DeadArgumentElimination.cpp revision 30156524734c5a4ac49a1e8c607c375346770fa5
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() const { 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(const RetOrArg &RA); 136 void MarkLive(const Function &F); 137 void PropagateLiveness(const RetOrArg &RA); 138 bool RemoveDeadStuffFromFunction(Function *F); 139 bool DeleteDeadVarargs(Function &Fn); 140 }; 141} 142 143 144char DAE::ID = 0; 145static RegisterPass<DAE> 146X("deadargelim", "Dead Argument Elimination"); 147 148namespace { 149 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 150 /// deletes arguments to functions which are external. This is only for use 151 /// by bugpoint. 152 struct DAH : public DAE { 153 static char ID; 154 virtual bool ShouldHackArguments() const { return true; } 155 }; 156} 157 158char DAH::ID = 0; 159static RegisterPass<DAH> 160Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 161 162/// createDeadArgEliminationPass - This pass removes arguments from functions 163/// which are not used by the body of the function. 164/// 165ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 166ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 167 168/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 169/// llvm.vastart is never called, the varargs list is dead for the function. 170bool DAE::DeleteDeadVarargs(Function &Fn) { 171 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 172 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false; 173 174 // Ensure that the function is only directly called. 175 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) { 176 // If this use is anything other than a call site, give up. 177 CallSite CS = CallSite::get(*I); 178 Instruction *TheCall = CS.getInstruction(); 179 if (!TheCall) return false; // Not a direct call site? 180 181 // The addr of this function is passed to the call. 182 if (I.getOperandNo() != 0) return false; 183 } 184 185 // Okay, we know we can transform this function if safe. Scan its body 186 // looking for calls to llvm.vastart. 187 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 188 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 189 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 190 if (II->getIntrinsicID() == Intrinsic::vastart) 191 return false; 192 } 193 } 194 } 195 196 // If we get here, there are no calls to llvm.vastart in the function body, 197 // remove the "..." and adjust all the calls. 198 199 // Start by computing a new prototype for the function, which is the same as 200 // the old function, but doesn't have isVarArg set. 201 const FunctionType *FTy = Fn.getFunctionType(); 202 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 203 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false); 204 unsigned NumArgs = Params.size(); 205 206 // Create the new function body and insert it into the module... 207 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 208 NF->copyAttributesFrom(&Fn); 209 Fn.getParent()->getFunctionList().insert(&Fn, NF); 210 NF->takeName(&Fn); 211 212 // Loop over all of the callers of the function, transforming the call sites 213 // to pass in a smaller number of arguments into the new function. 214 // 215 std::vector<Value*> Args; 216 while (!Fn.use_empty()) { 217 CallSite CS = CallSite::get(Fn.use_back()); 218 Instruction *Call = CS.getInstruction(); 219 220 // Pass all the same arguments. 221 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 222 223 // Drop any attributes that were on the vararg arguments. 224 PAListPtr PAL = CS.getParamAttrs(); 225 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 226 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 227 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 228 ParamAttrsVec.push_back(PAL.getSlot(i)); 229 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 230 } 231 232 Instruction *New; 233 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 234 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 235 Args.begin(), Args.end(), "", Call); 236 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 237 cast<InvokeInst>(New)->setParamAttrs(PAL); 238 } else { 239 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 240 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 241 cast<CallInst>(New)->setParamAttrs(PAL); 242 if (cast<CallInst>(Call)->isTailCall()) 243 cast<CallInst>(New)->setTailCall(); 244 } 245 Args.clear(); 246 247 if (!Call->use_empty()) 248 Call->replaceAllUsesWith(New); 249 250 New->takeName(Call); 251 252 // Finally, remove the old call from the program, reducing the use-count of 253 // F. 254 Call->eraseFromParent(); 255 } 256 257 // Since we have now created the new function, splice the body of the old 258 // function right into the new function, leaving the old rotting hulk of the 259 // function empty. 260 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 261 262 // Loop over the argument list, transfering uses of the old arguments over to 263 // the new arguments, also transfering over the names as well. While we're at 264 // it, remove the dead arguments from the DeadArguments list. 265 // 266 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 267 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 268 // Move the name and users over to the new version. 269 I->replaceAllUsesWith(I2); 270 I2->takeName(I); 271 } 272 273 // Finally, nuke the old function. 274 Fn.eraseFromParent(); 275 return true; 276} 277 278/// Convenience function that returns the number of return values. It returns 0 279/// for void functions and 1 for functions not returning a struct. It returns 280/// the number of struct elements for functions returning a struct. 281static unsigned NumRetVals(const Function *F) { 282 if (F->getReturnType() == Type::VoidTy) 283 return 0; 284 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 285 return STy->getNumElements(); 286 else 287 return 1; 288} 289 290/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 291/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 292/// liveness of Use. 293DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 294 // We're live if our use is already marked as live. 295 if (LiveValues.count(Use)) 296 return Live; 297 298 // We're maybe live otherwise, but remember that we must become live if 299 // Use becomes live. 300 MaybeLiveUses.push_back(Use); 301 return MaybeLive; 302} 303 304 305/// SurveyUse - This looks at a single use of an argument or return value 306/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 307/// if it causes the used value to become MaybeAlive. 308/// 309/// RetValNum is the return value number to use when this use is used in a 310/// return instruction. This is used in the recursion, you should always leave 311/// it at 0. 312DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 313 unsigned RetValNum) { 314 Value *V = *U; 315 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 316 // The value is returned from a function. It's only live when the 317 // function's return value is live. We use RetValNum here, for the case 318 // that U is really a use of an insertvalue instruction that uses the 319 // orginal Use. 320 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 321 // We might be live, depending on the liveness of Use. 322 return MarkIfNotLive(Use, MaybeLiveUses); 323 } 324 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 325 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 326 && IV->hasIndices()) 327 // The use we are examining is inserted into an aggregate. Our liveness 328 // depends on all uses of that aggregate, but if it is used as a return 329 // value, only index at which we were inserted counts. 330 RetValNum = *IV->idx_begin(); 331 332 // Note that if we are used as the aggregate operand to the insertvalue, 333 // we don't change RetValNum, but do survey all our uses. 334 335 Liveness Result = MaybeLive; 336 for (Value::use_iterator I = IV->use_begin(), 337 E = V->use_end(); I != E; ++I) { 338 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 339 if (Result == Live) 340 break; 341 } 342 return Result; 343 } 344 CallSite CS = CallSite::get(V); 345 if (CS.getInstruction()) { 346 Function *F = CS.getCalledFunction(); 347 if (F) { 348 // Used in a direct call. 349 350 // Find the argument number. We know for sure that this use is an 351 // argument, since if it was the function argument this would be an 352 // indirect call and the we know can't be looking at a value of the 353 // label type (for the invoke instruction). 354 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 355 356 if (ArgNo >= F->getFunctionType()->getNumParams()) 357 // The value is passed in through a vararg! Must be live. 358 return Live; 359 360 assert(CS.getArgument(ArgNo) 361 == CS.getInstruction()->getOperand(U.getOperandNo()) 362 && "Argument is not where we expected it"); 363 364 // Value passed to a normal call. It's only live when the corresponding 365 // argument to the called function turns out live. 366 RetOrArg Use = CreateArg(F, ArgNo); 367 return MarkIfNotLive(Use, MaybeLiveUses); 368 } 369 } 370 // Used in any other way? Value must be live. 371 return Live; 372} 373 374/// SurveyUses - This looks at all the uses of the given value 375/// Returns the Liveness deduced from the uses of this value. 376/// 377/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 378/// the result is Live, MaybeLiveUses might be modified but its content should 379/// be ignored (since it might not be complete). 380DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 381 // Assume it's dead (which will only hold if there are no uses at all..). 382 Liveness Result = MaybeLive; 383 // Check each use. 384 for (Value::use_iterator I = V->use_begin(), 385 E = V->use_end(); I != E; ++I) { 386 Result = SurveyUse(I, MaybeLiveUses); 387 if (Result == Live) 388 break; 389 } 390 return Result; 391} 392 393// SurveyFunction - This performs the initial survey of the specified function, 394// checking out whether or not it uses any of its incoming arguments or whether 395// any callers use the return value. This fills in the LiveValues set and Uses 396// map. 397// 398// We consider arguments of non-internal functions to be intrinsically alive as 399// well as arguments to functions which have their "address taken". 400// 401void DAE::SurveyFunction(Function &F) { 402 unsigned RetCount = NumRetVals(&F); 403 // Assume all return values are dead 404 typedef SmallVector<Liveness, 5> RetVals; 405 RetVals RetValLiveness(RetCount, MaybeLive); 406 407 typedef SmallVector<UseVector, 5> RetUses; 408 // These vectors map each return value to the uses that make it MaybeLive, so 409 // we can add those to the Uses map if the return value really turns out to be 410 // MaybeLive. Initialized to a list of RetCount empty lists. 411 RetUses MaybeLiveRetUses(RetCount); 412 413 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 414 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 415 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 416 != F.getFunctionType()->getReturnType()) { 417 // We don't support old style multiple return values. 418 MarkLive(F); 419 return; 420 } 421 422 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 423 MarkLive(F); 424 return; 425 } 426 427 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 428 // Keep track of the number of live retvals, so we can skip checks once all 429 // of them turn out to be live. 430 unsigned NumLiveRetVals = 0; 431 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 432 // Loop all uses of the function. 433 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 434 // If the function is PASSED IN as an argument, its address has been 435 // taken. 436 if (I.getOperandNo() != 0) { 437 MarkLive(F); 438 return; 439 } 440 441 // If this use is anything other than a call site, the function is alive. 442 CallSite CS = CallSite::get(*I); 443 Instruction *TheCall = CS.getInstruction(); 444 if (!TheCall) { // Not a direct call site? 445 MarkLive(F); 446 return; 447 } 448 449 // If we end up here, we are looking at a direct call to our function. 450 451 // Now, check how our return value(s) is/are used in this caller. Don't 452 // bother checking return values if all of them are live already. 453 if (NumLiveRetVals != RetCount) { 454 if (STy) { 455 // Check all uses of the return value. 456 for (Value::use_iterator I = TheCall->use_begin(), 457 E = TheCall->use_end(); I != E; ++I) { 458 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 459 if (Ext && Ext->hasIndices()) { 460 // This use uses a part of our return value, survey the uses of 461 // that part and store the results for this index only. 462 unsigned Idx = *Ext->idx_begin(); 463 if (RetValLiveness[Idx] != Live) { 464 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 465 if (RetValLiveness[Idx] == Live) 466 NumLiveRetVals++; 467 } 468 } else { 469 // Used by something else than extractvalue. Mark all return 470 // values as live. 471 for (unsigned i = 0; i != RetCount; ++i ) 472 RetValLiveness[i] = Live; 473 NumLiveRetVals = RetCount; 474 break; 475 } 476 } 477 } else { 478 // Single return value 479 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 480 if (RetValLiveness[0] == Live) 481 NumLiveRetVals = RetCount; 482 } 483 } 484 } 485 486 // Now we've inspected all callers, record the liveness of our return values. 487 for (unsigned i = 0; i != RetCount; ++i) 488 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 489 490 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 491 492 // Now, check all of our arguments. 493 unsigned i = 0; 494 UseVector MaybeLiveArgUses; 495 for (Function::arg_iterator AI = F.arg_begin(), 496 E = F.arg_end(); AI != E; ++AI, ++i) { 497 // See what the effect of this use is (recording any uses that cause 498 // MaybeLive in MaybeLiveArgUses). 499 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 500 // Mark the result. 501 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 502 // Clear the vector again for the next iteration. 503 MaybeLiveArgUses.clear(); 504 } 505} 506 507/// MarkValue - This function marks the liveness of RA depending on L. If L is 508/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 509/// such that RA will be marked live if any use in MaybeLiveUses gets marked 510/// live later on. 511void DAE::MarkValue(const RetOrArg &RA, Liveness L, 512 const UseVector &MaybeLiveUses) { 513 switch (L) { 514 case Live: MarkLive(RA); break; 515 case MaybeLive: 516 { 517 // Note any uses of this value, so this return value can be 518 // marked live whenever one of the uses becomes live. 519 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 520 UE = MaybeLiveUses.end(); UI != UE; ++UI) 521 Uses.insert(std::make_pair(*UI, RA)); 522 break; 523 } 524 } 525} 526 527/// MarkLive - Mark the given Function as alive, meaning that it cannot be 528/// changed in any way. Additionally, 529/// mark any values that are used as this function's parameters or by its return 530/// values (according to Uses) live as well. 531void DAE::MarkLive(const Function &F) { 532 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 533 // Mark all arguments as live. 534 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 535 MarkLive(CreateArg(&F, i)); 536 // Mark all return values as live. 537 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 538 MarkLive(CreateRet(&F, i)); 539} 540 541/// MarkLive - Mark the given return value or argument as live. Additionally, 542/// mark any values that are used by this value (according to Uses) live as 543/// well. 544void DAE::MarkLive(const RetOrArg &RA) { 545 if (!LiveValues.insert(RA).second) 546 return; // We were already marked Live. 547 548 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 549 PropagateLiveness(RA); 550} 551 552/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 553/// to any other values it uses (according to Uses). 554void DAE::PropagateLiveness(const RetOrArg &RA) { 555 // We don't use upper_bound (or equal_range) here, because our recursive call 556 // to ourselves is likely to cause the upper_bound (which is the first value 557 // not belonging to RA) to become erased and the iterator invalidated. 558 UseMap::iterator Begin = Uses.lower_bound(RA); 559 UseMap::iterator E = Uses.end(); 560 UseMap::iterator I; 561 for (I = Begin; I != E && I->first == RA; ++I) 562 MarkLive(I->second); 563 564 // Erase RA from the Uses map (from the lower bound to wherever we ended up 565 // after the loop). 566 Uses.erase(Begin, I); 567} 568 569// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 570// that are not in LiveValues. Transform the function and all of the callees of 571// the function to not have these arguments and return values. 572// 573bool DAE::RemoveDeadStuffFromFunction(Function *F) { 574 // Quick exit path for external functions 575 if (!F->hasInternalLinkage() && (!ShouldHackArguments() || F->isIntrinsic())) 576 return false; 577 578 // Start by computing a new prototype for the function, which is the same as 579 // the old function, but has fewer arguments and a different return type. 580 const FunctionType *FTy = F->getFunctionType(); 581 std::vector<const Type*> Params; 582 583 // Set up to build a new list of parameter attributes. 584 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 585 const PAListPtr &PAL = F->getParamAttrs(); 586 587 // The existing function return attributes. 588 ParameterAttributes RAttrs = PAL.getParamAttrs(0); 589 590 591 // Find out the new return value. 592 593 const Type *RetTy = FTy->getReturnType(); 594 const Type *NRetTy = NULL; 595 unsigned RetCount = NumRetVals(F); 596 // Explicitly track if anything changed, for debugging. 597 bool Changed = false; 598 // -1 means unused, other numbers are the new index 599 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 600 std::vector<const Type*> RetTypes; 601 if (RetTy == Type::VoidTy) { 602 NRetTy = Type::VoidTy; 603 } else { 604 const StructType *STy = dyn_cast<StructType>(RetTy); 605 if (STy) 606 // Look at each of the original return values individually. 607 for (unsigned i = 0; i != RetCount; ++i) { 608 RetOrArg Ret = CreateRet(F, i); 609 if (LiveValues.erase(Ret)) { 610 RetTypes.push_back(STy->getElementType(i)); 611 NewRetIdxs[i] = RetTypes.size() - 1; 612 } else { 613 ++NumRetValsEliminated; 614 DOUT << "DAE - Removing return value " << i << " from " 615 << F->getNameStart() << "\n"; 616 Changed = true; 617 } 618 } 619 else 620 // We used to return a single value. 621 if (LiveValues.erase(CreateRet(F, 0))) { 622 RetTypes.push_back(RetTy); 623 NewRetIdxs[0] = 0; 624 } else { 625 DOUT << "DAE - Removing return value from " << F->getNameStart() 626 << "\n"; 627 ++NumRetValsEliminated; 628 Changed = true; 629 } 630 if (RetTypes.size() > 1 || (STy && STy->getNumElements()==RetTypes.size())) 631 // More than one return type? Return a struct with them. Also, if we used 632 // to return a struct and didn't change the number of return values, 633 // return a struct again. This prevents changing {something} into 634 // something and {} into void. 635 // Make the new struct packed if we used to return a packed struct 636 // already. 637 NRetTy = StructType::get(RetTypes, STy->isPacked()); 638 else if (RetTypes.size() == 1) 639 // One return type? Just a simple value then, but only if we didn't use to 640 // return a struct with that simple value before. 641 NRetTy = RetTypes.front(); 642 else if (RetTypes.size() == 0) 643 // No return types? Make it void, but only if we didn't use to return {}. 644 NRetTy = Type::VoidTy; 645 } 646 647 assert(NRetTy && "No new return type found?"); 648 649 // Remove any incompatible attributes, but only if we removed all return 650 // values. Otherwise, ensure that we don't have any conflicting attributes 651 // here. Currently, this should not be possible, but special handling might be 652 // required when new return value attributes are added. 653 if (NRetTy == Type::VoidTy) 654 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy); 655 else 656 assert((RAttrs & ParamAttr::typeIncompatible(NRetTy)) == 0 657 && "Return attributes no longer compatible?"); 658 659 if (RAttrs) 660 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 661 662 // Remember which arguments are still alive. 663 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 664 // Construct the new parameter list from non-dead arguments. Also construct 665 // a new set of parameter attributes to correspond. Skip the first parameter 666 // attribute, since that belongs to the return value. 667 unsigned i = 0; 668 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 669 I != E; ++I, ++i) { 670 RetOrArg Arg = CreateArg(F, i); 671 if (LiveValues.erase(Arg)) { 672 Params.push_back(I->getType()); 673 ArgAlive[i] = true; 674 675 // Get the original parameter attributes (skipping the first one, that is 676 // for the return value. 677 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1)) 678 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs)); 679 } else { 680 ++NumArgumentsEliminated; 681 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 682 << ") from " << F->getNameStart() << "\n"; 683 Changed = true; 684 } 685 } 686 687 // Reconstruct the ParamAttrsList based on the vector we constructed. 688 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 689 690 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 691 // have zero fixed arguments. 692 // 693 // Note that we apply this hack for a vararg fuction that does not have any 694 // arguments anymore, but did have them before (so don't bother fixing 695 // functions that were already broken wrt CWriter). 696 bool ExtraArgHack = false; 697 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 698 ExtraArgHack = true; 699 Params.push_back(Type::Int32Ty); 700 } 701 702 // Create the new function type based on the recomputed parameters. 703 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 704 705 // No change? 706 if (NFTy == FTy) 707 return false; 708 709 // The function type is only allowed to be different if we actually left out 710 // an argument or return value. 711 assert(Changed && "Function type changed while no arguments or return values" 712 "were removed!"); 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->setParamAttrs(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 ParamAttrsVec.clear(); 732 const PAListPtr &CallPAL = CS.getParamAttrs(); 733 734 // The call return attributes. 735 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0); 736 // Adjust in case the function was changed to return void. 737 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType()); 738 if (RAttrs) 739 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 740 741 // Declare these outside of the loops, so we can reuse them for the second 742 // loop, which loops the varargs. 743 CallSite::arg_iterator I = CS.arg_begin(); 744 unsigned i = 0; 745 // Loop over those operands, corresponding to the normal arguments to the 746 // original function, and add those that are still alive. 747 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 748 if (ArgAlive[i]) { 749 Args.push_back(*I); 750 // Get original parameter attributes, but skip return attributes. 751 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 752 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 753 } 754 755 if (ExtraArgHack) 756 Args.push_back(UndefValue::get(Type::Int32Ty)); 757 758 // Push any varargs arguments on the list. Don't forget their attributes. 759 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 760 Args.push_back(*I); 761 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 762 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 763 } 764 765 // Reconstruct the ParamAttrsList based on the vector we constructed. 766 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(), 767 ParamAttrsVec.end()); 768 769 Instruction *New; 770 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 771 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 772 Args.begin(), Args.end(), "", Call); 773 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 774 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL); 775 } else { 776 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 777 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 778 cast<CallInst>(New)->setParamAttrs(NewCallPAL); 779 if (cast<CallInst>(Call)->isTailCall()) 780 cast<CallInst>(New)->setTailCall(); 781 } 782 Args.clear(); 783 784 if (!Call->use_empty()) { 785 if (New->getType() == Call->getType()) { 786 // Return type not changed? Just replace users then. 787 Call->replaceAllUsesWith(New); 788 New->takeName(Call); 789 } else if (New->getType() == Type::VoidTy) { 790 // Our return value has uses, but they will get removed later on. 791 // Replace by null for now. 792 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 793 } else { 794 assert(isa<StructType>(RetTy) && "Return type changed, but not into a" 795 "void. The old return type must have" 796 "been a struct!"); 797 // The original return value was a struct, update all uses (which are 798 // all extractvalue instructions). 799 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end(); 800 I != E;) { 801 assert(isa<ExtractValueInst>(*I) && "Return value not only used by" 802 "extractvalue?"); 803 ExtractValueInst *EV = cast<ExtractValueInst>(*I); 804 // Increment now, since we're about to throw away this use. 805 ++I; 806 assert(EV->hasIndices() && "Return value used by extractvalue without" 807 "indices?"); 808 unsigned Idx = *EV->idx_begin(); 809 if (NewRetIdxs[Idx] != -1) { 810 if (RetTypes.size() > 1) { 811 // We're still returning a struct, create a new extractvalue 812 // instruction with the first index updated 813 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end()); 814 NewIdxs[0] = NewRetIdxs[Idx]; 815 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(), 816 NewIdxs.end(), "retval", 817 EV); 818 EV->replaceAllUsesWith(NEV); 819 EV->eraseFromParent(); 820 } else { 821 // We are now only returning a simple value, remove the 822 // extractvalue. 823 EV->replaceAllUsesWith(New); 824 EV->eraseFromParent(); 825 } 826 } else { 827 // Value unused, replace uses by null for now, they will get removed 828 // later on. 829 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType())); 830 EV->eraseFromParent(); 831 } 832 } 833 New->takeName(Call); 834 } 835 } 836 837 // Finally, remove the old call from the program, reducing the use-count of 838 // F. 839 Call->eraseFromParent(); 840 } 841 842 // Since we have now created the new function, splice the body of the old 843 // function right into the new function, leaving the old rotting hulk of the 844 // function empty. 845 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 846 847 // Loop over the argument list, transfering uses of the old arguments over to 848 // the new arguments, also transfering over the names as well. 849 i = 0; 850 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 851 I2 = NF->arg_begin(); I != E; ++I, ++i) 852 if (ArgAlive[i]) { 853 // If this is a live argument, move the name and users over to the new 854 // version. 855 I->replaceAllUsesWith(I2); 856 I2->takeName(I); 857 ++I2; 858 } else { 859 // If this argument is dead, replace any uses of it with null constants 860 // (these are guaranteed to become unused later on). 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() == Type::VoidTy) { 872 RetVal = 0; 873 } else { 874 assert (isa<StructType>(RetTy)); 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 = llvm::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(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 DOUT << "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 DOUT << "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