DeadArgumentElimination.cpp revision 280031
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#include "llvm/Transforms/IPO.h" 21249423Sdim#include "llvm/ADT/DenseMap.h" 22249423Sdim#include "llvm/ADT/SmallVector.h" 23249423Sdim#include "llvm/ADT/Statistic.h" 24249423Sdim#include "llvm/ADT/StringExtras.h" 25276479Sdim#include "llvm/IR/CallSite.h" 26249423Sdim#include "llvm/IR/CallingConv.h" 27249423Sdim#include "llvm/IR/Constant.h" 28276479Sdim#include "llvm/IR/DIBuilder.h" 29276479Sdim#include "llvm/IR/DebugInfo.h" 30249423Sdim#include "llvm/IR/DerivedTypes.h" 31249423Sdim#include "llvm/IR/Instructions.h" 32249423Sdim#include "llvm/IR/IntrinsicInst.h" 33249423Sdim#include "llvm/IR/LLVMContext.h" 34249423Sdim#include "llvm/IR/Module.h" 35193323Sed#include "llvm/Pass.h" 36193323Sed#include "llvm/Support/Debug.h" 37198090Srdivacky#include "llvm/Support/raw_ostream.h" 38193323Sed#include <map> 39193323Sed#include <set> 40276479Sdim#include <tuple> 41193323Sedusing namespace llvm; 42193323Sed 43276479Sdim#define DEBUG_TYPE "deadargelim" 44276479Sdim 45193323SedSTATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 46193323SedSTATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 47218893SdimSTATISTIC(NumArgumentsReplacedWithUndef, 48218893Sdim "Number of unread args replaced with undef"); 49193323Sednamespace { 50193323Sed /// DAE - The dead argument elimination pass. 51193323Sed /// 52198892Srdivacky class DAE : public ModulePass { 53193323Sed public: 54193323Sed 55193323Sed /// Struct that represents (part of) either a return value or a function 56193323Sed /// argument. Used so that arguments and return values can be used 57221345Sdim /// interchangeably. 58193323Sed struct RetOrArg { 59206083Srdivacky RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 60193323Sed IsArg(IsArg) {} 61193323Sed const Function *F; 62193323Sed unsigned Idx; 63193323Sed bool IsArg; 64193323Sed 65193323Sed /// Make RetOrArg comparable, so we can put it into a map. 66193323Sed bool operator<(const RetOrArg &O) const { 67276479Sdim return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg); 68193323Sed } 69193323Sed 70193323Sed /// Make RetOrArg comparable, so we can easily iterate the multimap. 71193323Sed bool operator==(const RetOrArg &O) const { 72193323Sed return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 73193323Sed } 74193323Sed 75193323Sed std::string getDescription() const { 76206083Srdivacky return std::string((IsArg ? "Argument #" : "Return value #")) 77234353Sdim + utostr(Idx) + " of function " + F->getName().str(); 78193323Sed } 79193323Sed }; 80193323Sed 81193323Sed /// Liveness enum - During our initial pass over the program, we determine 82193323Sed /// that things are either alive or maybe alive. We don't mark anything 83193323Sed /// explicitly dead (even if we know they are), since anything not alive 84193323Sed /// with no registered uses (in Uses) will never be marked alive and will 85193323Sed /// thus become dead in the end. 86193323Sed enum Liveness { Live, MaybeLive }; 87193323Sed 88193323Sed /// Convenience wrapper 89193323Sed RetOrArg CreateRet(const Function *F, unsigned Idx) { 90193323Sed return RetOrArg(F, Idx, false); 91193323Sed } 92193323Sed /// Convenience wrapper 93193323Sed RetOrArg CreateArg(const Function *F, unsigned Idx) { 94193323Sed return RetOrArg(F, Idx, true); 95193323Sed } 96193323Sed 97193323Sed typedef std::multimap<RetOrArg, RetOrArg> UseMap; 98193323Sed /// This maps a return value or argument to any MaybeLive return values or 99193323Sed /// arguments it uses. This allows the MaybeLive values to be marked live 100193323Sed /// when any of its users is marked live. 101193323Sed /// For example (indices are left out for clarity): 102193323Sed /// - Uses[ret F] = ret G 103193323Sed /// This means that F calls G, and F returns the value returned by G. 104193323Sed /// - Uses[arg F] = ret G 105193323Sed /// This means that some function calls G and passes its result as an 106193323Sed /// argument to F. 107193323Sed /// - Uses[ret F] = arg F 108193323Sed /// This means that F returns one of its own arguments. 109193323Sed /// - Uses[arg F] = arg G 110193323Sed /// This means that G calls F and passes one of its own (G's) arguments 111193323Sed /// directly to F. 112193323Sed UseMap Uses; 113193323Sed 114193323Sed typedef std::set<RetOrArg> LiveSet; 115193323Sed typedef std::set<const Function*> LiveFuncSet; 116193323Sed 117193323Sed /// This set contains all values that have been determined to be live. 118193323Sed LiveSet LiveValues; 119193323Sed /// This set contains all values that are cannot be changed in any way. 120193323Sed LiveFuncSet LiveFunctions; 121193323Sed 122193323Sed typedef SmallVector<RetOrArg, 5> UseVector; 123193323Sed 124243830Sdim // Map each LLVM function to corresponding metadata with debug info. If 125243830Sdim // the function is replaced with another one, we should patch the pointer 126243830Sdim // to LLVM function in metadata. 127243830Sdim // As the code generation for module is finished (and DIBuilder is 128243830Sdim // finalized) we assume that subprogram descriptors won't be changed, and 129243830Sdim // they are stored in map for short duration anyway. 130276479Sdim DenseMap<const Function *, DISubprogram> FunctionDIs; 131243830Sdim 132210299Sed protected: 133210299Sed // DAH uses this to specify a different ID. 134212904Sdim explicit DAE(char &ID) : ModulePass(ID) {} 135210299Sed 136193323Sed public: 137193323Sed static char ID; // Pass identification, replacement for typeid 138218893Sdim DAE() : ModulePass(ID) { 139218893Sdim initializeDAEPass(*PassRegistry::getPassRegistry()); 140218893Sdim } 141210299Sed 142276479Sdim bool runOnModule(Module &M) override; 143193323Sed 144193323Sed virtual bool ShouldHackArguments() const { return false; } 145193323Sed 146193323Sed private: 147193323Sed Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 148276479Sdim Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses, 149193323Sed unsigned RetValNum = 0); 150206083Srdivacky Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 151193323Sed 152206083Srdivacky void SurveyFunction(const Function &F); 153193323Sed void MarkValue(const RetOrArg &RA, Liveness L, 154193323Sed const UseVector &MaybeLiveUses); 155193323Sed void MarkLive(const RetOrArg &RA); 156193323Sed void MarkLive(const Function &F); 157193323Sed void PropagateLiveness(const RetOrArg &RA); 158193323Sed bool RemoveDeadStuffFromFunction(Function *F); 159193323Sed bool DeleteDeadVarargs(Function &Fn); 160218893Sdim bool RemoveDeadArgumentsFromCallers(Function &Fn); 161193323Sed }; 162193323Sed} 163193323Sed 164193323Sed 165193323Sedchar DAE::ID = 0; 166218893SdimINITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false) 167193323Sed 168193323Sednamespace { 169193323Sed /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 170193323Sed /// deletes arguments to functions which are external. This is only for use 171193323Sed /// by bugpoint. 172193323Sed struct DAH : public DAE { 173193323Sed static char ID; 174212904Sdim DAH() : DAE(ID) {} 175210299Sed 176276479Sdim bool ShouldHackArguments() const override { return true; } 177193323Sed }; 178193323Sed} 179193323Sed 180193323Sedchar DAH::ID = 0; 181212904SdimINITIALIZE_PASS(DAH, "deadarghaX0r", 182212904Sdim "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)", 183218893Sdim false, false) 184193323Sed 185193323Sed/// createDeadArgEliminationPass - This pass removes arguments from functions 186193323Sed/// which are not used by the body of the function. 187193323Sed/// 188193323SedModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 189193323SedModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 190193323Sed 191193323Sed/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 192193323Sed/// llvm.vastart is never called, the varargs list is dead for the function. 193193323Sedbool DAE::DeleteDeadVarargs(Function &Fn) { 194193323Sed assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 195193323Sed if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 196193323Sed 197193323Sed // Ensure that the function is only directly called. 198194178Sed if (Fn.hasAddressTaken()) 199194178Sed return false; 200193323Sed 201193323Sed // Okay, we know we can transform this function if safe. Scan its body 202280031Sdim // looking for calls marked musttail or calls to llvm.vastart. 203193323Sed for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 204193323Sed for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 205280031Sdim CallInst *CI = dyn_cast<CallInst>(I); 206280031Sdim if (!CI) 207280031Sdim continue; 208280031Sdim if (CI->isMustTailCall()) 209280031Sdim return false; 210280031Sdim if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) { 211193323Sed if (II->getIntrinsicID() == Intrinsic::vastart) 212193323Sed return false; 213193323Sed } 214193323Sed } 215193323Sed } 216193323Sed 217193323Sed // If we get here, there are no calls to llvm.vastart in the function body, 218193323Sed // remove the "..." and adjust all the calls. 219193323Sed 220193323Sed // Start by computing a new prototype for the function, which is the same as 221193323Sed // the old function, but doesn't have isVarArg set. 222226633Sdim FunctionType *FTy = Fn.getFunctionType(); 223206083Srdivacky 224224145Sdim std::vector<Type*> Params(FTy->param_begin(), FTy->param_end()); 225198090Srdivacky FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 226198090Srdivacky Params, false); 227193323Sed unsigned NumArgs = Params.size(); 228193323Sed 229193323Sed // Create the new function body and insert it into the module... 230193323Sed Function *NF = Function::Create(NFTy, Fn.getLinkage()); 231193323Sed NF->copyAttributesFrom(&Fn); 232193323Sed Fn.getParent()->getFunctionList().insert(&Fn, NF); 233193323Sed NF->takeName(&Fn); 234193323Sed 235193323Sed // Loop over all of the callers of the function, transforming the call sites 236193323Sed // to pass in a smaller number of arguments into the new function. 237193323Sed // 238193323Sed std::vector<Value*> Args; 239276479Sdim for (Value::user_iterator I = Fn.user_begin(), E = Fn.user_end(); I != E; ) { 240261991Sdim CallSite CS(*I++); 241261991Sdim if (!CS) 242261991Sdim continue; 243193323Sed Instruction *Call = CS.getInstruction(); 244193323Sed 245193323Sed // Pass all the same arguments. 246212904Sdim Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs); 247193323Sed 248193323Sed // Drop any attributes that were on the vararg arguments. 249249423Sdim AttributeSet PAL = CS.getAttributes(); 250249423Sdim if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) { 251249423Sdim SmallVector<AttributeSet, 8> AttributesVec; 252249423Sdim for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i) 253249423Sdim AttributesVec.push_back(PAL.getSlotAttributes(i)); 254249423Sdim if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 255249423Sdim AttributesVec.push_back(AttributeSet::get(Fn.getContext(), 256249423Sdim PAL.getFnAttributes())); 257249423Sdim PAL = AttributeSet::get(Fn.getContext(), AttributesVec); 258193323Sed } 259193323Sed 260193323Sed Instruction *New; 261193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 262193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 263224145Sdim Args, "", Call); 264193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 265193323Sed cast<InvokeInst>(New)->setAttributes(PAL); 266193323Sed } else { 267224145Sdim New = CallInst::Create(NF, Args, "", Call); 268193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 269193323Sed cast<CallInst>(New)->setAttributes(PAL); 270193323Sed if (cast<CallInst>(Call)->isTailCall()) 271193323Sed cast<CallInst>(New)->setTailCall(); 272193323Sed } 273212904Sdim New->setDebugLoc(Call->getDebugLoc()); 274207618Srdivacky 275193323Sed Args.clear(); 276193323Sed 277193323Sed if (!Call->use_empty()) 278193323Sed Call->replaceAllUsesWith(New); 279193323Sed 280193323Sed New->takeName(Call); 281193323Sed 282193323Sed // Finally, remove the old call from the program, reducing the use-count of 283193323Sed // F. 284193323Sed Call->eraseFromParent(); 285193323Sed } 286193323Sed 287193323Sed // Since we have now created the new function, splice the body of the old 288193323Sed // function right into the new function, leaving the old rotting hulk of the 289193323Sed // function empty. 290193323Sed NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 291193323Sed 292221345Sdim // Loop over the argument list, transferring uses of the old arguments over to 293221345Sdim // the new arguments, also transferring over the names as well. While we're at 294193323Sed // it, remove the dead arguments from the DeadArguments list. 295193323Sed // 296193323Sed for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 297193323Sed I2 = NF->arg_begin(); I != E; ++I, ++I2) { 298193323Sed // Move the name and users over to the new version. 299193323Sed I->replaceAllUsesWith(I2); 300193323Sed I2->takeName(I); 301193323Sed } 302193323Sed 303243830Sdim // Patch the pointer to LLVM function in debug info descriptor. 304276479Sdim auto DI = FunctionDIs.find(&Fn); 305280031Sdim if (DI != FunctionDIs.end()) { 306280031Sdim DISubprogram SP = DI->second; 307280031Sdim SP.replaceFunction(NF); 308280031Sdim // Ensure the map is updated so it can be reused on non-varargs argument 309280031Sdim // eliminations of the same function. 310280031Sdim FunctionDIs.erase(DI); 311280031Sdim FunctionDIs[NF] = SP; 312280031Sdim } 313243830Sdim 314261991Sdim // Fix up any BlockAddresses that refer to the function. 315261991Sdim Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType())); 316261991Sdim // Delete the bitcast that we just created, so that NF does not 317261991Sdim // appear to be address-taken. 318261991Sdim NF->removeDeadConstantUsers(); 319193323Sed // Finally, nuke the old function. 320193323Sed Fn.eraseFromParent(); 321193323Sed return true; 322193323Sed} 323193323Sed 324218893Sdim/// RemoveDeadArgumentsFromCallers - Checks if the given function has any 325218893Sdim/// arguments that are unused, and changes the caller parameters to be undefined 326218893Sdim/// instead. 327218893Sdimbool DAE::RemoveDeadArgumentsFromCallers(Function &Fn) 328218893Sdim{ 329221345Sdim if (Fn.isDeclaration() || Fn.mayBeOverridden()) 330218893Sdim return false; 331218893Sdim 332261991Sdim // Functions with local linkage should already have been handled, except the 333261991Sdim // fragile (variadic) ones which we can improve here. 334261991Sdim if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg()) 335218893Sdim return false; 336218893Sdim 337261991Sdim // If a function seen at compile time is not necessarily the one linked to 338261991Sdim // the binary being built, it is illegal to change the actual arguments 339261991Sdim // passed to it. These functions can be captured by isWeakForLinker(). 340261991Sdim // *NOTE* that mayBeOverridden() is insufficient for this purpose as it 341261991Sdim // doesn't include linkage types like AvailableExternallyLinkage and 342261991Sdim // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of 343261991Sdim // *EQUIVALENT* globals that can be merged at link-time. However, the 344261991Sdim // semantic of *EQUIVALENT*-functions includes parameters. Changing 345261991Sdim // parameters breaks this assumption. 346261991Sdim // 347261991Sdim if (Fn.isWeakForLinker()) 348261991Sdim return false; 349261991Sdim 350218893Sdim if (Fn.use_empty()) 351218893Sdim return false; 352218893Sdim 353249423Sdim SmallVector<unsigned, 8> UnusedArgs; 354218893Sdim for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(); 355218893Sdim I != E; ++I) { 356218893Sdim Argument *Arg = I; 357218893Sdim 358276479Sdim if (Arg->use_empty() && !Arg->hasByValOrInAllocaAttr()) 359218893Sdim UnusedArgs.push_back(Arg->getArgNo()); 360218893Sdim } 361218893Sdim 362218893Sdim if (UnusedArgs.empty()) 363218893Sdim return false; 364218893Sdim 365218893Sdim bool Changed = false; 366218893Sdim 367276479Sdim for (Use &U : Fn.uses()) { 368276479Sdim CallSite CS(U.getUser()); 369276479Sdim if (!CS || !CS.isCallee(&U)) 370218893Sdim continue; 371218893Sdim 372218893Sdim // Now go through all unused args and replace them with "undef". 373218893Sdim for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) { 374218893Sdim unsigned ArgNo = UnusedArgs[I]; 375218893Sdim 376218893Sdim Value *Arg = CS.getArgument(ArgNo); 377218893Sdim CS.setArgument(ArgNo, UndefValue::get(Arg->getType())); 378218893Sdim ++NumArgumentsReplacedWithUndef; 379218893Sdim Changed = true; 380218893Sdim } 381218893Sdim } 382218893Sdim 383218893Sdim return Changed; 384218893Sdim} 385218893Sdim 386193323Sed/// Convenience function that returns the number of return values. It returns 0 387193323Sed/// for void functions and 1 for functions not returning a struct. It returns 388193323Sed/// the number of struct elements for functions returning a struct. 389193323Sedstatic unsigned NumRetVals(const Function *F) { 390206083Srdivacky if (F->getReturnType()->isVoidTy()) 391193323Sed return 0; 392226633Sdim else if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) 393193323Sed return STy->getNumElements(); 394193323Sed else 395193323Sed return 1; 396193323Sed} 397193323Sed 398193323Sed/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 399193323Sed/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 400193323Sed/// liveness of Use. 401193323SedDAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 402193323Sed // We're live if our use or its Function is already marked as live. 403193323Sed if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 404193323Sed return Live; 405193323Sed 406193323Sed // We're maybe live otherwise, but remember that we must become live if 407193323Sed // Use becomes live. 408193323Sed MaybeLiveUses.push_back(Use); 409193323Sed return MaybeLive; 410193323Sed} 411193323Sed 412193323Sed 413193323Sed/// SurveyUse - This looks at a single use of an argument or return value 414193323Sed/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 415206083Srdivacky/// if it causes the used value to become MaybeLive. 416193323Sed/// 417193323Sed/// RetValNum is the return value number to use when this use is used in a 418193323Sed/// return instruction. This is used in the recursion, you should always leave 419193323Sed/// it at 0. 420276479SdimDAE::Liveness DAE::SurveyUse(const Use *U, 421206083Srdivacky UseVector &MaybeLiveUses, unsigned RetValNum) { 422276479Sdim const User *V = U->getUser(); 423206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 424193323Sed // The value is returned from a function. It's only live when the 425193323Sed // function's return value is live. We use RetValNum here, for the case 426193323Sed // that U is really a use of an insertvalue instruction that uses the 427221345Sdim // original Use. 428193323Sed RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 429193323Sed // We might be live, depending on the liveness of Use. 430193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 431193323Sed } 432206083Srdivacky if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 433276479Sdim if (U->getOperandNo() != InsertValueInst::getAggregateOperandIndex() 434193323Sed && IV->hasIndices()) 435193323Sed // The use we are examining is inserted into an aggregate. Our liveness 436193323Sed // depends on all uses of that aggregate, but if it is used as a return 437193323Sed // value, only index at which we were inserted counts. 438193323Sed RetValNum = *IV->idx_begin(); 439193323Sed 440193323Sed // Note that if we are used as the aggregate operand to the insertvalue, 441193323Sed // we don't change RetValNum, but do survey all our uses. 442193323Sed 443193323Sed Liveness Result = MaybeLive; 444276479Sdim for (const Use &UU : IV->uses()) { 445276479Sdim Result = SurveyUse(&UU, MaybeLiveUses, RetValNum); 446193323Sed if (Result == Live) 447193323Sed break; 448193323Sed } 449193323Sed return Result; 450193323Sed } 451206083Srdivacky 452206083Srdivacky if (ImmutableCallSite CS = V) { 453206083Srdivacky const Function *F = CS.getCalledFunction(); 454193323Sed if (F) { 455193323Sed // Used in a direct call. 456206083Srdivacky 457193323Sed // Find the argument number. We know for sure that this use is an 458193323Sed // argument, since if it was the function argument this would be an 459193323Sed // indirect call and the we know can't be looking at a value of the 460193323Sed // label type (for the invoke instruction). 461206083Srdivacky unsigned ArgNo = CS.getArgumentNo(U); 462193323Sed 463193323Sed if (ArgNo >= F->getFunctionType()->getNumParams()) 464193323Sed // The value is passed in through a vararg! Must be live. 465193323Sed return Live; 466193323Sed 467206083Srdivacky assert(CS.getArgument(ArgNo) 468276479Sdim == CS->getOperand(U->getOperandNo()) 469193323Sed && "Argument is not where we expected it"); 470193323Sed 471193323Sed // Value passed to a normal call. It's only live when the corresponding 472193323Sed // argument to the called function turns out live. 473193323Sed RetOrArg Use = CreateArg(F, ArgNo); 474193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 475193323Sed } 476193323Sed } 477193323Sed // Used in any other way? Value must be live. 478193323Sed return Live; 479193323Sed} 480193323Sed 481193323Sed/// SurveyUses - This looks at all the uses of the given value 482193323Sed/// Returns the Liveness deduced from the uses of this value. 483193323Sed/// 484193323Sed/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 485193323Sed/// the result is Live, MaybeLiveUses might be modified but its content should 486193323Sed/// be ignored (since it might not be complete). 487206083SrdivackyDAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 488193323Sed // Assume it's dead (which will only hold if there are no uses at all..). 489193323Sed Liveness Result = MaybeLive; 490193323Sed // Check each use. 491276479Sdim for (const Use &U : V->uses()) { 492276479Sdim Result = SurveyUse(&U, MaybeLiveUses); 493193323Sed if (Result == Live) 494193323Sed break; 495193323Sed } 496193323Sed return Result; 497193323Sed} 498193323Sed 499193323Sed// SurveyFunction - This performs the initial survey of the specified function, 500193323Sed// checking out whether or not it uses any of its incoming arguments or whether 501193323Sed// any callers use the return value. This fills in the LiveValues set and Uses 502193323Sed// map. 503193323Sed// 504193323Sed// We consider arguments of non-internal functions to be intrinsically alive as 505193323Sed// well as arguments to functions which have their "address taken". 506193323Sed// 507206083Srdivackyvoid DAE::SurveyFunction(const Function &F) { 508276479Sdim // Functions with inalloca parameters are expecting args in a particular 509276479Sdim // register and memory layout. 510276479Sdim if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca)) { 511276479Sdim MarkLive(F); 512276479Sdim return; 513276479Sdim } 514276479Sdim 515193323Sed unsigned RetCount = NumRetVals(&F); 516193323Sed // Assume all return values are dead 517193323Sed typedef SmallVector<Liveness, 5> RetVals; 518193323Sed RetVals RetValLiveness(RetCount, MaybeLive); 519193323Sed 520193323Sed typedef SmallVector<UseVector, 5> RetUses; 521193323Sed // These vectors map each return value to the uses that make it MaybeLive, so 522193323Sed // we can add those to the Uses map if the return value really turns out to be 523193323Sed // MaybeLive. Initialized to a list of RetCount empty lists. 524193323Sed RetUses MaybeLiveRetUses(RetCount); 525193323Sed 526206083Srdivacky for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 527206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 528193323Sed if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 529193323Sed != F.getFunctionType()->getReturnType()) { 530193323Sed // We don't support old style multiple return values. 531193323Sed MarkLive(F); 532193323Sed return; 533193323Sed } 534193323Sed 535193323Sed if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 536193323Sed MarkLive(F); 537193323Sed return; 538193323Sed } 539193323Sed 540202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 541193323Sed // Keep track of the number of live retvals, so we can skip checks once all 542193323Sed // of them turn out to be live. 543193323Sed unsigned NumLiveRetVals = 0; 544226633Sdim Type *STy = dyn_cast<StructType>(F.getReturnType()); 545193323Sed // Loop all uses of the function. 546276479Sdim for (const Use &U : F.uses()) { 547193323Sed // If the function is PASSED IN as an argument, its address has been 548193323Sed // taken. 549276479Sdim ImmutableCallSite CS(U.getUser()); 550276479Sdim if (!CS || !CS.isCallee(&U)) { 551193323Sed MarkLive(F); 552193323Sed return; 553193323Sed } 554193323Sed 555193323Sed // If this use is anything other than a call site, the function is alive. 556206083Srdivacky const Instruction *TheCall = CS.getInstruction(); 557193323Sed if (!TheCall) { // Not a direct call site? 558193323Sed MarkLive(F); 559193323Sed return; 560193323Sed } 561193323Sed 562193323Sed // If we end up here, we are looking at a direct call to our function. 563193323Sed 564193323Sed // Now, check how our return value(s) is/are used in this caller. Don't 565193323Sed // bother checking return values if all of them are live already. 566193323Sed if (NumLiveRetVals != RetCount) { 567193323Sed if (STy) { 568193323Sed // Check all uses of the return value. 569276479Sdim for (const User *U : TheCall->users()) { 570276479Sdim const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(U); 571193323Sed if (Ext && Ext->hasIndices()) { 572193323Sed // This use uses a part of our return value, survey the uses of 573193323Sed // that part and store the results for this index only. 574193323Sed unsigned Idx = *Ext->idx_begin(); 575193323Sed if (RetValLiveness[Idx] != Live) { 576193323Sed RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 577193323Sed if (RetValLiveness[Idx] == Live) 578193323Sed NumLiveRetVals++; 579193323Sed } 580193323Sed } else { 581193323Sed // Used by something else than extractvalue. Mark all return 582193323Sed // values as live. 583193323Sed for (unsigned i = 0; i != RetCount; ++i ) 584193323Sed RetValLiveness[i] = Live; 585193323Sed NumLiveRetVals = RetCount; 586193323Sed break; 587193323Sed } 588193323Sed } 589193323Sed } else { 590193323Sed // Single return value 591193323Sed RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 592193323Sed if (RetValLiveness[0] == Live) 593193323Sed NumLiveRetVals = RetCount; 594193323Sed } 595193323Sed } 596193323Sed } 597193323Sed 598193323Sed // Now we've inspected all callers, record the liveness of our return values. 599193323Sed for (unsigned i = 0; i != RetCount; ++i) 600193323Sed MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 601193323Sed 602202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 603193323Sed 604193323Sed // Now, check all of our arguments. 605193323Sed unsigned i = 0; 606193323Sed UseVector MaybeLiveArgUses; 607206083Srdivacky for (Function::const_arg_iterator AI = F.arg_begin(), 608193323Sed E = F.arg_end(); AI != E; ++AI, ++i) { 609261991Sdim Liveness Result; 610261991Sdim if (F.getFunctionType()->isVarArg()) { 611261991Sdim // Variadic functions will already have a va_arg function expanded inside 612261991Sdim // them, making them potentially very sensitive to ABI changes resulting 613261991Sdim // from removing arguments entirely, so don't. For example AArch64 handles 614261991Sdim // register and stack HFAs very differently, and this is reflected in the 615261991Sdim // IR which has already been generated. 616261991Sdim Result = Live; 617261991Sdim } else { 618261991Sdim // See what the effect of this use is (recording any uses that cause 619261991Sdim // MaybeLive in MaybeLiveArgUses). 620261991Sdim Result = SurveyUses(AI, MaybeLiveArgUses); 621261991Sdim } 622261991Sdim 623193323Sed // Mark the result. 624193323Sed MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 625193323Sed // Clear the vector again for the next iteration. 626193323Sed MaybeLiveArgUses.clear(); 627193323Sed } 628193323Sed} 629193323Sed 630193323Sed/// MarkValue - This function marks the liveness of RA depending on L. If L is 631193323Sed/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 632193323Sed/// such that RA will be marked live if any use in MaybeLiveUses gets marked 633193323Sed/// live later on. 634193323Sedvoid DAE::MarkValue(const RetOrArg &RA, Liveness L, 635193323Sed const UseVector &MaybeLiveUses) { 636193323Sed switch (L) { 637193323Sed case Live: MarkLive(RA); break; 638193323Sed case MaybeLive: 639193323Sed { 640193323Sed // Note any uses of this value, so this return value can be 641193323Sed // marked live whenever one of the uses becomes live. 642193323Sed for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 643193323Sed UE = MaybeLiveUses.end(); UI != UE; ++UI) 644193323Sed Uses.insert(std::make_pair(*UI, RA)); 645193323Sed break; 646193323Sed } 647193323Sed } 648193323Sed} 649193323Sed 650193323Sed/// MarkLive - Mark the given Function as alive, meaning that it cannot be 651193323Sed/// changed in any way. Additionally, 652193323Sed/// mark any values that are used as this function's parameters or by its return 653193323Sed/// values (according to Uses) live as well. 654193323Sedvoid DAE::MarkLive(const Function &F) { 655202375Srdivacky DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 656208599Srdivacky // Mark the function as live. 657208599Srdivacky LiveFunctions.insert(&F); 658208599Srdivacky // Mark all arguments as live. 659208599Srdivacky for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 660208599Srdivacky PropagateLiveness(CreateArg(&F, i)); 661208599Srdivacky // Mark all return values as live. 662208599Srdivacky for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 663208599Srdivacky PropagateLiveness(CreateRet(&F, i)); 664193323Sed} 665193323Sed 666193323Sed/// MarkLive - Mark the given return value or argument as live. Additionally, 667193323Sed/// mark any values that are used by this value (according to Uses) live as 668193323Sed/// well. 669193323Sedvoid DAE::MarkLive(const RetOrArg &RA) { 670193323Sed if (LiveFunctions.count(RA.F)) 671193323Sed return; // Function was already marked Live. 672193323Sed 673193323Sed if (!LiveValues.insert(RA).second) 674193323Sed return; // We were already marked Live. 675193323Sed 676202375Srdivacky DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 677193323Sed PropagateLiveness(RA); 678193323Sed} 679193323Sed 680193323Sed/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 681193323Sed/// to any other values it uses (according to Uses). 682193323Sedvoid DAE::PropagateLiveness(const RetOrArg &RA) { 683193323Sed // We don't use upper_bound (or equal_range) here, because our recursive call 684193323Sed // to ourselves is likely to cause the upper_bound (which is the first value 685193323Sed // not belonging to RA) to become erased and the iterator invalidated. 686193323Sed UseMap::iterator Begin = Uses.lower_bound(RA); 687193323Sed UseMap::iterator E = Uses.end(); 688193323Sed UseMap::iterator I; 689193323Sed for (I = Begin; I != E && I->first == RA; ++I) 690193323Sed MarkLive(I->second); 691193323Sed 692193323Sed // Erase RA from the Uses map (from the lower bound to wherever we ended up 693193323Sed // after the loop). 694193323Sed Uses.erase(Begin, I); 695193323Sed} 696193323Sed 697193323Sed// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 698193323Sed// that are not in LiveValues. Transform the function and all of the callees of 699193323Sed// the function to not have these arguments and return values. 700193323Sed// 701193323Sedbool DAE::RemoveDeadStuffFromFunction(Function *F) { 702193323Sed // Don't modify fully live functions 703193323Sed if (LiveFunctions.count(F)) 704193323Sed return false; 705193323Sed 706193323Sed // Start by computing a new prototype for the function, which is the same as 707193323Sed // the old function, but has fewer arguments and a different return type. 708226633Sdim FunctionType *FTy = F->getFunctionType(); 709224145Sdim std::vector<Type*> Params; 710193323Sed 711261991Sdim // Keep track of if we have a live 'returned' argument 712261991Sdim bool HasLiveReturnedArg = false; 713261991Sdim 714193323Sed // Set up to build a new list of parameter attributes. 715249423Sdim SmallVector<AttributeSet, 8> AttributesVec; 716249423Sdim const AttributeSet &PAL = F->getAttributes(); 717193323Sed 718261991Sdim // Remember which arguments are still alive. 719261991Sdim SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 720261991Sdim // Construct the new parameter list from non-dead arguments. Also construct 721261991Sdim // a new set of parameter attributes to correspond. Skip the first parameter 722261991Sdim // attribute, since that belongs to the return value. 723261991Sdim unsigned i = 0; 724261991Sdim for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 725261991Sdim I != E; ++I, ++i) { 726261991Sdim RetOrArg Arg = CreateArg(F, i); 727261991Sdim if (LiveValues.erase(Arg)) { 728261991Sdim Params.push_back(I->getType()); 729261991Sdim ArgAlive[i] = true; 730261991Sdim 731261991Sdim // Get the original parameter attributes (skipping the first one, that is 732261991Sdim // for the return value. 733261991Sdim if (PAL.hasAttributes(i + 1)) { 734261991Sdim AttrBuilder B(PAL, i + 1); 735261991Sdim if (B.contains(Attribute::Returned)) 736261991Sdim HasLiveReturnedArg = true; 737261991Sdim AttributesVec. 738261991Sdim push_back(AttributeSet::get(F->getContext(), Params.size(), B)); 739261991Sdim } 740261991Sdim } else { 741261991Sdim ++NumArgumentsEliminated; 742261991Sdim DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 743261991Sdim << ") from " << F->getName() << "\n"); 744261991Sdim } 745261991Sdim } 746261991Sdim 747193323Sed // Find out the new return value. 748224145Sdim Type *RetTy = FTy->getReturnType(); 749276479Sdim Type *NRetTy = nullptr; 750193323Sed unsigned RetCount = NumRetVals(F); 751206083Srdivacky 752193323Sed // -1 means unused, other numbers are the new index 753193323Sed SmallVector<int, 5> NewRetIdxs(RetCount, -1); 754224145Sdim std::vector<Type*> RetTypes; 755261991Sdim 756261991Sdim // If there is a function with a live 'returned' argument but a dead return 757261991Sdim // value, then there are two possible actions: 758261991Sdim // 1) Eliminate the return value and take off the 'returned' attribute on the 759261991Sdim // argument. 760261991Sdim // 2) Retain the 'returned' attribute and treat the return value (but not the 761261991Sdim // entire function) as live so that it is not eliminated. 762261991Sdim // 763261991Sdim // It's not clear in the general case which option is more profitable because, 764261991Sdim // even in the absence of explicit uses of the return value, code generation 765261991Sdim // is free to use the 'returned' attribute to do things like eliding 766261991Sdim // save/restores of registers across calls. Whether or not this happens is 767261991Sdim // target and ABI-specific as well as depending on the amount of register 768261991Sdim // pressure, so there's no good way for an IR-level pass to figure this out. 769261991Sdim // 770261991Sdim // Fortunately, the only places where 'returned' is currently generated by 771261991Sdim // the FE are places where 'returned' is basically free and almost always a 772261991Sdim // performance win, so the second option can just be used always for now. 773261991Sdim // 774261991Sdim // This should be revisited if 'returned' is ever applied more liberally. 775261991Sdim if (RetTy->isVoidTy() || HasLiveReturnedArg) { 776206083Srdivacky NRetTy = RetTy; 777193323Sed } else { 778226633Sdim StructType *STy = dyn_cast<StructType>(RetTy); 779193323Sed if (STy) 780193323Sed // Look at each of the original return values individually. 781193323Sed for (unsigned i = 0; i != RetCount; ++i) { 782193323Sed RetOrArg Ret = CreateRet(F, i); 783193323Sed if (LiveValues.erase(Ret)) { 784193323Sed RetTypes.push_back(STy->getElementType(i)); 785193323Sed NewRetIdxs[i] = RetTypes.size() - 1; 786193323Sed } else { 787193323Sed ++NumRetValsEliminated; 788202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 789198090Srdivacky << F->getName() << "\n"); 790193323Sed } 791193323Sed } 792193323Sed else 793193323Sed // We used to return a single value. 794193323Sed if (LiveValues.erase(CreateRet(F, 0))) { 795193323Sed RetTypes.push_back(RetTy); 796193323Sed NewRetIdxs[0] = 0; 797193323Sed } else { 798202375Srdivacky DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 799198090Srdivacky << "\n"); 800193323Sed ++NumRetValsEliminated; 801193323Sed } 802193323Sed if (RetTypes.size() > 1) 803193323Sed // More than one return type? Return a struct with them. Also, if we used 804193323Sed // to return a struct and didn't change the number of return values, 805193323Sed // return a struct again. This prevents changing {something} into 806193323Sed // something and {} into void. 807193323Sed // Make the new struct packed if we used to return a packed struct 808193323Sed // already. 809198090Srdivacky NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 810193323Sed else if (RetTypes.size() == 1) 811193323Sed // One return type? Just a simple value then, but only if we didn't use to 812193323Sed // return a struct with that simple value before. 813193323Sed NRetTy = RetTypes.front(); 814193323Sed else if (RetTypes.size() == 0) 815193323Sed // No return types? Make it void, but only if we didn't use to return {}. 816198090Srdivacky NRetTy = Type::getVoidTy(F->getContext()); 817193323Sed } 818193323Sed 819193323Sed assert(NRetTy && "No new return type found?"); 820193323Sed 821249423Sdim // The existing function return attributes. 822249423Sdim AttributeSet RAttrs = PAL.getRetAttributes(); 823249423Sdim 824193323Sed // Remove any incompatible attributes, but only if we removed all return 825193323Sed // values. Otherwise, ensure that we don't have any conflicting attributes 826193323Sed // here. Currently, this should not be possible, but special handling might be 827193323Sed // required when new return value attributes are added. 828206083Srdivacky if (NRetTy->isVoidTy()) 829243830Sdim RAttrs = 830249423Sdim AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex, 831249423Sdim AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 832249423Sdim removeAttributes(AttributeFuncs:: 833249423Sdim typeIncompatible(NRetTy, AttributeSet::ReturnIndex), 834249423Sdim AttributeSet::ReturnIndex)); 835193323Sed else 836249423Sdim assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 837249423Sdim hasAttributes(AttributeFuncs:: 838249423Sdim typeIncompatible(NRetTy, AttributeSet::ReturnIndex), 839249423Sdim AttributeSet::ReturnIndex) && 840243830Sdim "Return attributes no longer compatible?"); 841193323Sed 842249423Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 843249423Sdim AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs)); 844193323Sed 845249423Sdim if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 846249423Sdim AttributesVec.push_back(AttributeSet::get(F->getContext(), 847249423Sdim PAL.getFnAttributes())); 848193323Sed 849193323Sed // Reconstruct the AttributesList based on the vector we constructed. 850249423Sdim AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec); 851193323Sed 852193323Sed // Create the new function type based on the recomputed parameters. 853206083Srdivacky FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 854193323Sed 855193323Sed // No change? 856193323Sed if (NFTy == FTy) 857193323Sed return false; 858193323Sed 859193323Sed // Create the new function body and insert it into the module... 860193323Sed Function *NF = Function::Create(NFTy, F->getLinkage()); 861193323Sed NF->copyAttributesFrom(F); 862193323Sed NF->setAttributes(NewPAL); 863193323Sed // Insert the new function before the old function, so we won't be processing 864193323Sed // it again. 865193323Sed F->getParent()->getFunctionList().insert(F, NF); 866193323Sed NF->takeName(F); 867193323Sed 868193323Sed // Loop over all of the callers of the function, transforming the call sites 869193323Sed // to pass in a smaller number of arguments into the new function. 870193323Sed // 871193323Sed std::vector<Value*> Args; 872193323Sed while (!F->use_empty()) { 873276479Sdim CallSite CS(F->user_back()); 874193323Sed Instruction *Call = CS.getInstruction(); 875193323Sed 876193323Sed AttributesVec.clear(); 877249423Sdim const AttributeSet &CallPAL = CS.getAttributes(); 878193323Sed 879193323Sed // The call return attributes. 880249423Sdim AttributeSet RAttrs = CallPAL.getRetAttributes(); 881249423Sdim 882193323Sed // Adjust in case the function was changed to return void. 883243830Sdim RAttrs = 884249423Sdim AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex, 885249423Sdim AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 886249423Sdim removeAttributes(AttributeFuncs:: 887249423Sdim typeIncompatible(NF->getReturnType(), 888249423Sdim AttributeSet::ReturnIndex), 889249423Sdim AttributeSet::ReturnIndex)); 890249423Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 891249423Sdim AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs)); 892193323Sed 893193323Sed // Declare these outside of the loops, so we can reuse them for the second 894193323Sed // loop, which loops the varargs. 895193323Sed CallSite::arg_iterator I = CS.arg_begin(); 896193323Sed unsigned i = 0; 897193323Sed // Loop over those operands, corresponding to the normal arguments to the 898193323Sed // original function, and add those that are still alive. 899193323Sed for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 900193323Sed if (ArgAlive[i]) { 901193323Sed Args.push_back(*I); 902193323Sed // Get original parameter attributes, but skip return attributes. 903249423Sdim if (CallPAL.hasAttributes(i + 1)) { 904249423Sdim AttrBuilder B(CallPAL, i + 1); 905261991Sdim // If the return type has changed, then get rid of 'returned' on the 906261991Sdim // call site. The alternative is to make all 'returned' attributes on 907261991Sdim // call sites keep the return value alive just like 'returned' 908261991Sdim // attributes on function declaration but it's less clearly a win 909261991Sdim // and this is not an expected case anyway 910261991Sdim if (NRetTy != RetTy && B.contains(Attribute::Returned)) 911261991Sdim B.removeAttribute(Attribute::Returned); 912249423Sdim AttributesVec. 913249423Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 914249423Sdim } 915193323Sed } 916193323Sed 917193323Sed // Push any varargs arguments on the list. Don't forget their attributes. 918193323Sed for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 919193323Sed Args.push_back(*I); 920249423Sdim if (CallPAL.hasAttributes(i + 1)) { 921249423Sdim AttrBuilder B(CallPAL, i + 1); 922249423Sdim AttributesVec. 923249423Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 924249423Sdim } 925193323Sed } 926193323Sed 927249423Sdim if (CallPAL.hasAttributes(AttributeSet::FunctionIndex)) 928249423Sdim AttributesVec.push_back(AttributeSet::get(Call->getContext(), 929249423Sdim CallPAL.getFnAttributes())); 930193323Sed 931193323Sed // Reconstruct the AttributesList based on the vector we constructed. 932249423Sdim AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec); 933193323Sed 934193323Sed Instruction *New; 935193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 936193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 937224145Sdim Args, "", Call); 938193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 939193323Sed cast<InvokeInst>(New)->setAttributes(NewCallPAL); 940193323Sed } else { 941224145Sdim New = CallInst::Create(NF, Args, "", Call); 942193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 943193323Sed cast<CallInst>(New)->setAttributes(NewCallPAL); 944193323Sed if (cast<CallInst>(Call)->isTailCall()) 945193323Sed cast<CallInst>(New)->setTailCall(); 946193323Sed } 947212904Sdim New->setDebugLoc(Call->getDebugLoc()); 948207618Srdivacky 949193323Sed Args.clear(); 950193323Sed 951193323Sed if (!Call->use_empty()) { 952193323Sed if (New->getType() == Call->getType()) { 953193323Sed // Return type not changed? Just replace users then. 954193323Sed Call->replaceAllUsesWith(New); 955193323Sed New->takeName(Call); 956206083Srdivacky } else if (New->getType()->isVoidTy()) { 957193323Sed // Our return value has uses, but they will get removed later on. 958193323Sed // Replace by null for now. 959218893Sdim if (!Call->getType()->isX86_MMXTy()) 960218893Sdim Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 961193323Sed } else { 962204642Srdivacky assert(RetTy->isStructTy() && 963193323Sed "Return type changed, but not into a void. The old return type" 964193323Sed " must have been a struct!"); 965193323Sed Instruction *InsertPt = Call; 966193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 967193323Sed BasicBlock::iterator IP = II->getNormalDest()->begin(); 968193323Sed while (isa<PHINode>(IP)) ++IP; 969193323Sed InsertPt = IP; 970193323Sed } 971206083Srdivacky 972193323Sed // We used to return a struct. Instead of doing smart stuff with all the 973193323Sed // uses of this struct, we will just rebuild it using 974193323Sed // extract/insertvalue chaining and let instcombine clean that up. 975193323Sed // 976193323Sed // Start out building up our return value from undef 977198090Srdivacky Value *RetVal = UndefValue::get(RetTy); 978193323Sed for (unsigned i = 0; i != RetCount; ++i) 979193323Sed if (NewRetIdxs[i] != -1) { 980193323Sed Value *V; 981193323Sed if (RetTypes.size() > 1) 982193323Sed // We are still returning a struct, so extract the value from our 983193323Sed // return value 984193323Sed V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 985193323Sed InsertPt); 986193323Sed else 987193323Sed // We are now returning a single element, so just insert that 988193323Sed V = New; 989193323Sed // Insert the value at the old position 990193323Sed RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 991193323Sed } 992193323Sed // Now, replace all uses of the old call instruction with the return 993193323Sed // struct we built 994193323Sed Call->replaceAllUsesWith(RetVal); 995193323Sed New->takeName(Call); 996193323Sed } 997193323Sed } 998193323Sed 999193323Sed // Finally, remove the old call from the program, reducing the use-count of 1000193323Sed // F. 1001193323Sed Call->eraseFromParent(); 1002193323Sed } 1003193323Sed 1004193323Sed // Since we have now created the new function, splice the body of the old 1005193323Sed // function right into the new function, leaving the old rotting hulk of the 1006193323Sed // function empty. 1007193323Sed NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 1008193323Sed 1009221345Sdim // Loop over the argument list, transferring uses of the old arguments over to 1010221345Sdim // the new arguments, also transferring over the names as well. 1011193323Sed i = 0; 1012193323Sed for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 1013193323Sed I2 = NF->arg_begin(); I != E; ++I, ++i) 1014193323Sed if (ArgAlive[i]) { 1015193323Sed // If this is a live argument, move the name and users over to the new 1016193323Sed // version. 1017193323Sed I->replaceAllUsesWith(I2); 1018193323Sed I2->takeName(I); 1019193323Sed ++I2; 1020193323Sed } else { 1021193323Sed // If this argument is dead, replace any uses of it with null constants 1022193323Sed // (these are guaranteed to become unused later on). 1023218893Sdim if (!I->getType()->isX86_MMXTy()) 1024218893Sdim I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 1025193323Sed } 1026193323Sed 1027193323Sed // If we change the return value of the function we must rewrite any return 1028193323Sed // instructions. Check this now. 1029193323Sed if (F->getReturnType() != NF->getReturnType()) 1030193323Sed for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 1031193323Sed if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 1032193323Sed Value *RetVal; 1033193323Sed 1034208599Srdivacky if (NFTy->getReturnType()->isVoidTy()) { 1035276479Sdim RetVal = nullptr; 1036193323Sed } else { 1037204642Srdivacky assert (RetTy->isStructTy()); 1038193323Sed // The original return value was a struct, insert 1039193323Sed // extractvalue/insertvalue chains to extract only the values we need 1040193323Sed // to return and insert them into our new result. 1041193323Sed // This does generate messy code, but we'll let it to instcombine to 1042193323Sed // clean that up. 1043193323Sed Value *OldRet = RI->getOperand(0); 1044193323Sed // Start out building up our return value from undef 1045198090Srdivacky RetVal = UndefValue::get(NRetTy); 1046193323Sed for (unsigned i = 0; i != RetCount; ++i) 1047193323Sed if (NewRetIdxs[i] != -1) { 1048193323Sed ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 1049193323Sed "oldret", RI); 1050193323Sed if (RetTypes.size() > 1) { 1051193323Sed // We're still returning a struct, so reinsert the value into 1052193323Sed // our new return value at the new index 1053193323Sed 1054193323Sed RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 1055193323Sed "newret", RI); 1056193323Sed } else { 1057193323Sed // We are now only returning a simple value, so just return the 1058193323Sed // extracted value. 1059193323Sed RetVal = EV; 1060193323Sed } 1061193323Sed } 1062193323Sed } 1063193323Sed // Replace the return instruction with one returning the new return 1064193323Sed // value (possibly 0 if we became void). 1065198090Srdivacky ReturnInst::Create(F->getContext(), RetVal, RI); 1066193323Sed BB->getInstList().erase(RI); 1067193323Sed } 1068193323Sed 1069243830Sdim // Patch the pointer to LLVM function in debug info descriptor. 1070276479Sdim auto DI = FunctionDIs.find(F); 1071243830Sdim if (DI != FunctionDIs.end()) 1072243830Sdim DI->second.replaceFunction(NF); 1073243830Sdim 1074193323Sed // Now that the old function is dead, delete it. 1075193323Sed F->eraseFromParent(); 1076193323Sed 1077193323Sed return true; 1078193323Sed} 1079193323Sed 1080193323Sedbool DAE::runOnModule(Module &M) { 1081193323Sed bool Changed = false; 1082193323Sed 1083243830Sdim // Collect debug info descriptors for functions. 1084276479Sdim FunctionDIs = makeSubprogramMap(M); 1085243830Sdim 1086193323Sed // First pass: Do a simple check to see if any functions can have their "..." 1087193323Sed // removed. We can do this if they never call va_start. This loop cannot be 1088193323Sed // fused with the next loop, because deleting a function invalidates 1089193323Sed // information computed while surveying other functions. 1090202375Srdivacky DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 1091193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1092193323Sed Function &F = *I++; 1093193323Sed if (F.getFunctionType()->isVarArg()) 1094193323Sed Changed |= DeleteDeadVarargs(F); 1095193323Sed } 1096193323Sed 1097193323Sed // Second phase:loop through the module, determining which arguments are live. 1098193323Sed // We assume all arguments are dead unless proven otherwise (allowing us to 1099193323Sed // determine that dead arguments passed into recursive functions are dead). 1100193323Sed // 1101202375Srdivacky DEBUG(dbgs() << "DAE - Determining liveness\n"); 1102280031Sdim for (auto &F : M) 1103280031Sdim SurveyFunction(F); 1104206083Srdivacky 1105193323Sed // Now, remove all dead arguments and return values from each function in 1106206083Srdivacky // turn. 1107193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1108206083Srdivacky // Increment now, because the function will probably get removed (ie. 1109193323Sed // replaced by a new one). 1110193323Sed Function *F = I++; 1111193323Sed Changed |= RemoveDeadStuffFromFunction(F); 1112193323Sed } 1113218893Sdim 1114218893Sdim // Finally, look for any unused parameters in functions with non-local 1115218893Sdim // linkage and replace the passed in parameters with undef. 1116280031Sdim for (auto &F : M) 1117218893Sdim Changed |= RemoveDeadArgumentsFromCallers(F); 1118218893Sdim 1119193323Sed return Changed; 1120193323Sed} 1121