LLVM API Documentation
00001 //===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This pass deletes dead arguments from internal functions. Dead argument 00011 // elimination removes arguments which are directly dead, as well as arguments 00012 // only passed into function calls as dead arguments of other functions. This 00013 // pass also deletes dead arguments in a similar way. 00014 // 00015 // This pass is often useful as a cleanup pass to run after aggressive 00016 // interprocedural passes, which add possibly-dead arguments. 00017 // 00018 //===----------------------------------------------------------------------===// 00019 00020 #define DEBUG_TYPE "deadargelim" 00021 #include "llvm/Transforms/IPO.h" 00022 #include "llvm/Module.h" 00023 #include "llvm/Pass.h" 00024 #include "llvm/DerivedTypes.h" 00025 #include "llvm/Constant.h" 00026 #include "llvm/Instructions.h" 00027 #include "llvm/Support/CallSite.h" 00028 #include "llvm/Support/Debug.h" 00029 #include "llvm/ADT/Statistic.h" 00030 #include "llvm/ADT/iterator" 00031 #include <iostream> 00032 #include <set> 00033 using namespace llvm; 00034 00035 namespace { 00036 Statistic<> NumArgumentsEliminated("deadargelim", 00037 "Number of unread args removed"); 00038 Statistic<> NumRetValsEliminated("deadargelim", 00039 "Number of unused return values removed"); 00040 00041 /// DAE - The dead argument elimination pass. 00042 /// 00043 class DAE : public ModulePass { 00044 /// Liveness enum - During our initial pass over the program, we determine 00045 /// that things are either definately alive, definately dead, or in need of 00046 /// interprocedural analysis (MaybeLive). 00047 /// 00048 enum Liveness { Live, MaybeLive, Dead }; 00049 00050 /// LiveArguments, MaybeLiveArguments, DeadArguments - These sets contain 00051 /// all of the arguments in the program. The Dead set contains arguments 00052 /// which are completely dead (never used in the function). The MaybeLive 00053 /// set contains arguments which are only passed into other function calls, 00054 /// thus may be live and may be dead. The Live set contains arguments which 00055 /// are known to be alive. 00056 /// 00057 std::set<Argument*> DeadArguments, MaybeLiveArguments, LiveArguments; 00058 00059 /// DeadRetVal, MaybeLiveRetVal, LifeRetVal - These sets contain all of the 00060 /// functions in the program. The Dead set contains functions whose return 00061 /// value is known to be dead. The MaybeLive set contains functions whose 00062 /// return values are only used by return instructions, and the Live set 00063 /// contains functions whose return values are used, functions that are 00064 /// external, and functions that already return void. 00065 /// 00066 std::set<Function*> DeadRetVal, MaybeLiveRetVal, LiveRetVal; 00067 00068 /// InstructionsToInspect - As we mark arguments and return values 00069 /// MaybeLive, we keep track of which instructions could make the values 00070 /// live here. Once the entire program has had the return value and 00071 /// arguments analyzed, this set is scanned to promote the MaybeLive objects 00072 /// to be Live if they really are used. 00073 std::vector<Instruction*> InstructionsToInspect; 00074 00075 /// CallSites - Keep track of the call sites of functions that have 00076 /// MaybeLive arguments or return values. 00077 std::multimap<Function*, CallSite> CallSites; 00078 00079 public: 00080 bool runOnModule(Module &M); 00081 00082 virtual bool ShouldHackArguments() const { return false; } 00083 00084 private: 00085 Liveness getArgumentLiveness(const Argument &A); 00086 bool isMaybeLiveArgumentNowLive(Argument *Arg); 00087 00088 void SurveyFunction(Function &Fn); 00089 00090 void MarkArgumentLive(Argument *Arg); 00091 void MarkRetValLive(Function *F); 00092 void MarkReturnInstArgumentLive(ReturnInst *RI); 00093 00094 void RemoveDeadArgumentsFromFunction(Function *F); 00095 }; 00096 RegisterOpt<DAE> X("deadargelim", "Dead Argument Elimination"); 00097 00098 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 00099 /// deletes arguments to functions which are external. This is only for use 00100 /// by bugpoint. 00101 struct DAH : public DAE { 00102 virtual bool ShouldHackArguments() const { return true; } 00103 }; 00104 RegisterPass<DAH> Y("deadarghaX0r", 00105 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 00106 } 00107 00108 /// createDeadArgEliminationPass - This pass removes arguments from functions 00109 /// which are not used by the body of the function. 00110 /// 00111 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 00112 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 00113 00114 static inline bool CallPassesValueThoughVararg(Instruction *Call, 00115 const Value *Arg) { 00116 CallSite CS = CallSite::get(Call); 00117 const Type *CalledValueTy = CS.getCalledValue()->getType(); 00118 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType(); 00119 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams(); 00120 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs; 00121 AI != CS.arg_end(); ++AI) 00122 if (AI->get() == Arg) 00123 return true; 00124 return false; 00125 } 00126 00127 // getArgumentLiveness - Inspect an argument, determining if is known Live 00128 // (used in a computation), MaybeLive (only passed as an argument to a call), or 00129 // Dead (not used). 00130 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) { 00131 if (A.use_empty()) return Dead; // First check, directly dead? 00132 00133 // Scan through all of the uses, looking for non-argument passing uses. 00134 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) { 00135 // Return instructions do not immediately effect liveness. 00136 if (isa<ReturnInst>(*I)) 00137 continue; 00138 00139 CallSite CS = CallSite::get(const_cast<User*>(*I)); 00140 if (!CS.getInstruction()) { 00141 // If its used by something that is not a call or invoke, it's alive! 00142 return Live; 00143 } 00144 // If it's an indirect call, mark it alive... 00145 Function *Callee = CS.getCalledFunction(); 00146 if (!Callee) return Live; 00147 00148 // Check to see if it's passed through a va_arg area: if so, we cannot 00149 // remove it. 00150 if (CallPassesValueThoughVararg(CS.getInstruction(), &A)) 00151 return Live; // If passed through va_arg area, we cannot remove it 00152 } 00153 00154 return MaybeLive; // It must be used, but only as argument to a function 00155 } 00156 00157 00158 // SurveyFunction - This performs the initial survey of the specified function, 00159 // checking out whether or not it uses any of its incoming arguments or whether 00160 // any callers use the return value. This fills in the 00161 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets. 00162 // 00163 // We consider arguments of non-internal functions to be intrinsically alive as 00164 // well as arguments to functions which have their "address taken". 00165 // 00166 void DAE::SurveyFunction(Function &F) { 00167 bool FunctionIntrinsicallyLive = false; 00168 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead; 00169 00170 if (!F.hasInternalLinkage() && 00171 (!ShouldHackArguments() || F.getIntrinsicID())) 00172 FunctionIntrinsicallyLive = true; 00173 else 00174 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 00175 // If this use is anything other than a call site, the function is alive. 00176 CallSite CS = CallSite::get(*I); 00177 Instruction *TheCall = CS.getInstruction(); 00178 if (!TheCall) { // Not a direct call site? 00179 FunctionIntrinsicallyLive = true; 00180 break; 00181 } 00182 00183 // Check to see if the return value is used... 00184 if (RetValLiveness != Live) 00185 for (Value::use_iterator I = TheCall->use_begin(), 00186 E = TheCall->use_end(); I != E; ++I) 00187 if (isa<ReturnInst>(cast<Instruction>(*I))) { 00188 RetValLiveness = MaybeLive; 00189 } else if (isa<CallInst>(cast<Instruction>(*I)) || 00190 isa<InvokeInst>(cast<Instruction>(*I))) { 00191 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) || 00192 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) { 00193 RetValLiveness = Live; 00194 break; 00195 } else { 00196 RetValLiveness = MaybeLive; 00197 } 00198 } else { 00199 RetValLiveness = Live; 00200 break; 00201 } 00202 00203 // If the function is PASSED IN as an argument, its address has been taken 00204 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end(); 00205 AI != E; ++AI) 00206 if (AI->get() == &F) { 00207 FunctionIntrinsicallyLive = true; 00208 break; 00209 } 00210 if (FunctionIntrinsicallyLive) break; 00211 } 00212 00213 if (FunctionIntrinsicallyLive) { 00214 DEBUG(std::cerr << " Intrinsically live fn: " << F.getName() << "\n"); 00215 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); 00216 AI != E; ++AI) 00217 LiveArguments.insert(AI); 00218 LiveRetVal.insert(&F); 00219 return; 00220 } 00221 00222 switch (RetValLiveness) { 00223 case Live: LiveRetVal.insert(&F); break; 00224 case MaybeLive: MaybeLiveRetVal.insert(&F); break; 00225 case Dead: DeadRetVal.insert(&F); break; 00226 } 00227 00228 DEBUG(std::cerr << " Inspecting args for fn: " << F.getName() << "\n"); 00229 00230 // If it is not intrinsically alive, we know that all users of the 00231 // function are call sites. Mark all of the arguments live which are 00232 // directly used, and keep track of all of the call sites of this function 00233 // if there are any arguments we assume that are dead. 00234 // 00235 bool AnyMaybeLiveArgs = false; 00236 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); 00237 AI != E; ++AI) 00238 switch (getArgumentLiveness(*AI)) { 00239 case Live: 00240 DEBUG(std::cerr << " Arg live by use: " << AI->getName() << "\n"); 00241 LiveArguments.insert(AI); 00242 break; 00243 case Dead: 00244 DEBUG(std::cerr << " Arg definitely dead: " <<AI->getName()<<"\n"); 00245 DeadArguments.insert(AI); 00246 break; 00247 case MaybeLive: 00248 DEBUG(std::cerr << " Arg only passed to calls: " 00249 << AI->getName() << "\n"); 00250 AnyMaybeLiveArgs = true; 00251 MaybeLiveArguments.insert(AI); 00252 break; 00253 } 00254 00255 // If there are any "MaybeLive" arguments, we need to check callees of 00256 // this function when/if they become alive. Record which functions are 00257 // callees... 00258 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive) 00259 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); 00260 I != E; ++I) { 00261 if (AnyMaybeLiveArgs) 00262 CallSites.insert(std::make_pair(&F, CallSite::get(*I))); 00263 00264 if (RetValLiveness == MaybeLive) 00265 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 00266 UI != E; ++UI) 00267 InstructionsToInspect.push_back(cast<Instruction>(*UI)); 00268 } 00269 } 00270 00271 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we 00272 // know that the only uses of Arg are to be passed in as an argument to a 00273 // function call or return. Check to see if the formal argument passed in is in 00274 // the LiveArguments set. If so, return true. 00275 // 00276 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) { 00277 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){ 00278 if (isa<ReturnInst>(*I)) { 00279 if (LiveRetVal.count(Arg->getParent())) return true; 00280 continue; 00281 } 00282 00283 CallSite CS = CallSite::get(*I); 00284 00285 // We know that this can only be used for direct calls... 00286 Function *Callee = CS.getCalledFunction(); 00287 00288 // Loop over all of the arguments (because Arg may be passed into the call 00289 // multiple times) and check to see if any are now alive... 00290 CallSite::arg_iterator CSAI = CS.arg_begin(); 00291 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end(); 00292 AI != E; ++AI, ++CSAI) 00293 // If this is the argument we are looking for, check to see if it's alive 00294 if (*CSAI == Arg && LiveArguments.count(AI)) 00295 return true; 00296 } 00297 return false; 00298 } 00299 00300 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive. 00301 /// Mark it live in the specified sets and recursively mark arguments in callers 00302 /// live that are needed to pass in a value. 00303 /// 00304 void DAE::MarkArgumentLive(Argument *Arg) { 00305 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg); 00306 if (It == MaybeLiveArguments.end() || *It != Arg) return; 00307 00308 DEBUG(std::cerr << " MaybeLive argument now live: " << Arg->getName()<<"\n"); 00309 MaybeLiveArguments.erase(It); 00310 LiveArguments.insert(Arg); 00311 00312 // Loop over all of the call sites of the function, making any arguments 00313 // passed in to provide a value for this argument live as necessary. 00314 // 00315 Function *Fn = Arg->getParent(); 00316 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg)); 00317 00318 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn); 00319 for (; I != CallSites.end() && I->first == Fn; ++I) { 00320 CallSite CS = I->second; 00321 Value *ArgVal = *(CS.arg_begin()+ArgNo); 00322 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) { 00323 MarkArgumentLive(ActualArg); 00324 } else { 00325 // If the value passed in at this call site is a return value computed by 00326 // some other call site, make sure to mark the return value at the other 00327 // call site as being needed. 00328 CallSite ArgCS = CallSite::get(ArgVal); 00329 if (ArgCS.getInstruction()) 00330 if (Function *Fn = ArgCS.getCalledFunction()) 00331 MarkRetValLive(Fn); 00332 } 00333 } 00334 } 00335 00336 /// MarkArgumentLive - The MaybeLive return value for the specified function is 00337 /// now known to be alive. Propagate this fact to the return instructions which 00338 /// produce it. 00339 void DAE::MarkRetValLive(Function *F) { 00340 assert(F && "Shame shame, we can't have null pointers here!"); 00341 00342 // Check to see if we already knew it was live 00343 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F); 00344 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive! 00345 00346 DEBUG(std::cerr << " MaybeLive retval now live: " << F->getName() << "\n"); 00347 00348 MaybeLiveRetVal.erase(I); 00349 LiveRetVal.insert(F); // It is now known to be live! 00350 00351 // Loop over all of the functions, noticing that the return value is now live. 00352 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 00353 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 00354 MarkReturnInstArgumentLive(RI); 00355 } 00356 00357 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) { 00358 Value *Op = RI->getOperand(0); 00359 if (Argument *A = dyn_cast<Argument>(Op)) { 00360 MarkArgumentLive(A); 00361 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) { 00362 if (Function *F = CI->getCalledFunction()) 00363 MarkRetValLive(F); 00364 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) { 00365 if (Function *F = II->getCalledFunction()) 00366 MarkRetValLive(F); 00367 } 00368 } 00369 00370 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as 00371 // specified by the DeadArguments list. Transform the function and all of the 00372 // callees of the function to not have these arguments. 00373 // 00374 void DAE::RemoveDeadArgumentsFromFunction(Function *F) { 00375 // Start by computing a new prototype for the function, which is the same as 00376 // the old function, but has fewer arguments. 00377 const FunctionType *FTy = F->getFunctionType(); 00378 std::vector<const Type*> Params; 00379 00380 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) 00381 if (!DeadArguments.count(I)) 00382 Params.push_back(I->getType()); 00383 00384 const Type *RetTy = FTy->getReturnType(); 00385 if (DeadRetVal.count(F)) { 00386 RetTy = Type::VoidTy; 00387 DeadRetVal.erase(F); 00388 } 00389 00390 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 00391 // have zero fixed arguments. 00392 // 00393 // FIXME: once this bug is fixed in the CWriter, this hack should be removed. 00394 // 00395 bool ExtraArgHack = false; 00396 if (Params.empty() && FTy->isVarArg()) { 00397 ExtraArgHack = true; 00398 Params.push_back(Type::IntTy); 00399 } 00400 00401 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 00402 00403 // Create the new function body and insert it into the module... 00404 Function *NF = new Function(NFTy, F->getLinkage(), F->getName()); 00405 NF->setCallingConv(F->getCallingConv()); 00406 F->getParent()->getFunctionList().insert(F, NF); 00407 00408 // Loop over all of the callers of the function, transforming the call sites 00409 // to pass in a smaller number of arguments into the new function. 00410 // 00411 std::vector<Value*> Args; 00412 while (!F->use_empty()) { 00413 CallSite CS = CallSite::get(F->use_back()); 00414 Instruction *Call = CS.getInstruction(); 00415 00416 // Loop over the operands, deleting dead ones... 00417 CallSite::arg_iterator AI = CS.arg_begin(); 00418 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 00419 I != E; ++I, ++AI) 00420 if (!DeadArguments.count(I)) // Remove operands for dead arguments 00421 Args.push_back(*AI); 00422 00423 if (ExtraArgHack) 00424 Args.push_back(Constant::getNullValue(Type::IntTy)); 00425 00426 // Push any varargs arguments on the list 00427 for (; AI != CS.arg_end(); ++AI) 00428 Args.push_back(*AI); 00429 00430 Instruction *New; 00431 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 00432 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(), 00433 Args, "", Call); 00434 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 00435 } else { 00436 New = new CallInst(NF, Args, "", Call); 00437 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 00438 if (cast<CallInst>(Call)->isTailCall()) 00439 cast<CallInst>(New)->setTailCall(); 00440 } 00441 Args.clear(); 00442 00443 if (!Call->use_empty()) { 00444 if (New->getType() == Type::VoidTy) 00445 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 00446 else { 00447 Call->replaceAllUsesWith(New); 00448 std::string Name = Call->getName(); 00449 Call->setName(""); 00450 New->setName(Name); 00451 } 00452 } 00453 00454 // Finally, remove the old call from the program, reducing the use-count of 00455 // F. 00456 Call->getParent()->getInstList().erase(Call); 00457 } 00458 00459 // Since we have now created the new function, splice the body of the old 00460 // function right into the new function, leaving the old rotting hulk of the 00461 // function empty. 00462 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 00463 00464 // Loop over the argument list, transfering uses of the old arguments over to 00465 // the new arguments, also transfering over the names as well. While we're at 00466 // it, remove the dead arguments from the DeadArguments list. 00467 // 00468 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 00469 I2 = NF->arg_begin(); 00470 I != E; ++I) 00471 if (!DeadArguments.count(I)) { 00472 // If this is a live argument, move the name and users over to the new 00473 // version. 00474 I->replaceAllUsesWith(I2); 00475 I2->setName(I->getName()); 00476 ++I2; 00477 } else { 00478 // If this argument is dead, replace any uses of it with null constants 00479 // (these are guaranteed to only be operands to call instructions which 00480 // will later be simplified). 00481 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 00482 DeadArguments.erase(I); 00483 } 00484 00485 // If we change the return value of the function we must rewrite any return 00486 // instructions. Check this now. 00487 if (F->getReturnType() != NF->getReturnType()) 00488 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 00489 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 00490 new ReturnInst(0, RI); 00491 BB->getInstList().erase(RI); 00492 } 00493 00494 // Now that the old function is dead, delete it. 00495 F->getParent()->getFunctionList().erase(F); 00496 } 00497 00498 bool DAE::runOnModule(Module &M) { 00499 // First phase: loop through the module, determining which arguments are live. 00500 // We assume all arguments are dead unless proven otherwise (allowing us to 00501 // determine that dead arguments passed into recursive functions are dead). 00502 // 00503 DEBUG(std::cerr << "DAE - Determining liveness\n"); 00504 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 00505 SurveyFunction(*I); 00506 00507 // Loop over the instructions to inspect, propagating liveness among arguments 00508 // and return values which are MaybeLive. 00509 00510 while (!InstructionsToInspect.empty()) { 00511 Instruction *I = InstructionsToInspect.back(); 00512 InstructionsToInspect.pop_back(); 00513 00514 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) { 00515 // For return instructions, we just have to check to see if the return 00516 // value for the current function is known now to be alive. If so, any 00517 // arguments used by it are now alive, and any call instruction return 00518 // value is alive as well. 00519 if (LiveRetVal.count(RI->getParent()->getParent())) 00520 MarkReturnInstArgumentLive(RI); 00521 00522 } else { 00523 CallSite CS = CallSite::get(I); 00524 assert(CS.getInstruction() && "Unknown instruction for the I2I list!"); 00525 00526 Function *Callee = CS.getCalledFunction(); 00527 00528 // If we found a call or invoke instruction on this list, that means that 00529 // an argument of the function is a call instruction. If the argument is 00530 // live, then the return value of the called instruction is now live. 00531 // 00532 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator 00533 for (Function::arg_iterator FI = Callee->arg_begin(), 00534 E = Callee->arg_end(); FI != E; ++AI, ++FI) { 00535 // If this argument is another call... 00536 CallSite ArgCS = CallSite::get(*AI); 00537 if (ArgCS.getInstruction() && LiveArguments.count(FI)) 00538 if (Function *Callee = ArgCS.getCalledFunction()) 00539 MarkRetValLive(Callee); 00540 } 00541 } 00542 } 00543 00544 // Now we loop over all of the MaybeLive arguments, promoting them to be live 00545 // arguments if one of the calls that uses the arguments to the calls they are 00546 // passed into requires them to be live. Of course this could make other 00547 // arguments live, so process callers recursively. 00548 // 00549 // Because elements can be removed from the MaybeLiveArguments set, copy it to 00550 // a temporary vector. 00551 // 00552 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(), 00553 MaybeLiveArguments.end()); 00554 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) { 00555 Argument *MLA = TmpArgList[i]; 00556 if (MaybeLiveArguments.count(MLA) && 00557 isMaybeLiveArgumentNowLive(MLA)) 00558 MarkArgumentLive(MLA); 00559 } 00560 00561 // Recover memory early... 00562 CallSites.clear(); 00563 00564 // At this point, we know that all arguments in DeadArguments and 00565 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing 00566 // to do. 00567 if (MaybeLiveArguments.empty() && DeadArguments.empty() && 00568 MaybeLiveRetVal.empty() && DeadRetVal.empty()) 00569 return false; 00570 00571 // Otherwise, compact into one set, and start eliminating the arguments from 00572 // the functions. 00573 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end()); 00574 MaybeLiveArguments.clear(); 00575 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end()); 00576 MaybeLiveRetVal.clear(); 00577 00578 LiveArguments.clear(); 00579 LiveRetVal.clear(); 00580 00581 NumArgumentsEliminated += DeadArguments.size(); 00582 NumRetValsEliminated += DeadRetVal.size(); 00583 while (!DeadArguments.empty()) 00584 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent()); 00585 00586 while (!DeadRetVal.empty()) 00587 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin()); 00588 return true; 00589 }