DeadArgumentElimination.cpp revision 24ca635521d9598de3a46872aab85ae759da8828
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/Module.h" 28#include "llvm/Pass.h" 29#include "llvm/Support/CallSite.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/ADT/SmallVector.h" 32#include "llvm/ADT/Statistic.h" 33#include "llvm/ADT/StringExtras.h" 34#include "llvm/Support/Compiler.h" 35#include <map> 36#include <set> 37using namespace llvm; 38 39STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 40STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 41 42namespace { 43 /// DAE - The dead argument elimination pass. 44 /// 45 class VISIBILITY_HIDDEN DAE : public ModulePass { 46 public: 47 48 /// Struct that represents (part of) either a return value or a function 49 /// argument. Used so that arguments and return values can be used 50 /// interchangably. 51 struct RetOrArg { 52 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 53 IsArg(IsArg) {} 54 const Function *F; 55 unsigned Idx; 56 bool IsArg; 57 58 /// Make RetOrArg comparable, so we can put it into a map. 59 bool operator<(const RetOrArg &O) const { 60 if (F != O.F) 61 return F < O.F; 62 else if (Idx != O.Idx) 63 return Idx < O.Idx; 64 else 65 return IsArg < O.IsArg; 66 } 67 68 /// Make RetOrArg comparable, so we can easily iterate the multimap. 69 bool operator==(const RetOrArg &O) const { 70 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 71 } 72 73 std::string getDescription() { 74 return std::string((IsArg ? "Argument #" : "Return value #")) 75 + utostr(Idx) + " of function " + F->getName(); 76 } 77 }; 78 79 /// Liveness enum - During our initial pass over the program, we determine 80 /// that things are either alive or maybe alive. We don't mark anything 81 /// explicitly dead (even if we know they are), since anything not alive 82 /// with no registered uses (in Uses) will never be marked alive and will 83 /// thus become dead in the end. 84 enum Liveness { Live, MaybeLive }; 85 86 /// Convenience wrapper 87 RetOrArg CreateRet(const Function *F, unsigned Idx) { 88 return RetOrArg(F, Idx, false); 89 } 90 /// Convenience wrapper 91 RetOrArg CreateArg(const Function *F, unsigned Idx) { 92 return RetOrArg(F, Idx, true); 93 } 94 95 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 96 /// This maps a return value or argument to any MaybeLive return values or 97 /// arguments it uses. This allows the MaybeLive values to be marked live 98 /// when any of its users is marked live. 99 /// For example (indices are left out for clarity): 100 /// - Uses[ret F] = ret G 101 /// This means that F calls G, and F returns the value returned by G. 102 /// - Uses[arg F] = ret G 103 /// This means that some function calls G and passes its result as an 104 /// argument to F. 105 /// - Uses[ret F] = arg F 106 /// This means that F returns one of its own arguments. 107 /// - Uses[arg F] = arg G 108 /// This means that G calls F and passes one of its own (G's) arguments 109 /// directly to F. 110 UseMap Uses; 111 112 typedef std::set<RetOrArg> LiveSet; 113 114 /// This set contains all values that have been determined to be live. 115 LiveSet LiveValues; 116 117 typedef SmallVector<RetOrArg, 5> UseVector; 118 119 public: 120 static char ID; // Pass identification, replacement for typeid 121 DAE() : ModulePass((intptr_t)&ID) {} 122 bool runOnModule(Module &M); 123 124 virtual bool ShouldHackArguments() const { return false; } 125 126 private: 127 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 128 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 129 unsigned RetValNum = 0); 130 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 131 132 void SurveyFunction(Function &F); 133 void MarkValue(const RetOrArg &RA, Liveness L, 134 const UseVector &MaybeLiveUses); 135 void MarkLive(RetOrArg RA); 136 void MarkLive(const Function &F); 137 bool RemoveDeadStuffFromFunction(Function *F); 138 bool DeleteDeadVarargs(Function &Fn); 139 }; 140} 141 142 143char DAE::ID = 0; 144static RegisterPass<DAE> 145X("deadargelim", "Dead Argument Elimination"); 146 147namespace { 148 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 149 /// deletes arguments to functions which are external. This is only for use 150 /// by bugpoint. 151 struct DAH : public DAE { 152 static char ID; 153 virtual bool ShouldHackArguments() const { return true; } 154 }; 155} 156 157char DAH::ID = 0; 158static RegisterPass<DAH> 159Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 160 161/// createDeadArgEliminationPass - This pass removes arguments from functions 162/// which are not used by the body of the function. 163/// 164ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 165ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 166 167/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 168/// llvm.vastart is never called, the varargs list is dead for the function. 169bool DAE::DeleteDeadVarargs(Function &Fn) { 170 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 171 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false; 172 173 // Ensure that the function is only directly called. 174 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) { 175 // If this use is anything other than a call site, give up. 176 CallSite CS = CallSite::get(*I); 177 Instruction *TheCall = CS.getInstruction(); 178 if (!TheCall) return false; // Not a direct call site? 179 180 // The addr of this function is passed to the call. 181 if (I.getOperandNo() != 0) return false; 182 } 183 184 // Okay, we know we can transform this function if safe. Scan its body 185 // looking for calls to llvm.vastart. 186 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 187 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 188 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 189 if (II->getIntrinsicID() == Intrinsic::vastart) 190 return false; 191 } 192 } 193 } 194 195 // If we get here, there are no calls to llvm.vastart in the function body, 196 // remove the "..." and adjust all the calls. 197 198 // Start by computing a new prototype for the function, which is the same as 199 // the old function, but doesn't have isVarArg set. 200 const FunctionType *FTy = Fn.getFunctionType(); 201 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 202 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 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 PAListPtr PAL = CS.getParamAttrs(); 224 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 225 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 226 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 227 ParamAttrsVec.push_back(PAL.getSlot(i)); 228 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 229 } 230 231 Instruction *New; 232 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 233 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 234 Args.begin(), Args.end(), "", Call); 235 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 236 cast<InvokeInst>(New)->setParamAttrs(PAL); 237 } else { 238 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 239 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 240 cast<CallInst>(New)->setParamAttrs(PAL); 241 if (cast<CallInst>(Call)->isTailCall()) 242 cast<CallInst>(New)->setTailCall(); 243 } 244 Args.clear(); 245 246 if (!Call->use_empty()) 247 Call->replaceAllUsesWith(New); 248 249 New->takeName(Call); 250 251 // Finally, remove the old call from the program, reducing the use-count of 252 // F. 253 Call->eraseFromParent(); 254 } 255 256 // Since we have now created the new function, splice the body of the old 257 // function right into the new function, leaving the old rotting hulk of the 258 // function empty. 259 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 260 261 // Loop over the argument list, transfering uses of the old arguments over to 262 // the new arguments, also transfering over the names as well. While we're at 263 // it, remove the dead arguments from the DeadArguments list. 264 // 265 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 266 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 267 // Move the name and users over to the new version. 268 I->replaceAllUsesWith(I2); 269 I2->takeName(I); 270 } 271 272 // Finally, nuke the old function. 273 Fn.eraseFromParent(); 274 return true; 275} 276 277/// Convenience function that returns the number of return values. It returns 0 278/// for void functions and 1 for functions not returning a struct. It returns 279/// the number of struct elements for functions returning a struct. 280static unsigned NumRetVals(const Function *F) { 281 if (F->getReturnType() == Type::VoidTy) 282 return 0; 283 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 284 return STy->getNumElements(); 285 else 286 return 1; 287} 288 289/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 290/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 291/// liveness of Use. 292DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 293 // We're live if our use is already marked as live. 294 if (LiveValues.count(Use)) 295 return Live; 296 297 // We're maybe live otherwise, but remember that we must become live if 298 // Use becomes live. 299 MaybeLiveUses.push_back(Use); 300 return MaybeLive; 301} 302 303 304/// SurveyUse - This looks at a single use of an argument or return value 305/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 306/// if it causes the used value to become MaybeAlive. 307/// 308/// RetValNum is the return value number to use when this use is used in a 309/// return instruction. This is used in the recursion, you should always leave 310/// it at 0. 311DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 312 unsigned RetValNum) { 313 Value *V = *U; 314 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 315 // The value is returned from a function. It's only live when the 316 // function's return value is live. We use RetValNum here, for the case 317 // that U is really a use of an insertvalue instruction that uses the 318 // orginal Use. 319 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 320 // We might be live, depending on the liveness of Use. 321 return MarkIfNotLive(Use, MaybeLiveUses); 322 } 323 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 324 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 325 && IV->hasIndices()) 326 // The use we are examining is inserted into an aggregate. Our liveness 327 // depends on all uses of that aggregate, but if it is used as a return 328 // value, only index at which we were inserted counts. 329 RetValNum = *IV->idx_begin(); 330 331 // Note that if we are used as the aggregate operand to the insertvalue, 332 // we don't change RetValNum, but do survey all our uses. 333 334 Liveness Result = MaybeLive; 335 for (Value::use_iterator I = IV->use_begin(), 336 E = V->use_end(); I != E; ++I) { 337 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 338 if (Result == Live) 339 break; 340 } 341 return Result; 342 } 343 CallSite CS = CallSite::get(V); 344 if (CS.getInstruction()) { 345 Function *F = CS.getCalledFunction(); 346 if (F) { 347 // Used in a direct call. 348 349 // Find the argument number. We know for sure that this use is an 350 // argument, since if it was the function argument this would be an 351 // indirect call and the we know can't be looking at a value of the 352 // label type (for the invoke instruction). 353 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 354 355 if (ArgNo >= F->getFunctionType()->getNumParams()) 356 // The value is passed in through a vararg! Must be live. 357 return Live; 358 359 assert(CS.getArgument(ArgNo) 360 == CS.getInstruction()->getOperand(U.getOperandNo()) 361 && "Argument is not where we expected it"); 362 363 // Value passed to a normal call. It's only live when the corresponding 364 // argument to the called function turns out live. 365 RetOrArg Use = CreateArg(F, ArgNo); 366 return MarkIfNotLive(Use, MaybeLiveUses); 367 } 368 } 369 // Used in any other way? Value must be live. 370 return Live; 371} 372 373/// SurveyUses - This looks at all the uses of the given value 374/// Returns the Liveness deduced from the uses of this value. 375/// 376/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 377/// the result is Live, MaybeLiveUses might be modified but its content should 378/// be ignored (since it might not be complete). 379DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 380 // Assume it's dead (which will only hold if there are no uses at all..). 381 Liveness Result = MaybeLive; 382 // Check each use. 383 for (Value::use_iterator I = V->use_begin(), 384 E = V->use_end(); I != E; ++I) { 385 Result = SurveyUse(I, MaybeLiveUses); 386 if (Result == Live) 387 break; 388 } 389 return Result; 390} 391 392// SurveyFunction - This performs the initial survey of the specified function, 393// checking out whether or not it uses any of its incoming arguments or whether 394// any callers use the return value. This fills in the LiveValues set and Uses 395// map. 396// 397// We consider arguments of non-internal functions to be intrinsically alive as 398// well as arguments to functions which have their "address taken". 399// 400void DAE::SurveyFunction(Function &F) { 401 unsigned RetCount = NumRetVals(&F); 402 // Assume all return values are dead 403 typedef SmallVector<Liveness, 5> RetVals; 404 RetVals RetValLiveness(RetCount, MaybeLive); 405 406 typedef SmallVector<UseVector, 5> RetUses; 407 // These vectors map each return value to the uses that make it MaybeLive, so 408 // we can add those to the Uses map if the return value really turns out to be 409 // MaybeLive. Initialized to a list of RetCount empty lists. 410 RetUses MaybeLiveRetUses(RetCount); 411 412 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 413 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 414 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 415 != F.getFunctionType()->getReturnType()) { 416 // We don't support old style multiple return values. 417 MarkLive(F); 418 return; 419 } 420 421 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 422 MarkLive(F); 423 return; 424 } 425 426 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 427 // Keep track of the number of live retvals, so we can skip checks once all 428 // of them turn out to be live. 429 unsigned NumLiveRetVals = 0; 430 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 431 // Loop all uses of the function. 432 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 433 // If the function is PASSED IN as an argument, its address has been 434 // taken. 435 if (I.getOperandNo() != 0) { 436 MarkLive(F); 437 return; 438 } 439 440 // If this use is anything other than a call site, the function is alive. 441 CallSite CS = CallSite::get(*I); 442 Instruction *TheCall = CS.getInstruction(); 443 if (!TheCall) { // Not a direct call site? 444 MarkLive(F); 445 return; 446 } 447 448 // If we end up here, we are looking at a direct call to our function. 449 450 // Now, check how our return value(s) is/are used in this caller. Don't 451 // bother checking return values if all of them are live already. 452 if (NumLiveRetVals != RetCount) { 453 if (STy) { 454 // Check all uses of the return value. 455 for (Value::use_iterator I = TheCall->use_begin(), 456 E = TheCall->use_end(); I != E; ++I) { 457 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 458 if (Ext && Ext->hasIndices()) { 459 // This use uses a part of our return value, survey the uses of 460 // that part and store the results for this index only. 461 unsigned Idx = *Ext->idx_begin(); 462 if (RetValLiveness[Idx] != Live) { 463 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 464 if (RetValLiveness[Idx] == Live) 465 NumLiveRetVals++; 466 } 467 } else { 468 // Used by something else than extractvalue. Mark all return 469 // values as live. 470 for (unsigned i = 0; i != RetCount; ++i ) 471 RetValLiveness[i] = Live; 472 NumLiveRetVals = RetCount; 473 break; 474 } 475 } 476 } else { 477 // Single return value 478 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 479 if (RetValLiveness[0] == Live) 480 NumLiveRetVals = RetCount; 481 } 482 } 483 } 484 485 // Now we've inspected all callers, record the liveness of our return values. 486 for (unsigned i = 0; i != RetCount; ++i) 487 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 488 489 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 490 491 // Now, check all of our arguments. 492 unsigned i = 0; 493 UseVector MaybeLiveArgUses; 494 for (Function::arg_iterator AI = F.arg_begin(), 495 E = F.arg_end(); AI != E; ++AI, ++i) { 496 // See what the effect of this use is (recording any uses that cause 497 // MaybeLive in MaybeLiveArgUses). 498 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 499 // Mark the result. 500 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 501 // Clear the vector again for the next iteration. 502 MaybeLiveArgUses.clear(); 503 } 504} 505 506/// MarkValue - This function marks the liveness of RA depending on L. If L is 507/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 508/// such that RA will be marked live if any use in MaybeLiveUses gets marked 509/// live later on. 510void DAE::MarkValue(const RetOrArg &RA, Liveness L, 511 const UseVector &MaybeLiveUses) { 512 switch (L) { 513 case Live: MarkLive(RA); break; 514 case MaybeLive: 515 { 516 // Note any uses of this value, so this return value can be 517 // marked live whenever one of the uses becomes live. 518 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 519 UE = MaybeLiveUses.end(); UI != UE; ++UI) 520 Uses.insert(std::make_pair(*UI, RA)); 521 break; 522 } 523 } 524} 525 526/// MarkLive - Mark the given Function as alive, meaning that it cannot be 527/// changed in any way. Additionally, 528/// mark any values that are used as this function's parameters or by its return 529/// values (according to Uses) live as well. 530void DAE::MarkLive(const Function &F) { 531 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 532 // Mark all arguments as live. 533 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 534 MarkLive(CreateArg(&F, i)); 535 // Mark all return values as live. 536 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 537 MarkLive(CreateRet(&F, i)); 538} 539 540/// MarkLive - Mark the given return value or argument as live. Additionally, 541/// mark any values that are used by this value (according to Uses) live as 542/// well. 543void DAE::MarkLive(RetOrArg RA) { 544 if (!LiveValues.insert(RA).second) 545 return; // We were already marked Live. 546 547 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 548 549 // We don't use upper_bound (or equal_range) here, because our recursive call 550 // to ourselves is likely to cause the upper_bound (which is the first value 551 // not belonging to RA) to become erased and the iterator invalidated. 552 UseMap::iterator Begin = Uses.lower_bound(RA); 553 UseMap::iterator E = Uses.end(); 554 UseMap::iterator I; 555 for (I = Begin; I != E && I->first == RA; ++I) 556 MarkLive(I->second); 557 558 // Erase RA from the Uses map (from the lower bound to wherever we ended up 559 // after the loop). 560 Uses.erase(Begin, I); 561} 562 563// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 564// that are not in LiveValues. Transform the function and all of the callees of 565// the function to not have these arguments and return values. 566// 567bool DAE::RemoveDeadStuffFromFunction(Function *F) { 568 // Quick exit path for external functions 569 if (!F->hasInternalLinkage() && (!ShouldHackArguments() || F->isIntrinsic())) 570 return false; 571 572 // Start by computing a new prototype for the function, which is the same as 573 // the old function, but has fewer arguments and a different return type. 574 const FunctionType *FTy = F->getFunctionType(); 575 std::vector<const Type*> Params; 576 577 // Set up to build a new list of parameter attributes. 578 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 579 const PAListPtr &PAL = F->getParamAttrs(); 580 581 // The existing function return attributes. 582 ParameterAttributes RAttrs = PAL.getParamAttrs(0); 583 584 585 // Find out the new return value. 586 587 const Type *RetTy = FTy->getReturnType(); 588 const Type *NRetTy = NULL; 589 unsigned RetCount = NumRetVals(F); 590 // Explicitly track if anything changed, for debugging. 591 bool Changed = false; 592 // -1 means unused, other numbers are the new index 593 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 594 std::vector<const Type*> RetTypes; 595 if (RetTy == Type::VoidTy) { 596 NRetTy = Type::VoidTy; 597 } else { 598 const StructType *STy = dyn_cast<StructType>(RetTy); 599 if (STy) 600 // Look at each of the original return values individually. 601 for (unsigned i = 0; i != RetCount; ++i) { 602 RetOrArg Ret = CreateRet(F, i); 603 if (LiveValues.erase(Ret)) { 604 RetTypes.push_back(STy->getElementType(i)); 605 NewRetIdxs[i] = RetTypes.size() - 1; 606 } else { 607 ++NumRetValsEliminated; 608 DOUT << "DAE - Removing return value " << i << " from " 609 << F->getNameStart() << "\n"; 610 Changed = true; 611 } 612 } 613 else 614 // We used to return a single value. 615 if (LiveValues.erase(CreateRet(F, 0))) { 616 RetTypes.push_back(RetTy); 617 NewRetIdxs[0] = 0; 618 } else { 619 DOUT << "DAE - Removing return value from " << F->getNameStart() 620 << "\n"; 621 ++NumRetValsEliminated; 622 Changed = true; 623 } 624 if (RetTypes.size() > 1 || (STy && STy->getNumElements()==RetTypes.size())) 625 // More than one return type? Return a struct with them. Also, if we used 626 // to return a struct and didn't change the number of return values, 627 // return a struct again. This prevents changing {something} into 628 // something and {} into void. 629 // Make the new struct packed if we used to return a packed struct 630 // already. 631 NRetTy = StructType::get(RetTypes, STy->isPacked()); 632 else if (RetTypes.size() == 1) 633 // One return type? Just a simple value then, but only if we didn't use to 634 // return a struct with that simple value before. 635 NRetTy = RetTypes.front(); 636 else if (RetTypes.size() == 0) 637 // No return types? Make it void, but only if we didn't use to return {}. 638 NRetTy = Type::VoidTy; 639 } 640 641 assert(NRetTy && "No new return type found?"); 642 643 // Remove any incompatible attributes, but only if we removed all return 644 // values. Otherwise, ensure that we don't have any conflicting attributes 645 // here. Currently, this should not be possible, but special handling might be 646 // required when new return value attributes are added. 647 if (NRetTy == Type::VoidTy) 648 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy); 649 else 650 assert((RAttrs & ParamAttr::typeIncompatible(NRetTy)) == 0 651 && "Return attributes no longer compatible?"); 652 653 if (RAttrs) 654 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 655 656 // Remember which arguments are still alive. 657 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 658 // Construct the new parameter list from non-dead arguments. Also construct 659 // a new set of parameter attributes to correspond. Skip the first parameter 660 // attribute, since that belongs to the return value. 661 unsigned i = 0; 662 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 663 I != E; ++I, ++i) { 664 RetOrArg Arg = CreateArg(F, i); 665 if (LiveValues.erase(Arg)) { 666 Params.push_back(I->getType()); 667 ArgAlive[i] = true; 668 669 // Get the original parameter attributes (skipping the first one, that is 670 // for the return value. 671 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1)) 672 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs)); 673 } else { 674 ++NumArgumentsEliminated; 675 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 676 << ") from " << F->getNameStart() << "\n"; 677 Changed = true; 678 } 679 } 680 681 // Reconstruct the ParamAttrsList based on the vector we constructed. 682 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 683 684 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 685 // have zero fixed arguments. 686 // 687 // Note that we apply this hack for a vararg fuction that does not have any 688 // arguments anymore, but did have them before (so don't bother fixing 689 // functions that were already broken wrt CWriter). 690 bool ExtraArgHack = false; 691 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 692 ExtraArgHack = true; 693 Params.push_back(Type::Int32Ty); 694 } 695 696 // Create the new function type based on the recomputed parameters. 697 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 698 699 // No change? 700 if (NFTy == FTy) 701 return false; 702 703 // The function type is only allowed to be different if we actually left out 704 // an argument or return value. 705 assert(Changed && "Function type changed while no arguments or return values" 706 "were removed!"); 707 708 // Create the new function body and insert it into the module... 709 Function *NF = Function::Create(NFTy, F->getLinkage()); 710 NF->copyAttributesFrom(F); 711 NF->setParamAttrs(NewPAL); 712 // Insert the new function before the old function, so we won't be processing 713 // it again. 714 F->getParent()->getFunctionList().insert(F, NF); 715 NF->takeName(F); 716 717 // Loop over all of the callers of the function, transforming the call sites 718 // to pass in a smaller number of arguments into the new function. 719 // 720 std::vector<Value*> Args; 721 while (!F->use_empty()) { 722 CallSite CS = CallSite::get(F->use_back()); 723 Instruction *Call = CS.getInstruction(); 724 725 ParamAttrsVec.clear(); 726 const PAListPtr &CallPAL = CS.getParamAttrs(); 727 728 // The call return attributes. 729 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0); 730 // Adjust in case the function was changed to return void. 731 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType()); 732 if (RAttrs) 733 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 734 735 // Declare these outside of the loops, so we can reuse them for the second 736 // loop, which loops the varargs. 737 CallSite::arg_iterator I = CS.arg_begin(); 738 unsigned i = 0; 739 // Loop over those operands, corresponding to the normal arguments to the 740 // original function, and add those that are still alive. 741 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 742 if (ArgAlive[i]) { 743 Args.push_back(*I); 744 // Get original parameter attributes, but skip return attributes. 745 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 746 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 747 } 748 749 if (ExtraArgHack) 750 Args.push_back(UndefValue::get(Type::Int32Ty)); 751 752 // Push any varargs arguments on the list. Don't forget their attributes. 753 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 754 Args.push_back(*I); 755 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 756 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 757 } 758 759 // Reconstruct the ParamAttrsList based on the vector we constructed. 760 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(), 761 ParamAttrsVec.end()); 762 763 Instruction *New; 764 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 765 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 766 Args.begin(), Args.end(), "", Call); 767 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 768 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL); 769 } else { 770 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 771 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 772 cast<CallInst>(New)->setParamAttrs(NewCallPAL); 773 if (cast<CallInst>(Call)->isTailCall()) 774 cast<CallInst>(New)->setTailCall(); 775 } 776 Args.clear(); 777 778 if (!Call->use_empty()) { 779 if (New->getType() == Call->getType()) { 780 // Return type not changed? Just replace users then. 781 Call->replaceAllUsesWith(New); 782 New->takeName(Call); 783 } else if (New->getType() == Type::VoidTy) { 784 // Our return value has uses, but they will get removed later on. 785 // Replace by null for now. 786 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 787 } else { 788 assert(isa<StructType>(RetTy) && "Return type changed, but not into a" 789 "void. The old return type must have" 790 "been a struct!"); 791 // The original return value was a struct, update all uses (which are 792 // all extractvalue instructions). 793 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end(); 794 I != E;) { 795 assert(isa<ExtractValueInst>(*I) && "Return value not only used by" 796 "extractvalue?"); 797 ExtractValueInst *EV = cast<ExtractValueInst>(*I); 798 // Increment now, since we're about to throw away this use. 799 ++I; 800 assert(EV->hasIndices() && "Return value used by extractvalue without" 801 "indices?"); 802 unsigned Idx = *EV->idx_begin(); 803 if (NewRetIdxs[Idx] != -1) { 804 if (RetTypes.size() > 1) { 805 // We're still returning a struct, create a new extractvalue 806 // instruction with the first index updated 807 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end()); 808 NewIdxs[0] = NewRetIdxs[Idx]; 809 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(), 810 NewIdxs.end(), "retval", 811 EV); 812 EV->replaceAllUsesWith(NEV); 813 EV->eraseFromParent(); 814 } else { 815 // We are now only returning a simple value, remove the 816 // extractvalue. 817 EV->replaceAllUsesWith(New); 818 EV->eraseFromParent(); 819 } 820 } else { 821 // Value unused, replace uses by null for now, they will get removed 822 // later on. 823 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType())); 824 EV->eraseFromParent(); 825 } 826 } 827 New->takeName(Call); 828 } 829 } 830 831 // Finally, remove the old call from the program, reducing the use-count of 832 // F. 833 Call->eraseFromParent(); 834 } 835 836 // Since we have now created the new function, splice the body of the old 837 // function right into the new function, leaving the old rotting hulk of the 838 // function empty. 839 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 840 841 // Loop over the argument list, transfering uses of the old arguments over to 842 // the new arguments, also transfering over the names as well. 843 i = 0; 844 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 845 I2 = NF->arg_begin(); I != E; ++I, ++i) 846 if (ArgAlive[i]) { 847 // If this is a live argument, move the name and users over to the new 848 // version. 849 I->replaceAllUsesWith(I2); 850 I2->takeName(I); 851 ++I2; 852 } else { 853 // If this argument is dead, replace any uses of it with null constants 854 // (these are guaranteed to become unused later on). 855 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 856 } 857 858 // If we change the return value of the function we must rewrite any return 859 // instructions. Check this now. 860 if (F->getReturnType() != NF->getReturnType()) 861 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 862 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 863 Value *RetVal; 864 865 if (NFTy->getReturnType() == Type::VoidTy) { 866 RetVal = 0; 867 } else { 868 assert (isa<StructType>(RetTy)); 869 // The original return value was a struct, insert 870 // extractvalue/insertvalue chains to extract only the values we need 871 // to return and insert them into our new result. 872 // This does generate messy code, but we'll let it to instcombine to 873 // clean that up. 874 Value *OldRet = RI->getOperand(0); 875 // Start out building up our return value from undef 876 RetVal = llvm::UndefValue::get(NRetTy); 877 for (unsigned i = 0; i != RetCount; ++i) 878 if (NewRetIdxs[i] != -1) { 879 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 880 "oldret", RI); 881 if (RetTypes.size() > 1) { 882 // We're still returning a struct, so reinsert the value into 883 // our new return value at the new index 884 885 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 886 "newret", RI); 887 } else { 888 // We are now only returning a simple value, so just return the 889 // extracted value. 890 RetVal = EV; 891 } 892 } 893 } 894 // Replace the return instruction with one returning the new return 895 // value (possibly 0 if we became void). 896 ReturnInst::Create(RetVal, RI); 897 BB->getInstList().erase(RI); 898 } 899 900 // Now that the old function is dead, delete it. 901 F->eraseFromParent(); 902 903 return true; 904} 905 906bool DAE::runOnModule(Module &M) { 907 bool Changed = false; 908 909 // First pass: Do a simple check to see if any functions can have their "..." 910 // removed. We can do this if they never call va_start. This loop cannot be 911 // fused with the next loop, because deleting a function invalidates 912 // information computed while surveying other functions. 913 DOUT << "DAE - Deleting dead varargs\n"; 914 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 915 Function &F = *I++; 916 if (F.getFunctionType()->isVarArg()) 917 Changed |= DeleteDeadVarargs(F); 918 } 919 920 // Second phase:loop through the module, determining which arguments are live. 921 // We assume all arguments are dead unless proven otherwise (allowing us to 922 // determine that dead arguments passed into recursive functions are dead). 923 // 924 DOUT << "DAE - Determining liveness\n"; 925 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 926 SurveyFunction(*I); 927 928 // Now, remove all dead arguments and return values from each function in 929 // turn 930 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 931 // Increment now, because the function will probably get removed (ie 932 // replaced by a new one). 933 Function *F = I++; 934 Changed |= RemoveDeadStuffFromFunction(F); 935 } 936 return Changed; 937} 938