok to perform this promotion.
150 bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {
153 // No users. OK to modify signature.
156 for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
157 FnUseI != FnUseE; ++FnUseI) {
158 // The function is passed in as an argument to (possibly) another function,
159 // we can't change it!
160 CallSite CS = CallSite::get(*FnUseI);
161 Instruction *Call = CS.getInstruction();
162 // The function is used by something else than a call or invoke instruction,
163 // we can't change it!
164 if (!Call || !CS.isCallee(FnUseI))
166 CallSite::arg_iterator AI = CS.arg_begin();
167 Value *FirstArg = *AI;
169 if (!isa<AllocaInst>(FirstArg))
172 // Check FirstArg's users.
173 for (Value::use_iterator ArgI = FirstArg->use_begin(),
174 ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {
176 // If FirstArg user is a CallInst that does not correspond to current
177 // call site then this function F is not suitable for sret promotion.
178 if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
182 // If FirstArg user is a GEP whose all users are not LoadInst then
183 // this function F is not suitable for sret promotion.
184 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
185 // TODO : Use dom info and insert PHINodes to collect get results
186 // from multiple call sites for this GEP.
187 if (GEP->getParent() != Call->getParent())
189 for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
190 GEPI != GEPE; ++GEPI)
191 if (!isa<LoadInst>(GEPI))
194 // Any other FirstArg users make this function unsuitable for sret
204 /// cloneFunctionBody - Create a new function based on F and
205 /// insert it into module. Remove first argument. Use STy as
206 /// the return type for new function.
207 Function *SRETPromotion::cloneFunctionBody(Function *F,
208 const StructType *STy) {
210 const FunctionType *FTy = F->getFunctionType();
211 std::vector<const Type*> Params;
213 // Attributes - Keep track of the parameter attributes for the arguments.
214 SmallVector<AttributeWithIndex, 8> AttributesVec;
215 const AttrListPtr &PAL = F->getAttributes();
217 // Add any return attributes.
218 if (Attributes attrs = PAL.getRetAttributes())
219 AttributesVec.push_back(AttributeWithIndex::get(0, attrs));
221 // Skip first argument.
222 Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
224 // 0th parameter attribute is reserved for return type.
225 // 1th parameter attribute is for first 1st sret argument.
226 unsigned ParamIndex = 2;
228 Params.push_back(I->getType());
229 if (Attributes Attrs = PAL.getParamAttributes(ParamIndex))
230 AttributesVec.push_back(AttributeWithIndex::get(ParamIndex - 1, Attrs));
235 // Add any fn attributes.
236 if (Attributes attrs = PAL.getFnAttributes())
237 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs));
240 FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
241 Function *NF = Function::Create(NFTy, F->getLinkage());
243 NF->copyAttributesFrom(F);
244 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()));
245 F->getParent()->getFunctionList().insert(F, NF);
246 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
251 Function::arg_iterator NI = NF->arg_begin();
254 I->replaceAllUsesWith(NI);
263 /// updateCallSites - Update all sites that call F to use NF.
264 CallGraphNode *SRETPromotion::updateCallSites(Function *F, Function *NF) {
265 CallGraph &CG = getAnalysis<CallGraph>();
266 SmallVector<Value*, 16> Args;
268 // Attributes - Keep track of the parameter attributes for the arguments.
269 SmallVector<AttributeWithIndex, 8> ArgAttrsVec;
271 // Get a new callgraph node for NF.
272 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
274 while (!F->use_empty()) {
275 CallSite CS = CallSite::get(*F->use_begin());
276 Instruction *Call = CS.getInstruction();
278 const AttrListPtr &PAL = F->getAttributes();
279 // Add any return attributes.
280 if (Attributes attrs = PAL.getRetAttributes())
281 ArgAttrsVec.push_back(AttributeWithIndex::get(0, attrs));
283 // Copy arguments, however skip first one.
284 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
285 Value *FirstCArg = *AI;
287 // 0th parameter attribute is reserved for return type.
288 // 1th parameter attribute is for first 1st sret argument.
289 unsigned ParamIndex = 2;
292 if (Attributes Attrs = PAL.getParamAttributes(ParamIndex))
293 ArgAttrsVec.push_back(AttributeWithIndex::get(ParamIndex - 1, Attrs));
298 // Add any function attributes.
299 if (Attributes attrs = PAL.getFnAttributes())
300 ArgAttrsVec.push_back(AttributeWithIndex::get(~0, attrs));
302 AttrListPtr NewPAL = AttrListPtr::get(ArgAttrsVec.begin(), ArgAttrsVec.end());
304 // Build new call instruction.
306 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
307 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
308 Args.begin(), Args.end(), "", Call);
309 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
310 cast<InvokeInst>(New)->setAttributes(NewPAL);
312 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
313 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
314 cast<CallInst>(New)->setAttributes(NewPAL);
315 if (cast<CallInst>(Call)->isTailCall())
316 cast<CallInst>(New)->setTailCall();
322 // Update the callgraph to know that the callsite has been transformed.
323 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
324 CalleeNode->removeCallEdgeFor(Call);
325 CalleeNode->addCalledFunction(New, NF_CGN);
327 // Update all users of sret parameter to extract value using extractvalue.
328 for (Value::use_iterator UI = FirstCArg->use_begin(),
329 UE = FirstCArg->use_end(); UI != UE; ) {
331 CallInst *C2 = dyn_cast<CallInst>(U2);
332 if (C2 && (C2 == Call))
335 GetElementPtrInst *UGEP = cast<GetElementPtrInst>(U2);
336 ConstantInt *Idx = cast<ConstantInt>(UGEP->getOperand(2));
337 Value *GR = ExtractValueInst::Create(New, Idx->getZExtValue(),
339 while(!UGEP->use_empty()) {
340 // isSafeToUpdateAllCallers has checked that all GEP uses are
342 LoadInst *L = cast<LoadInst>(*UGEP->use_begin());
343 L->replaceAllUsesWith(GR);
344 L->eraseFromParent();
346 UGEP->eraseFromParent();
349 Call->eraseFromParent();
355 /// nestedStructType - Return true if STy includes any
356 /// other aggregate types
357 bool SRETPromotion::nestedStructType(const StructType *STy) {
358 unsigned Num = STy->getNumElements();
359 for (unsigned i = 0; i < Num; i++) {
360 const Type *Ty = STy->getElementType(i);
361 if (!Ty->isSingleValueType() && Ty != Type::getVoidTy(STy->getContext()))