DeadArgumentElimination.cpp revision a65d6a686e6ad865c61aec70c5bdfb30bf6f5b22
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 protected: 124 // DAH uses this to specify a different ID. 125 explicit DAE(char &ID) : ModulePass(ID) {} 126 127 public: 128 static char ID; // Pass identification, replacement for typeid 129 DAE() : ModulePass(ID) { 130 initializeDAEPass(*PassRegistry::getPassRegistry()); 131 } 132 133 bool runOnModule(Module &M); 134 135 virtual bool ShouldHackArguments() const { return false; } 136 137 private: 138 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 139 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses, 140 unsigned RetValNum = 0); 141 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 142 143 void SurveyFunction(const Function &F); 144 void MarkValue(const RetOrArg &RA, Liveness L, 145 const UseVector &MaybeLiveUses); 146 void MarkLive(const RetOrArg &RA); 147 void MarkLive(const Function &F); 148 void PropagateLiveness(const RetOrArg &RA); 149 bool RemoveDeadStuffFromFunction(Function *F); 150 bool DeleteDeadVarargs(Function &Fn); 151 }; 152} 153 154 155char DAE::ID = 0; 156INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false) 157 158namespace { 159 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 160 /// deletes arguments to functions which are external. This is only for use 161 /// by bugpoint. 162 struct DAH : public DAE { 163 static char ID; 164 DAH() : DAE(ID) {} 165 166 virtual bool ShouldHackArguments() const { return true; } 167 }; 168} 169 170char DAH::ID = 0; 171INITIALIZE_PASS(DAH, "deadarghaX0r", 172 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)", 173 false, false) 174 175/// createDeadArgEliminationPass - This pass removes arguments from functions 176/// which are not used by the body of the function. 177/// 178ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 179ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 180 181/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 182/// llvm.vastart is never called, the varargs list is dead for the function. 183bool DAE::DeleteDeadVarargs(Function &Fn) { 184 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 185 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 186 187 // Ensure that the function is only directly called. 188 if (Fn.hasAddressTaken()) 189 return false; 190 191 // Okay, we know we can transform this function if safe. Scan its body 192 // looking for calls to llvm.vastart. 193 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 194 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 195 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 196 if (II->getIntrinsicID() == Intrinsic::vastart) 197 return false; 198 } 199 } 200 } 201 202 // If we get here, there are no calls to llvm.vastart in the function body, 203 // remove the "..." and adjust all the calls. 204 205 // Start by computing a new prototype for the function, which is the same as 206 // the old function, but doesn't have isVarArg set. 207 const FunctionType *FTy = Fn.getFunctionType(); 208 209 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 210 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 211 Params, false); 212 unsigned NumArgs = Params.size(); 213 214 // Create the new function body and insert it into the module... 215 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 216 NF->copyAttributesFrom(&Fn); 217 Fn.getParent()->getFunctionList().insert(&Fn, NF); 218 NF->takeName(&Fn); 219 220 // Loop over all of the callers of the function, transforming the call sites 221 // to pass in a smaller number of arguments into the new function. 222 // 223 std::vector<Value*> Args; 224 while (!Fn.use_empty()) { 225 CallSite CS(Fn.use_back()); 226 Instruction *Call = CS.getInstruction(); 227 228 // Pass all the same arguments. 229 Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs); 230 231 // Drop any attributes that were on the vararg arguments. 232 AttrListPtr PAL = CS.getAttributes(); 233 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 234 SmallVector<AttributeWithIndex, 8> AttributesVec; 235 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 236 AttributesVec.push_back(PAL.getSlot(i)); 237 if (Attributes FnAttrs = PAL.getFnAttributes()) 238 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 239 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 240 } 241 242 Instruction *New; 243 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 244 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 245 Args.begin(), Args.end(), "", Call); 246 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 247 cast<InvokeInst>(New)->setAttributes(PAL); 248 } else { 249 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 250 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 251 cast<CallInst>(New)->setAttributes(PAL); 252 if (cast<CallInst>(Call)->isTailCall()) 253 cast<CallInst>(New)->setTailCall(); 254 } 255 New->setDebugLoc(Call->getDebugLoc()); 256 257 Args.clear(); 258 259 if (!Call->use_empty()) 260 Call->replaceAllUsesWith(New); 261 262 New->takeName(Call); 263 264 // Finally, remove the old call from the program, reducing the use-count of 265 // F. 266 Call->eraseFromParent(); 267 } 268 269 // Since we have now created the new function, splice the body of the old 270 // function right into the new function, leaving the old rotting hulk of the 271 // function empty. 272 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 273 274 // Loop over the argument list, transfering uses of the old arguments over to 275 // the new arguments, also transfering over the names as well. While we're at 276 // it, remove the dead arguments from the DeadArguments list. 277 // 278 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 279 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 280 // Move the name and users over to the new version. 281 I->replaceAllUsesWith(I2); 282 I2->takeName(I); 283 } 284 285 // Finally, nuke the old function. 286 Fn.eraseFromParent(); 287 return true; 288} 289 290/// Convenience function that returns the number of return values. It returns 0 291/// for void functions and 1 for functions not returning a struct. It returns 292/// the number of struct elements for functions returning a struct. 293static unsigned NumRetVals(const Function *F) { 294 if (F->getReturnType()->isVoidTy()) 295 return 0; 296 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 297 return STy->getNumElements(); 298 else 299 return 1; 300} 301 302/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 303/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 304/// liveness of Use. 305DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 306 // We're live if our use or its Function is already marked as live. 307 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 308 return Live; 309 310 // We're maybe live otherwise, but remember that we must become live if 311 // Use becomes live. 312 MaybeLiveUses.push_back(Use); 313 return MaybeLive; 314} 315 316 317/// SurveyUse - This looks at a single use of an argument or return value 318/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 319/// if it causes the used value to become MaybeLive. 320/// 321/// RetValNum is the return value number to use when this use is used in a 322/// return instruction. This is used in the recursion, you should always leave 323/// it at 0. 324DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U, 325 UseVector &MaybeLiveUses, unsigned RetValNum) { 326 const User *V = *U; 327 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 328 // The value is returned from a function. It's only live when the 329 // function's return value is live. We use RetValNum here, for the case 330 // that U is really a use of an insertvalue instruction that uses the 331 // orginal Use. 332 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 333 // We might be live, depending on the liveness of Use. 334 return MarkIfNotLive(Use, MaybeLiveUses); 335 } 336 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 337 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 338 && IV->hasIndices()) 339 // The use we are examining is inserted into an aggregate. Our liveness 340 // depends on all uses of that aggregate, but if it is used as a return 341 // value, only index at which we were inserted counts. 342 RetValNum = *IV->idx_begin(); 343 344 // Note that if we are used as the aggregate operand to the insertvalue, 345 // we don't change RetValNum, but do survey all our uses. 346 347 Liveness Result = MaybeLive; 348 for (Value::const_use_iterator I = IV->use_begin(), 349 E = V->use_end(); I != E; ++I) { 350 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 351 if (Result == Live) 352 break; 353 } 354 return Result; 355 } 356 357 if (ImmutableCallSite CS = V) { 358 const Function *F = CS.getCalledFunction(); 359 if (F) { 360 // Used in a direct call. 361 362 // Find the argument number. We know for sure that this use is an 363 // argument, since if it was the function argument this would be an 364 // indirect call and the we know can't be looking at a value of the 365 // label type (for the invoke instruction). 366 unsigned ArgNo = CS.getArgumentNo(U); 367 368 if (ArgNo >= F->getFunctionType()->getNumParams()) 369 // The value is passed in through a vararg! Must be live. 370 return Live; 371 372 assert(CS.getArgument(ArgNo) 373 == CS->getOperand(U.getOperandNo()) 374 && "Argument is not where we expected it"); 375 376 // Value passed to a normal call. It's only live when the corresponding 377 // argument to the called function turns out live. 378 RetOrArg Use = CreateArg(F, ArgNo); 379 return MarkIfNotLive(Use, MaybeLiveUses); 380 } 381 } 382 // Used in any other way? Value must be live. 383 return Live; 384} 385 386/// SurveyUses - This looks at all the uses of the given value 387/// Returns the Liveness deduced from the uses of this value. 388/// 389/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 390/// the result is Live, MaybeLiveUses might be modified but its content should 391/// be ignored (since it might not be complete). 392DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 393 // Assume it's dead (which will only hold if there are no uses at all..). 394 Liveness Result = MaybeLive; 395 // Check each use. 396 for (Value::const_use_iterator I = V->use_begin(), 397 E = V->use_end(); I != E; ++I) { 398 Result = SurveyUse(I, MaybeLiveUses); 399 if (Result == Live) 400 break; 401 } 402 return Result; 403} 404 405// SurveyFunction - This performs the initial survey of the specified function, 406// checking out whether or not it uses any of its incoming arguments or whether 407// any callers use the return value. This fills in the LiveValues set and Uses 408// map. 409// 410// We consider arguments of non-internal functions to be intrinsically alive as 411// well as arguments to functions which have their "address taken". 412// 413void DAE::SurveyFunction(const Function &F) { 414 unsigned RetCount = NumRetVals(&F); 415 // Assume all return values are dead 416 typedef SmallVector<Liveness, 5> RetVals; 417 RetVals RetValLiveness(RetCount, MaybeLive); 418 419 typedef SmallVector<UseVector, 5> RetUses; 420 // These vectors map each return value to the uses that make it MaybeLive, so 421 // we can add those to the Uses map if the return value really turns out to be 422 // MaybeLive. Initialized to a list of RetCount empty lists. 423 RetUses MaybeLiveRetUses(RetCount); 424 425 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 426 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 427 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 428 != F.getFunctionType()->getReturnType()) { 429 // We don't support old style multiple return values. 430 MarkLive(F); 431 return; 432 } 433 434 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 435 MarkLive(F); 436 return; 437 } 438 439 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 440 // Keep track of the number of live retvals, so we can skip checks once all 441 // of them turn out to be live. 442 unsigned NumLiveRetVals = 0; 443 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 444 // Loop all uses of the function. 445 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end(); 446 I != E; ++I) { 447 // If the function is PASSED IN as an argument, its address has been 448 // taken. 449 ImmutableCallSite CS(*I); 450 if (!CS || !CS.isCallee(I)) { 451 MarkLive(F); 452 return; 453 } 454 455 // If this use is anything other than a call site, the function is alive. 456 const Instruction *TheCall = CS.getInstruction(); 457 if (!TheCall) { // Not a direct call site? 458 MarkLive(F); 459 return; 460 } 461 462 // If we end up here, we are looking at a direct call to our function. 463 464 // Now, check how our return value(s) is/are used in this caller. Don't 465 // bother checking return values if all of them are live already. 466 if (NumLiveRetVals != RetCount) { 467 if (STy) { 468 // Check all uses of the return value. 469 for (Value::const_use_iterator I = TheCall->use_begin(), 470 E = TheCall->use_end(); I != E; ++I) { 471 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 472 if (Ext && Ext->hasIndices()) { 473 // This use uses a part of our return value, survey the uses of 474 // that part and store the results for this index only. 475 unsigned Idx = *Ext->idx_begin(); 476 if (RetValLiveness[Idx] != Live) { 477 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 478 if (RetValLiveness[Idx] == Live) 479 NumLiveRetVals++; 480 } 481 } else { 482 // Used by something else than extractvalue. Mark all return 483 // values as live. 484 for (unsigned i = 0; i != RetCount; ++i ) 485 RetValLiveness[i] = Live; 486 NumLiveRetVals = RetCount; 487 break; 488 } 489 } 490 } else { 491 // Single return value 492 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 493 if (RetValLiveness[0] == Live) 494 NumLiveRetVals = RetCount; 495 } 496 } 497 } 498 499 // Now we've inspected all callers, record the liveness of our return values. 500 for (unsigned i = 0; i != RetCount; ++i) 501 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 502 503 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 504 505 // Now, check all of our arguments. 506 unsigned i = 0; 507 UseVector MaybeLiveArgUses; 508 for (Function::const_arg_iterator AI = F.arg_begin(), 509 E = F.arg_end(); AI != E; ++AI, ++i) { 510 // See what the effect of this use is (recording any uses that cause 511 // MaybeLive in MaybeLiveArgUses). 512 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 513 // Mark the result. 514 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 515 // Clear the vector again for the next iteration. 516 MaybeLiveArgUses.clear(); 517 } 518} 519 520/// MarkValue - This function marks the liveness of RA depending on L. If L is 521/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 522/// such that RA will be marked live if any use in MaybeLiveUses gets marked 523/// live later on. 524void DAE::MarkValue(const RetOrArg &RA, Liveness L, 525 const UseVector &MaybeLiveUses) { 526 switch (L) { 527 case Live: MarkLive(RA); break; 528 case MaybeLive: 529 { 530 // Note any uses of this value, so this return value can be 531 // marked live whenever one of the uses becomes live. 532 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 533 UE = MaybeLiveUses.end(); UI != UE; ++UI) 534 Uses.insert(std::make_pair(*UI, RA)); 535 break; 536 } 537 } 538} 539 540/// MarkLive - Mark the given Function as alive, meaning that it cannot be 541/// changed in any way. Additionally, 542/// mark any values that are used as this function's parameters or by its return 543/// values (according to Uses) live as well. 544void DAE::MarkLive(const Function &F) { 545 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 546 // Mark the function as live. 547 LiveFunctions.insert(&F); 548 // Mark all arguments as live. 549 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 550 PropagateLiveness(CreateArg(&F, i)); 551 // Mark all return values as live. 552 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 553 PropagateLiveness(CreateRet(&F, i)); 554} 555 556/// MarkLive - Mark the given return value or argument as live. Additionally, 557/// mark any values that are used by this value (according to Uses) live as 558/// well. 559void DAE::MarkLive(const RetOrArg &RA) { 560 if (LiveFunctions.count(RA.F)) 561 return; // Function was already marked Live. 562 563 if (!LiveValues.insert(RA).second) 564 return; // We were already marked Live. 565 566 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 567 PropagateLiveness(RA); 568} 569 570/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 571/// to any other values it uses (according to Uses). 572void DAE::PropagateLiveness(const RetOrArg &RA) { 573 // We don't use upper_bound (or equal_range) here, because our recursive call 574 // to ourselves is likely to cause the upper_bound (which is the first value 575 // not belonging to RA) to become erased and the iterator invalidated. 576 UseMap::iterator Begin = Uses.lower_bound(RA); 577 UseMap::iterator E = Uses.end(); 578 UseMap::iterator I; 579 for (I = Begin; I != E && I->first == RA; ++I) 580 MarkLive(I->second); 581 582 // Erase RA from the Uses map (from the lower bound to wherever we ended up 583 // after the loop). 584 Uses.erase(Begin, I); 585} 586 587// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 588// that are not in LiveValues. Transform the function and all of the callees of 589// the function to not have these arguments and return values. 590// 591bool DAE::RemoveDeadStuffFromFunction(Function *F) { 592 // Don't modify fully live functions 593 if (LiveFunctions.count(F)) 594 return false; 595 596 // Start by computing a new prototype for the function, which is the same as 597 // the old function, but has fewer arguments and a different return type. 598 const FunctionType *FTy = F->getFunctionType(); 599 std::vector<const Type*> Params; 600 601 // Set up to build a new list of parameter attributes. 602 SmallVector<AttributeWithIndex, 8> AttributesVec; 603 const AttrListPtr &PAL = F->getAttributes(); 604 605 // The existing function return attributes. 606 Attributes RAttrs = PAL.getRetAttributes(); 607 Attributes FnAttrs = PAL.getFnAttributes(); 608 609 // Find out the new return value. 610 611 const Type *RetTy = FTy->getReturnType(); 612 const Type *NRetTy = NULL; 613 unsigned RetCount = NumRetVals(F); 614 615 // -1 means unused, other numbers are the new index 616 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 617 std::vector<const Type*> RetTypes; 618 if (RetTy->isVoidTy()) { 619 NRetTy = RetTy; 620 } else { 621 const StructType *STy = dyn_cast<StructType>(RetTy); 622 if (STy) 623 // Look at each of the original return values individually. 624 for (unsigned i = 0; i != RetCount; ++i) { 625 RetOrArg Ret = CreateRet(F, i); 626 if (LiveValues.erase(Ret)) { 627 RetTypes.push_back(STy->getElementType(i)); 628 NewRetIdxs[i] = RetTypes.size() - 1; 629 } else { 630 ++NumRetValsEliminated; 631 DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 632 << F->getName() << "\n"); 633 } 634 } 635 else 636 // We used to return a single value. 637 if (LiveValues.erase(CreateRet(F, 0))) { 638 RetTypes.push_back(RetTy); 639 NewRetIdxs[0] = 0; 640 } else { 641 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 642 << "\n"); 643 ++NumRetValsEliminated; 644 } 645 if (RetTypes.size() > 1) 646 // More than one return type? Return a struct with them. Also, if we used 647 // to return a struct and didn't change the number of return values, 648 // return a struct again. This prevents changing {something} into 649 // something and {} into void. 650 // Make the new struct packed if we used to return a packed struct 651 // already. 652 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 653 else if (RetTypes.size() == 1) 654 // One return type? Just a simple value then, but only if we didn't use to 655 // return a struct with that simple value before. 656 NRetTy = RetTypes.front(); 657 else if (RetTypes.size() == 0) 658 // No return types? Make it void, but only if we didn't use to return {}. 659 NRetTy = Type::getVoidTy(F->getContext()); 660 } 661 662 assert(NRetTy && "No new return type found?"); 663 664 // Remove any incompatible attributes, but only if we removed all return 665 // values. Otherwise, ensure that we don't have any conflicting attributes 666 // here. Currently, this should not be possible, but special handling might be 667 // required when new return value attributes are added. 668 if (NRetTy->isVoidTy()) 669 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 670 else 671 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 672 && "Return attributes no longer compatible?"); 673 674 if (RAttrs) 675 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 676 677 // Remember which arguments are still alive. 678 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 679 // Construct the new parameter list from non-dead arguments. Also construct 680 // a new set of parameter attributes to correspond. Skip the first parameter 681 // attribute, since that belongs to the return value. 682 unsigned i = 0; 683 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 684 I != E; ++I, ++i) { 685 RetOrArg Arg = CreateArg(F, i); 686 if (LiveValues.erase(Arg)) { 687 Params.push_back(I->getType()); 688 ArgAlive[i] = true; 689 690 // Get the original parameter attributes (skipping the first one, that is 691 // for the return value. 692 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 693 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 694 } else { 695 ++NumArgumentsEliminated; 696 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 697 << ") from " << F->getName() << "\n"); 698 } 699 } 700 701 if (FnAttrs != Attribute::None) 702 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 703 704 // Reconstruct the AttributesList based on the vector we constructed. 705 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), 706 AttributesVec.end()); 707 708 // Create the new function type based on the recomputed parameters. 709 FunctionType *NFTy = FunctionType::get(NRetTy, Params, 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(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 // Push any varargs arguments on the list. Don't forget their attributes. 758 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 759 Args.push_back(*I); 760 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 761 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 762 } 763 764 if (FnAttrs != Attribute::None) 765 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 766 767 // Reconstruct the AttributesList based on the vector we constructed. 768 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 769 AttributesVec.end()); 770 771 Instruction *New; 772 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 773 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 774 Args.begin(), Args.end(), "", Call); 775 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 776 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 777 } else { 778 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 779 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 780 cast<CallInst>(New)->setAttributes(NewCallPAL); 781 if (cast<CallInst>(Call)->isTailCall()) 782 cast<CallInst>(New)->setTailCall(); 783 } 784 New->setDebugLoc(Call->getDebugLoc()); 785 786 Args.clear(); 787 788 if (!Call->use_empty()) { 789 if (New->getType() == Call->getType()) { 790 // Return type not changed? Just replace users then. 791 Call->replaceAllUsesWith(New); 792 New->takeName(Call); 793 } else if (New->getType()->isVoidTy()) { 794 // Our return value has uses, but they will get removed later on. 795 // Replace by null for now. 796 if (!Call->getType()->isX86_MMXTy()) 797 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 798 } else { 799 assert(RetTy->isStructTy() && 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 if (!I->getType()->isX86_MMXTy()) 861 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 862 } 863 864 // If we change the return value of the function we must rewrite any return 865 // instructions. Check this now. 866 if (F->getReturnType() != NF->getReturnType()) 867 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 868 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 869 Value *RetVal; 870 871 if (NFTy->getReturnType()->isVoidTy()) { 872 RetVal = 0; 873 } else { 874 assert (RetTy->isStructTy()); 875 // The original return value was a struct, insert 876 // extractvalue/insertvalue chains to extract only the values we need 877 // to return and insert them into our new result. 878 // This does generate messy code, but we'll let it to instcombine to 879 // clean that up. 880 Value *OldRet = RI->getOperand(0); 881 // Start out building up our return value from undef 882 RetVal = UndefValue::get(NRetTy); 883 for (unsigned i = 0; i != RetCount; ++i) 884 if (NewRetIdxs[i] != -1) { 885 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 886 "oldret", RI); 887 if (RetTypes.size() > 1) { 888 // We're still returning a struct, so reinsert the value into 889 // our new return value at the new index 890 891 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 892 "newret", RI); 893 } else { 894 // We are now only returning a simple value, so just return the 895 // extracted value. 896 RetVal = EV; 897 } 898 } 899 } 900 // Replace the return instruction with one returning the new return 901 // value (possibly 0 if we became void). 902 ReturnInst::Create(F->getContext(), RetVal, RI); 903 BB->getInstList().erase(RI); 904 } 905 906 // Now that the old function is dead, delete it. 907 F->eraseFromParent(); 908 909 return true; 910} 911 912bool DAE::runOnModule(Module &M) { 913 bool Changed = false; 914 915 // First pass: Do a simple check to see if any functions can have their "..." 916 // removed. We can do this if they never call va_start. This loop cannot be 917 // fused with the next loop, because deleting a function invalidates 918 // information computed while surveying other functions. 919 DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 920 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 921 Function &F = *I++; 922 if (F.getFunctionType()->isVarArg()) 923 Changed |= DeleteDeadVarargs(F); 924 } 925 926 // Second phase:loop through the module, determining which arguments are live. 927 // We assume all arguments are dead unless proven otherwise (allowing us to 928 // determine that dead arguments passed into recursive functions are dead). 929 // 930 DEBUG(dbgs() << "DAE - Determining liveness\n"); 931 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 932 SurveyFunction(*I); 933 934 // Now, remove all dead arguments and return values from each function in 935 // turn. 936 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 937 // Increment now, because the function will probably get removed (ie. 938 // replaced by a new one). 939 Function *F = I++; 940 Changed |= RemoveDeadStuffFromFunction(F); 941 } 942 return Changed; 943} 944