DeadArgumentElimination.cpp revision 208599
1193323Sed//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2193323Sed// 3193323Sed// The LLVM Compiler Infrastructure 4193323Sed// 5193323Sed// This file is distributed under the University of Illinois Open Source 6193323Sed// License. See LICENSE.TXT for details. 7193323Sed// 8193323Sed//===----------------------------------------------------------------------===// 9193323Sed// 10193323Sed// This pass deletes dead arguments from internal functions. Dead argument 11193323Sed// elimination removes arguments which are directly dead, as well as arguments 12193323Sed// only passed into function calls as dead arguments of other functions. This 13193323Sed// pass also deletes dead return values in a similar way. 14193323Sed// 15193323Sed// This pass is often useful as a cleanup pass to run after aggressive 16193323Sed// interprocedural passes, which add possibly-dead arguments or return values. 17193323Sed// 18193323Sed//===----------------------------------------------------------------------===// 19193323Sed 20193323Sed#define DEBUG_TYPE "deadargelim" 21193323Sed#include "llvm/Transforms/IPO.h" 22193323Sed#include "llvm/CallingConv.h" 23193323Sed#include "llvm/Constant.h" 24193323Sed#include "llvm/DerivedTypes.h" 25193323Sed#include "llvm/Instructions.h" 26193323Sed#include "llvm/IntrinsicInst.h" 27198090Srdivacky#include "llvm/LLVMContext.h" 28193323Sed#include "llvm/Module.h" 29193323Sed#include "llvm/Pass.h" 30193323Sed#include "llvm/Support/CallSite.h" 31193323Sed#include "llvm/Support/Debug.h" 32198090Srdivacky#include "llvm/Support/raw_ostream.h" 33193323Sed#include "llvm/ADT/SmallVector.h" 34193323Sed#include "llvm/ADT/Statistic.h" 35193323Sed#include "llvm/ADT/StringExtras.h" 36193323Sed#include <map> 37193323Sed#include <set> 38193323Sedusing namespace llvm; 39193323Sed 40193323SedSTATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 41193323SedSTATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 42193323Sed 43193323Sednamespace { 44193323Sed /// DAE - The dead argument elimination pass. 45193323Sed /// 46198892Srdivacky class DAE : public ModulePass { 47193323Sed public: 48193323Sed 49193323Sed /// Struct that represents (part of) either a return value or a function 50193323Sed /// argument. Used so that arguments and return values can be used 51193323Sed /// interchangably. 52193323Sed struct RetOrArg { 53206083Srdivacky RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 54193323Sed IsArg(IsArg) {} 55193323Sed const Function *F; 56193323Sed unsigned Idx; 57193323Sed bool IsArg; 58193323Sed 59193323Sed /// Make RetOrArg comparable, so we can put it into a map. 60193323Sed bool operator<(const RetOrArg &O) const { 61193323Sed if (F != O.F) 62193323Sed return F < O.F; 63193323Sed else if (Idx != O.Idx) 64193323Sed return Idx < O.Idx; 65193323Sed else 66193323Sed return IsArg < O.IsArg; 67193323Sed } 68193323Sed 69193323Sed /// Make RetOrArg comparable, so we can easily iterate the multimap. 70193323Sed bool operator==(const RetOrArg &O) const { 71193323Sed return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 72193323Sed } 73193323Sed 74193323Sed std::string getDescription() const { 75206083Srdivacky return std::string((IsArg ? "Argument #" : "Return value #")) 76198090Srdivacky + utostr(Idx) + " of function " + F->getNameStr(); 77193323Sed } 78193323Sed }; 79193323Sed 80193323Sed /// Liveness enum - During our initial pass over the program, we determine 81193323Sed /// that things are either alive or maybe alive. We don't mark anything 82193323Sed /// explicitly dead (even if we know they are), since anything not alive 83193323Sed /// with no registered uses (in Uses) will never be marked alive and will 84193323Sed /// thus become dead in the end. 85193323Sed enum Liveness { Live, MaybeLive }; 86193323Sed 87193323Sed /// Convenience wrapper 88193323Sed RetOrArg CreateRet(const Function *F, unsigned Idx) { 89193323Sed return RetOrArg(F, Idx, false); 90193323Sed } 91193323Sed /// Convenience wrapper 92193323Sed RetOrArg CreateArg(const Function *F, unsigned Idx) { 93193323Sed return RetOrArg(F, Idx, true); 94193323Sed } 95193323Sed 96193323Sed typedef std::multimap<RetOrArg, RetOrArg> UseMap; 97193323Sed /// This maps a return value or argument to any MaybeLive return values or 98193323Sed /// arguments it uses. This allows the MaybeLive values to be marked live 99193323Sed /// when any of its users is marked live. 100193323Sed /// For example (indices are left out for clarity): 101193323Sed /// - Uses[ret F] = ret G 102193323Sed /// This means that F calls G, and F returns the value returned by G. 103193323Sed /// - Uses[arg F] = ret G 104193323Sed /// This means that some function calls G and passes its result as an 105193323Sed /// argument to F. 106193323Sed /// - Uses[ret F] = arg F 107193323Sed /// This means that F returns one of its own arguments. 108193323Sed /// - Uses[arg F] = arg G 109193323Sed /// This means that G calls F and passes one of its own (G's) arguments 110193323Sed /// directly to F. 111193323Sed UseMap Uses; 112193323Sed 113193323Sed typedef std::set<RetOrArg> LiveSet; 114193323Sed typedef std::set<const Function*> LiveFuncSet; 115193323Sed 116193323Sed /// This set contains all values that have been determined to be live. 117193323Sed LiveSet LiveValues; 118193323Sed /// This set contains all values that are cannot be changed in any way. 119193323Sed LiveFuncSet LiveFunctions; 120193323Sed 121193323Sed typedef SmallVector<RetOrArg, 5> UseVector; 122193323Sed 123193323Sed public: 124193323Sed static char ID; // Pass identification, replacement for typeid 125193323Sed DAE() : ModulePass(&ID) {} 126193323Sed bool runOnModule(Module &M); 127193323Sed 128193323Sed virtual bool ShouldHackArguments() const { return false; } 129193323Sed 130193323Sed private: 131193323Sed Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 132206083Srdivacky Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses, 133193323Sed unsigned RetValNum = 0); 134206083Srdivacky Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 135193323Sed 136206083Srdivacky void SurveyFunction(const Function &F); 137193323Sed void MarkValue(const RetOrArg &RA, Liveness L, 138193323Sed const UseVector &MaybeLiveUses); 139193323Sed void MarkLive(const RetOrArg &RA); 140193323Sed void MarkLive(const Function &F); 141193323Sed void PropagateLiveness(const RetOrArg &RA); 142193323Sed bool RemoveDeadStuffFromFunction(Function *F); 143193323Sed bool DeleteDeadVarargs(Function &Fn); 144193323Sed }; 145193323Sed} 146193323Sed 147193323Sed 148193323Sedchar DAE::ID = 0; 149193323Sedstatic RegisterPass<DAE> 150193323SedX("deadargelim", "Dead Argument Elimination"); 151193323Sed 152193323Sednamespace { 153193323Sed /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 154193323Sed /// deletes arguments to functions which are external. This is only for use 155193323Sed /// by bugpoint. 156193323Sed struct DAH : public DAE { 157193323Sed static char ID; 158193323Sed virtual bool ShouldHackArguments() const { return true; } 159193323Sed }; 160193323Sed} 161193323Sed 162193323Sedchar DAH::ID = 0; 163193323Sedstatic RegisterPass<DAH> 164193323SedY("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 165193323Sed 166193323Sed/// createDeadArgEliminationPass - This pass removes arguments from functions 167193323Sed/// which are not used by the body of the function. 168193323Sed/// 169193323SedModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 170193323SedModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 171193323Sed 172193323Sed/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 173193323Sed/// llvm.vastart is never called, the varargs list is dead for the function. 174193323Sedbool DAE::DeleteDeadVarargs(Function &Fn) { 175193323Sed assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 176193323Sed if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 177193323Sed 178193323Sed // Ensure that the function is only directly called. 179194178Sed if (Fn.hasAddressTaken()) 180194178Sed return false; 181193323Sed 182193323Sed // Okay, we know we can transform this function if safe. Scan its body 183193323Sed // looking for calls to llvm.vastart. 184193323Sed for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 185193323Sed for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 186193323Sed if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 187193323Sed if (II->getIntrinsicID() == Intrinsic::vastart) 188193323Sed return false; 189193323Sed } 190193323Sed } 191193323Sed } 192193323Sed 193193323Sed // If we get here, there are no calls to llvm.vastart in the function body, 194193323Sed // remove the "..." and adjust all the calls. 195193323Sed 196193323Sed // Start by computing a new prototype for the function, which is the same as 197193323Sed // the old function, but doesn't have isVarArg set. 198193323Sed const FunctionType *FTy = Fn.getFunctionType(); 199206083Srdivacky 200193323Sed std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 201198090Srdivacky FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 202198090Srdivacky Params, false); 203193323Sed unsigned NumArgs = Params.size(); 204193323Sed 205193323Sed // Create the new function body and insert it into the module... 206193323Sed Function *NF = Function::Create(NFTy, Fn.getLinkage()); 207193323Sed NF->copyAttributesFrom(&Fn); 208193323Sed Fn.getParent()->getFunctionList().insert(&Fn, NF); 209193323Sed NF->takeName(&Fn); 210193323Sed 211193323Sed // Loop over all of the callers of the function, transforming the call sites 212193323Sed // to pass in a smaller number of arguments into the new function. 213193323Sed // 214193323Sed std::vector<Value*> Args; 215193323Sed while (!Fn.use_empty()) { 216193323Sed CallSite CS = CallSite::get(Fn.use_back()); 217193323Sed Instruction *Call = CS.getInstruction(); 218193323Sed 219193323Sed // Pass all the same arguments. 220193323Sed Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 221193323Sed 222193323Sed // Drop any attributes that were on the vararg arguments. 223193323Sed AttrListPtr PAL = CS.getAttributes(); 224193323Sed if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 225193323Sed SmallVector<AttributeWithIndex, 8> AttributesVec; 226193323Sed for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 227193323Sed AttributesVec.push_back(PAL.getSlot(i)); 228206083Srdivacky if (Attributes FnAttrs = PAL.getFnAttributes()) 229193323Sed AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 230193323Sed PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 231193323Sed } 232193323Sed 233193323Sed Instruction *New; 234193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 235193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 236193323Sed Args.begin(), Args.end(), "", Call); 237193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 238193323Sed cast<InvokeInst>(New)->setAttributes(PAL); 239193323Sed } else { 240193323Sed New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 241193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 242193323Sed cast<CallInst>(New)->setAttributes(PAL); 243193323Sed if (cast<CallInst>(Call)->isTailCall()) 244193323Sed cast<CallInst>(New)->setTailCall(); 245193323Sed } 246207618Srdivacky if (MDNode *N = Call->getDbgMetadata()) 247207618Srdivacky New->setDbgMetadata(N); 248207618Srdivacky 249193323Sed Args.clear(); 250193323Sed 251193323Sed if (!Call->use_empty()) 252193323Sed Call->replaceAllUsesWith(New); 253193323Sed 254193323Sed New->takeName(Call); 255193323Sed 256193323Sed // Finally, remove the old call from the program, reducing the use-count of 257193323Sed // F. 258193323Sed Call->eraseFromParent(); 259193323Sed } 260193323Sed 261193323Sed // Since we have now created the new function, splice the body of the old 262193323Sed // function right into the new function, leaving the old rotting hulk of the 263193323Sed // function empty. 264193323Sed NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 265193323Sed 266193323Sed // Loop over the argument list, transfering uses of the old arguments over to 267193323Sed // the new arguments, also transfering over the names as well. While we're at 268193323Sed // it, remove the dead arguments from the DeadArguments list. 269193323Sed // 270193323Sed for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 271193323Sed I2 = NF->arg_begin(); I != E; ++I, ++I2) { 272193323Sed // Move the name and users over to the new version. 273193323Sed I->replaceAllUsesWith(I2); 274193323Sed I2->takeName(I); 275193323Sed } 276193323Sed 277193323Sed // Finally, nuke the old function. 278193323Sed Fn.eraseFromParent(); 279193323Sed return true; 280193323Sed} 281193323Sed 282193323Sed/// Convenience function that returns the number of return values. It returns 0 283193323Sed/// for void functions and 1 for functions not returning a struct. It returns 284193323Sed/// the number of struct elements for functions returning a struct. 285193323Sedstatic unsigned NumRetVals(const Function *F) { 286206083Srdivacky if (F->getReturnType()->isVoidTy()) 287193323Sed return 0; 288193323Sed else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 289193323Sed return STy->getNumElements(); 290193323Sed else 291193323Sed return 1; 292193323Sed} 293193323Sed 294193323Sed/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 295193323Sed/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 296193323Sed/// liveness of Use. 297193323SedDAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 298193323Sed // We're live if our use or its Function is already marked as live. 299193323Sed if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 300193323Sed return Live; 301193323Sed 302193323Sed // We're maybe live otherwise, but remember that we must become live if 303193323Sed // Use becomes live. 304193323Sed MaybeLiveUses.push_back(Use); 305193323Sed return MaybeLive; 306193323Sed} 307193323Sed 308193323Sed 309193323Sed/// SurveyUse - This looks at a single use of an argument or return value 310193323Sed/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 311206083Srdivacky/// if it causes the used value to become MaybeLive. 312193323Sed/// 313193323Sed/// RetValNum is the return value number to use when this use is used in a 314193323Sed/// return instruction. This is used in the recursion, you should always leave 315193323Sed/// it at 0. 316206083SrdivackyDAE::Liveness DAE::SurveyUse(Value::const_use_iterator U, 317206083Srdivacky UseVector &MaybeLiveUses, unsigned RetValNum) { 318206083Srdivacky const User *V = *U; 319206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 320193323Sed // The value is returned from a function. It's only live when the 321193323Sed // function's return value is live. We use RetValNum here, for the case 322193323Sed // that U is really a use of an insertvalue instruction that uses the 323193323Sed // orginal Use. 324193323Sed RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 325193323Sed // We might be live, depending on the liveness of Use. 326193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 327193323Sed } 328206083Srdivacky if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 329193323Sed if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 330193323Sed && IV->hasIndices()) 331193323Sed // The use we are examining is inserted into an aggregate. Our liveness 332193323Sed // depends on all uses of that aggregate, but if it is used as a return 333193323Sed // value, only index at which we were inserted counts. 334193323Sed RetValNum = *IV->idx_begin(); 335193323Sed 336193323Sed // Note that if we are used as the aggregate operand to the insertvalue, 337193323Sed // we don't change RetValNum, but do survey all our uses. 338193323Sed 339193323Sed Liveness Result = MaybeLive; 340206083Srdivacky for (Value::const_use_iterator I = IV->use_begin(), 341193323Sed E = V->use_end(); I != E; ++I) { 342193323Sed Result = SurveyUse(I, MaybeLiveUses, RetValNum); 343193323Sed if (Result == Live) 344193323Sed break; 345193323Sed } 346193323Sed return Result; 347193323Sed } 348206083Srdivacky 349206083Srdivacky if (ImmutableCallSite CS = V) { 350206083Srdivacky const Function *F = CS.getCalledFunction(); 351193323Sed if (F) { 352193323Sed // Used in a direct call. 353206083Srdivacky 354193323Sed // Find the argument number. We know for sure that this use is an 355193323Sed // argument, since if it was the function argument this would be an 356193323Sed // indirect call and the we know can't be looking at a value of the 357193323Sed // label type (for the invoke instruction). 358206083Srdivacky unsigned ArgNo = CS.getArgumentNo(U); 359193323Sed 360193323Sed if (ArgNo >= F->getFunctionType()->getNumParams()) 361193323Sed // The value is passed in through a vararg! Must be live. 362193323Sed return Live; 363193323Sed 364206083Srdivacky assert(CS.getArgument(ArgNo) 365206083Srdivacky == CS->getOperand(U.getOperandNo()) 366193323Sed && "Argument is not where we expected it"); 367193323Sed 368193323Sed // Value passed to a normal call. It's only live when the corresponding 369193323Sed // argument to the called function turns out live. 370193323Sed RetOrArg Use = CreateArg(F, ArgNo); 371193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 372193323Sed } 373193323Sed } 374193323Sed // Used in any other way? Value must be live. 375193323Sed return Live; 376193323Sed} 377193323Sed 378193323Sed/// SurveyUses - This looks at all the uses of the given value 379193323Sed/// Returns the Liveness deduced from the uses of this value. 380193323Sed/// 381193323Sed/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 382193323Sed/// the result is Live, MaybeLiveUses might be modified but its content should 383193323Sed/// be ignored (since it might not be complete). 384206083SrdivackyDAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 385193323Sed // Assume it's dead (which will only hold if there are no uses at all..). 386193323Sed Liveness Result = MaybeLive; 387193323Sed // Check each use. 388206083Srdivacky for (Value::const_use_iterator I = V->use_begin(), 389193323Sed E = V->use_end(); I != E; ++I) { 390193323Sed Result = SurveyUse(I, MaybeLiveUses); 391193323Sed if (Result == Live) 392193323Sed break; 393193323Sed } 394193323Sed return Result; 395193323Sed} 396193323Sed 397193323Sed// SurveyFunction - This performs the initial survey of the specified function, 398193323Sed// checking out whether or not it uses any of its incoming arguments or whether 399193323Sed// any callers use the return value. This fills in the LiveValues set and Uses 400193323Sed// map. 401193323Sed// 402193323Sed// We consider arguments of non-internal functions to be intrinsically alive as 403193323Sed// well as arguments to functions which have their "address taken". 404193323Sed// 405206083Srdivackyvoid DAE::SurveyFunction(const Function &F) { 406193323Sed unsigned RetCount = NumRetVals(&F); 407193323Sed // Assume all return values are dead 408193323Sed typedef SmallVector<Liveness, 5> RetVals; 409193323Sed RetVals RetValLiveness(RetCount, MaybeLive); 410193323Sed 411193323Sed typedef SmallVector<UseVector, 5> RetUses; 412193323Sed // These vectors map each return value to the uses that make it MaybeLive, so 413193323Sed // we can add those to the Uses map if the return value really turns out to be 414193323Sed // MaybeLive. Initialized to a list of RetCount empty lists. 415193323Sed RetUses MaybeLiveRetUses(RetCount); 416193323Sed 417206083Srdivacky for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 418206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 419193323Sed if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 420193323Sed != F.getFunctionType()->getReturnType()) { 421193323Sed // We don't support old style multiple return values. 422193323Sed MarkLive(F); 423193323Sed return; 424193323Sed } 425193323Sed 426193323Sed if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 427193323Sed MarkLive(F); 428193323Sed return; 429193323Sed } 430193323Sed 431202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 432193323Sed // Keep track of the number of live retvals, so we can skip checks once all 433193323Sed // of them turn out to be live. 434193323Sed unsigned NumLiveRetVals = 0; 435193323Sed const Type *STy = dyn_cast<StructType>(F.getReturnType()); 436193323Sed // Loop all uses of the function. 437206083Srdivacky for (Value::const_use_iterator I = F.use_begin(), E = F.use_end(); 438206083Srdivacky I != E; ++I) { 439193323Sed // If the function is PASSED IN as an argument, its address has been 440193323Sed // taken. 441206083Srdivacky ImmutableCallSite CS(*I); 442206083Srdivacky if (!CS || !CS.isCallee(I)) { 443193323Sed MarkLive(F); 444193323Sed return; 445193323Sed } 446193323Sed 447193323Sed // If this use is anything other than a call site, the function is alive. 448206083Srdivacky const Instruction *TheCall = CS.getInstruction(); 449193323Sed if (!TheCall) { // Not a direct call site? 450193323Sed MarkLive(F); 451193323Sed return; 452193323Sed } 453193323Sed 454193323Sed // If we end up here, we are looking at a direct call to our function. 455193323Sed 456193323Sed // Now, check how our return value(s) is/are used in this caller. Don't 457193323Sed // bother checking return values if all of them are live already. 458193323Sed if (NumLiveRetVals != RetCount) { 459193323Sed if (STy) { 460193323Sed // Check all uses of the return value. 461206083Srdivacky for (Value::const_use_iterator I = TheCall->use_begin(), 462193323Sed E = TheCall->use_end(); I != E; ++I) { 463206083Srdivacky const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 464193323Sed if (Ext && Ext->hasIndices()) { 465193323Sed // This use uses a part of our return value, survey the uses of 466193323Sed // that part and store the results for this index only. 467193323Sed unsigned Idx = *Ext->idx_begin(); 468193323Sed if (RetValLiveness[Idx] != Live) { 469193323Sed RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 470193323Sed if (RetValLiveness[Idx] == Live) 471193323Sed NumLiveRetVals++; 472193323Sed } 473193323Sed } else { 474193323Sed // Used by something else than extractvalue. Mark all return 475193323Sed // values as live. 476193323Sed for (unsigned i = 0; i != RetCount; ++i ) 477193323Sed RetValLiveness[i] = Live; 478193323Sed NumLiveRetVals = RetCount; 479193323Sed break; 480193323Sed } 481193323Sed } 482193323Sed } else { 483193323Sed // Single return value 484193323Sed RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 485193323Sed if (RetValLiveness[0] == Live) 486193323Sed NumLiveRetVals = RetCount; 487193323Sed } 488193323Sed } 489193323Sed } 490193323Sed 491193323Sed // Now we've inspected all callers, record the liveness of our return values. 492193323Sed for (unsigned i = 0; i != RetCount; ++i) 493193323Sed MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 494193323Sed 495202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 496193323Sed 497193323Sed // Now, check all of our arguments. 498193323Sed unsigned i = 0; 499193323Sed UseVector MaybeLiveArgUses; 500206083Srdivacky for (Function::const_arg_iterator AI = F.arg_begin(), 501193323Sed E = F.arg_end(); AI != E; ++AI, ++i) { 502193323Sed // See what the effect of this use is (recording any uses that cause 503193323Sed // MaybeLive in MaybeLiveArgUses). 504193323Sed Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 505193323Sed // Mark the result. 506193323Sed MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 507193323Sed // Clear the vector again for the next iteration. 508193323Sed MaybeLiveArgUses.clear(); 509193323Sed } 510193323Sed} 511193323Sed 512193323Sed/// MarkValue - This function marks the liveness of RA depending on L. If L is 513193323Sed/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 514193323Sed/// such that RA will be marked live if any use in MaybeLiveUses gets marked 515193323Sed/// live later on. 516193323Sedvoid DAE::MarkValue(const RetOrArg &RA, Liveness L, 517193323Sed const UseVector &MaybeLiveUses) { 518193323Sed switch (L) { 519193323Sed case Live: MarkLive(RA); break; 520193323Sed case MaybeLive: 521193323Sed { 522193323Sed // Note any uses of this value, so this return value can be 523193323Sed // marked live whenever one of the uses becomes live. 524193323Sed for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 525193323Sed UE = MaybeLiveUses.end(); UI != UE; ++UI) 526193323Sed Uses.insert(std::make_pair(*UI, RA)); 527193323Sed break; 528193323Sed } 529193323Sed } 530193323Sed} 531193323Sed 532193323Sed/// MarkLive - Mark the given Function as alive, meaning that it cannot be 533193323Sed/// changed in any way. Additionally, 534193323Sed/// mark any values that are used as this function's parameters or by its return 535193323Sed/// values (according to Uses) live as well. 536193323Sedvoid DAE::MarkLive(const Function &F) { 537202375Srdivacky DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 538208599Srdivacky // Mark the function as live. 539208599Srdivacky LiveFunctions.insert(&F); 540208599Srdivacky // Mark all arguments as live. 541208599Srdivacky for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 542208599Srdivacky PropagateLiveness(CreateArg(&F, i)); 543208599Srdivacky // Mark all return values as live. 544208599Srdivacky for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 545208599Srdivacky PropagateLiveness(CreateRet(&F, i)); 546193323Sed} 547193323Sed 548193323Sed/// MarkLive - Mark the given return value or argument as live. Additionally, 549193323Sed/// mark any values that are used by this value (according to Uses) live as 550193323Sed/// well. 551193323Sedvoid DAE::MarkLive(const RetOrArg &RA) { 552193323Sed if (LiveFunctions.count(RA.F)) 553193323Sed return; // Function was already marked Live. 554193323Sed 555193323Sed if (!LiveValues.insert(RA).second) 556193323Sed return; // We were already marked Live. 557193323Sed 558202375Srdivacky DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 559193323Sed PropagateLiveness(RA); 560193323Sed} 561193323Sed 562193323Sed/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 563193323Sed/// to any other values it uses (according to Uses). 564193323Sedvoid DAE::PropagateLiveness(const RetOrArg &RA) { 565193323Sed // We don't use upper_bound (or equal_range) here, because our recursive call 566193323Sed // to ourselves is likely to cause the upper_bound (which is the first value 567193323Sed // not belonging to RA) to become erased and the iterator invalidated. 568193323Sed UseMap::iterator Begin = Uses.lower_bound(RA); 569193323Sed UseMap::iterator E = Uses.end(); 570193323Sed UseMap::iterator I; 571193323Sed for (I = Begin; I != E && I->first == RA; ++I) 572193323Sed MarkLive(I->second); 573193323Sed 574193323Sed // Erase RA from the Uses map (from the lower bound to wherever we ended up 575193323Sed // after the loop). 576193323Sed Uses.erase(Begin, I); 577193323Sed} 578193323Sed 579193323Sed// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 580193323Sed// that are not in LiveValues. Transform the function and all of the callees of 581193323Sed// the function to not have these arguments and return values. 582193323Sed// 583193323Sedbool DAE::RemoveDeadStuffFromFunction(Function *F) { 584193323Sed // Don't modify fully live functions 585193323Sed if (LiveFunctions.count(F)) 586193323Sed return false; 587193323Sed 588193323Sed // Start by computing a new prototype for the function, which is the same as 589193323Sed // the old function, but has fewer arguments and a different return type. 590193323Sed const FunctionType *FTy = F->getFunctionType(); 591193323Sed std::vector<const Type*> Params; 592193323Sed 593193323Sed // Set up to build a new list of parameter attributes. 594193323Sed SmallVector<AttributeWithIndex, 8> AttributesVec; 595193323Sed const AttrListPtr &PAL = F->getAttributes(); 596193323Sed 597193323Sed // The existing function return attributes. 598193323Sed Attributes RAttrs = PAL.getRetAttributes(); 599193323Sed Attributes FnAttrs = PAL.getFnAttributes(); 600193323Sed 601193323Sed // Find out the new return value. 602193323Sed 603193323Sed const Type *RetTy = FTy->getReturnType(); 604193323Sed const Type *NRetTy = NULL; 605193323Sed unsigned RetCount = NumRetVals(F); 606206083Srdivacky 607193323Sed // -1 means unused, other numbers are the new index 608193323Sed SmallVector<int, 5> NewRetIdxs(RetCount, -1); 609193323Sed std::vector<const Type*> RetTypes; 610206083Srdivacky if (RetTy->isVoidTy()) { 611206083Srdivacky NRetTy = RetTy; 612193323Sed } else { 613193323Sed const StructType *STy = dyn_cast<StructType>(RetTy); 614193323Sed if (STy) 615193323Sed // Look at each of the original return values individually. 616193323Sed for (unsigned i = 0; i != RetCount; ++i) { 617193323Sed RetOrArg Ret = CreateRet(F, i); 618193323Sed if (LiveValues.erase(Ret)) { 619193323Sed RetTypes.push_back(STy->getElementType(i)); 620193323Sed NewRetIdxs[i] = RetTypes.size() - 1; 621193323Sed } else { 622193323Sed ++NumRetValsEliminated; 623202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 624198090Srdivacky << F->getName() << "\n"); 625193323Sed } 626193323Sed } 627193323Sed else 628193323Sed // We used to return a single value. 629193323Sed if (LiveValues.erase(CreateRet(F, 0))) { 630193323Sed RetTypes.push_back(RetTy); 631193323Sed NewRetIdxs[0] = 0; 632193323Sed } else { 633202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 634198090Srdivacky << "\n"); 635193323Sed ++NumRetValsEliminated; 636193323Sed } 637193323Sed if (RetTypes.size() > 1) 638193323Sed // More than one return type? Return a struct with them. Also, if we used 639193323Sed // to return a struct and didn't change the number of return values, 640193323Sed // return a struct again. This prevents changing {something} into 641193323Sed // something and {} into void. 642193323Sed // Make the new struct packed if we used to return a packed struct 643193323Sed // already. 644198090Srdivacky NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 645193323Sed else if (RetTypes.size() == 1) 646193323Sed // One return type? Just a simple value then, but only if we didn't use to 647193323Sed // return a struct with that simple value before. 648193323Sed NRetTy = RetTypes.front(); 649193323Sed else if (RetTypes.size() == 0) 650193323Sed // No return types? Make it void, but only if we didn't use to return {}. 651198090Srdivacky NRetTy = Type::getVoidTy(F->getContext()); 652193323Sed } 653193323Sed 654193323Sed assert(NRetTy && "No new return type found?"); 655193323Sed 656193323Sed // Remove any incompatible attributes, but only if we removed all return 657193323Sed // values. Otherwise, ensure that we don't have any conflicting attributes 658193323Sed // here. Currently, this should not be possible, but special handling might be 659193323Sed // required when new return value attributes are added. 660206083Srdivacky if (NRetTy->isVoidTy()) 661193323Sed RAttrs &= ~Attribute::typeIncompatible(NRetTy); 662193323Sed else 663206083Srdivacky assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 664193323Sed && "Return attributes no longer compatible?"); 665193323Sed 666193323Sed if (RAttrs) 667193323Sed AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 668193323Sed 669193323Sed // Remember which arguments are still alive. 670193323Sed SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 671193323Sed // Construct the new parameter list from non-dead arguments. Also construct 672193323Sed // a new set of parameter attributes to correspond. Skip the first parameter 673193323Sed // attribute, since that belongs to the return value. 674193323Sed unsigned i = 0; 675193323Sed for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 676193323Sed I != E; ++I, ++i) { 677193323Sed RetOrArg Arg = CreateArg(F, i); 678193323Sed if (LiveValues.erase(Arg)) { 679193323Sed Params.push_back(I->getType()); 680193323Sed ArgAlive[i] = true; 681193323Sed 682193323Sed // Get the original parameter attributes (skipping the first one, that is 683193323Sed // for the return value. 684193323Sed if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 685193323Sed AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 686193323Sed } else { 687193323Sed ++NumArgumentsEliminated; 688202375Srdivacky DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 689198090Srdivacky << ") from " << F->getName() << "\n"); 690193323Sed } 691193323Sed } 692193323Sed 693206083Srdivacky if (FnAttrs != Attribute::None) 694193323Sed AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 695193323Sed 696193323Sed // Reconstruct the AttributesList based on the vector we constructed. 697206083Srdivacky AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), 698206083Srdivacky AttributesVec.end()); 699193323Sed 700193323Sed // Create the new function type based on the recomputed parameters. 701206083Srdivacky FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 702193323Sed 703193323Sed // No change? 704193323Sed if (NFTy == FTy) 705193323Sed return false; 706193323Sed 707193323Sed // Create the new function body and insert it into the module... 708193323Sed Function *NF = Function::Create(NFTy, F->getLinkage()); 709193323Sed NF->copyAttributesFrom(F); 710193323Sed NF->setAttributes(NewPAL); 711193323Sed // Insert the new function before the old function, so we won't be processing 712193323Sed // it again. 713193323Sed F->getParent()->getFunctionList().insert(F, NF); 714193323Sed NF->takeName(F); 715193323Sed 716193323Sed // Loop over all of the callers of the function, transforming the call sites 717193323Sed // to pass in a smaller number of arguments into the new function. 718193323Sed // 719193323Sed std::vector<Value*> Args; 720193323Sed while (!F->use_empty()) { 721193323Sed CallSite CS = CallSite::get(F->use_back()); 722193323Sed Instruction *Call = CS.getInstruction(); 723193323Sed 724193323Sed AttributesVec.clear(); 725193323Sed const AttrListPtr &CallPAL = CS.getAttributes(); 726193323Sed 727193323Sed // The call return attributes. 728193323Sed Attributes RAttrs = CallPAL.getRetAttributes(); 729193323Sed Attributes FnAttrs = CallPAL.getFnAttributes(); 730193323Sed // Adjust in case the function was changed to return void. 731193323Sed RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 732193323Sed if (RAttrs) 733193323Sed AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 734193323Sed 735193323Sed // Declare these outside of the loops, so we can reuse them for the second 736193323Sed // loop, which loops the varargs. 737193323Sed CallSite::arg_iterator I = CS.arg_begin(); 738193323Sed unsigned i = 0; 739193323Sed // Loop over those operands, corresponding to the normal arguments to the 740193323Sed // original function, and add those that are still alive. 741193323Sed for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 742193323Sed if (ArgAlive[i]) { 743193323Sed Args.push_back(*I); 744193323Sed // Get original parameter attributes, but skip return attributes. 745193323Sed if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 746193323Sed AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 747193323Sed } 748193323Sed 749193323Sed // Push any varargs arguments on the list. Don't forget their attributes. 750193323Sed for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 751193323Sed Args.push_back(*I); 752193323Sed if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 753193323Sed AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 754193323Sed } 755193323Sed 756193323Sed if (FnAttrs != Attribute::None) 757193323Sed AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 758193323Sed 759193323Sed // Reconstruct the AttributesList based on the vector we constructed. 760193323Sed AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 761193323Sed AttributesVec.end()); 762193323Sed 763193323Sed Instruction *New; 764193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 765193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 766193323Sed Args.begin(), Args.end(), "", Call); 767193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 768193323Sed cast<InvokeInst>(New)->setAttributes(NewCallPAL); 769193323Sed } else { 770193323Sed New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 771193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 772193323Sed cast<CallInst>(New)->setAttributes(NewCallPAL); 773193323Sed if (cast<CallInst>(Call)->isTailCall()) 774193323Sed cast<CallInst>(New)->setTailCall(); 775193323Sed } 776207618Srdivacky if (MDNode *N = Call->getDbgMetadata()) 777207618Srdivacky New->setDbgMetadata(N); 778207618Srdivacky 779193323Sed Args.clear(); 780193323Sed 781193323Sed if (!Call->use_empty()) { 782193323Sed if (New->getType() == Call->getType()) { 783193323Sed // Return type not changed? Just replace users then. 784193323Sed Call->replaceAllUsesWith(New); 785193323Sed New->takeName(Call); 786206083Srdivacky } else if (New->getType()->isVoidTy()) { 787193323Sed // Our return value has uses, but they will get removed later on. 788193323Sed // Replace by null for now. 789193323Sed Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 790193323Sed } else { 791204642Srdivacky assert(RetTy->isStructTy() && 792193323Sed "Return type changed, but not into a void. The old return type" 793193323Sed " must have been a struct!"); 794193323Sed Instruction *InsertPt = Call; 795193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 796193323Sed BasicBlock::iterator IP = II->getNormalDest()->begin(); 797193323Sed while (isa<PHINode>(IP)) ++IP; 798193323Sed InsertPt = IP; 799193323Sed } 800206083Srdivacky 801193323Sed // We used to return a struct. Instead of doing smart stuff with all the 802193323Sed // uses of this struct, we will just rebuild it using 803193323Sed // extract/insertvalue chaining and let instcombine clean that up. 804193323Sed // 805193323Sed // Start out building up our return value from undef 806198090Srdivacky Value *RetVal = UndefValue::get(RetTy); 807193323Sed for (unsigned i = 0; i != RetCount; ++i) 808193323Sed if (NewRetIdxs[i] != -1) { 809193323Sed Value *V; 810193323Sed if (RetTypes.size() > 1) 811193323Sed // We are still returning a struct, so extract the value from our 812193323Sed // return value 813193323Sed V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 814193323Sed InsertPt); 815193323Sed else 816193323Sed // We are now returning a single element, so just insert that 817193323Sed V = New; 818193323Sed // Insert the value at the old position 819193323Sed RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 820193323Sed } 821193323Sed // Now, replace all uses of the old call instruction with the return 822193323Sed // struct we built 823193323Sed Call->replaceAllUsesWith(RetVal); 824193323Sed New->takeName(Call); 825193323Sed } 826193323Sed } 827193323Sed 828193323Sed // Finally, remove the old call from the program, reducing the use-count of 829193323Sed // F. 830193323Sed Call->eraseFromParent(); 831193323Sed } 832193323Sed 833193323Sed // Since we have now created the new function, splice the body of the old 834193323Sed // function right into the new function, leaving the old rotting hulk of the 835193323Sed // function empty. 836193323Sed NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 837193323Sed 838193323Sed // Loop over the argument list, transfering uses of the old arguments over to 839193323Sed // the new arguments, also transfering over the names as well. 840193323Sed i = 0; 841193323Sed for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 842193323Sed I2 = NF->arg_begin(); I != E; ++I, ++i) 843193323Sed if (ArgAlive[i]) { 844193323Sed // If this is a live argument, move the name and users over to the new 845193323Sed // version. 846193323Sed I->replaceAllUsesWith(I2); 847193323Sed I2->takeName(I); 848193323Sed ++I2; 849193323Sed } else { 850193323Sed // If this argument is dead, replace any uses of it with null constants 851193323Sed // (these are guaranteed to become unused later on). 852193323Sed I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 853193323Sed } 854193323Sed 855193323Sed // If we change the return value of the function we must rewrite any return 856193323Sed // instructions. Check this now. 857193323Sed if (F->getReturnType() != NF->getReturnType()) 858193323Sed for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 859193323Sed if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 860193323Sed Value *RetVal; 861193323Sed 862208599Srdivacky if (NFTy->getReturnType()->isVoidTy()) { 863193323Sed RetVal = 0; 864193323Sed } else { 865204642Srdivacky assert (RetTy->isStructTy()); 866193323Sed // The original return value was a struct, insert 867193323Sed // extractvalue/insertvalue chains to extract only the values we need 868193323Sed // to return and insert them into our new result. 869193323Sed // This does generate messy code, but we'll let it to instcombine to 870193323Sed // clean that up. 871193323Sed Value *OldRet = RI->getOperand(0); 872193323Sed // Start out building up our return value from undef 873198090Srdivacky RetVal = UndefValue::get(NRetTy); 874193323Sed for (unsigned i = 0; i != RetCount; ++i) 875193323Sed if (NewRetIdxs[i] != -1) { 876193323Sed ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 877193323Sed "oldret", RI); 878193323Sed if (RetTypes.size() > 1) { 879193323Sed // We're still returning a struct, so reinsert the value into 880193323Sed // our new return value at the new index 881193323Sed 882193323Sed RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 883193323Sed "newret", RI); 884193323Sed } else { 885193323Sed // We are now only returning a simple value, so just return the 886193323Sed // extracted value. 887193323Sed RetVal = EV; 888193323Sed } 889193323Sed } 890193323Sed } 891193323Sed // Replace the return instruction with one returning the new return 892193323Sed // value (possibly 0 if we became void). 893198090Srdivacky ReturnInst::Create(F->getContext(), RetVal, RI); 894193323Sed BB->getInstList().erase(RI); 895193323Sed } 896193323Sed 897193323Sed // Now that the old function is dead, delete it. 898193323Sed F->eraseFromParent(); 899193323Sed 900193323Sed return true; 901193323Sed} 902193323Sed 903193323Sedbool DAE::runOnModule(Module &M) { 904193323Sed bool Changed = false; 905193323Sed 906193323Sed // First pass: Do a simple check to see if any functions can have their "..." 907193323Sed // removed. We can do this if they never call va_start. This loop cannot be 908193323Sed // fused with the next loop, because deleting a function invalidates 909193323Sed // information computed while surveying other functions. 910202375Srdivacky DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 911193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 912193323Sed Function &F = *I++; 913193323Sed if (F.getFunctionType()->isVarArg()) 914193323Sed Changed |= DeleteDeadVarargs(F); 915193323Sed } 916193323Sed 917193323Sed // Second phase:loop through the module, determining which arguments are live. 918193323Sed // We assume all arguments are dead unless proven otherwise (allowing us to 919193323Sed // determine that dead arguments passed into recursive functions are dead). 920193323Sed // 921202375Srdivacky DEBUG(dbgs() << "DAE - Determining liveness\n"); 922193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 923193323Sed SurveyFunction(*I); 924206083Srdivacky 925193323Sed // Now, remove all dead arguments and return values from each function in 926206083Srdivacky // turn. 927193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 928206083Srdivacky // Increment now, because the function will probably get removed (ie. 929193323Sed // replaced by a new one). 930193323Sed Function *F = I++; 931193323Sed Changed |= RemoveDeadStuffFromFunction(F); 932193323Sed } 933193323Sed return Changed; 934193323Sed} 935