DeadArgumentElimination.cpp revision 296417
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" 38296417Sdim#include "llvm/Transforms/Utils/BasicBlockUtils.h" 39193323Sed#include <map> 40193323Sed#include <set> 41276479Sdim#include <tuple> 42193323Sedusing namespace llvm; 43193323Sed 44276479Sdim#define DEBUG_TYPE "deadargelim" 45276479Sdim 46193323SedSTATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 47193323SedSTATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 48218893SdimSTATISTIC(NumArgumentsReplacedWithUndef, 49218893Sdim "Number of unread args replaced with undef"); 50193323Sednamespace { 51193323Sed /// DAE - The dead argument elimination pass. 52193323Sed /// 53198892Srdivacky class DAE : public ModulePass { 54193323Sed public: 55193323Sed 56193323Sed /// Struct that represents (part of) either a return value or a function 57193323Sed /// argument. Used so that arguments and return values can be used 58221345Sdim /// interchangeably. 59193323Sed struct RetOrArg { 60206083Srdivacky RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 61193323Sed IsArg(IsArg) {} 62193323Sed const Function *F; 63193323Sed unsigned Idx; 64193323Sed bool IsArg; 65193323Sed 66193323Sed /// Make RetOrArg comparable, so we can put it into a map. 67193323Sed bool operator<(const RetOrArg &O) const { 68276479Sdim return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg); 69193323Sed } 70193323Sed 71193323Sed /// Make RetOrArg comparable, so we can easily iterate the multimap. 72193323Sed bool operator==(const RetOrArg &O) const { 73193323Sed return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 74193323Sed } 75193323Sed 76193323Sed std::string getDescription() const { 77288943Sdim return (Twine(IsArg ? "Argument #" : "Return value #") + utostr(Idx) + 78288943Sdim " of function " + F->getName()).str(); 79193323Sed } 80193323Sed }; 81193323Sed 82193323Sed /// Liveness enum - During our initial pass over the program, we determine 83193323Sed /// that things are either alive or maybe alive. We don't mark anything 84193323Sed /// explicitly dead (even if we know they are), since anything not alive 85193323Sed /// with no registered uses (in Uses) will never be marked alive and will 86193323Sed /// thus become dead in the end. 87193323Sed enum Liveness { Live, MaybeLive }; 88193323Sed 89193323Sed /// Convenience wrapper 90193323Sed RetOrArg CreateRet(const Function *F, unsigned Idx) { 91193323Sed return RetOrArg(F, Idx, false); 92193323Sed } 93193323Sed /// Convenience wrapper 94193323Sed RetOrArg CreateArg(const Function *F, unsigned Idx) { 95193323Sed return RetOrArg(F, Idx, true); 96193323Sed } 97193323Sed 98193323Sed typedef std::multimap<RetOrArg, RetOrArg> UseMap; 99193323Sed /// This maps a return value or argument to any MaybeLive return values or 100193323Sed /// arguments it uses. This allows the MaybeLive values to be marked live 101193323Sed /// when any of its users is marked live. 102193323Sed /// For example (indices are left out for clarity): 103193323Sed /// - Uses[ret F] = ret G 104193323Sed /// This means that F calls G, and F returns the value returned by G. 105193323Sed /// - Uses[arg F] = ret G 106193323Sed /// This means that some function calls G and passes its result as an 107193323Sed /// argument to F. 108193323Sed /// - Uses[ret F] = arg F 109193323Sed /// This means that F returns one of its own arguments. 110193323Sed /// - Uses[arg F] = arg G 111193323Sed /// This means that G calls F and passes one of its own (G's) arguments 112193323Sed /// directly to F. 113193323Sed UseMap Uses; 114193323Sed 115193323Sed typedef std::set<RetOrArg> LiveSet; 116193323Sed typedef std::set<const Function*> LiveFuncSet; 117193323Sed 118193323Sed /// This set contains all values that have been determined to be live. 119193323Sed LiveSet LiveValues; 120193323Sed /// This set contains all values that are cannot be changed in any way. 121193323Sed LiveFuncSet LiveFunctions; 122193323Sed 123193323Sed typedef SmallVector<RetOrArg, 5> UseVector; 124193323Sed 125210299Sed protected: 126210299Sed // DAH uses this to specify a different ID. 127212904Sdim explicit DAE(char &ID) : ModulePass(ID) {} 128210299Sed 129193323Sed public: 130193323Sed static char ID; // Pass identification, replacement for typeid 131218893Sdim DAE() : ModulePass(ID) { 132218893Sdim initializeDAEPass(*PassRegistry::getPassRegistry()); 133218893Sdim } 134210299Sed 135276479Sdim bool runOnModule(Module &M) override; 136193323Sed 137193323Sed virtual bool ShouldHackArguments() const { return false; } 138193323Sed 139193323Sed private: 140193323Sed Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 141276479Sdim Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses, 142288943Sdim unsigned RetValNum = -1U); 143206083Srdivacky Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 144193323Sed 145206083Srdivacky void SurveyFunction(const Function &F); 146193323Sed void MarkValue(const RetOrArg &RA, Liveness L, 147193323Sed const UseVector &MaybeLiveUses); 148193323Sed void MarkLive(const RetOrArg &RA); 149193323Sed void MarkLive(const Function &F); 150193323Sed void PropagateLiveness(const RetOrArg &RA); 151193323Sed bool RemoveDeadStuffFromFunction(Function *F); 152193323Sed bool DeleteDeadVarargs(Function &Fn); 153218893Sdim bool RemoveDeadArgumentsFromCallers(Function &Fn); 154193323Sed }; 155193323Sed} 156193323Sed 157193323Sed 158193323Sedchar DAE::ID = 0; 159218893SdimINITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false) 160193323Sed 161193323Sednamespace { 162193323Sed /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 163193323Sed /// deletes arguments to functions which are external. This is only for use 164193323Sed /// by bugpoint. 165193323Sed struct DAH : public DAE { 166193323Sed static char ID; 167212904Sdim DAH() : DAE(ID) {} 168210299Sed 169276479Sdim bool ShouldHackArguments() const override { return true; } 170193323Sed }; 171193323Sed} 172193323Sed 173193323Sedchar DAH::ID = 0; 174212904SdimINITIALIZE_PASS(DAH, "deadarghaX0r", 175212904Sdim "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)", 176218893Sdim false, false) 177193323Sed 178193323Sed/// createDeadArgEliminationPass - This pass removes arguments from functions 179193323Sed/// which are not used by the body of the function. 180193323Sed/// 181193323SedModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 182193323SedModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 183193323Sed 184193323Sed/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 185193323Sed/// llvm.vastart is never called, the varargs list is dead for the function. 186193323Sedbool DAE::DeleteDeadVarargs(Function &Fn) { 187193323Sed assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 188193323Sed if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 189193323Sed 190193323Sed // Ensure that the function is only directly called. 191194178Sed if (Fn.hasAddressTaken()) 192194178Sed return false; 193193323Sed 194296417Sdim // Don't touch naked functions. The assembly might be using an argument, or 195296417Sdim // otherwise rely on the frame layout in a way that this analysis will not 196296417Sdim // see. 197296417Sdim if (Fn.hasFnAttribute(Attribute::Naked)) { 198296417Sdim return false; 199296417Sdim } 200296417Sdim 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); 232296417Sdim Fn.getParent()->getFunctionList().insert(Fn.getIterator(), 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. 299296417Sdim I->replaceAllUsesWith(&*I2); 300296417Sdim I2->takeName(&*I); 301193323Sed } 302193323Sed 303243830Sdim // Patch the pointer to LLVM function in debug info descriptor. 304296417Sdim NF->setSubprogram(Fn.getSubprogram()); 305243830Sdim 306261991Sdim // Fix up any BlockAddresses that refer to the function. 307261991Sdim Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType())); 308261991Sdim // Delete the bitcast that we just created, so that NF does not 309261991Sdim // appear to be address-taken. 310261991Sdim NF->removeDeadConstantUsers(); 311193323Sed // Finally, nuke the old function. 312193323Sed Fn.eraseFromParent(); 313193323Sed return true; 314193323Sed} 315193323Sed 316218893Sdim/// RemoveDeadArgumentsFromCallers - Checks if the given function has any 317218893Sdim/// arguments that are unused, and changes the caller parameters to be undefined 318218893Sdim/// instead. 319218893Sdimbool DAE::RemoveDeadArgumentsFromCallers(Function &Fn) 320218893Sdim{ 321288943Sdim // We cannot change the arguments if this TU does not define the function or 322288943Sdim // if the linker may choose a function body from another TU, even if the 323288943Sdim // nominal linkage indicates that other copies of the function have the same 324288943Sdim // semantics. In the below example, the dead load from %p may not have been 325288943Sdim // eliminated from the linker-chosen copy of f, so replacing %p with undef 326288943Sdim // in callers may introduce undefined behavior. 327288943Sdim // 328288943Sdim // define linkonce_odr void @f(i32* %p) { 329288943Sdim // %v = load i32 %p 330288943Sdim // ret void 331288943Sdim // } 332288943Sdim if (!Fn.isStrongDefinitionForLinker()) 333218893Sdim return false; 334218893Sdim 335261991Sdim // Functions with local linkage should already have been handled, except the 336261991Sdim // fragile (variadic) ones which we can improve here. 337261991Sdim if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg()) 338218893Sdim return false; 339218893Sdim 340296417Sdim // Don't touch naked functions. The assembly might be using an argument, or 341296417Sdim // otherwise rely on the frame layout in a way that this analysis will not 342296417Sdim // see. 343296417Sdim if (Fn.hasFnAttribute(Attribute::Naked)) 344296417Sdim return false; 345296417Sdim 346218893Sdim if (Fn.use_empty()) 347218893Sdim return false; 348218893Sdim 349249423Sdim SmallVector<unsigned, 8> UnusedArgs; 350296417Sdim for (Argument &Arg : Fn.args()) { 351296417Sdim if (Arg.use_empty() && !Arg.hasByValOrInAllocaAttr()) 352296417Sdim UnusedArgs.push_back(Arg.getArgNo()); 353218893Sdim } 354218893Sdim 355218893Sdim if (UnusedArgs.empty()) 356218893Sdim return false; 357218893Sdim 358218893Sdim bool Changed = false; 359218893Sdim 360276479Sdim for (Use &U : Fn.uses()) { 361276479Sdim CallSite CS(U.getUser()); 362276479Sdim if (!CS || !CS.isCallee(&U)) 363218893Sdim continue; 364218893Sdim 365218893Sdim // Now go through all unused args and replace them with "undef". 366218893Sdim for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) { 367218893Sdim unsigned ArgNo = UnusedArgs[I]; 368218893Sdim 369218893Sdim Value *Arg = CS.getArgument(ArgNo); 370218893Sdim CS.setArgument(ArgNo, UndefValue::get(Arg->getType())); 371218893Sdim ++NumArgumentsReplacedWithUndef; 372218893Sdim Changed = true; 373218893Sdim } 374218893Sdim } 375218893Sdim 376218893Sdim return Changed; 377218893Sdim} 378218893Sdim 379193323Sed/// Convenience function that returns the number of return values. It returns 0 380193323Sed/// for void functions and 1 for functions not returning a struct. It returns 381193323Sed/// the number of struct elements for functions returning a struct. 382193323Sedstatic unsigned NumRetVals(const Function *F) { 383288943Sdim Type *RetTy = F->getReturnType(); 384288943Sdim if (RetTy->isVoidTy()) 385193323Sed return 0; 386288943Sdim else if (StructType *STy = dyn_cast<StructType>(RetTy)) 387193323Sed return STy->getNumElements(); 388288943Sdim else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy)) 389288943Sdim return ATy->getNumElements(); 390193323Sed else 391193323Sed return 1; 392193323Sed} 393193323Sed 394288943Sdim/// Returns the sub-type a function will return at a given Idx. Should 395288943Sdim/// correspond to the result type of an ExtractValue instruction executed with 396288943Sdim/// just that one Idx (i.e. only top-level structure is considered). 397288943Sdimstatic Type *getRetComponentType(const Function *F, unsigned Idx) { 398288943Sdim Type *RetTy = F->getReturnType(); 399288943Sdim assert(!RetTy->isVoidTy() && "void type has no subtype"); 400288943Sdim 401288943Sdim if (StructType *STy = dyn_cast<StructType>(RetTy)) 402288943Sdim return STy->getElementType(Idx); 403288943Sdim else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy)) 404288943Sdim return ATy->getElementType(); 405288943Sdim else 406288943Sdim return RetTy; 407288943Sdim} 408288943Sdim 409193323Sed/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 410193323Sed/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 411193323Sed/// liveness of Use. 412193323SedDAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 413193323Sed // We're live if our use or its Function is already marked as live. 414193323Sed if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 415193323Sed return Live; 416193323Sed 417193323Sed // We're maybe live otherwise, but remember that we must become live if 418193323Sed // Use becomes live. 419193323Sed MaybeLiveUses.push_back(Use); 420193323Sed return MaybeLive; 421193323Sed} 422193323Sed 423193323Sed 424193323Sed/// SurveyUse - This looks at a single use of an argument or return value 425193323Sed/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 426206083Srdivacky/// if it causes the used value to become MaybeLive. 427193323Sed/// 428193323Sed/// RetValNum is the return value number to use when this use is used in a 429193323Sed/// return instruction. This is used in the recursion, you should always leave 430193323Sed/// it at 0. 431276479SdimDAE::Liveness DAE::SurveyUse(const Use *U, 432206083Srdivacky UseVector &MaybeLiveUses, unsigned RetValNum) { 433276479Sdim const User *V = U->getUser(); 434206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 435193323Sed // The value is returned from a function. It's only live when the 436193323Sed // function's return value is live. We use RetValNum here, for the case 437193323Sed // that U is really a use of an insertvalue instruction that uses the 438221345Sdim // original Use. 439288943Sdim const Function *F = RI->getParent()->getParent(); 440288943Sdim if (RetValNum != -1U) { 441288943Sdim RetOrArg Use = CreateRet(F, RetValNum); 442288943Sdim // We might be live, depending on the liveness of Use. 443288943Sdim return MarkIfNotLive(Use, MaybeLiveUses); 444288943Sdim } else { 445288943Sdim DAE::Liveness Result = MaybeLive; 446288943Sdim for (unsigned i = 0; i < NumRetVals(F); ++i) { 447288943Sdim RetOrArg Use = CreateRet(F, i); 448288943Sdim // We might be live, depending on the liveness of Use. If any 449288943Sdim // sub-value is live, then the entire value is considered live. This 450288943Sdim // is a conservative choice, and better tracking is possible. 451288943Sdim DAE::Liveness SubResult = MarkIfNotLive(Use, MaybeLiveUses); 452288943Sdim if (Result != Live) 453288943Sdim Result = SubResult; 454288943Sdim } 455288943Sdim return Result; 456288943Sdim } 457193323Sed } 458206083Srdivacky if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 459276479Sdim if (U->getOperandNo() != InsertValueInst::getAggregateOperandIndex() 460193323Sed && IV->hasIndices()) 461193323Sed // The use we are examining is inserted into an aggregate. Our liveness 462193323Sed // depends on all uses of that aggregate, but if it is used as a return 463193323Sed // value, only index at which we were inserted counts. 464193323Sed RetValNum = *IV->idx_begin(); 465193323Sed 466193323Sed // Note that if we are used as the aggregate operand to the insertvalue, 467193323Sed // we don't change RetValNum, but do survey all our uses. 468193323Sed 469193323Sed Liveness Result = MaybeLive; 470276479Sdim for (const Use &UU : IV->uses()) { 471276479Sdim Result = SurveyUse(&UU, MaybeLiveUses, RetValNum); 472193323Sed if (Result == Live) 473193323Sed break; 474193323Sed } 475193323Sed return Result; 476193323Sed } 477206083Srdivacky 478288943Sdim if (auto CS = ImmutableCallSite(V)) { 479206083Srdivacky const Function *F = CS.getCalledFunction(); 480193323Sed if (F) { 481193323Sed // Used in a direct call. 482206083Srdivacky 483296417Sdim // The function argument is live if it is used as a bundle operand. 484296417Sdim if (CS.isBundleOperand(U)) 485296417Sdim return Live; 486296417Sdim 487193323Sed // Find the argument number. We know for sure that this use is an 488193323Sed // argument, since if it was the function argument this would be an 489193323Sed // indirect call and the we know can't be looking at a value of the 490193323Sed // label type (for the invoke instruction). 491206083Srdivacky unsigned ArgNo = CS.getArgumentNo(U); 492193323Sed 493193323Sed if (ArgNo >= F->getFunctionType()->getNumParams()) 494193323Sed // The value is passed in through a vararg! Must be live. 495193323Sed return Live; 496193323Sed 497206083Srdivacky assert(CS.getArgument(ArgNo) 498276479Sdim == CS->getOperand(U->getOperandNo()) 499193323Sed && "Argument is not where we expected it"); 500193323Sed 501193323Sed // Value passed to a normal call. It's only live when the corresponding 502193323Sed // argument to the called function turns out live. 503193323Sed RetOrArg Use = CreateArg(F, ArgNo); 504193323Sed return MarkIfNotLive(Use, MaybeLiveUses); 505193323Sed } 506193323Sed } 507193323Sed // Used in any other way? Value must be live. 508193323Sed return Live; 509193323Sed} 510193323Sed 511193323Sed/// SurveyUses - This looks at all the uses of the given value 512193323Sed/// Returns the Liveness deduced from the uses of this value. 513193323Sed/// 514193323Sed/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 515193323Sed/// the result is Live, MaybeLiveUses might be modified but its content should 516193323Sed/// be ignored (since it might not be complete). 517206083SrdivackyDAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 518193323Sed // Assume it's dead (which will only hold if there are no uses at all..). 519193323Sed Liveness Result = MaybeLive; 520193323Sed // Check each use. 521276479Sdim for (const Use &U : V->uses()) { 522276479Sdim Result = SurveyUse(&U, MaybeLiveUses); 523193323Sed if (Result == Live) 524193323Sed break; 525193323Sed } 526193323Sed return Result; 527193323Sed} 528193323Sed 529193323Sed// SurveyFunction - This performs the initial survey of the specified function, 530193323Sed// checking out whether or not it uses any of its incoming arguments or whether 531193323Sed// any callers use the return value. This fills in the LiveValues set and Uses 532193323Sed// map. 533193323Sed// 534193323Sed// We consider arguments of non-internal functions to be intrinsically alive as 535193323Sed// well as arguments to functions which have their "address taken". 536193323Sed// 537206083Srdivackyvoid DAE::SurveyFunction(const Function &F) { 538276479Sdim // Functions with inalloca parameters are expecting args in a particular 539276479Sdim // register and memory layout. 540276479Sdim if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca)) { 541276479Sdim MarkLive(F); 542276479Sdim return; 543276479Sdim } 544276479Sdim 545296417Sdim // Don't touch naked functions. The assembly might be using an argument, or 546296417Sdim // otherwise rely on the frame layout in a way that this analysis will not 547296417Sdim // see. 548296417Sdim if (F.hasFnAttribute(Attribute::Naked)) { 549296417Sdim MarkLive(F); 550296417Sdim return; 551296417Sdim } 552296417Sdim 553193323Sed unsigned RetCount = NumRetVals(&F); 554193323Sed // Assume all return values are dead 555193323Sed typedef SmallVector<Liveness, 5> RetVals; 556193323Sed RetVals RetValLiveness(RetCount, MaybeLive); 557193323Sed 558193323Sed typedef SmallVector<UseVector, 5> RetUses; 559193323Sed // These vectors map each return value to the uses that make it MaybeLive, so 560193323Sed // we can add those to the Uses map if the return value really turns out to be 561193323Sed // MaybeLive. Initialized to a list of RetCount empty lists. 562193323Sed RetUses MaybeLiveRetUses(RetCount); 563193323Sed 564206083Srdivacky for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 565206083Srdivacky if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 566193323Sed if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 567193323Sed != F.getFunctionType()->getReturnType()) { 568193323Sed // We don't support old style multiple return values. 569193323Sed MarkLive(F); 570193323Sed return; 571193323Sed } 572193323Sed 573193323Sed if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 574193323Sed MarkLive(F); 575193323Sed return; 576193323Sed } 577193323Sed 578202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 579193323Sed // Keep track of the number of live retvals, so we can skip checks once all 580193323Sed // of them turn out to be live. 581193323Sed unsigned NumLiveRetVals = 0; 582193323Sed // Loop all uses of the function. 583276479Sdim for (const Use &U : F.uses()) { 584193323Sed // If the function is PASSED IN as an argument, its address has been 585193323Sed // taken. 586276479Sdim ImmutableCallSite CS(U.getUser()); 587276479Sdim if (!CS || !CS.isCallee(&U)) { 588193323Sed MarkLive(F); 589193323Sed return; 590193323Sed } 591193323Sed 592193323Sed // If this use is anything other than a call site, the function is alive. 593206083Srdivacky const Instruction *TheCall = CS.getInstruction(); 594193323Sed if (!TheCall) { // Not a direct call site? 595193323Sed MarkLive(F); 596193323Sed return; 597193323Sed } 598193323Sed 599193323Sed // If we end up here, we are looking at a direct call to our function. 600193323Sed 601193323Sed // Now, check how our return value(s) is/are used in this caller. Don't 602193323Sed // bother checking return values if all of them are live already. 603288943Sdim if (NumLiveRetVals == RetCount) 604288943Sdim continue; 605288943Sdim 606288943Sdim // Check all uses of the return value. 607288943Sdim for (const Use &U : TheCall->uses()) { 608288943Sdim if (ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(U.getUser())) { 609288943Sdim // This use uses a part of our return value, survey the uses of 610288943Sdim // that part and store the results for this index only. 611288943Sdim unsigned Idx = *Ext->idx_begin(); 612288943Sdim if (RetValLiveness[Idx] != Live) { 613288943Sdim RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 614288943Sdim if (RetValLiveness[Idx] == Live) 615288943Sdim NumLiveRetVals++; 616193323Sed } 617193323Sed } else { 618288943Sdim // Used by something else than extractvalue. Survey, but assume that the 619288943Sdim // result applies to all sub-values. 620288943Sdim UseVector MaybeLiveAggregateUses; 621288943Sdim if (SurveyUse(&U, MaybeLiveAggregateUses) == Live) { 622193323Sed NumLiveRetVals = RetCount; 623288943Sdim RetValLiveness.assign(RetCount, Live); 624288943Sdim break; 625288943Sdim } else { 626288943Sdim for (unsigned i = 0; i != RetCount; ++i) { 627288943Sdim if (RetValLiveness[i] != Live) 628288943Sdim MaybeLiveRetUses[i].append(MaybeLiveAggregateUses.begin(), 629288943Sdim MaybeLiveAggregateUses.end()); 630288943Sdim } 631288943Sdim } 632193323Sed } 633193323Sed } 634193323Sed } 635193323Sed 636193323Sed // Now we've inspected all callers, record the liveness of our return values. 637193323Sed for (unsigned i = 0; i != RetCount; ++i) 638193323Sed MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 639193323Sed 640202375Srdivacky DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 641193323Sed 642193323Sed // Now, check all of our arguments. 643193323Sed unsigned i = 0; 644193323Sed UseVector MaybeLiveArgUses; 645206083Srdivacky for (Function::const_arg_iterator AI = F.arg_begin(), 646193323Sed E = F.arg_end(); AI != E; ++AI, ++i) { 647261991Sdim Liveness Result; 648261991Sdim if (F.getFunctionType()->isVarArg()) { 649261991Sdim // Variadic functions will already have a va_arg function expanded inside 650261991Sdim // them, making them potentially very sensitive to ABI changes resulting 651261991Sdim // from removing arguments entirely, so don't. For example AArch64 handles 652261991Sdim // register and stack HFAs very differently, and this is reflected in the 653261991Sdim // IR which has already been generated. 654261991Sdim Result = Live; 655261991Sdim } else { 656261991Sdim // See what the effect of this use is (recording any uses that cause 657261991Sdim // MaybeLive in MaybeLiveArgUses). 658296417Sdim Result = SurveyUses(&*AI, MaybeLiveArgUses); 659261991Sdim } 660261991Sdim 661193323Sed // Mark the result. 662193323Sed MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 663193323Sed // Clear the vector again for the next iteration. 664193323Sed MaybeLiveArgUses.clear(); 665193323Sed } 666193323Sed} 667193323Sed 668193323Sed/// MarkValue - This function marks the liveness of RA depending on L. If L is 669193323Sed/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 670193323Sed/// such that RA will be marked live if any use in MaybeLiveUses gets marked 671193323Sed/// live later on. 672193323Sedvoid DAE::MarkValue(const RetOrArg &RA, Liveness L, 673193323Sed const UseVector &MaybeLiveUses) { 674193323Sed switch (L) { 675193323Sed case Live: MarkLive(RA); break; 676193323Sed case MaybeLive: 677193323Sed { 678193323Sed // Note any uses of this value, so this return value can be 679193323Sed // marked live whenever one of the uses becomes live. 680193323Sed for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 681193323Sed UE = MaybeLiveUses.end(); UI != UE; ++UI) 682193323Sed Uses.insert(std::make_pair(*UI, RA)); 683193323Sed break; 684193323Sed } 685193323Sed } 686193323Sed} 687193323Sed 688193323Sed/// MarkLive - Mark the given Function as alive, meaning that it cannot be 689193323Sed/// changed in any way. Additionally, 690193323Sed/// mark any values that are used as this function's parameters or by its return 691193323Sed/// values (according to Uses) live as well. 692193323Sedvoid DAE::MarkLive(const Function &F) { 693202375Srdivacky DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 694208599Srdivacky // Mark the function as live. 695208599Srdivacky LiveFunctions.insert(&F); 696208599Srdivacky // Mark all arguments as live. 697208599Srdivacky for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 698208599Srdivacky PropagateLiveness(CreateArg(&F, i)); 699208599Srdivacky // Mark all return values as live. 700208599Srdivacky for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 701208599Srdivacky PropagateLiveness(CreateRet(&F, i)); 702193323Sed} 703193323Sed 704193323Sed/// MarkLive - Mark the given return value or argument as live. Additionally, 705193323Sed/// mark any values that are used by this value (according to Uses) live as 706193323Sed/// well. 707193323Sedvoid DAE::MarkLive(const RetOrArg &RA) { 708193323Sed if (LiveFunctions.count(RA.F)) 709193323Sed return; // Function was already marked Live. 710193323Sed 711193323Sed if (!LiveValues.insert(RA).second) 712193323Sed return; // We were already marked Live. 713193323Sed 714202375Srdivacky DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 715193323Sed PropagateLiveness(RA); 716193323Sed} 717193323Sed 718193323Sed/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 719193323Sed/// to any other values it uses (according to Uses). 720193323Sedvoid DAE::PropagateLiveness(const RetOrArg &RA) { 721193323Sed // We don't use upper_bound (or equal_range) here, because our recursive call 722193323Sed // to ourselves is likely to cause the upper_bound (which is the first value 723193323Sed // not belonging to RA) to become erased and the iterator invalidated. 724193323Sed UseMap::iterator Begin = Uses.lower_bound(RA); 725193323Sed UseMap::iterator E = Uses.end(); 726193323Sed UseMap::iterator I; 727193323Sed for (I = Begin; I != E && I->first == RA; ++I) 728193323Sed MarkLive(I->second); 729193323Sed 730193323Sed // Erase RA from the Uses map (from the lower bound to wherever we ended up 731193323Sed // after the loop). 732193323Sed Uses.erase(Begin, I); 733193323Sed} 734193323Sed 735193323Sed// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 736193323Sed// that are not in LiveValues. Transform the function and all of the callees of 737193323Sed// the function to not have these arguments and return values. 738193323Sed// 739193323Sedbool DAE::RemoveDeadStuffFromFunction(Function *F) { 740193323Sed // Don't modify fully live functions 741193323Sed if (LiveFunctions.count(F)) 742193323Sed return false; 743193323Sed 744193323Sed // Start by computing a new prototype for the function, which is the same as 745193323Sed // the old function, but has fewer arguments and a different return type. 746226633Sdim FunctionType *FTy = F->getFunctionType(); 747224145Sdim std::vector<Type*> Params; 748193323Sed 749261991Sdim // Keep track of if we have a live 'returned' argument 750261991Sdim bool HasLiveReturnedArg = false; 751261991Sdim 752193323Sed // Set up to build a new list of parameter attributes. 753249423Sdim SmallVector<AttributeSet, 8> AttributesVec; 754249423Sdim const AttributeSet &PAL = F->getAttributes(); 755193323Sed 756261991Sdim // Remember which arguments are still alive. 757261991Sdim SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 758261991Sdim // Construct the new parameter list from non-dead arguments. Also construct 759261991Sdim // a new set of parameter attributes to correspond. Skip the first parameter 760261991Sdim // attribute, since that belongs to the return value. 761261991Sdim unsigned i = 0; 762261991Sdim for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 763261991Sdim I != E; ++I, ++i) { 764261991Sdim RetOrArg Arg = CreateArg(F, i); 765261991Sdim if (LiveValues.erase(Arg)) { 766261991Sdim Params.push_back(I->getType()); 767261991Sdim ArgAlive[i] = true; 768261991Sdim 769261991Sdim // Get the original parameter attributes (skipping the first one, that is 770261991Sdim // for the return value. 771261991Sdim if (PAL.hasAttributes(i + 1)) { 772261991Sdim AttrBuilder B(PAL, i + 1); 773261991Sdim if (B.contains(Attribute::Returned)) 774261991Sdim HasLiveReturnedArg = true; 775261991Sdim AttributesVec. 776261991Sdim push_back(AttributeSet::get(F->getContext(), Params.size(), B)); 777261991Sdim } 778261991Sdim } else { 779261991Sdim ++NumArgumentsEliminated; 780261991Sdim DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 781261991Sdim << ") from " << F->getName() << "\n"); 782261991Sdim } 783261991Sdim } 784261991Sdim 785193323Sed // Find out the new return value. 786224145Sdim Type *RetTy = FTy->getReturnType(); 787276479Sdim Type *NRetTy = nullptr; 788193323Sed unsigned RetCount = NumRetVals(F); 789206083Srdivacky 790193323Sed // -1 means unused, other numbers are the new index 791193323Sed SmallVector<int, 5> NewRetIdxs(RetCount, -1); 792224145Sdim std::vector<Type*> RetTypes; 793261991Sdim 794261991Sdim // If there is a function with a live 'returned' argument but a dead return 795261991Sdim // value, then there are two possible actions: 796261991Sdim // 1) Eliminate the return value and take off the 'returned' attribute on the 797261991Sdim // argument. 798261991Sdim // 2) Retain the 'returned' attribute and treat the return value (but not the 799261991Sdim // entire function) as live so that it is not eliminated. 800261991Sdim // 801261991Sdim // It's not clear in the general case which option is more profitable because, 802261991Sdim // even in the absence of explicit uses of the return value, code generation 803261991Sdim // is free to use the 'returned' attribute to do things like eliding 804261991Sdim // save/restores of registers across calls. Whether or not this happens is 805261991Sdim // target and ABI-specific as well as depending on the amount of register 806261991Sdim // pressure, so there's no good way for an IR-level pass to figure this out. 807261991Sdim // 808261991Sdim // Fortunately, the only places where 'returned' is currently generated by 809261991Sdim // the FE are places where 'returned' is basically free and almost always a 810261991Sdim // performance win, so the second option can just be used always for now. 811261991Sdim // 812261991Sdim // This should be revisited if 'returned' is ever applied more liberally. 813261991Sdim if (RetTy->isVoidTy() || HasLiveReturnedArg) { 814206083Srdivacky NRetTy = RetTy; 815193323Sed } else { 816288943Sdim // Look at each of the original return values individually. 817288943Sdim for (unsigned i = 0; i != RetCount; ++i) { 818288943Sdim RetOrArg Ret = CreateRet(F, i); 819288943Sdim if (LiveValues.erase(Ret)) { 820288943Sdim RetTypes.push_back(getRetComponentType(F, i)); 821288943Sdim NewRetIdxs[i] = RetTypes.size() - 1; 822193323Sed } else { 823193323Sed ++NumRetValsEliminated; 824288943Sdim DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 825288943Sdim << F->getName() << "\n"); 826193323Sed } 827288943Sdim } 828288943Sdim if (RetTypes.size() > 1) { 829288943Sdim // More than one return type? Reduce it down to size. 830288943Sdim if (StructType *STy = dyn_cast<StructType>(RetTy)) { 831288943Sdim // Make the new struct packed if we used to return a packed struct 832288943Sdim // already. 833288943Sdim NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 834288943Sdim } else { 835288943Sdim assert(isa<ArrayType>(RetTy) && "unexpected multi-value return"); 836288943Sdim NRetTy = ArrayType::get(RetTypes[0], RetTypes.size()); 837288943Sdim } 838288943Sdim } else if (RetTypes.size() == 1) 839193323Sed // One return type? Just a simple value then, but only if we didn't use to 840193323Sed // return a struct with that simple value before. 841193323Sed NRetTy = RetTypes.front(); 842193323Sed else if (RetTypes.size() == 0) 843193323Sed // No return types? Make it void, but only if we didn't use to return {}. 844198090Srdivacky NRetTy = Type::getVoidTy(F->getContext()); 845193323Sed } 846193323Sed 847193323Sed assert(NRetTy && "No new return type found?"); 848193323Sed 849249423Sdim // The existing function return attributes. 850249423Sdim AttributeSet RAttrs = PAL.getRetAttributes(); 851249423Sdim 852193323Sed // Remove any incompatible attributes, but only if we removed all return 853193323Sed // values. Otherwise, ensure that we don't have any conflicting attributes 854193323Sed // here. Currently, this should not be possible, but special handling might be 855193323Sed // required when new return value attributes are added. 856206083Srdivacky if (NRetTy->isVoidTy()) 857288943Sdim RAttrs = RAttrs.removeAttributes(NRetTy->getContext(), 858288943Sdim AttributeSet::ReturnIndex, 859288943Sdim AttributeFuncs::typeIncompatible(NRetTy)); 860193323Sed else 861249423Sdim assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex). 862288943Sdim overlaps(AttributeFuncs::typeIncompatible(NRetTy)) && 863243830Sdim "Return attributes no longer compatible?"); 864193323Sed 865249423Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 866249423Sdim AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs)); 867193323Sed 868249423Sdim if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 869249423Sdim AttributesVec.push_back(AttributeSet::get(F->getContext(), 870249423Sdim PAL.getFnAttributes())); 871193323Sed 872193323Sed // Reconstruct the AttributesList based on the vector we constructed. 873249423Sdim AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec); 874193323Sed 875193323Sed // Create the new function type based on the recomputed parameters. 876206083Srdivacky FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 877193323Sed 878193323Sed // No change? 879193323Sed if (NFTy == FTy) 880193323Sed return false; 881193323Sed 882193323Sed // Create the new function body and insert it into the module... 883193323Sed Function *NF = Function::Create(NFTy, F->getLinkage()); 884193323Sed NF->copyAttributesFrom(F); 885193323Sed NF->setAttributes(NewPAL); 886193323Sed // Insert the new function before the old function, so we won't be processing 887193323Sed // it again. 888296417Sdim F->getParent()->getFunctionList().insert(F->getIterator(), NF); 889193323Sed NF->takeName(F); 890193323Sed 891193323Sed // Loop over all of the callers of the function, transforming the call sites 892193323Sed // to pass in a smaller number of arguments into the new function. 893193323Sed // 894193323Sed std::vector<Value*> Args; 895193323Sed while (!F->use_empty()) { 896276479Sdim CallSite CS(F->user_back()); 897193323Sed Instruction *Call = CS.getInstruction(); 898193323Sed 899193323Sed AttributesVec.clear(); 900249423Sdim const AttributeSet &CallPAL = CS.getAttributes(); 901193323Sed 902193323Sed // The call return attributes. 903249423Sdim AttributeSet RAttrs = CallPAL.getRetAttributes(); 904249423Sdim 905193323Sed // Adjust in case the function was changed to return void. 906288943Sdim RAttrs = RAttrs.removeAttributes(NRetTy->getContext(), 907288943Sdim AttributeSet::ReturnIndex, 908288943Sdim AttributeFuncs::typeIncompatible(NF->getReturnType())); 909249423Sdim if (RAttrs.hasAttributes(AttributeSet::ReturnIndex)) 910249423Sdim AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs)); 911193323Sed 912193323Sed // Declare these outside of the loops, so we can reuse them for the second 913193323Sed // loop, which loops the varargs. 914193323Sed CallSite::arg_iterator I = CS.arg_begin(); 915193323Sed unsigned i = 0; 916193323Sed // Loop over those operands, corresponding to the normal arguments to the 917193323Sed // original function, and add those that are still alive. 918193323Sed for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 919193323Sed if (ArgAlive[i]) { 920193323Sed Args.push_back(*I); 921193323Sed // Get original parameter attributes, but skip return attributes. 922249423Sdim if (CallPAL.hasAttributes(i + 1)) { 923249423Sdim AttrBuilder B(CallPAL, i + 1); 924261991Sdim // If the return type has changed, then get rid of 'returned' on the 925261991Sdim // call site. The alternative is to make all 'returned' attributes on 926261991Sdim // call sites keep the return value alive just like 'returned' 927261991Sdim // attributes on function declaration but it's less clearly a win 928261991Sdim // and this is not an expected case anyway 929261991Sdim if (NRetTy != RetTy && B.contains(Attribute::Returned)) 930261991Sdim B.removeAttribute(Attribute::Returned); 931249423Sdim AttributesVec. 932249423Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 933249423Sdim } 934193323Sed } 935193323Sed 936193323Sed // Push any varargs arguments on the list. Don't forget their attributes. 937193323Sed for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 938193323Sed Args.push_back(*I); 939249423Sdim if (CallPAL.hasAttributes(i + 1)) { 940249423Sdim AttrBuilder B(CallPAL, i + 1); 941249423Sdim AttributesVec. 942249423Sdim push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 943249423Sdim } 944193323Sed } 945193323Sed 946249423Sdim if (CallPAL.hasAttributes(AttributeSet::FunctionIndex)) 947249423Sdim AttributesVec.push_back(AttributeSet::get(Call->getContext(), 948249423Sdim CallPAL.getFnAttributes())); 949193323Sed 950193323Sed // Reconstruct the AttributesList based on the vector we constructed. 951249423Sdim AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec); 952193323Sed 953193323Sed Instruction *New; 954193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 955193323Sed New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 956296417Sdim Args, "", Call->getParent()); 957193323Sed cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 958193323Sed cast<InvokeInst>(New)->setAttributes(NewCallPAL); 959193323Sed } else { 960224145Sdim New = CallInst::Create(NF, Args, "", Call); 961193323Sed cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 962193323Sed cast<CallInst>(New)->setAttributes(NewCallPAL); 963193323Sed if (cast<CallInst>(Call)->isTailCall()) 964193323Sed cast<CallInst>(New)->setTailCall(); 965193323Sed } 966212904Sdim New->setDebugLoc(Call->getDebugLoc()); 967207618Srdivacky 968193323Sed Args.clear(); 969193323Sed 970193323Sed if (!Call->use_empty()) { 971193323Sed if (New->getType() == Call->getType()) { 972193323Sed // Return type not changed? Just replace users then. 973193323Sed Call->replaceAllUsesWith(New); 974193323Sed New->takeName(Call); 975206083Srdivacky } else if (New->getType()->isVoidTy()) { 976193323Sed // Our return value has uses, but they will get removed later on. 977193323Sed // Replace by null for now. 978218893Sdim if (!Call->getType()->isX86_MMXTy()) 979218893Sdim Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 980193323Sed } else { 981288943Sdim assert((RetTy->isStructTy() || RetTy->isArrayTy()) && 982193323Sed "Return type changed, but not into a void. The old return type" 983288943Sdim " must have been a struct or an array!"); 984193323Sed Instruction *InsertPt = Call; 985193323Sed if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 986296417Sdim BasicBlock *NewEdge = SplitEdge(New->getParent(), II->getNormalDest()); 987296417Sdim InsertPt = &*NewEdge->getFirstInsertionPt(); 988193323Sed } 989206083Srdivacky 990288943Sdim // We used to return a struct or array. Instead of doing smart stuff 991288943Sdim // with all the uses, we will just rebuild it using extract/insertvalue 992288943Sdim // chaining and let instcombine clean that up. 993193323Sed // 994193323Sed // Start out building up our return value from undef 995198090Srdivacky Value *RetVal = UndefValue::get(RetTy); 996193323Sed for (unsigned i = 0; i != RetCount; ++i) 997193323Sed if (NewRetIdxs[i] != -1) { 998193323Sed Value *V; 999193323Sed if (RetTypes.size() > 1) 1000193323Sed // We are still returning a struct, so extract the value from our 1001193323Sed // return value 1002193323Sed V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 1003193323Sed InsertPt); 1004193323Sed else 1005193323Sed // We are now returning a single element, so just insert that 1006193323Sed V = New; 1007193323Sed // Insert the value at the old position 1008193323Sed RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 1009193323Sed } 1010193323Sed // Now, replace all uses of the old call instruction with the return 1011193323Sed // struct we built 1012193323Sed Call->replaceAllUsesWith(RetVal); 1013193323Sed New->takeName(Call); 1014193323Sed } 1015193323Sed } 1016193323Sed 1017193323Sed // Finally, remove the old call from the program, reducing the use-count of 1018193323Sed // F. 1019193323Sed Call->eraseFromParent(); 1020193323Sed } 1021193323Sed 1022193323Sed // Since we have now created the new function, splice the body of the old 1023193323Sed // function right into the new function, leaving the old rotting hulk of the 1024193323Sed // function empty. 1025193323Sed NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 1026193323Sed 1027221345Sdim // Loop over the argument list, transferring uses of the old arguments over to 1028221345Sdim // the new arguments, also transferring over the names as well. 1029193323Sed i = 0; 1030193323Sed for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 1031193323Sed I2 = NF->arg_begin(); I != E; ++I, ++i) 1032193323Sed if (ArgAlive[i]) { 1033193323Sed // If this is a live argument, move the name and users over to the new 1034193323Sed // version. 1035296417Sdim I->replaceAllUsesWith(&*I2); 1036296417Sdim I2->takeName(&*I); 1037193323Sed ++I2; 1038193323Sed } else { 1039193323Sed // If this argument is dead, replace any uses of it with null constants 1040193323Sed // (these are guaranteed to become unused later on). 1041218893Sdim if (!I->getType()->isX86_MMXTy()) 1042218893Sdim I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 1043193323Sed } 1044193323Sed 1045193323Sed // If we change the return value of the function we must rewrite any return 1046193323Sed // instructions. Check this now. 1047193323Sed if (F->getReturnType() != NF->getReturnType()) 1048193323Sed for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 1049193323Sed if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 1050193323Sed Value *RetVal; 1051193323Sed 1052208599Srdivacky if (NFTy->getReturnType()->isVoidTy()) { 1053276479Sdim RetVal = nullptr; 1054193323Sed } else { 1055288943Sdim assert(RetTy->isStructTy() || RetTy->isArrayTy()); 1056288943Sdim // The original return value was a struct or array, insert 1057193323Sed // extractvalue/insertvalue chains to extract only the values we need 1058193323Sed // to return and insert them into our new result. 1059193323Sed // This does generate messy code, but we'll let it to instcombine to 1060193323Sed // clean that up. 1061193323Sed Value *OldRet = RI->getOperand(0); 1062193323Sed // Start out building up our return value from undef 1063198090Srdivacky RetVal = UndefValue::get(NRetTy); 1064193323Sed for (unsigned i = 0; i != RetCount; ++i) 1065193323Sed if (NewRetIdxs[i] != -1) { 1066193323Sed ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 1067193323Sed "oldret", RI); 1068193323Sed if (RetTypes.size() > 1) { 1069193323Sed // We're still returning a struct, so reinsert the value into 1070193323Sed // our new return value at the new index 1071193323Sed 1072193323Sed RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 1073193323Sed "newret", RI); 1074193323Sed } else { 1075193323Sed // We are now only returning a simple value, so just return the 1076193323Sed // extracted value. 1077193323Sed RetVal = EV; 1078193323Sed } 1079193323Sed } 1080193323Sed } 1081193323Sed // Replace the return instruction with one returning the new return 1082193323Sed // value (possibly 0 if we became void). 1083198090Srdivacky ReturnInst::Create(F->getContext(), RetVal, RI); 1084193323Sed BB->getInstList().erase(RI); 1085193323Sed } 1086193323Sed 1087243830Sdim // Patch the pointer to LLVM function in debug info descriptor. 1088296417Sdim NF->setSubprogram(F->getSubprogram()); 1089243830Sdim 1090193323Sed // Now that the old function is dead, delete it. 1091193323Sed F->eraseFromParent(); 1092193323Sed 1093193323Sed return true; 1094193323Sed} 1095193323Sed 1096193323Sedbool DAE::runOnModule(Module &M) { 1097193323Sed bool Changed = false; 1098193323Sed 1099193323Sed // First pass: Do a simple check to see if any functions can have their "..." 1100193323Sed // removed. We can do this if they never call va_start. This loop cannot be 1101193323Sed // fused with the next loop, because deleting a function invalidates 1102193323Sed // information computed while surveying other functions. 1103202375Srdivacky DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 1104193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1105193323Sed Function &F = *I++; 1106193323Sed if (F.getFunctionType()->isVarArg()) 1107193323Sed Changed |= DeleteDeadVarargs(F); 1108193323Sed } 1109193323Sed 1110193323Sed // Second phase:loop through the module, determining which arguments are live. 1111193323Sed // We assume all arguments are dead unless proven otherwise (allowing us to 1112193323Sed // determine that dead arguments passed into recursive functions are dead). 1113193323Sed // 1114202375Srdivacky DEBUG(dbgs() << "DAE - Determining liveness\n"); 1115280031Sdim for (auto &F : M) 1116280031Sdim SurveyFunction(F); 1117206083Srdivacky 1118193323Sed // Now, remove all dead arguments and return values from each function in 1119206083Srdivacky // turn. 1120193323Sed for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 1121206083Srdivacky // Increment now, because the function will probably get removed (ie. 1122193323Sed // replaced by a new one). 1123296417Sdim Function *F = &*I++; 1124193323Sed Changed |= RemoveDeadStuffFromFunction(F); 1125193323Sed } 1126218893Sdim 1127218893Sdim // Finally, look for any unused parameters in functions with non-local 1128218893Sdim // linkage and replace the passed in parameters with undef. 1129280031Sdim for (auto &F : M) 1130218893Sdim Changed |= RemoveDeadArgumentsFromCallers(F); 1131218893Sdim 1132193323Sed return Changed; 1133193323Sed} 1134