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" 22252723Sdim#include "llvm/ADT/DenseMap.h" 23252723Sdim#include "llvm/ADT/SmallVector.h" 24252723Sdim#include "llvm/ADT/Statistic.h" 25252723Sdim#include "llvm/ADT/StringExtras.h" 26252723Sdim#include "llvm/DIBuilder.h" 27245431Sdim#include "llvm/DebugInfo.h" 28252723Sdim#include "llvm/IR/CallingConv.h" 29252723Sdim#include "llvm/IR/Constant.h" 30252723Sdim#include "llvm/IR/DerivedTypes.h" 31252723Sdim#include "llvm/IR/Instructions.h" 32252723Sdim#include "llvm/IR/IntrinsicInst.h" 33252723Sdim#include "llvm/IR/LLVMContext.h" 34252723Sdim#include "llvm/IR/Module.h" 35193323Sed#include "llvm/Pass.h" 36193323Sed#include "llvm/Support/CallSite.h" 37193323Sed#include "llvm/Support/Debug.h" 38198090Srdivacky#include "llvm/Support/raw_ostream.h" 39193323Sed#include <map> 40193323Sed#include <set> 41193323Sedusing namespace llvm; 42193323Sed 43193323SedSTATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 44193323SedSTATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 45218893SdimSTATISTIC(NumArgumentsReplacedWithUndef, 46218893Sdim "Number of unread args replaced with undef"); 47193323Sednamespace { 48193323Sed /// DAE - The dead argument elimination pass. 49193323Sed /// 50198892Srdivacky class DAE : public ModulePass { 51193323Sed public: 52193323Sed 53193323Sed /// Struct that represents (part of) either a return value or a function 54193323Sed /// argument. Used so that arguments and return values can be used 55221345Sdim /// interchangeably. 56193323Sed struct RetOrArg { 57206083Srdivacky RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 58193323Sed IsArg(IsArg) {} 59193323Sed const Function *F; 60193323Sed unsigned Idx; 61193323Sed bool IsArg; 62193323Sed 63193323Sed /// Make RetOrArg comparable, so we can put it into a map. 64193323Sed bool operator<(const RetOrArg &O) const { 65193323Sed if (F != O.F) 66193323Sed return F < O.F; 67193323Sed else if (Idx != O.Idx) 68193323Sed return Idx < O.Idx; 69193323Sed else 70193323Sed return IsArg < O.IsArg; 71193323Sed } 72193323Sed 73193323Sed /// Make RetOrArg comparable, so we can easily iterate the multimap. 74193323Sed bool operator==(const RetOrArg &O) const { 75193323Sed return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 76193323Sed } 77193323Sed 78193323Sed std::string getDescription() const { 79206083Srdivacky return std::string((IsArg ? "Argument #" : "Return value #")) 80235633Sdim + utostr(Idx) + " of function " + F->getName().str(); 81193323Sed } 82193323Sed }; 83193323Sed 84193323Sed /// Liveness enum - During our initial pass over the program, we determine 85193323Sed /// that things are either alive or maybe alive. We don't mark anything 86193323Sed /// explicitly dead (even if we know they are), since anything not alive 87193323Sed /// with no registered uses (in Uses) will never be marked alive and will 88193323Sed /// thus become dead in the end. 89193323Sed enum Liveness { Live, MaybeLive }; 90193323Sed 91193323Sed /// Convenience wrapper 92193323Sed RetOrArg CreateRet(const Function *F, unsigned Idx) { 93193323Sed return RetOrArg(F, Idx, false); 94193323Sed } 95193323Sed /// Convenience wrapper 96193323Sed RetOrArg CreateArg(const Function *F, unsigned Idx) { 97193323Sed return RetOrArg(F, Idx, true); 98193323Sed } 99193323Sed 100193323Sed typedef std::multimap<RetOrArg, RetOrArg> UseMap; 101193323Sed /// This maps a return value or argument to any MaybeLive return values or 102193323Sed /// arguments it uses. This allows the MaybeLive values to be marked live 103193323Sed /// when any of its users is marked live. 104193323Sed /// For example (indices are left out for clarity): 105193323Sed /// - Uses[ret F] = ret G 106193323Sed /// This means that F calls G, and F returns the value returned by G. 107193323Sed /// - Uses[arg F] = ret G 108193323Sed /// This means that some function calls G and passes its result as an 109193323Sed /// argument to F. 110193323Sed /// - Uses[ret F] = arg F 111193323Sed /// This means that F returns one of its own arguments. 112193323Sed /// - Uses[arg F] = arg G 113193323Sed /// This means that G calls F and passes one of its own (G's) arguments 114193323Sed /// directly to F. 115193323Sed UseMap Uses; 116193323Sed 117193323Sed typedef std::set<RetOrArg> LiveSet; 118193323Sed typedef std::set<const Function*> LiveFuncSet; 119193323Sed 120193323Sed /// This set contains all values that have been determined to be live. 121193323Sed LiveSet LiveValues; 122193323Sed /// This set contains all values that are cannot be changed in any way. 123193323Sed LiveFuncSet LiveFunctions; 124193323Sed 125193323Sed typedef SmallVector<RetOrArg, 5> UseVector; 126193323Sed 127245431Sdim // Map each LLVM function to corresponding metadata with debug info. If 128245431Sdim // the function is replaced with another one, we should patch the pointer 129245431Sdim // to LLVM function in metadata. 130245431Sdim // As the code generation for module is finished (and DIBuilder is 131245431Sdim // finalized) we assume that subprogram descriptors won't be changed, and 132245431Sdim // they are stored in map for short duration anyway. 133245431Sdim typedef DenseMap<Function*, DISubprogram> FunctionDIMap; 134245431Sdim FunctionDIMap FunctionDIs; 135245431Sdim 136210299Sed protected: 137210299Sed // DAH uses this to specify a different ID. 138212904Sdim explicit DAE(char &ID) : ModulePass(ID) {} 139210299Sed 140193323Sed public: 141193323Sed static char ID; // Pass identification, replacement for typeid 142218893Sdim DAE() : ModulePass(ID) { 143218893Sdim initializeDAEPass(*PassRegistry::getPassRegistry()); 144218893Sdim } 145210299Sed 146193323Sed bool runOnModule(Module &M); 147193323Sed 148193323Sed virtual bool ShouldHackArguments() const { return false; } 149193323Sed 150193323Sed private: 151193323Sed Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 152206083Srdivacky Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses, 153193323Sed unsigned RetValNum = 0); 154206083Srdivacky Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 155193323Sed 156245431Sdim void CollectFunctionDIs(Module &M); 157206083Srdivacky void SurveyFunction(const Function &F); 158193323Sed void MarkValue(const RetOrArg &RA, Liveness L, 159193323Sed const UseVector &MaybeLiveUses); 160193323Sed void MarkLive(const RetOrArg &RA); 161193323Sed void MarkLive(const Function &F); 162193323Sed void PropagateLiveness(const RetOrArg &RA); 163193323Sed bool RemoveDeadStuffFromFunction(Function *F); 164193323Sed bool DeleteDeadVarargs(Function &Fn); 165218893Sdim bool RemoveDeadArgumentsFromCallers(Function &Fn); 166193323Sed }; 167193323Sed} 168193323Sed 169193323Sed 170193323Sedchar DAE::ID = 0; 171218893SdimINITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false) 172193323Sed 173193323Sednamespace { 174193323Sed /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 175193323Sed /// deletes arguments to functions which are external. This is only for use 176193323Sed /// by bugpoint. 177193323Sed struct DAH : public DAE { 178193323Sed static char ID; 179212904Sdim DAH() : DAE(ID) {} 180210299Sed 181193323Sed virtual bool ShouldHackArguments() const { return true; } 182193323Sed }; 183193323Sed} 184193323Sed 185193323Sedchar DAH::ID = 0; 186212904SdimINITIALIZE_PASS(DAH, "deadarghaX0r", 187212904Sdim "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)", 188218893Sdim false, false) 189193323Sed 190193323Sed/// createDeadArgEliminationPass - This pass removes arguments from functions 191193323Sed/// which are not used by the body of the function. 192193323Sed/// 193193323SedModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 194193323SedModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 195193323Sed 196245431Sdim/// CollectFunctionDIs - Map each function in the module to its debug info 197245431Sdim/// descriptor. 198245431Sdimvoid DAE::CollectFunctionDIs(Module &M) { 199245431Sdim FunctionDIs.clear(); 200245431Sdim 201245431Sdim for (Module::named_metadata_iterator I = M.named_metadata_begin(), 202245431Sdim E = M.named_metadata_end(); I != E; ++I) { 203245431Sdim NamedMDNode &NMD = *I; 204245431Sdim for (unsigned MDIndex = 0, MDNum = NMD.getNumOperands(); 205245431Sdim MDIndex < MDNum; ++MDIndex) { 206245431Sdim MDNode *Node = NMD.getOperand(MDIndex); 207245431Sdim if (!DIDescriptor(Node).isCompileUnit()) 208245431Sdim continue; 209245431Sdim DICompileUnit CU(Node); 210245431Sdim const DIArray &SPs = CU.getSubprograms(); 211245431Sdim for (unsigned SPIndex = 0, SPNum = SPs.getNumElements(); 212245431Sdim SPIndex < SPNum; ++SPIndex) { 213245431Sdim DISubprogram SP(SPs.getElement(SPIndex)); 214263509Sdim assert((!SP || SP.isSubprogram()) && 215263509Sdim "A MDNode in subprograms of a CU should be null or a DISubprogram."); 216263509Sdim if (!SP) 217245431Sdim continue; 218245431Sdim if (Function *F = SP.getFunction()) 219245431Sdim FunctionDIs[F] = SP; 220245431Sdim } 221245431Sdim } 222245431Sdim } 223245431Sdim} 224245431Sdim 225193323Sed/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 226193323Sed/// llvm.vastart is never called, the varargs list is dead for the function. 227193323Sedbool DAE::DeleteDeadVarargs(Function &Fn) { 228193323Sed assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 229193323Sed if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 230193323Sed 231193323Sed // Ensure that the function is only directly called. 232194178Sed if (Fn.hasAddressTaken()) 233194178Sed return false; 234193323Sed 235193323Sed // Okay, we know we can transform this function if safe. Scan its body 236193323Sed // looking for calls to llvm.vastart. 237193323Sed for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 238193323Sed for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 239193323Sed if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 240193323Sed if (II->getIntrinsicID() == Intrinsic::vastart) 241193323Sed return false; 242193323Sed } 243193323Sed } 244193323Sed } 245193323Sed 246193323Sed // If we get here, there are no calls to llvm.vastart in the function body, 247193323Sed // remove the "..." and adjust all the calls. 248193323Sed 249193323Sed // Start by computing a new prototype for the function, which is the same as 250193323Sed // the old function, but doesn't have isVarArg set. 251226890Sdim FunctionType *FTy = Fn.getFunctionType(); 252206083Srdivacky 253224145Sdim std::vector<Type*> Params(FTy->param_begin(), FTy->param_end()); 254198090Srdivacky FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 255198090Srdivacky Params, false); 256193323Sed unsigned NumArgs = Params.size(); 257193323Sed 258193323Sed // Create the new function body and insert it into the module... 259193323Sed Function *NF = Function::Create(NFTy, Fn.getLinkage()); 260193323Sed NF->copyAttributesFrom(&Fn); 261193323Sed Fn.getParent()->getFunctionList().insert(&Fn, NF); 262193323Sed NF->takeName(&Fn); 263193323Sed 264193323Sed // Loop over all of the callers of the function, transforming the call sites 265193323Sed // to pass in a smaller number of arguments into the new function. 266193323Sed // 267193323Sed std::vector<Value*> Args; 268263509Sdim for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ) { 269263509Sdim CallSite CS(*I++); 270263509Sdim if (!CS) 271263509Sdim continue; 272193323Sed Instruction *Call = CS.getInstruction(); 273193323Sed 274193323Sed // Pass all the same arguments. 275212904Sdim Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs); 276193323Sed 277193323Sed // Drop any attributes that were on the vararg arguments. 278252723Sdim AttributeSet PAL = CS.getAttributes(); 279252723Sdim if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) { 280252723Sdim SmallVector<AttributeSet, 8> AttributesVec; 281252723Sdim for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i) 282252723Sdim AttributesVec.push_back(PAL.getSlotAttributes(i)); 283252723Sdim if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 284252723Sdim AttributesVec.push_back(AttributeSet::get(Fn.getContext(), 285252723Sdim PAL.getFnAttributes())); 286252723Sdim PAL = AttributeSet::get(Fn.getContext(), AttributesVec); 287193323Sed } 288193323Sed 289193323Sed Instruction *New; 290193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 291193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 292224145Sdim Args, "", Call); 293193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 294193323Sed cast<InvokeInst>(New)->setAttributes(PAL); 295193323Sed } else { 296224145Sdim New = CallInst::Create(NF, Args, "", Call); 297193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 298193323Sed cast<CallInst>(New)->setAttributes(PAL); 299193323Sed if (cast<CallInst>(Call)->isTailCall()) 300193323Sed cast<CallInst>(New)->setTailCall(); 301193323Sed } 302212904Sdim New->setDebugLoc(Call->getDebugLoc()); 303207618Srdivacky 304193323Sed Args.clear(); 305193323Sed 306193323Sed if (!Call->use_empty()) 307193323Sed Call->replaceAllUsesWith(New); 308193323Sed 309193323Sed New->takeName(Call); 310193323Sed 311193323Sed // Finally, remove the old call from the program, reducing the use-count of 312193323Sed // F. 313193323Sed Call->eraseFromParent(); 314193323Sed } 315193323Sed 316193323Sed // Since we have now created the new function, splice the body of the old 317193323Sed // function right into the new function, leaving the old rotting hulk of the 318193323Sed // function empty. 319193323Sed NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 320193323Sed 321221345Sdim // Loop over the argument list, transferring uses of the old arguments over to 322221345Sdim // the new arguments, also transferring over the names as well. While we're at 323193323Sed // it, remove the dead arguments from the DeadArguments list. 324193323Sed // 325193323Sed for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 326193323Sed I2 = NF->arg_begin(); I != E; ++I, ++I2) { 327193323Sed // Move the name and users over to the new version. 328193323Sed I->replaceAllUsesWith(I2); 329193323Sed I2->takeName(I); 330193323Sed } 331193323Sed 332245431Sdim // Patch the pointer to LLVM function in debug info descriptor. 333245431Sdim FunctionDIMap::iterator DI = FunctionDIs.find(&Fn); 334245431Sdim if (DI != FunctionDIs.end()) 335245431Sdim DI->second.replaceFunction(NF); 336245431Sdim 337263509Sdim // Fix up any BlockAddresses that refer to the function. 338263509Sdim Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType())); 339263509Sdim // Delete the bitcast that we just created, so that NF does not 340263509Sdim // appear to be address-taken. 341263509Sdim NF->removeDeadConstantUsers(); 342193323Sed // Finally, nuke the old function. 343193323Sed Fn.eraseFromParent(); 344193323Sed return true; 345193323Sed} 346193323Sed 347218893Sdim/// RemoveDeadArgumentsFromCallers - Checks if the given function has any 348218893Sdim/// arguments that are unused, and changes the caller parameters to be undefined 349218893Sdim/// instead. 350218893Sdimbool DAE::RemoveDeadArgumentsFromCallers(Function &Fn) 351218893Sdim{ 352221345Sdim if (Fn.isDeclaration() || Fn.mayBeOverridden()) 353218893Sdim return false; 354218893Sdim 355263509Sdim // Functions with local linkage should already have been handled, except the 356263509Sdim // fragile (variadic) ones which we can improve here. 357263509Sdim if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg()) 358218893Sdim return false; 359218893Sdim 360263509Sdim // If a function seen at compile time is not necessarily the one linked to 361263509Sdim // the binary being built, it is illegal to change the actual arguments 362263509Sdim // passed to it. These functions can be captured by isWeakForLinker(). 363263509Sdim // *NOTE* that mayBeOverridden() is insufficient for this purpose as it 364263509Sdim // doesn't include linkage types like AvailableExternallyLinkage and 365263509Sdim // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of 366263509Sdim // *EQUIVALENT* globals that can be merged at link-time. However, the 367263509Sdim // semantic of *EQUIVALENT*-functions includes parameters. Changing 368263509Sdim // parameters breaks this assumption. 369263509Sdim // 370263509Sdim if (Fn.isWeakForLinker()) 371263509Sdim return false; 372263509Sdim 373218893Sdim if (Fn.use_empty()) 374218893Sdim return false; 375218893Sdim 376252723Sdim SmallVector<unsigned, 8> UnusedArgs; 377218893Sdim for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(); 378218893Sdim I != E; ++I) { 379218893Sdim Argument *Arg = I; 380218893Sdim 381218893Sdim if (Arg->use_empty() && !Arg->hasByValAttr()) 382218893Sdim UnusedArgs.push_back(Arg->getArgNo()); 383218893Sdim } 384218893Sdim 385218893Sdim if (UnusedArgs.empty()) 386218893Sdim return false; 387218893Sdim 388218893Sdim bool Changed = false; 389218893Sdim 390218893Sdim for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end(); 391218893Sdim I != E; ++I) { 392218893Sdim CallSite CS(*I); 393218893Sdim if (!CS || !CS.isCallee(I)) 394218893Sdim continue; 395218893Sdim 396218893Sdim // Now go through all unused args and replace them with "undef". 397218893Sdim for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) { 398218893Sdim unsigned ArgNo = UnusedArgs[I]; 399218893Sdim 400218893Sdim Value *Arg = CS.getArgument(ArgNo); 401218893Sdim CS.setArgument(ArgNo, UndefValue::get(Arg->getType())); 402218893Sdim ++NumArgumentsReplacedWithUndef; 403218893Sdim Changed = true; 404218893Sdim } 405218893Sdim } 406218893Sdim 407218893Sdim return Changed; 408218893Sdim} 409218893Sdim 410193323Sed/// Convenience function that returns the number of return values. It returns 0 411193323Sed/// for void functions and 1 for functions not returning a struct. It returns 412193323Sed/// the number of struct elements for functions returning a struct. 413193323Sedstatic unsigned NumRetVals(const Function *F) { 414206083Srdivacky if (F->getReturnType()->isVoidTy()) 415193323Sed return 0; 416226890Sdim else if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) 417193323Sed return STy->getNumElements(); 418193323Sed else 419193323Sed return 1; 420193323Sed} 421193323Sed 422193323Sed/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 423193323Sed/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 424193323Sed/// liveness of Use. 425193323SedDAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 426193323Sed // We're live if our use or its Function is already marked as live. 427193323Sed if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 428193323Sed return Live; 429193323Sed 430193323Sed // We're maybe live otherwise, but remember that we must become live if 431193323Sed // Use becomes live. 432193323Sed MaybeLiveUses.push_back(Use); 433193323Sed return MaybeLive; 434193323Sed} 435193323Sed 436193323Sed 437193323Sed/// SurveyUse - This looks at a single use of an argument or return value 438193323Sed/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 439206083Srdivacky/// if it causes the used value to become MaybeLive. 440193323Sed/// 441193323Sed/// RetValNum is the return value number to use when this use is used in a 442193323Sed/// return instruction. This is used in the recursion, you should always leave 443193323Sed/// it at 0. 444206083SrdivackyDAE::Liveness DAE::SurveyUse(Value::const_use_iterator U, 445206083Srdivacky UseVector &MaybeLiveUses, unsigned RetValNum) { 446206083Srdivacky const User *V = *U; 447206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 448193323Sed // The value is returned from a function. It's only live when the 449193323Sed // function's return value is live. We use RetValNum here, for the case 450193323Sed // that U is really a use of an insertvalue instruction that uses the 451221345Sdim // original Use. 452193323Sed RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 453193323Sed // We might be live, depending on the liveness of Use. 454193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 455193323Sed } 456206083Srdivacky if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 457193323Sed if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 458193323Sed && IV->hasIndices()) 459193323Sed // The use we are examining is inserted into an aggregate. Our liveness 460193323Sed // depends on all uses of that aggregate, but if it is used as a return 461193323Sed // value, only index at which we were inserted counts. 462193323Sed RetValNum = *IV->idx_begin(); 463193323Sed 464193323Sed // Note that if we are used as the aggregate operand to the insertvalue, 465193323Sed // we don't change RetValNum, but do survey all our uses. 466193323Sed 467193323Sed Liveness Result = MaybeLive; 468206083Srdivacky for (Value::const_use_iterator I = IV->use_begin(), 469193323Sed E = V->use_end(); I != E; ++I) { 470193323Sed Result = SurveyUse(I, MaybeLiveUses, RetValNum); 471193323Sed if (Result == Live) 472193323Sed break; 473193323Sed } 474193323Sed return Result; 475193323Sed } 476206083Srdivacky 477206083Srdivacky if (ImmutableCallSite CS = V) { 478206083Srdivacky const Function *F = CS.getCalledFunction(); 479193323Sed if (F) { 480193323Sed // Used in a direct call. 481206083Srdivacky 482193323Sed // Find the argument number. We know for sure that this use is an 483193323Sed // argument, since if it was the function argument this would be an 484193323Sed // indirect call and the we know can't be looking at a value of the 485193323Sed // label type (for the invoke instruction). 486206083Srdivacky unsigned ArgNo = CS.getArgumentNo(U); 487193323Sed 488193323Sed if (ArgNo >= F->getFunctionType()->getNumParams()) 489193323Sed // The value is passed in through a vararg! Must be live. 490193323Sed return Live; 491193323Sed 492206083Srdivacky assert(CS.getArgument(ArgNo) 493206083Srdivacky == CS->getOperand(U.getOperandNo()) 494193323Sed && "Argument is not where we expected it"); 495193323Sed 496193323Sed // Value passed to a normal call. It's only live when the corresponding 497193323Sed // argument to the called function turns out live. 498193323Sed RetOrArg Use = CreateArg(F, ArgNo); 499193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 500193323Sed } 501193323Sed } 502193323Sed // Used in any other way? Value must be live. 503193323Sed return Live; 504193323Sed} 505193323Sed 506193323Sed/// SurveyUses - This looks at all the uses of the given value 507193323Sed/// Returns the Liveness deduced from the uses of this value. 508193323Sed/// 509193323Sed/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 510193323Sed/// the result is Live, MaybeLiveUses might be modified but its content should 511193323Sed/// be ignored (since it might not be complete). 512206083SrdivackyDAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 513193323Sed // Assume it's dead (which will only hold if there are no uses at all..). 514193323Sed Liveness Result = MaybeLive; 515193323Sed // Check each use. 516206083Srdivacky for (Value::const_use_iterator I = V->use_begin(), 517193323Sed E = V->use_end(); I != E; ++I) { 518193323Sed Result = SurveyUse(I, MaybeLiveUses); 519193323Sed if (Result == Live) 520193323Sed break; 521193323Sed } 522193323Sed return Result; 523193323Sed} 524193323Sed 525193323Sed// SurveyFunction - This performs the initial survey of the specified function, 526193323Sed// checking out whether or not it uses any of its incoming arguments or whether 527193323Sed// any callers use the return value. This fills in the LiveValues set and Uses 528193323Sed// map. 529193323Sed// 530193323Sed// We consider arguments of non-internal functions to be intrinsically alive as 531193323Sed// well as arguments to functions which have their "address taken". 532193323Sed// 533206083Srdivackyvoid DAE::SurveyFunction(const Function &F) { 534193323Sed unsigned RetCount = NumRetVals(&F); 535193323Sed // Assume all return values are dead 536193323Sed typedef SmallVector<Liveness, 5> RetVals; 537193323Sed RetVals RetValLiveness(RetCount, MaybeLive); 538193323Sed 539193323Sed typedef SmallVector<UseVector, 5> RetUses; 540193323Sed // These vectors map each return value to the uses that make it MaybeLive, so 541193323Sed // we can add those to the Uses map if the return value really turns out to be 542193323Sed // MaybeLive. Initialized to a list of RetCount empty lists. 543193323Sed RetUses MaybeLiveRetUses(RetCount); 544193323Sed 545206083Srdivacky for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 546206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 547193323Sed if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 548193323Sed != F.getFunctionType()->getReturnType()) { 549193323Sed // We don't support old style multiple return values. 550193323Sed MarkLive(F); 551193323Sed return; 552193323Sed } 553193323Sed 554193323Sed if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 555193323Sed MarkLive(F); 556193323Sed return; 557193323Sed } 558193323Sed 559202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 560193323Sed // Keep track of the number of live retvals, so we can skip checks once all 561193323Sed // of them turn out to be live. 562193323Sed unsigned NumLiveRetVals = 0; 563226890Sdim Type *STy = dyn_cast<StructType>(F.getReturnType()); 564193323Sed // Loop all uses of the function. 565206083Srdivacky for (Value::const_use_iterator I = F.use_begin(), E = F.use_end(); 566206083Srdivacky I != E; ++I) { 567193323Sed // If the function is PASSED IN as an argument, its address has been 568193323Sed // taken. 569206083Srdivacky ImmutableCallSite CS(*I); 570206083Srdivacky if (!CS || !CS.isCallee(I)) { 571193323Sed MarkLive(F); 572193323Sed return; 573193323Sed } 574193323Sed 575193323Sed // If this use is anything other than a call site, the function is alive. 576206083Srdivacky const Instruction *TheCall = CS.getInstruction(); 577193323Sed if (!TheCall) { // Not a direct call site? 578193323Sed MarkLive(F); 579193323Sed return; 580193323Sed } 581193323Sed 582193323Sed // If we end up here, we are looking at a direct call to our function. 583193323Sed 584193323Sed // Now, check how our return value(s) is/are used in this caller. Don't 585193323Sed // bother checking return values if all of them are live already. 586193323Sed if (NumLiveRetVals != RetCount) { 587193323Sed if (STy) { 588193323Sed // Check all uses of the return value. 589206083Srdivacky for (Value::const_use_iterator I = TheCall->use_begin(), 590193323Sed E = TheCall->use_end(); I != E; ++I) { 591206083Srdivacky const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 592193323Sed if (Ext && Ext->hasIndices()) { 593193323Sed // This use uses a part of our return value, survey the uses of 594193323Sed // that part and store the results for this index only. 595193323Sed unsigned Idx = *Ext->idx_begin(); 596193323Sed if (RetValLiveness[Idx] != Live) { 597193323Sed RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 598193323Sed if (RetValLiveness[Idx] == Live) 599193323Sed NumLiveRetVals++; 600193323Sed } 601193323Sed } else { 602193323Sed // Used by something else than extractvalue. Mark all return 603193323Sed // values as live. 604193323Sed for (unsigned i = 0; i != RetCount; ++i ) 605193323Sed RetValLiveness[i] = Live; 606193323Sed NumLiveRetVals = RetCount; 607193323Sed break; 608193323Sed } 609193323Sed } 610193323Sed } else { 611193323Sed // Single return value 612193323Sed RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 613193323Sed if (RetValLiveness[0] == Live) 614193323Sed NumLiveRetVals = RetCount; 615193323Sed } 616193323Sed } 617193323Sed } 618193323Sed 619193323Sed // Now we've inspected all callers, record the liveness of our return values. 620193323Sed for (unsigned i = 0; i != RetCount; ++i) 621193323Sed MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 622193323Sed 623202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 624193323Sed 625193323Sed // Now, check all of our arguments. 626193323Sed unsigned i = 0; 627193323Sed UseVector MaybeLiveArgUses; 628206083Srdivacky for (Function::const_arg_iterator AI = F.arg_begin(), 629193323Sed E = F.arg_end(); AI != E; ++AI, ++i) { 630263509Sdim Liveness Result; 631263509Sdim if (F.getFunctionType()->isVarArg()) { 632263509Sdim // Variadic functions will already have a va_arg function expanded inside 633263509Sdim // them, making them potentially very sensitive to ABI changes resulting 634263509Sdim // from removing arguments entirely, so don't. For example AArch64 handles 635263509Sdim // register and stack HFAs very differently, and this is reflected in the 636263509Sdim // IR which has already been generated. 637263509Sdim Result = Live; 638263509Sdim } else { 639263509Sdim // See what the effect of this use is (recording any uses that cause 640263509Sdim // MaybeLive in MaybeLiveArgUses). 641263509Sdim Result = SurveyUses(AI, MaybeLiveArgUses); 642263509Sdim } 643263509Sdim 644193323Sed // Mark the result. 645193323Sed MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 646193323Sed // Clear the vector again for the next iteration. 647193323Sed MaybeLiveArgUses.clear(); 648193323Sed } 649193323Sed} 650193323Sed 651193323Sed/// MarkValue - This function marks the liveness of RA depending on L. If L is 652193323Sed/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 653193323Sed/// such that RA will be marked live if any use in MaybeLiveUses gets marked 654193323Sed/// live later on. 655193323Sedvoid DAE::MarkValue(const RetOrArg &RA, Liveness L, 656193323Sed const UseVector &MaybeLiveUses) { 657193323Sed switch (L) { 658193323Sed case Live: MarkLive(RA); break; 659193323Sed case MaybeLive: 660193323Sed { 661193323Sed // Note any uses of this value, so this return value can be 662193323Sed // marked live whenever one of the uses becomes live. 663193323Sed for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 664193323Sed UE = MaybeLiveUses.end(); UI != UE; ++UI) 665193323Sed Uses.insert(std::make_pair(*UI, RA)); 666193323Sed break; 667193323Sed } 668193323Sed } 669193323Sed} 670193323Sed 671193323Sed/// MarkLive - Mark the given Function as alive, meaning that it cannot be 672193323Sed/// changed in any way. Additionally, 673193323Sed/// mark any values that are used as this function's parameters or by its return 674193323Sed/// values (according to Uses) live as well. 675193323Sedvoid DAE::MarkLive(const Function &F) { 676202375Srdivacky DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 677208599Srdivacky // Mark the function as live. 678208599Srdivacky LiveFunctions.insert(&F); 679208599Srdivacky // Mark all arguments as live. 680208599Srdivacky for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 681208599Srdivacky PropagateLiveness(CreateArg(&F, i)); 682208599Srdivacky // Mark all return values as live. 683208599Srdivacky for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 684208599Srdivacky PropagateLiveness(CreateRet(&F, i)); 685193323Sed} 686193323Sed 687193323Sed/// MarkLive - Mark the given return value or argument as live. Additionally, 688193323Sed/// mark any values that are used by this value (according to Uses) live as 689193323Sed/// well. 690193323Sedvoid DAE::MarkLive(const RetOrArg &RA) { 691193323Sed if (LiveFunctions.count(RA.F)) 692193323Sed return; // Function was already marked Live. 693193323Sed 694193323Sed if (!LiveValues.insert(RA).second) 695193323Sed return; // We were already marked Live. 696193323Sed 697202375Srdivacky DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 698193323Sed PropagateLiveness(RA); 699193323Sed} 700193323Sed 701193323Sed/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 702193323Sed/// to any other values it uses (according to Uses). 703193323Sedvoid DAE::PropagateLiveness(const RetOrArg &RA) { 704193323Sed // We don't use upper_bound (or equal_range) here, because our recursive call 705193323Sed // to ourselves is likely to cause the upper_bound (which is the first value 706193323Sed // not belonging to RA) to become erased and the iterator invalidated. 707193323Sed UseMap::iterator Begin = Uses.lower_bound(RA); 708193323Sed UseMap::iterator E = Uses.end(); 709193323Sed UseMap::iterator I; 710193323Sed for (I = Begin; I != E && I->first == RA; ++I) 711193323Sed MarkLive(I->second); 712193323Sed 713193323Sed // Erase RA from the Uses map (from the lower bound to wherever we ended up 714193323Sed // after the loop). 715193323Sed Uses.erase(Begin, I); 716193323Sed} 717193323Sed 718193323Sed// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 719193323Sed// that are not in LiveValues. Transform the function and all of the callees of 720193323Sed// the function to not have these arguments and return values. 721193323Sed// 722193323Sedbool DAE::RemoveDeadStuffFromFunction(Function *F) { 723193323Sed // Don't modify fully live functions 724193323Sed if (LiveFunctions.count(F)) 725193323Sed return false; 726193323Sed 727193323Sed // Start by computing a new prototype for the function, which is the same as 728193323Sed // the old function, but has fewer arguments and a different return type. 729226890Sdim FunctionType *FTy = F->getFunctionType(); 730224145Sdim std::vector<Type*> Params; 731193323Sed 732263509Sdim // Keep track of if we have a live 'returned' argument 733263509Sdim bool HasLiveReturnedArg = false; 734263509Sdim 735193323Sed // Set up to build a new list of parameter attributes. 736252723Sdim SmallVector<AttributeSet, 8> AttributesVec; 737252723Sdim const AttributeSet &PAL = F->getAttributes(); 738193323Sed 739263509Sdim // Remember which arguments are still alive. 740263509Sdim SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 741263509Sdim // Construct the new parameter list from non-dead arguments. Also construct 742263509Sdim // a new set of parameter attributes to correspond. Skip the first parameter 743263509Sdim // attribute, since that belongs to the return value. 744263509Sdim unsigned i = 0; 745263509Sdim for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 746263509Sdim I != E; ++I, ++i) { 747263509Sdim RetOrArg Arg = CreateArg(F, i); 748263509Sdim if (LiveValues.erase(Arg)) { 749263509Sdim Params.push_back(I->getType()); 750263509Sdim ArgAlive[i] = true; 751263509Sdim 752263509Sdim // Get the original parameter attributes (skipping the first one, that is 753263509Sdim // for the return value. 754263509Sdim if (PAL.hasAttributes(i + 1)) { 755263509Sdim AttrBuilder B(PAL, i + 1); 756263509Sdim if (B.contains(Attribute::Returned)) 757263509Sdim HasLiveReturnedArg = true; 758263509Sdim AttributesVec. 759263509Sdim push_back(AttributeSet::get(F->getContext(), Params.size(), B)); 760263509Sdim } 761263509Sdim } else { 762263509Sdim ++NumArgumentsEliminated; 763263509Sdim DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 764263509Sdim << ") from " << F->getName() << "\n"); 765263509Sdim } 766263509Sdim } 767263509Sdim 768193323Sed // Find out the new return value. 769224145Sdim Type *RetTy = FTy->getReturnType(); 770226890Sdim Type *NRetTy = NULL; 771193323Sed unsigned RetCount = NumRetVals(F); 772206083Srdivacky 773193323Sed // -1 means unused, other numbers are the new index 774193323Sed SmallVector<int, 5> NewRetIdxs(RetCount, -1); 775224145Sdim std::vector<Type*> RetTypes; 776263509Sdim 777263509Sdim // If there is a function with a live 'returned' argument but a dead return 778263509Sdim // value, then there are two possible actions: 779263509Sdim // 1) Eliminate the return value and take off the 'returned' attribute on the 780263509Sdim // argument. 781263509Sdim // 2) Retain the 'returned' attribute and treat the return value (but not the 782263509Sdim // entire function) as live so that it is not eliminated. 783263509Sdim // 784263509Sdim // It's not clear in the general case which option is more profitable because, 785263509Sdim // even in the absence of explicit uses of the return value, code generation 786263509Sdim // is free to use the 'returned' attribute to do things like eliding 787263509Sdim // save/restores of registers across calls. Whether or not this happens is 788263509Sdim // target and ABI-specific as well as depending on the amount of register 789263509Sdim // pressure, so there's no good way for an IR-level pass to figure this out. 790263509Sdim // 791263509Sdim // Fortunately, the only places where 'returned' is currently generated by 792263509Sdim // the FE are places where 'returned' is basically free and almost always a 793263509Sdim // performance win, so the second option can just be used always for now. 794263509Sdim // 795263509Sdim // This should be revisited if 'returned' is ever applied more liberally. 796263509Sdim if (RetTy->isVoidTy() || HasLiveReturnedArg) { 797206083Srdivacky NRetTy = RetTy; 798193323Sed } else { 799226890Sdim StructType *STy = dyn_cast<StructType>(RetTy); 800193323Sed if (STy) 801193323Sed // Look at each of the original return values individually. 802193323Sed for (unsigned i = 0; i != RetCount; ++i) { 803193323Sed RetOrArg Ret = CreateRet(F, i); 804193323Sed if (LiveValues.erase(Ret)) { 805193323Sed RetTypes.push_back(STy->getElementType(i)); 806193323Sed NewRetIdxs[i] = RetTypes.size() - 1; 807193323Sed } else { 808193323Sed ++NumRetValsEliminated; 809202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 810198090Srdivacky << F->getName() << "\n"); 811193323Sed } 812193323Sed } 813193323Sed else 814193323Sed // We used to return a single value. 815193323Sed if (LiveValues.erase(CreateRet(F, 0))) { 816193323Sed RetTypes.push_back(RetTy); 817193323Sed NewRetIdxs[0] = 0; 818193323Sed } else { 819202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 820198090Srdivacky << "\n"); 821193323Sed ++NumRetValsEliminated; 822193323Sed } 823193323Sed if (RetTypes.size() > 1) 824193323Sed // More than one return type? Return a struct with them. Also, if we used 825193323Sed // to return a struct and didn't change the number of return values, 826193323Sed // return a struct again. This prevents changing {something} into 827193323Sed // something and {} into void. 828193323Sed // Make the new struct packed if we used to return a packed struct 829193323Sed // already. 830198090Srdivacky NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 831193323Sed else if (RetTypes.size() == 1) 832193323Sed // One return type? Just a simple value then, but only if we didn't use to 833193323Sed // return a struct with that simple value before. 834193323Sed NRetTy = RetTypes.front(); 835193323Sed else if (RetTypes.size() == 0) 836193323Sed // No return types? Make it void, but only if we didn't use to return {}. 837198090Srdivacky NRetTy = Type::getVoidTy(F->getContext()); 838193323Sed } 839193323Sed 840193323Sed assert(NRetTy && "No new return type found?"); 841193323Sed 842252723Sdim // The existing function return attributes. 843252723Sdim AttributeSet RAttrs = PAL.getRetAttributes(); 844252723Sdim 845193323Sed // Remove any incompatible attributes, but only if we removed all return 846193323Sed // values. Otherwise, ensure that we don't have any conflicting attributes 847193323Sed // here. Currently, this should not be possible, but special handling might be 848193323Sed // required when new return value attributes are added. 849206083Srdivacky if (NRetTy->isVoidTy()) 850245431Sdim RAttrs = 851252723Sdim AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex, 852252723Sdim AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 853252723Sdim removeAttributes(AttributeFuncs:: 854252723Sdim typeIncompatible(NRetTy, AttributeSet::ReturnIndex), 855252723Sdim AttributeSet::ReturnIndex)); 856193323Sed else 857252723Sdim assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 858252723Sdim hasAttributes(AttributeFuncs:: 859252723Sdim typeIncompatible(NRetTy, AttributeSet::ReturnIndex), 860252723Sdim AttributeSet::ReturnIndex) && 861245431Sdim "Return attributes no longer compatible?"); 862193323Sed 863252723Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 864252723Sdim AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs)); 865193323Sed 866252723Sdim if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 867252723Sdim AttributesVec.push_back(AttributeSet::get(F->getContext(), 868252723Sdim PAL.getFnAttributes())); 869193323Sed 870193323Sed // Reconstruct the AttributesList based on the vector we constructed. 871252723Sdim AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec); 872193323Sed 873193323Sed // Create the new function type based on the recomputed parameters. 874206083Srdivacky FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 875193323Sed 876193323Sed // No change? 877193323Sed if (NFTy == FTy) 878193323Sed return false; 879193323Sed 880193323Sed // Create the new function body and insert it into the module... 881193323Sed Function *NF = Function::Create(NFTy, F->getLinkage()); 882193323Sed NF->copyAttributesFrom(F); 883193323Sed NF->setAttributes(NewPAL); 884193323Sed // Insert the new function before the old function, so we won't be processing 885193323Sed // it again. 886193323Sed F->getParent()->getFunctionList().insert(F, NF); 887193323Sed NF->takeName(F); 888193323Sed 889193323Sed // Loop over all of the callers of the function, transforming the call sites 890193323Sed // to pass in a smaller number of arguments into the new function. 891193323Sed // 892193323Sed std::vector<Value*> Args; 893193323Sed while (!F->use_empty()) { 894212904Sdim CallSite CS(F->use_back()); 895193323Sed Instruction *Call = CS.getInstruction(); 896193323Sed 897193323Sed AttributesVec.clear(); 898252723Sdim const AttributeSet &CallPAL = CS.getAttributes(); 899193323Sed 900193323Sed // The call return attributes. 901252723Sdim AttributeSet RAttrs = CallPAL.getRetAttributes(); 902252723Sdim 903193323Sed // Adjust in case the function was changed to return void. 904245431Sdim RAttrs = 905252723Sdim AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex, 906252723Sdim AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 907252723Sdim removeAttributes(AttributeFuncs:: 908252723Sdim typeIncompatible(NF->getReturnType(), 909252723Sdim AttributeSet::ReturnIndex), 910252723Sdim AttributeSet::ReturnIndex)); 911252723Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 912252723Sdim AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs)); 913193323Sed 914193323Sed // Declare these outside of the loops, so we can reuse them for the second 915193323Sed // loop, which loops the varargs. 916193323Sed CallSite::arg_iterator I = CS.arg_begin(); 917193323Sed unsigned i = 0; 918193323Sed // Loop over those operands, corresponding to the normal arguments to the 919193323Sed // original function, and add those that are still alive. 920193323Sed for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 921193323Sed if (ArgAlive[i]) { 922193323Sed Args.push_back(*I); 923193323Sed // Get original parameter attributes, but skip return attributes. 924252723Sdim if (CallPAL.hasAttributes(i + 1)) { 925252723Sdim AttrBuilder B(CallPAL, i + 1); 926263509Sdim // If the return type has changed, then get rid of 'returned' on the 927263509Sdim // call site. The alternative is to make all 'returned' attributes on 928263509Sdim // call sites keep the return value alive just like 'returned' 929263509Sdim // attributes on function declaration but it's less clearly a win 930263509Sdim // and this is not an expected case anyway 931263509Sdim if (NRetTy != RetTy && B.contains(Attribute::Returned)) 932263509Sdim B.removeAttribute(Attribute::Returned); 933252723Sdim AttributesVec. 934252723Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 935252723Sdim } 936193323Sed } 937193323Sed 938193323Sed // Push any varargs arguments on the list. Don't forget their attributes. 939193323Sed for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 940193323Sed Args.push_back(*I); 941252723Sdim if (CallPAL.hasAttributes(i + 1)) { 942252723Sdim AttrBuilder B(CallPAL, i + 1); 943252723Sdim AttributesVec. 944252723Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 945252723Sdim } 946193323Sed } 947193323Sed 948252723Sdim if (CallPAL.hasAttributes(AttributeSet::FunctionIndex)) 949252723Sdim AttributesVec.push_back(AttributeSet::get(Call->getContext(), 950252723Sdim CallPAL.getFnAttributes())); 951193323Sed 952193323Sed // Reconstruct the AttributesList based on the vector we constructed. 953252723Sdim AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec); 954193323Sed 955193323Sed Instruction *New; 956193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 957193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 958224145Sdim Args, "", Call); 959193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 960193323Sed cast<InvokeInst>(New)->setAttributes(NewCallPAL); 961193323Sed } else { 962224145Sdim New = CallInst::Create(NF, Args, "", Call); 963193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 964193323Sed cast<CallInst>(New)->setAttributes(NewCallPAL); 965193323Sed if (cast<CallInst>(Call)->isTailCall()) 966193323Sed cast<CallInst>(New)->setTailCall(); 967193323Sed } 968212904Sdim New->setDebugLoc(Call->getDebugLoc()); 969207618Srdivacky 970193323Sed Args.clear(); 971193323Sed 972193323Sed if (!Call->use_empty()) { 973193323Sed if (New->getType() == Call->getType()) { 974193323Sed // Return type not changed? Just replace users then. 975193323Sed Call->replaceAllUsesWith(New); 976193323Sed New->takeName(Call); 977206083Srdivacky } else if (New->getType()->isVoidTy()) { 978193323Sed // Our return value has uses, but they will get removed later on. 979193323Sed // Replace by null for now. 980218893Sdim if (!Call->getType()->isX86_MMXTy()) 981218893Sdim Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 982193323Sed } else { 983204642Srdivacky assert(RetTy->isStructTy() && 984193323Sed "Return type changed, but not into a void. The old return type" 985193323Sed " must have been a struct!"); 986193323Sed Instruction *InsertPt = Call; 987193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 988193323Sed BasicBlock::iterator IP = II->getNormalDest()->begin(); 989193323Sed while (isa<PHINode>(IP)) ++IP; 990193323Sed InsertPt = IP; 991193323Sed } 992206083Srdivacky 993193323Sed // We used to return a struct. Instead of doing smart stuff with all the 994193323Sed // uses of this struct, we will just rebuild it using 995193323Sed // extract/insertvalue chaining and let instcombine clean that up. 996193323Sed // 997193323Sed // Start out building up our return value from undef 998198090Srdivacky Value *RetVal = UndefValue::get(RetTy); 999193323Sed for (unsigned i = 0; i != RetCount; ++i) 1000193323Sed if (NewRetIdxs[i] != -1) { 1001193323Sed Value *V; 1002193323Sed if (RetTypes.size() > 1) 1003193323Sed // We are still returning a struct, so extract the value from our 1004193323Sed // return value 1005193323Sed V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 1006193323Sed InsertPt); 1007193323Sed else 1008193323Sed // We are now returning a single element, so just insert that 1009193323Sed V = New; 1010193323Sed // Insert the value at the old position 1011193323Sed RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 1012193323Sed } 1013193323Sed // Now, replace all uses of the old call instruction with the return 1014193323Sed // struct we built 1015193323Sed Call->replaceAllUsesWith(RetVal); 1016193323Sed New->takeName(Call); 1017193323Sed } 1018193323Sed } 1019193323Sed 1020193323Sed // Finally, remove the old call from the program, reducing the use-count of 1021193323Sed // F. 1022193323Sed Call->eraseFromParent(); 1023193323Sed } 1024193323Sed 1025193323Sed // Since we have now created the new function, splice the body of the old 1026193323Sed // function right into the new function, leaving the old rotting hulk of the 1027193323Sed // function empty. 1028193323Sed NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 1029193323Sed 1030221345Sdim // Loop over the argument list, transferring uses of the old arguments over to 1031221345Sdim // the new arguments, also transferring over the names as well. 1032193323Sed i = 0; 1033193323Sed for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 1034193323Sed I2 = NF->arg_begin(); I != E; ++I, ++i) 1035193323Sed if (ArgAlive[i]) { 1036193323Sed // If this is a live argument, move the name and users over to the new 1037193323Sed // version. 1038193323Sed I->replaceAllUsesWith(I2); 1039193323Sed I2->takeName(I); 1040193323Sed ++I2; 1041193323Sed } else { 1042193323Sed // If this argument is dead, replace any uses of it with null constants 1043193323Sed // (these are guaranteed to become unused later on). 1044218893Sdim if (!I->getType()->isX86_MMXTy()) 1045218893Sdim I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 1046193323Sed } 1047193323Sed 1048193323Sed // If we change the return value of the function we must rewrite any return 1049193323Sed // instructions. Check this now. 1050193323Sed if (F->getReturnType() != NF->getReturnType()) 1051193323Sed for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 1052193323Sed if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 1053193323Sed Value *RetVal; 1054193323Sed 1055208599Srdivacky if (NFTy->getReturnType()->isVoidTy()) { 1056193323Sed RetVal = 0; 1057193323Sed } else { 1058204642Srdivacky assert (RetTy->isStructTy()); 1059193323Sed // The original return value was a struct, insert 1060193323Sed // extractvalue/insertvalue chains to extract only the values we need 1061193323Sed // to return and insert them into our new result. 1062193323Sed // This does generate messy code, but we'll let it to instcombine to 1063193323Sed // clean that up. 1064193323Sed Value *OldRet = RI->getOperand(0); 1065193323Sed // Start out building up our return value from undef 1066198090Srdivacky RetVal = UndefValue::get(NRetTy); 1067193323Sed for (unsigned i = 0; i != RetCount; ++i) 1068193323Sed if (NewRetIdxs[i] != -1) { 1069193323Sed ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 1070193323Sed "oldret", RI); 1071193323Sed if (RetTypes.size() > 1) { 1072193323Sed // We're still returning a struct, so reinsert the value into 1073193323Sed // our new return value at the new index 1074193323Sed 1075193323Sed RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 1076193323Sed "newret", RI); 1077193323Sed } else { 1078193323Sed // We are now only returning a simple value, so just return the 1079193323Sed // extracted value. 1080193323Sed RetVal = EV; 1081193323Sed } 1082193323Sed } 1083193323Sed } 1084193323Sed // Replace the return instruction with one returning the new return 1085193323Sed // value (possibly 0 if we became void). 1086198090Srdivacky ReturnInst::Create(F->getContext(), RetVal, RI); 1087193323Sed BB->getInstList().erase(RI); 1088193323Sed } 1089193323Sed 1090245431Sdim // Patch the pointer to LLVM function in debug info descriptor. 1091245431Sdim FunctionDIMap::iterator DI = FunctionDIs.find(F); 1092245431Sdim if (DI != FunctionDIs.end()) 1093245431Sdim DI->second.replaceFunction(NF); 1094245431Sdim 1095193323Sed // Now that the old function is dead, delete it. 1096193323Sed F->eraseFromParent(); 1097193323Sed 1098193323Sed return true; 1099193323Sed} 1100193323Sed 1101193323Sedbool DAE::runOnModule(Module &M) { 1102193323Sed bool Changed = false; 1103193323Sed 1104245431Sdim // Collect debug info descriptors for functions. 1105245431Sdim CollectFunctionDIs(M); 1106245431Sdim 1107193323Sed // First pass: Do a simple check to see if any functions can have their "..." 1108193323Sed // removed. We can do this if they never call va_start. This loop cannot be 1109193323Sed // fused with the next loop, because deleting a function invalidates 1110193323Sed // information computed while surveying other functions. 1111202375Srdivacky DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 1112193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1113193323Sed Function &F = *I++; 1114193323Sed if (F.getFunctionType()->isVarArg()) 1115193323Sed Changed |= DeleteDeadVarargs(F); 1116193323Sed } 1117193323Sed 1118193323Sed // Second phase:loop through the module, determining which arguments are live. 1119193323Sed // We assume all arguments are dead unless proven otherwise (allowing us to 1120193323Sed // determine that dead arguments passed into recursive functions are dead). 1121193323Sed // 1122202375Srdivacky DEBUG(dbgs() << "DAE - Determining liveness\n"); 1123193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 1124193323Sed SurveyFunction(*I); 1125206083Srdivacky 1126193323Sed // Now, remove all dead arguments and return values from each function in 1127206083Srdivacky // turn. 1128193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1129206083Srdivacky // Increment now, because the function will probably get removed (ie. 1130193323Sed // replaced by a new one). 1131193323Sed Function *F = I++; 1132193323Sed Changed |= RemoveDeadStuffFromFunction(F); 1133193323Sed } 1134218893Sdim 1135218893Sdim // Finally, look for any unused parameters in functions with non-local 1136218893Sdim // linkage and replace the passed in parameters with undef. 1137218893Sdim for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 1138218893Sdim Function& F = *I; 1139218893Sdim 1140218893Sdim Changed |= RemoveDeadArgumentsFromCallers(F); 1141218893Sdim } 1142218893Sdim 1143193323Sed return Changed; 1144193323Sed} 1145