DeadArgumentElimination.cpp revision 4a325cbf6f2acb1034635bbcc7f3e5ea9829d012
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(void *ID) : ModulePass(ID) {} 126 127 public: 128 static char ID; // Pass identification, replacement for typeid 129 DAE() : ModulePass(&ID) {} 130 131 bool runOnModule(Module &M); 132 133 virtual bool ShouldHackArguments() const { return false; } 134 135 private: 136 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 137 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses, 138 unsigned RetValNum = 0); 139 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 140 141 void SurveyFunction(const Function &F); 142 void MarkValue(const RetOrArg &RA, Liveness L, 143 const UseVector &MaybeLiveUses); 144 void MarkLive(const RetOrArg &RA); 145 void MarkLive(const Function &F); 146 void PropagateLiveness(const RetOrArg &RA); 147 bool RemoveDeadStuffFromFunction(Function *F); 148 bool DeleteDeadVarargs(Function &Fn); 149 }; 150} 151 152 153char DAE::ID = 0; 154static RegisterPass<DAE> 155X("deadargelim", "Dead Argument Elimination"); 156 157namespace { 158 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 159 /// deletes arguments to functions which are external. This is only for use 160 /// by bugpoint. 161 struct DAH : public DAE { 162 static char ID; 163 DAH() : DAE(&ID) {} 164 165 virtual bool ShouldHackArguments() const { return true; } 166 }; 167} 168 169char DAH::ID = 0; 170static RegisterPass<DAH> 171Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 172 173/// createDeadArgEliminationPass - This pass removes arguments from functions 174/// which are not used by the body of the function. 175/// 176ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 177ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 178 179/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 180/// llvm.vastart is never called, the varargs list is dead for the function. 181bool DAE::DeleteDeadVarargs(Function &Fn) { 182 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 183 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 184 185 // Ensure that the function is only directly called. 186 if (Fn.hasAddressTaken()) 187 return false; 188 189 // Okay, we know we can transform this function if safe. Scan its body 190 // looking for calls to llvm.vastart. 191 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 192 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 193 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 194 if (II->getIntrinsicID() == Intrinsic::vastart) 195 return false; 196 } 197 } 198 } 199 200 // If we get here, there are no calls to llvm.vastart in the function body, 201 // remove the "..." and adjust all the calls. 202 203 // Start by computing a new prototype for the function, which is the same as 204 // the old function, but doesn't have isVarArg set. 205 const FunctionType *FTy = Fn.getFunctionType(); 206 207 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 208 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 209 Params, false); 210 unsigned NumArgs = Params.size(); 211 212 // Create the new function body and insert it into the module... 213 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 214 NF->copyAttributesFrom(&Fn); 215 Fn.getParent()->getFunctionList().insert(&Fn, NF); 216 NF->takeName(&Fn); 217 218 // Loop over all of the callers of the function, transforming the call sites 219 // to pass in a smaller number of arguments into the new function. 220 // 221 std::vector<Value*> Args; 222 while (!Fn.use_empty()) { 223 CallSite CS = CallSite::get(Fn.use_back()); 224 Instruction *Call = CS.getInstruction(); 225 226 // Pass all the same arguments. 227 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 228 229 // Drop any attributes that were on the vararg arguments. 230 AttrListPtr PAL = CS.getAttributes(); 231 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 232 SmallVector<AttributeWithIndex, 8> AttributesVec; 233 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 234 AttributesVec.push_back(PAL.getSlot(i)); 235 if (Attributes FnAttrs = PAL.getFnAttributes()) 236 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 237 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 238 } 239 240 Instruction *New; 241 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 242 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 243 Args.begin(), Args.end(), "", Call); 244 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 245 cast<InvokeInst>(New)->setAttributes(PAL); 246 } else { 247 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 248 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 249 cast<CallInst>(New)->setAttributes(PAL); 250 if (cast<CallInst>(Call)->isTailCall()) 251 cast<CallInst>(New)->setTailCall(); 252 } 253 if (MDNode *N = Call->getDbgMetadata()) 254 New->setDbgMetadata(N); 255 256 Args.clear(); 257 258 if (!Call->use_empty()) 259 Call->replaceAllUsesWith(New); 260 261 New->takeName(Call); 262 263 // Finally, remove the old call from the program, reducing the use-count of 264 // F. 265 Call->eraseFromParent(); 266 } 267 268 // Since we have now created the new function, splice the body of the old 269 // function right into the new function, leaving the old rotting hulk of the 270 // function empty. 271 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 272 273 // Loop over the argument list, transfering uses of the old arguments over to 274 // the new arguments, also transfering over the names as well. While we're at 275 // it, remove the dead arguments from the DeadArguments list. 276 // 277 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 278 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 279 // Move the name and users over to the new version. 280 I->replaceAllUsesWith(I2); 281 I2->takeName(I); 282 } 283 284 // Finally, nuke the old function. 285 Fn.eraseFromParent(); 286 return true; 287} 288 289/// Convenience function that returns the number of return values. It returns 0 290/// for void functions and 1 for functions not returning a struct. It returns 291/// the number of struct elements for functions returning a struct. 292static unsigned NumRetVals(const Function *F) { 293 if (F->getReturnType()->isVoidTy()) 294 return 0; 295 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 296 return STy->getNumElements(); 297 else 298 return 1; 299} 300 301/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 302/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 303/// liveness of Use. 304DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 305 // We're live if our use or its Function is already marked as live. 306 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 307 return Live; 308 309 // We're maybe live otherwise, but remember that we must become live if 310 // Use becomes live. 311 MaybeLiveUses.push_back(Use); 312 return MaybeLive; 313} 314 315 316/// SurveyUse - This looks at a single use of an argument or return value 317/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 318/// if it causes the used value to become MaybeLive. 319/// 320/// RetValNum is the return value number to use when this use is used in a 321/// return instruction. This is used in the recursion, you should always leave 322/// it at 0. 323DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U, 324 UseVector &MaybeLiveUses, unsigned RetValNum) { 325 const User *V = *U; 326 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 327 // The value is returned from a function. It's only live when the 328 // function's return value is live. We use RetValNum here, for the case 329 // that U is really a use of an insertvalue instruction that uses the 330 // orginal Use. 331 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 332 // We might be live, depending on the liveness of Use. 333 return MarkIfNotLive(Use, MaybeLiveUses); 334 } 335 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 336 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 337 && IV->hasIndices()) 338 // The use we are examining is inserted into an aggregate. Our liveness 339 // depends on all uses of that aggregate, but if it is used as a return 340 // value, only index at which we were inserted counts. 341 RetValNum = *IV->idx_begin(); 342 343 // Note that if we are used as the aggregate operand to the insertvalue, 344 // we don't change RetValNum, but do survey all our uses. 345 346 Liveness Result = MaybeLive; 347 for (Value::const_use_iterator I = IV->use_begin(), 348 E = V->use_end(); I != E; ++I) { 349 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 350 if (Result == Live) 351 break; 352 } 353 return Result; 354 } 355 356 if (ImmutableCallSite CS = V) { 357 const Function *F = CS.getCalledFunction(); 358 if (F) { 359 // Used in a direct call. 360 361 // Find the argument number. We know for sure that this use is an 362 // argument, since if it was the function argument this would be an 363 // indirect call and the we know can't be looking at a value of the 364 // label type (for the invoke instruction). 365 unsigned ArgNo = CS.getArgumentNo(U); 366 367 if (ArgNo >= F->getFunctionType()->getNumParams()) 368 // The value is passed in through a vararg! Must be live. 369 return Live; 370 371 assert(CS.getArgument(ArgNo) 372 == CS->getOperand(U.getOperandNo()) 373 && "Argument is not where we expected it"); 374 375 // Value passed to a normal call. It's only live when the corresponding 376 // argument to the called function turns out live. 377 RetOrArg Use = CreateArg(F, ArgNo); 378 return MarkIfNotLive(Use, MaybeLiveUses); 379 } 380 } 381 // Used in any other way? Value must be live. 382 return Live; 383} 384 385/// SurveyUses - This looks at all the uses of the given value 386/// Returns the Liveness deduced from the uses of this value. 387/// 388/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 389/// the result is Live, MaybeLiveUses might be modified but its content should 390/// be ignored (since it might not be complete). 391DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 392 // Assume it's dead (which will only hold if there are no uses at all..). 393 Liveness Result = MaybeLive; 394 // Check each use. 395 for (Value::const_use_iterator I = V->use_begin(), 396 E = V->use_end(); I != E; ++I) { 397 Result = SurveyUse(I, MaybeLiveUses); 398 if (Result == Live) 399 break; 400 } 401 return Result; 402} 403 404// SurveyFunction - This performs the initial survey of the specified function, 405// checking out whether or not it uses any of its incoming arguments or whether 406// any callers use the return value. This fills in the LiveValues set and Uses 407// map. 408// 409// We consider arguments of non-internal functions to be intrinsically alive as 410// well as arguments to functions which have their "address taken". 411// 412void DAE::SurveyFunction(const Function &F) { 413 unsigned RetCount = NumRetVals(&F); 414 // Assume all return values are dead 415 typedef SmallVector<Liveness, 5> RetVals; 416 RetVals RetValLiveness(RetCount, MaybeLive); 417 418 typedef SmallVector<UseVector, 5> RetUses; 419 // These vectors map each return value to the uses that make it MaybeLive, so 420 // we can add those to the Uses map if the return value really turns out to be 421 // MaybeLive. Initialized to a list of RetCount empty lists. 422 RetUses MaybeLiveRetUses(RetCount); 423 424 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 425 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 426 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 427 != F.getFunctionType()->getReturnType()) { 428 // We don't support old style multiple return values. 429 MarkLive(F); 430 return; 431 } 432 433 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 434 MarkLive(F); 435 return; 436 } 437 438 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 439 // Keep track of the number of live retvals, so we can skip checks once all 440 // of them turn out to be live. 441 unsigned NumLiveRetVals = 0; 442 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 443 // Loop all uses of the function. 444 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end(); 445 I != E; ++I) { 446 // If the function is PASSED IN as an argument, its address has been 447 // taken. 448 ImmutableCallSite CS(*I); 449 if (!CS || !CS.isCallee(I)) { 450 MarkLive(F); 451 return; 452 } 453 454 // If this use is anything other than a call site, the function is alive. 455 const Instruction *TheCall = CS.getInstruction(); 456 if (!TheCall) { // Not a direct call site? 457 MarkLive(F); 458 return; 459 } 460 461 // If we end up here, we are looking at a direct call to our function. 462 463 // Now, check how our return value(s) is/are used in this caller. Don't 464 // bother checking return values if all of them are live already. 465 if (NumLiveRetVals != RetCount) { 466 if (STy) { 467 // Check all uses of the return value. 468 for (Value::const_use_iterator I = TheCall->use_begin(), 469 E = TheCall->use_end(); I != E; ++I) { 470 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 471 if (Ext && Ext->hasIndices()) { 472 // This use uses a part of our return value, survey the uses of 473 // that part and store the results for this index only. 474 unsigned Idx = *Ext->idx_begin(); 475 if (RetValLiveness[Idx] != Live) { 476 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 477 if (RetValLiveness[Idx] == Live) 478 NumLiveRetVals++; 479 } 480 } else { 481 // Used by something else than extractvalue. Mark all return 482 // values as live. 483 for (unsigned i = 0; i != RetCount; ++i ) 484 RetValLiveness[i] = Live; 485 NumLiveRetVals = RetCount; 486 break; 487 } 488 } 489 } else { 490 // Single return value 491 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 492 if (RetValLiveness[0] == Live) 493 NumLiveRetVals = RetCount; 494 } 495 } 496 } 497 498 // Now we've inspected all callers, record the liveness of our return values. 499 for (unsigned i = 0; i != RetCount; ++i) 500 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 501 502 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 503 504 // Now, check all of our arguments. 505 unsigned i = 0; 506 UseVector MaybeLiveArgUses; 507 for (Function::const_arg_iterator AI = F.arg_begin(), 508 E = F.arg_end(); AI != E; ++AI, ++i) { 509 // See what the effect of this use is (recording any uses that cause 510 // MaybeLive in MaybeLiveArgUses). 511 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 512 // Mark the result. 513 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 514 // Clear the vector again for the next iteration. 515 MaybeLiveArgUses.clear(); 516 } 517} 518 519/// MarkValue - This function marks the liveness of RA depending on L. If L is 520/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 521/// such that RA will be marked live if any use in MaybeLiveUses gets marked 522/// live later on. 523void DAE::MarkValue(const RetOrArg &RA, Liveness L, 524 const UseVector &MaybeLiveUses) { 525 switch (L) { 526 case Live: MarkLive(RA); break; 527 case MaybeLive: 528 { 529 // Note any uses of this value, so this return value can be 530 // marked live whenever one of the uses becomes live. 531 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 532 UE = MaybeLiveUses.end(); UI != UE; ++UI) 533 Uses.insert(std::make_pair(*UI, RA)); 534 break; 535 } 536 } 537} 538 539/// MarkLive - Mark the given Function as alive, meaning that it cannot be 540/// changed in any way. Additionally, 541/// mark any values that are used as this function's parameters or by its return 542/// values (according to Uses) live as well. 543void DAE::MarkLive(const Function &F) { 544 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 545 // Mark the function as live. 546 LiveFunctions.insert(&F); 547 // Mark all arguments as live. 548 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 549 PropagateLiveness(CreateArg(&F, i)); 550 // Mark all return values as live. 551 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 552 PropagateLiveness(CreateRet(&F, i)); 553} 554 555/// MarkLive - Mark the given return value or argument as live. Additionally, 556/// mark any values that are used by this value (according to Uses) live as 557/// well. 558void DAE::MarkLive(const RetOrArg &RA) { 559 if (LiveFunctions.count(RA.F)) 560 return; // Function was already marked Live. 561 562 if (!LiveValues.insert(RA).second) 563 return; // We were already marked Live. 564 565 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 566 PropagateLiveness(RA); 567} 568 569/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 570/// to any other values it uses (according to Uses). 571void DAE::PropagateLiveness(const RetOrArg &RA) { 572 // We don't use upper_bound (or equal_range) here, because our recursive call 573 // to ourselves is likely to cause the upper_bound (which is the first value 574 // not belonging to RA) to become erased and the iterator invalidated. 575 UseMap::iterator Begin = Uses.lower_bound(RA); 576 UseMap::iterator E = Uses.end(); 577 UseMap::iterator I; 578 for (I = Begin; I != E && I->first == RA; ++I) 579 MarkLive(I->second); 580 581 // Erase RA from the Uses map (from the lower bound to wherever we ended up 582 // after the loop). 583 Uses.erase(Begin, I); 584} 585 586// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 587// that are not in LiveValues. Transform the function and all of the callees of 588// the function to not have these arguments and return values. 589// 590bool DAE::RemoveDeadStuffFromFunction(Function *F) { 591 // Don't modify fully live functions 592 if (LiveFunctions.count(F)) 593 return false; 594 595 // Start by computing a new prototype for the function, which is the same as 596 // the old function, but has fewer arguments and a different return type. 597 const FunctionType *FTy = F->getFunctionType(); 598 std::vector<const Type*> Params; 599 600 // Set up to build a new list of parameter attributes. 601 SmallVector<AttributeWithIndex, 8> AttributesVec; 602 const AttrListPtr &PAL = F->getAttributes(); 603 604 // The existing function return attributes. 605 Attributes RAttrs = PAL.getRetAttributes(); 606 Attributes FnAttrs = PAL.getFnAttributes(); 607 608 // Find out the new return value. 609 610 const Type *RetTy = FTy->getReturnType(); 611 const Type *NRetTy = NULL; 612 unsigned RetCount = NumRetVals(F); 613 614 // -1 means unused, other numbers are the new index 615 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 616 std::vector<const Type*> RetTypes; 617 if (RetTy->isVoidTy()) { 618 NRetTy = RetTy; 619 } else { 620 const StructType *STy = dyn_cast<StructType>(RetTy); 621 if (STy) 622 // Look at each of the original return values individually. 623 for (unsigned i = 0; i != RetCount; ++i) { 624 RetOrArg Ret = CreateRet(F, i); 625 if (LiveValues.erase(Ret)) { 626 RetTypes.push_back(STy->getElementType(i)); 627 NewRetIdxs[i] = RetTypes.size() - 1; 628 } else { 629 ++NumRetValsEliminated; 630 DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 631 << F->getName() << "\n"); 632 } 633 } 634 else 635 // We used to return a single value. 636 if (LiveValues.erase(CreateRet(F, 0))) { 637 RetTypes.push_back(RetTy); 638 NewRetIdxs[0] = 0; 639 } else { 640 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 641 << "\n"); 642 ++NumRetValsEliminated; 643 } 644 if (RetTypes.size() > 1) 645 // More than one return type? Return a struct with them. Also, if we used 646 // to return a struct and didn't change the number of return values, 647 // return a struct again. This prevents changing {something} into 648 // something and {} into void. 649 // Make the new struct packed if we used to return a packed struct 650 // already. 651 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 652 else if (RetTypes.size() == 1) 653 // One return type? Just a simple value then, but only if we didn't use to 654 // return a struct with that simple value before. 655 NRetTy = RetTypes.front(); 656 else if (RetTypes.size() == 0) 657 // No return types? Make it void, but only if we didn't use to return {}. 658 NRetTy = Type::getVoidTy(F->getContext()); 659 } 660 661 assert(NRetTy && "No new return type found?"); 662 663 // Remove any incompatible attributes, but only if we removed all return 664 // values. Otherwise, ensure that we don't have any conflicting attributes 665 // here. Currently, this should not be possible, but special handling might be 666 // required when new return value attributes are added. 667 if (NRetTy->isVoidTy()) 668 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 669 else 670 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 671 && "Return attributes no longer compatible?"); 672 673 if (RAttrs) 674 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 675 676 // Remember which arguments are still alive. 677 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 678 // Construct the new parameter list from non-dead arguments. Also construct 679 // a new set of parameter attributes to correspond. Skip the first parameter 680 // attribute, since that belongs to the return value. 681 unsigned i = 0; 682 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 683 I != E; ++I, ++i) { 684 RetOrArg Arg = CreateArg(F, i); 685 if (LiveValues.erase(Arg)) { 686 Params.push_back(I->getType()); 687 ArgAlive[i] = true; 688 689 // Get the original parameter attributes (skipping the first one, that is 690 // for the return value. 691 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 692 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 693 } else { 694 ++NumArgumentsEliminated; 695 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 696 << ") from " << F->getName() << "\n"); 697 } 698 } 699 700 if (FnAttrs != Attribute::None) 701 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 702 703 // Reconstruct the AttributesList based on the vector we constructed. 704 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), 705 AttributesVec.end()); 706 707 // Create the new function type based on the recomputed parameters. 708 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 709 710 // No change? 711 if (NFTy == FTy) 712 return false; 713 714 // Create the new function body and insert it into the module... 715 Function *NF = Function::Create(NFTy, F->getLinkage()); 716 NF->copyAttributesFrom(F); 717 NF->setAttributes(NewPAL); 718 // Insert the new function before the old function, so we won't be processing 719 // it again. 720 F->getParent()->getFunctionList().insert(F, NF); 721 NF->takeName(F); 722 723 // Loop over all of the callers of the function, transforming the call sites 724 // to pass in a smaller number of arguments into the new function. 725 // 726 std::vector<Value*> Args; 727 while (!F->use_empty()) { 728 CallSite CS = CallSite::get(F->use_back()); 729 Instruction *Call = CS.getInstruction(); 730 731 AttributesVec.clear(); 732 const AttrListPtr &CallPAL = CS.getAttributes(); 733 734 // The call return attributes. 735 Attributes RAttrs = CallPAL.getRetAttributes(); 736 Attributes FnAttrs = CallPAL.getFnAttributes(); 737 // Adjust in case the function was changed to return void. 738 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 739 if (RAttrs) 740 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 741 742 // Declare these outside of the loops, so we can reuse them for the second 743 // loop, which loops the varargs. 744 CallSite::arg_iterator I = CS.arg_begin(); 745 unsigned i = 0; 746 // Loop over those operands, corresponding to the normal arguments to the 747 // original function, and add those that are still alive. 748 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 749 if (ArgAlive[i]) { 750 Args.push_back(*I); 751 // Get original parameter attributes, but skip return attributes. 752 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 753 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 754 } 755 756 // Push any varargs arguments on the list. Don't forget their attributes. 757 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 758 Args.push_back(*I); 759 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 760 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 761 } 762 763 if (FnAttrs != Attribute::None) 764 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 765 766 // Reconstruct the AttributesList based on the vector we constructed. 767 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 768 AttributesVec.end()); 769 770 Instruction *New; 771 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 772 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 773 Args.begin(), Args.end(), "", Call); 774 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 775 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 776 } else { 777 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 778 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 779 cast<CallInst>(New)->setAttributes(NewCallPAL); 780 if (cast<CallInst>(Call)->isTailCall()) 781 cast<CallInst>(New)->setTailCall(); 782 } 783 if (MDNode *N = Call->getDbgMetadata()) 784 New->setDbgMetadata(N); 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 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 797 } else { 798 assert(RetTy->isStructTy() && 799 "Return type changed, but not into a void. The old return type" 800 " must have been a struct!"); 801 Instruction *InsertPt = Call; 802 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 803 BasicBlock::iterator IP = II->getNormalDest()->begin(); 804 while (isa<PHINode>(IP)) ++IP; 805 InsertPt = IP; 806 } 807 808 // We used to return a struct. Instead of doing smart stuff with all the 809 // uses of this struct, we will just rebuild it using 810 // extract/insertvalue chaining and let instcombine clean that up. 811 // 812 // Start out building up our return value from undef 813 Value *RetVal = UndefValue::get(RetTy); 814 for (unsigned i = 0; i != RetCount; ++i) 815 if (NewRetIdxs[i] != -1) { 816 Value *V; 817 if (RetTypes.size() > 1) 818 // We are still returning a struct, so extract the value from our 819 // return value 820 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 821 InsertPt); 822 else 823 // We are now returning a single element, so just insert that 824 V = New; 825 // Insert the value at the old position 826 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 827 } 828 // Now, replace all uses of the old call instruction with the return 829 // struct we built 830 Call->replaceAllUsesWith(RetVal); 831 New->takeName(Call); 832 } 833 } 834 835 // Finally, remove the old call from the program, reducing the use-count of 836 // F. 837 Call->eraseFromParent(); 838 } 839 840 // Since we have now created the new function, splice the body of the old 841 // function right into the new function, leaving the old rotting hulk of the 842 // function empty. 843 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 844 845 // Loop over the argument list, transfering uses of the old arguments over to 846 // the new arguments, also transfering over the names as well. 847 i = 0; 848 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 849 I2 = NF->arg_begin(); I != E; ++I, ++i) 850 if (ArgAlive[i]) { 851 // If this is a live argument, move the name and users over to the new 852 // version. 853 I->replaceAllUsesWith(I2); 854 I2->takeName(I); 855 ++I2; 856 } else { 857 // If this argument is dead, replace any uses of it with null constants 858 // (these are guaranteed to become unused later on). 859 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 860 } 861 862 // If we change the return value of the function we must rewrite any return 863 // instructions. Check this now. 864 if (F->getReturnType() != NF->getReturnType()) 865 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 866 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 867 Value *RetVal; 868 869 if (NFTy->getReturnType()->isVoidTy()) { 870 RetVal = 0; 871 } else { 872 assert (RetTy->isStructTy()); 873 // The original return value was a struct, insert 874 // extractvalue/insertvalue chains to extract only the values we need 875 // to return and insert them into our new result. 876 // This does generate messy code, but we'll let it to instcombine to 877 // clean that up. 878 Value *OldRet = RI->getOperand(0); 879 // Start out building up our return value from undef 880 RetVal = UndefValue::get(NRetTy); 881 for (unsigned i = 0; i != RetCount; ++i) 882 if (NewRetIdxs[i] != -1) { 883 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 884 "oldret", RI); 885 if (RetTypes.size() > 1) { 886 // We're still returning a struct, so reinsert the value into 887 // our new return value at the new index 888 889 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 890 "newret", RI); 891 } else { 892 // We are now only returning a simple value, so just return the 893 // extracted value. 894 RetVal = EV; 895 } 896 } 897 } 898 // Replace the return instruction with one returning the new return 899 // value (possibly 0 if we became void). 900 ReturnInst::Create(F->getContext(), RetVal, RI); 901 BB->getInstList().erase(RI); 902 } 903 904 // Now that the old function is dead, delete it. 905 F->eraseFromParent(); 906 907 return true; 908} 909 910bool DAE::runOnModule(Module &M) { 911 bool Changed = false; 912 913 // First pass: Do a simple check to see if any functions can have their "..." 914 // removed. We can do this if they never call va_start. This loop cannot be 915 // fused with the next loop, because deleting a function invalidates 916 // information computed while surveying other functions. 917 DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 918 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 919 Function &F = *I++; 920 if (F.getFunctionType()->isVarArg()) 921 Changed |= DeleteDeadVarargs(F); 922 } 923 924 // Second phase:loop through the module, determining which arguments are live. 925 // We assume all arguments are dead unless proven otherwise (allowing us to 926 // determine that dead arguments passed into recursive functions are dead). 927 // 928 DEBUG(dbgs() << "DAE - Determining liveness\n"); 929 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 930 SurveyFunction(*I); 931 932 // Now, remove all dead arguments and return values from each function in 933 // turn. 934 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 935 // Increment now, because the function will probably get removed (ie. 936 // replaced by a new one). 937 Function *F = I++; 938 Changed |= RemoveDeadStuffFromFunction(F); 939 } 940 return Changed; 941} 942