DeadArgumentElimination.cpp revision f5a86f45e75ec744c203270ffa03659eb0a220c1
1//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass deletes dead arguments from internal functions. Dead argument 11// elimination removes arguments which are directly dead, as well as arguments 12// only passed into function calls as dead arguments of other functions. This 13// pass also deletes dead return values in a similar way. 14// 15// This pass is often useful as a cleanup pass to run after aggressive 16// interprocedural passes, which add possibly-dead arguments or return values. 17// 18//===----------------------------------------------------------------------===// 19 20#define DEBUG_TYPE "deadargelim" 21#include "llvm/Transforms/IPO.h" 22#include "llvm/CallingConv.h" 23#include "llvm/Constant.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/LLVMContext.h" 28#include "llvm/Module.h" 29#include "llvm/Pass.h" 30#include "llvm/Support/CallSite.h" 31#include "llvm/Support/Debug.h" 32#include "llvm/Support/raw_ostream.h" 33#include "llvm/ADT/SmallVector.h" 34#include "llvm/ADT/Statistic.h" 35#include "llvm/ADT/StringExtras.h" 36#include <map> 37#include <set> 38using namespace llvm; 39 40STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 41STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 42 43namespace { 44 /// DAE - The dead argument elimination pass. 45 /// 46 class DAE : public ModulePass { 47 public: 48 49 /// Struct that represents (part of) either a return value or a function 50 /// argument. Used so that arguments and return values can be used 51 /// interchangably. 52 struct RetOrArg { 53 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 54 IsArg(IsArg) {} 55 const Function *F; 56 unsigned Idx; 57 bool IsArg; 58 59 /// Make RetOrArg comparable, so we can put it into a map. 60 bool operator<(const RetOrArg &O) const { 61 if (F != O.F) 62 return F < O.F; 63 else if (Idx != O.Idx) 64 return Idx < O.Idx; 65 else 66 return IsArg < O.IsArg; 67 } 68 69 /// Make RetOrArg comparable, so we can easily iterate the multimap. 70 bool operator==(const RetOrArg &O) const { 71 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 72 } 73 74 std::string getDescription() const { 75 return std::string((IsArg ? "Argument #" : "Return value #")) 76 + utostr(Idx) + " of function " + F->getNameStr(); 77 } 78 }; 79 80 /// Liveness enum - During our initial pass over the program, we determine 81 /// that things are either alive or maybe alive. We don't mark anything 82 /// explicitly dead (even if we know they are), since anything not alive 83 /// with no registered uses (in Uses) will never be marked alive and will 84 /// thus become dead in the end. 85 enum Liveness { Live, MaybeLive }; 86 87 /// Convenience wrapper 88 RetOrArg CreateRet(const Function *F, unsigned Idx) { 89 return RetOrArg(F, Idx, false); 90 } 91 /// Convenience wrapper 92 RetOrArg CreateArg(const Function *F, unsigned Idx) { 93 return RetOrArg(F, Idx, true); 94 } 95 96 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 97 /// This maps a return value or argument to any MaybeLive return values or 98 /// arguments it uses. This allows the MaybeLive values to be marked live 99 /// when any of its users is marked live. 100 /// For example (indices are left out for clarity): 101 /// - Uses[ret F] = ret G 102 /// This means that F calls G, and F returns the value returned by G. 103 /// - Uses[arg F] = ret G 104 /// This means that some function calls G and passes its result as an 105 /// argument to F. 106 /// - Uses[ret F] = arg F 107 /// This means that F returns one of its own arguments. 108 /// - Uses[arg F] = arg G 109 /// This means that G calls F and passes one of its own (G's) arguments 110 /// directly to F. 111 UseMap Uses; 112 113 typedef std::set<RetOrArg> LiveSet; 114 typedef std::set<const Function*> LiveFuncSet; 115 116 /// This set contains all values that have been determined to be live. 117 LiveSet LiveValues; 118 /// This set contains all values that are cannot be changed in any way. 119 LiveFuncSet LiveFunctions; 120 121 typedef SmallVector<RetOrArg, 5> UseVector; 122 123 public: 124 static char ID; // Pass identification, replacement for typeid 125 DAE() : ModulePass(&ID) {} 126 bool runOnModule(Module &M); 127 128 virtual bool ShouldHackArguments() const { return false; } 129 130 private: 131 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 132 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 133 unsigned RetValNum = 0); 134 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 135 136 void SurveyFunction(Function &F); 137 void MarkValue(const RetOrArg &RA, Liveness L, 138 const UseVector &MaybeLiveUses); 139 void MarkLive(const RetOrArg &RA); 140 void MarkLive(const Function &F); 141 void PropagateLiveness(const RetOrArg &RA); 142 bool RemoveDeadStuffFromFunction(Function *F); 143 bool DeleteDeadVarargs(Function &Fn); 144 }; 145} 146 147 148char DAE::ID = 0; 149static RegisterPass<DAE> 150X("deadargelim", "Dead Argument Elimination"); 151 152namespace { 153 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 154 /// deletes arguments to functions which are external. This is only for use 155 /// by bugpoint. 156 struct DAH : public DAE { 157 static char ID; 158 virtual bool ShouldHackArguments() const { return true; } 159 }; 160} 161 162char DAH::ID = 0; 163static RegisterPass<DAH> 164Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 165 166/// createDeadArgEliminationPass - This pass removes arguments from functions 167/// which are not used by the body of the function. 168/// 169ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 170ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 171 172/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 173/// llvm.vastart is never called, the varargs list is dead for the function. 174bool DAE::DeleteDeadVarargs(Function &Fn) { 175 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 176 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 177 178 // Ensure that the function is only directly called. 179 if (Fn.hasAddressTaken()) 180 return false; 181 182 // Okay, we know we can transform this function if safe. Scan its body 183 // looking for calls to llvm.vastart. 184 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 185 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 186 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 187 if (II->getIntrinsicID() == Intrinsic::vastart) 188 return false; 189 } 190 } 191 } 192 193 // If we get here, there are no calls to llvm.vastart in the function body, 194 // remove the "..." and adjust all the calls. 195 196 // Start by computing a new prototype for the function, which is the same as 197 // the old function, but doesn't have isVarArg set. 198 const FunctionType *FTy = Fn.getFunctionType(); 199 200 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 201 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 202 Params, false); 203 unsigned NumArgs = Params.size(); 204 205 // Create the new function body and insert it into the module... 206 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 207 NF->copyAttributesFrom(&Fn); 208 Fn.getParent()->getFunctionList().insert(&Fn, NF); 209 NF->takeName(&Fn); 210 211 // Loop over all of the callers of the function, transforming the call sites 212 // to pass in a smaller number of arguments into the new function. 213 // 214 std::vector<Value*> Args; 215 while (!Fn.use_empty()) { 216 CallSite CS = CallSite::get(Fn.use_back()); 217 Instruction *Call = CS.getInstruction(); 218 219 // Pass all the same arguments. 220 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 221 222 // Drop any attributes that were on the vararg arguments. 223 AttrListPtr PAL = CS.getAttributes(); 224 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 225 SmallVector<AttributeWithIndex, 8> AttributesVec; 226 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 227 AttributesVec.push_back(PAL.getSlot(i)); 228 if (Attributes FnAttrs = PAL.getFnAttributes()) 229 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 230 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 231 } 232 233 Instruction *New; 234 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 235 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 236 Args.begin(), Args.end(), "", Call); 237 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 238 cast<InvokeInst>(New)->setAttributes(PAL); 239 } else { 240 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 241 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 242 cast<CallInst>(New)->setAttributes(PAL); 243 if (cast<CallInst>(Call)->isTailCall()) 244 cast<CallInst>(New)->setTailCall(); 245 } 246 Args.clear(); 247 248 if (!Call->use_empty()) 249 Call->replaceAllUsesWith(New); 250 251 New->takeName(Call); 252 253 // Finally, remove the old call from the program, reducing the use-count of 254 // F. 255 Call->eraseFromParent(); 256 } 257 258 // Since we have now created the new function, splice the body of the old 259 // function right into the new function, leaving the old rotting hulk of the 260 // function empty. 261 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 262 263 // Loop over the argument list, transfering uses of the old arguments over to 264 // the new arguments, also transfering over the names as well. While we're at 265 // it, remove the dead arguments from the DeadArguments list. 266 // 267 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 268 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 269 // Move the name and users over to the new version. 270 I->replaceAllUsesWith(I2); 271 I2->takeName(I); 272 } 273 274 // Finally, nuke the old function. 275 Fn.eraseFromParent(); 276 return true; 277} 278 279/// Convenience function that returns the number of return values. It returns 0 280/// for void functions and 1 for functions not returning a struct. It returns 281/// the number of struct elements for functions returning a struct. 282static unsigned NumRetVals(const Function *F) { 283 if (F->getReturnType() == Type::getVoidTy(F->getContext())) 284 return 0; 285 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 286 return STy->getNumElements(); 287 else 288 return 1; 289} 290 291/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 292/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 293/// liveness of Use. 294DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 295 // We're live if our use or its Function is already marked as live. 296 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 297 return Live; 298 299 // We're maybe live otherwise, but remember that we must become live if 300 // Use becomes live. 301 MaybeLiveUses.push_back(Use); 302 return MaybeLive; 303} 304 305 306/// SurveyUse - This looks at a single use of an argument or return value 307/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 308/// if it causes the used value to become MaybeAlive. 309/// 310/// RetValNum is the return value number to use when this use is used in a 311/// return instruction. This is used in the recursion, you should always leave 312/// it at 0. 313DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 314 unsigned RetValNum) { 315 Value *V = *U; 316 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 317 // The value is returned from a function. It's only live when the 318 // function's return value is live. We use RetValNum here, for the case 319 // that U is really a use of an insertvalue instruction that uses the 320 // orginal Use. 321 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 322 // We might be live, depending on the liveness of Use. 323 return MarkIfNotLive(Use, MaybeLiveUses); 324 } 325 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 326 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 327 && IV->hasIndices()) 328 // The use we are examining is inserted into an aggregate. Our liveness 329 // depends on all uses of that aggregate, but if it is used as a return 330 // value, only index at which we were inserted counts. 331 RetValNum = *IV->idx_begin(); 332 333 // Note that if we are used as the aggregate operand to the insertvalue, 334 // we don't change RetValNum, but do survey all our uses. 335 336 Liveness Result = MaybeLive; 337 for (Value::use_iterator I = IV->use_begin(), 338 E = V->use_end(); I != E; ++I) { 339 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 340 if (Result == Live) 341 break; 342 } 343 return Result; 344 } 345 CallSite CS = CallSite::get(V); 346 if (CS.getInstruction()) { 347 Function *F = CS.getCalledFunction(); 348 if (F) { 349 // Used in a direct call. 350 351 // Find the argument number. We know for sure that this use is an 352 // argument, since if it was the function argument this would be an 353 // indirect call and the we know can't be looking at a value of the 354 // label type (for the invoke instruction). 355 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 356 357 if (ArgNo >= F->getFunctionType()->getNumParams()) 358 // The value is passed in through a vararg! Must be live. 359 return Live; 360 361 assert(CS.getArgument(ArgNo) 362 == CS.getInstruction()->getOperand(U.getOperandNo()) 363 && "Argument is not where we expected it"); 364 365 // Value passed to a normal call. It's only live when the corresponding 366 // argument to the called function turns out live. 367 RetOrArg Use = CreateArg(F, ArgNo); 368 return MarkIfNotLive(Use, MaybeLiveUses); 369 } 370 } 371 // Used in any other way? Value must be live. 372 return Live; 373} 374 375/// SurveyUses - This looks at all the uses of the given value 376/// Returns the Liveness deduced from the uses of this value. 377/// 378/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 379/// the result is Live, MaybeLiveUses might be modified but its content should 380/// be ignored (since it might not be complete). 381DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 382 // Assume it's dead (which will only hold if there are no uses at all..). 383 Liveness Result = MaybeLive; 384 // Check each use. 385 for (Value::use_iterator I = V->use_begin(), 386 E = V->use_end(); I != E; ++I) { 387 Result = SurveyUse(I, MaybeLiveUses); 388 if (Result == Live) 389 break; 390 } 391 return Result; 392} 393 394// SurveyFunction - This performs the initial survey of the specified function, 395// checking out whether or not it uses any of its incoming arguments or whether 396// any callers use the return value. This fills in the LiveValues set and Uses 397// map. 398// 399// We consider arguments of non-internal functions to be intrinsically alive as 400// well as arguments to functions which have their "address taken". 401// 402void DAE::SurveyFunction(Function &F) { 403 unsigned RetCount = NumRetVals(&F); 404 // Assume all return values are dead 405 typedef SmallVector<Liveness, 5> RetVals; 406 RetVals RetValLiveness(RetCount, MaybeLive); 407 408 typedef SmallVector<UseVector, 5> RetUses; 409 // These vectors map each return value to the uses that make it MaybeLive, so 410 // we can add those to the Uses map if the return value really turns out to be 411 // MaybeLive. Initialized to a list of RetCount empty lists. 412 RetUses MaybeLiveRetUses(RetCount); 413 414 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 415 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 416 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 417 != F.getFunctionType()->getReturnType()) { 418 // We don't support old style multiple return values. 419 MarkLive(F); 420 return; 421 } 422 423 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 424 MarkLive(F); 425 return; 426 } 427 428 DEBUG(errs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 429 // Keep track of the number of live retvals, so we can skip checks once all 430 // of them turn out to be live. 431 unsigned NumLiveRetVals = 0; 432 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 433 // Loop all uses of the function. 434 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 435 // If the function is PASSED IN as an argument, its address has been 436 // taken. 437 CallSite CS = CallSite::get(*I); 438 if (!CS.getInstruction() || !CS.isCallee(I)) { 439 MarkLive(F); 440 return; 441 } 442 443 // If this use is anything other than a call site, the function is alive. 444 Instruction *TheCall = CS.getInstruction(); 445 if (!TheCall) { // Not a direct call site? 446 MarkLive(F); 447 return; 448 } 449 450 // If we end up here, we are looking at a direct call to our function. 451 452 // Now, check how our return value(s) is/are used in this caller. Don't 453 // bother checking return values if all of them are live already. 454 if (NumLiveRetVals != RetCount) { 455 if (STy) { 456 // Check all uses of the return value. 457 for (Value::use_iterator I = TheCall->use_begin(), 458 E = TheCall->use_end(); I != E; ++I) { 459 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 460 if (Ext && Ext->hasIndices()) { 461 // This use uses a part of our return value, survey the uses of 462 // that part and store the results for this index only. 463 unsigned Idx = *Ext->idx_begin(); 464 if (RetValLiveness[Idx] != Live) { 465 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 466 if (RetValLiveness[Idx] == Live) 467 NumLiveRetVals++; 468 } 469 } else { 470 // Used by something else than extractvalue. Mark all return 471 // values as live. 472 for (unsigned i = 0; i != RetCount; ++i ) 473 RetValLiveness[i] = Live; 474 NumLiveRetVals = RetCount; 475 break; 476 } 477 } 478 } else { 479 // Single return value 480 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 481 if (RetValLiveness[0] == Live) 482 NumLiveRetVals = RetCount; 483 } 484 } 485 } 486 487 // Now we've inspected all callers, record the liveness of our return values. 488 for (unsigned i = 0; i != RetCount; ++i) 489 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 490 491 DEBUG(errs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 492 493 // Now, check all of our arguments. 494 unsigned i = 0; 495 UseVector MaybeLiveArgUses; 496 for (Function::arg_iterator AI = F.arg_begin(), 497 E = F.arg_end(); AI != E; ++AI, ++i) { 498 // See what the effect of this use is (recording any uses that cause 499 // MaybeLive in MaybeLiveArgUses). 500 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 501 // Mark the result. 502 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 503 // Clear the vector again for the next iteration. 504 MaybeLiveArgUses.clear(); 505 } 506} 507 508/// MarkValue - This function marks the liveness of RA depending on L. If L is 509/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 510/// such that RA will be marked live if any use in MaybeLiveUses gets marked 511/// live later on. 512void DAE::MarkValue(const RetOrArg &RA, Liveness L, 513 const UseVector &MaybeLiveUses) { 514 switch (L) { 515 case Live: MarkLive(RA); break; 516 case MaybeLive: 517 { 518 // Note any uses of this value, so this return value can be 519 // marked live whenever one of the uses becomes live. 520 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 521 UE = MaybeLiveUses.end(); UI != UE; ++UI) 522 Uses.insert(std::make_pair(*UI, RA)); 523 break; 524 } 525 } 526} 527 528/// MarkLive - Mark the given Function as alive, meaning that it cannot be 529/// changed in any way. Additionally, 530/// mark any values that are used as this function's parameters or by its return 531/// values (according to Uses) live as well. 532void DAE::MarkLive(const Function &F) { 533 DEBUG(errs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 534 // Mark the function as live. 535 LiveFunctions.insert(&F); 536 // Mark all arguments as live. 537 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 538 PropagateLiveness(CreateArg(&F, i)); 539 // Mark all return values as live. 540 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 541 PropagateLiveness(CreateRet(&F, i)); 542} 543 544/// MarkLive - Mark the given return value or argument as live. Additionally, 545/// mark any values that are used by this value (according to Uses) live as 546/// well. 547void DAE::MarkLive(const RetOrArg &RA) { 548 if (LiveFunctions.count(RA.F)) 549 return; // Function was already marked Live. 550 551 if (!LiveValues.insert(RA).second) 552 return; // We were already marked Live. 553 554 DEBUG(errs() << "DAE - Marking " << RA.getDescription() << " live\n"); 555 PropagateLiveness(RA); 556} 557 558/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 559/// to any other values it uses (according to Uses). 560void DAE::PropagateLiveness(const RetOrArg &RA) { 561 // We don't use upper_bound (or equal_range) here, because our recursive call 562 // to ourselves is likely to cause the upper_bound (which is the first value 563 // not belonging to RA) to become erased and the iterator invalidated. 564 UseMap::iterator Begin = Uses.lower_bound(RA); 565 UseMap::iterator E = Uses.end(); 566 UseMap::iterator I; 567 for (I = Begin; I != E && I->first == RA; ++I) 568 MarkLive(I->second); 569 570 // Erase RA from the Uses map (from the lower bound to wherever we ended up 571 // after the loop). 572 Uses.erase(Begin, I); 573} 574 575// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 576// that are not in LiveValues. Transform the function and all of the callees of 577// the function to not have these arguments and return values. 578// 579bool DAE::RemoveDeadStuffFromFunction(Function *F) { 580 // Don't modify fully live functions 581 if (LiveFunctions.count(F)) 582 return false; 583 584 // Start by computing a new prototype for the function, which is the same as 585 // the old function, but has fewer arguments and a different return type. 586 const FunctionType *FTy = F->getFunctionType(); 587 std::vector<const Type*> Params; 588 589 // Set up to build a new list of parameter attributes. 590 SmallVector<AttributeWithIndex, 8> AttributesVec; 591 const AttrListPtr &PAL = F->getAttributes(); 592 593 // The existing function return attributes. 594 Attributes RAttrs = PAL.getRetAttributes(); 595 Attributes FnAttrs = PAL.getFnAttributes(); 596 597 // Find out the new return value. 598 599 const Type *RetTy = FTy->getReturnType(); 600 const Type *NRetTy = NULL; 601 unsigned RetCount = NumRetVals(F); 602 603 // -1 means unused, other numbers are the new index 604 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 605 std::vector<const Type*> RetTypes; 606 if (RetTy == Type::getVoidTy(F->getContext())) { 607 NRetTy = Type::getVoidTy(F->getContext()); 608 } else { 609 const StructType *STy = dyn_cast<StructType>(RetTy); 610 if (STy) 611 // Look at each of the original return values individually. 612 for (unsigned i = 0; i != RetCount; ++i) { 613 RetOrArg Ret = CreateRet(F, i); 614 if (LiveValues.erase(Ret)) { 615 RetTypes.push_back(STy->getElementType(i)); 616 NewRetIdxs[i] = RetTypes.size() - 1; 617 } else { 618 ++NumRetValsEliminated; 619 DEBUG(errs() << "DAE - Removing return value " << i << " from " 620 << F->getName() << "\n"); 621 } 622 } 623 else 624 // We used to return a single value. 625 if (LiveValues.erase(CreateRet(F, 0))) { 626 RetTypes.push_back(RetTy); 627 NewRetIdxs[0] = 0; 628 } else { 629 DEBUG(errs() << "DAE - Removing return value from " << F->getName() 630 << "\n"); 631 ++NumRetValsEliminated; 632 } 633 if (RetTypes.size() > 1) 634 // More than one return type? Return a struct with them. Also, if we used 635 // to return a struct and didn't change the number of return values, 636 // return a struct again. This prevents changing {something} into 637 // something and {} into void. 638 // Make the new struct packed if we used to return a packed struct 639 // already. 640 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 641 else if (RetTypes.size() == 1) 642 // One return type? Just a simple value then, but only if we didn't use to 643 // return a struct with that simple value before. 644 NRetTy = RetTypes.front(); 645 else if (RetTypes.size() == 0) 646 // No return types? Make it void, but only if we didn't use to return {}. 647 NRetTy = Type::getVoidTy(F->getContext()); 648 } 649 650 assert(NRetTy && "No new return type found?"); 651 652 // Remove any incompatible attributes, but only if we removed all return 653 // values. Otherwise, ensure that we don't have any conflicting attributes 654 // here. Currently, this should not be possible, but special handling might be 655 // required when new return value attributes are added. 656 if (NRetTy == Type::getVoidTy(F->getContext())) 657 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 658 else 659 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 660 && "Return attributes no longer compatible?"); 661 662 if (RAttrs) 663 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 664 665 // Remember which arguments are still alive. 666 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 667 // Construct the new parameter list from non-dead arguments. Also construct 668 // a new set of parameter attributes to correspond. Skip the first parameter 669 // attribute, since that belongs to the return value. 670 unsigned i = 0; 671 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 672 I != E; ++I, ++i) { 673 RetOrArg Arg = CreateArg(F, i); 674 if (LiveValues.erase(Arg)) { 675 Params.push_back(I->getType()); 676 ArgAlive[i] = true; 677 678 // Get the original parameter attributes (skipping the first one, that is 679 // for the return value. 680 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 681 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 682 } else { 683 ++NumArgumentsEliminated; 684 DEBUG(errs() << "DAE - Removing argument " << i << " (" << I->getName() 685 << ") from " << F->getName() << "\n"); 686 } 687 } 688 689 if (FnAttrs != Attribute::None) 690 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 691 692 // Reconstruct the AttributesList based on the vector we constructed. 693 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 694 695 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 696 // have zero fixed arguments. 697 // 698 // Note that we apply this hack for a vararg fuction that does not have any 699 // arguments anymore, but did have them before (so don't bother fixing 700 // functions that were already broken wrt CWriter). 701 bool ExtraArgHack = false; 702 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 703 ExtraArgHack = true; 704 Params.push_back(Type::getInt32Ty(F->getContext())); 705 } 706 707 // Create the new function type based on the recomputed parameters. 708 FunctionType *NFTy = FunctionType::get(NRetTy, Params, 709 FTy->isVarArg()); 710 711 // No change? 712 if (NFTy == FTy) 713 return false; 714 715 // Create the new function body and insert it into the module... 716 Function *NF = Function::Create(NFTy, F->getLinkage()); 717 NF->copyAttributesFrom(F); 718 NF->setAttributes(NewPAL); 719 // Insert the new function before the old function, so we won't be processing 720 // it again. 721 F->getParent()->getFunctionList().insert(F, NF); 722 NF->takeName(F); 723 724 // Loop over all of the callers of the function, transforming the call sites 725 // to pass in a smaller number of arguments into the new function. 726 // 727 std::vector<Value*> Args; 728 while (!F->use_empty()) { 729 CallSite CS = CallSite::get(F->use_back()); 730 Instruction *Call = CS.getInstruction(); 731 732 AttributesVec.clear(); 733 const AttrListPtr &CallPAL = CS.getAttributes(); 734 735 // The call return attributes. 736 Attributes RAttrs = CallPAL.getRetAttributes(); 737 Attributes FnAttrs = CallPAL.getFnAttributes(); 738 // Adjust in case the function was changed to return void. 739 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 740 if (RAttrs) 741 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 742 743 // Declare these outside of the loops, so we can reuse them for the second 744 // loop, which loops the varargs. 745 CallSite::arg_iterator I = CS.arg_begin(); 746 unsigned i = 0; 747 // Loop over those operands, corresponding to the normal arguments to the 748 // original function, and add those that are still alive. 749 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 750 if (ArgAlive[i]) { 751 Args.push_back(*I); 752 // Get original parameter attributes, but skip return attributes. 753 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 754 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 755 } 756 757 if (ExtraArgHack) 758 Args.push_back(UndefValue::get(Type::getInt32Ty(F->getContext()))); 759 760 // Push any varargs arguments on the list. Don't forget their attributes. 761 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 762 Args.push_back(*I); 763 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 764 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 765 } 766 767 if (FnAttrs != Attribute::None) 768 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 769 770 // Reconstruct the AttributesList based on the vector we constructed. 771 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 772 AttributesVec.end()); 773 774 Instruction *New; 775 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 776 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 777 Args.begin(), Args.end(), "", Call); 778 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 779 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 780 } else { 781 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 782 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 783 cast<CallInst>(New)->setAttributes(NewCallPAL); 784 if (cast<CallInst>(Call)->isTailCall()) 785 cast<CallInst>(New)->setTailCall(); 786 } 787 Args.clear(); 788 789 if (!Call->use_empty()) { 790 if (New->getType() == Call->getType()) { 791 // Return type not changed? Just replace users then. 792 Call->replaceAllUsesWith(New); 793 New->takeName(Call); 794 } else if (New->getType() == Type::getVoidTy(F->getContext())) { 795 // Our return value has uses, but they will get removed later on. 796 // Replace by null for now. 797 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 798 } else { 799 assert(isa<StructType>(RetTy) && 800 "Return type changed, but not into a void. The old return type" 801 " must have been a struct!"); 802 Instruction *InsertPt = Call; 803 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 804 BasicBlock::iterator IP = II->getNormalDest()->begin(); 805 while (isa<PHINode>(IP)) ++IP; 806 InsertPt = IP; 807 } 808 809 // We used to return a struct. Instead of doing smart stuff with all the 810 // uses of this struct, we will just rebuild it using 811 // extract/insertvalue chaining and let instcombine clean that up. 812 // 813 // Start out building up our return value from undef 814 Value *RetVal = UndefValue::get(RetTy); 815 for (unsigned i = 0; i != RetCount; ++i) 816 if (NewRetIdxs[i] != -1) { 817 Value *V; 818 if (RetTypes.size() > 1) 819 // We are still returning a struct, so extract the value from our 820 // return value 821 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 822 InsertPt); 823 else 824 // We are now returning a single element, so just insert that 825 V = New; 826 // Insert the value at the old position 827 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 828 } 829 // Now, replace all uses of the old call instruction with the return 830 // struct we built 831 Call->replaceAllUsesWith(RetVal); 832 New->takeName(Call); 833 } 834 } 835 836 // Finally, remove the old call from the program, reducing the use-count of 837 // F. 838 Call->eraseFromParent(); 839 } 840 841 // Since we have now created the new function, splice the body of the old 842 // function right into the new function, leaving the old rotting hulk of the 843 // function empty. 844 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 845 846 // Loop over the argument list, transfering uses of the old arguments over to 847 // the new arguments, also transfering over the names as well. 848 i = 0; 849 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 850 I2 = NF->arg_begin(); I != E; ++I, ++i) 851 if (ArgAlive[i]) { 852 // If this is a live argument, move the name and users over to the new 853 // version. 854 I->replaceAllUsesWith(I2); 855 I2->takeName(I); 856 ++I2; 857 } else { 858 // If this argument is dead, replace any uses of it with null constants 859 // (these are guaranteed to become unused later on). 860 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 861 } 862 863 // If we change the return value of the function we must rewrite any return 864 // instructions. Check this now. 865 if (F->getReturnType() != NF->getReturnType()) 866 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 867 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 868 Value *RetVal; 869 870 if (NFTy->getReturnType() == Type::getVoidTy(F->getContext())) { 871 RetVal = 0; 872 } else { 873 assert (isa<StructType>(RetTy)); 874 // The original return value was a struct, insert 875 // extractvalue/insertvalue chains to extract only the values we need 876 // to return and insert them into our new result. 877 // This does generate messy code, but we'll let it to instcombine to 878 // clean that up. 879 Value *OldRet = RI->getOperand(0); 880 // Start out building up our return value from undef 881 RetVal = UndefValue::get(NRetTy); 882 for (unsigned i = 0; i != RetCount; ++i) 883 if (NewRetIdxs[i] != -1) { 884 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 885 "oldret", RI); 886 if (RetTypes.size() > 1) { 887 // We're still returning a struct, so reinsert the value into 888 // our new return value at the new index 889 890 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 891 "newret", RI); 892 } else { 893 // We are now only returning a simple value, so just return the 894 // extracted value. 895 RetVal = EV; 896 } 897 } 898 } 899 // Replace the return instruction with one returning the new return 900 // value (possibly 0 if we became void). 901 ReturnInst::Create(F->getContext(), RetVal, RI); 902 BB->getInstList().erase(RI); 903 } 904 905 // Now that the old function is dead, delete it. 906 F->eraseFromParent(); 907 908 return true; 909} 910 911bool DAE::runOnModule(Module &M) { 912 bool Changed = false; 913 914 // First pass: Do a simple check to see if any functions can have their "..." 915 // removed. We can do this if they never call va_start. This loop cannot be 916 // fused with the next loop, because deleting a function invalidates 917 // information computed while surveying other functions. 918 DEBUG(errs() << "DAE - Deleting dead varargs\n"); 919 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 920 Function &F = *I++; 921 if (F.getFunctionType()->isVarArg()) 922 Changed |= DeleteDeadVarargs(F); 923 } 924 925 // Second phase:loop through the module, determining which arguments are live. 926 // We assume all arguments are dead unless proven otherwise (allowing us to 927 // determine that dead arguments passed into recursive functions are dead). 928 // 929 DEBUG(errs() << "DAE - Determining liveness\n"); 930 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 931 SurveyFunction(*I); 932 933 // Now, remove all dead arguments and return values from each function in 934 // turn 935 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 936 // Increment now, because the function will probably get removed (ie 937 // replaced by a new one). 938 Function *F = I++; 939 Changed |= RemoveDeadStuffFromFunction(F); 940 } 941 return Changed; 942} 943