DeadArgumentElimination.cpp revision 14ce9ef2e9013ba56e1daafebd91fe3ee1e8647e
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/ADT/SmallVector.h" 33#include "llvm/ADT/Statistic.h" 34#include "llvm/ADT/StringExtras.h" 35#include "llvm/Support/Compiler.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 VISIBILITY_HIDDEN 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->getName(); 77 } 78 }; 79 80 /// Liveness enum - During our initial pass over the program, we determine 81 /// that things are either alive or maybe alive. We don't mark anything 82 /// explicitly dead (even if we know they are), since anything not alive 83 /// with no registered uses (in Uses) will never be marked alive and will 84 /// thus become dead in the end. 85 enum Liveness { Live, MaybeLive }; 86 87 /// Convenience wrapper 88 RetOrArg CreateRet(const Function *F, unsigned Idx) { 89 return RetOrArg(F, Idx, false); 90 } 91 /// Convenience wrapper 92 RetOrArg CreateArg(const Function *F, unsigned Idx) { 93 return RetOrArg(F, Idx, true); 94 } 95 96 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 97 /// This maps a return value or argument to any MaybeLive return values or 98 /// arguments it uses. This allows the MaybeLive values to be marked live 99 /// when any of its users is marked live. 100 /// For example (indices are left out for clarity): 101 /// - Uses[ret F] = ret G 102 /// This means that F calls G, and F returns the value returned by G. 103 /// - Uses[arg F] = ret G 104 /// This means that some function calls G and passes its result as an 105 /// argument to F. 106 /// - Uses[ret F] = arg F 107 /// This means that F returns one of its own arguments. 108 /// - Uses[arg F] = arg G 109 /// This means that G calls F and passes one of its own (G's) arguments 110 /// directly to F. 111 UseMap Uses; 112 113 typedef std::set<RetOrArg> LiveSet; 114 typedef std::set<const Function*> LiveFuncSet; 115 116 /// This set contains all values that have been determined to be live. 117 LiveSet LiveValues; 118 /// This set contains all values that are cannot be changed in any way. 119 LiveFuncSet LiveFunctions; 120 121 typedef SmallVector<RetOrArg, 5> UseVector; 122 123 public: 124 static char ID; // Pass identification, replacement for typeid 125 DAE() : ModulePass(&ID) {} 126 bool runOnModule(Module &M); 127 128 virtual bool ShouldHackArguments() const { return false; } 129 130 private: 131 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 132 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 133 unsigned RetValNum = 0); 134 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 135 136 void SurveyFunction(Function &F); 137 void MarkValue(const RetOrArg &RA, Liveness L, 138 const UseVector &MaybeLiveUses); 139 void MarkLive(const RetOrArg &RA); 140 void MarkLive(const Function &F); 141 void PropagateLiveness(const RetOrArg &RA); 142 bool RemoveDeadStuffFromFunction(Function *F); 143 bool DeleteDeadVarargs(Function &Fn); 144 }; 145} 146 147 148char DAE::ID = 0; 149static RegisterPass<DAE> 150X("deadargelim", "Dead Argument Elimination"); 151 152namespace { 153 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 154 /// deletes arguments to functions which are external. This is only for use 155 /// by bugpoint. 156 struct DAH : public DAE { 157 static char ID; 158 virtual bool ShouldHackArguments() const { return true; } 159 }; 160} 161 162char DAH::ID = 0; 163static RegisterPass<DAH> 164Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 165 166/// createDeadArgEliminationPass - This pass removes arguments from functions 167/// which are not used by the body of the function. 168/// 169ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 170ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 171 172/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 173/// llvm.vastart is never called, the varargs list is dead for the function. 174bool DAE::DeleteDeadVarargs(Function &Fn) { 175 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 176 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 177 178 // Ensure that the function is only directly called. 179 if (Fn.hasAddressTaken()) 180 return false; 181 182 // Okay, we know we can transform this function if safe. Scan its body 183 // looking for calls to llvm.vastart. 184 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 185 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 186 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 187 if (II->getIntrinsicID() == Intrinsic::vastart) 188 return false; 189 } 190 } 191 } 192 193 // If we get here, there are no calls to llvm.vastart in the function body, 194 // remove the "..." and adjust all the calls. 195 196 // Start by computing a new prototype for the function, which is the same as 197 // the old function, but doesn't have isVarArg set. 198 const FunctionType *FTy = Fn.getFunctionType(); 199 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 200 FunctionType *NFTy = Context->getFunctionType(FTy->getReturnType(), 201 Params, false); 202 unsigned NumArgs = Params.size(); 203 204 // Create the new function body and insert it into the module... 205 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 206 NF->copyAttributesFrom(&Fn); 207 Fn.getParent()->getFunctionList().insert(&Fn, NF); 208 NF->takeName(&Fn); 209 210 // Loop over all of the callers of the function, transforming the call sites 211 // to pass in a smaller number of arguments into the new function. 212 // 213 std::vector<Value*> Args; 214 while (!Fn.use_empty()) { 215 CallSite CS = CallSite::get(Fn.use_back()); 216 Instruction *Call = CS.getInstruction(); 217 218 // Pass all the same arguments. 219 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 220 221 // Drop any attributes that were on the vararg arguments. 222 AttrListPtr PAL = CS.getAttributes(); 223 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 224 SmallVector<AttributeWithIndex, 8> AttributesVec; 225 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 226 AttributesVec.push_back(PAL.getSlot(i)); 227 if (Attributes FnAttrs = PAL.getFnAttributes()) 228 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 229 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.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)->setAttributes(PAL); 238 } else { 239 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 240 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 241 cast<CallInst>(New)->setAttributes(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 or its Function is already marked as live. 295 if (LiveFunctions.count(Use.F) || 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.hasLocalLinkage() && (!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 CallSite CS = CallSite::get(*I); 437 if (!CS.getInstruction() || !CS.isCallee(I)) { 438 MarkLive(F); 439 return; 440 } 441 442 // If this use is anything other than a call site, the function is alive. 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 the function as live. 534 LiveFunctions.insert(&F); 535 // Mark all arguments as live. 536 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 537 PropagateLiveness(CreateArg(&F, i)); 538 // Mark all return values as live. 539 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 540 PropagateLiveness(CreateRet(&F, i)); 541} 542 543/// MarkLive - Mark the given return value or argument as live. Additionally, 544/// mark any values that are used by this value (according to Uses) live as 545/// well. 546void DAE::MarkLive(const RetOrArg &RA) { 547 if (LiveFunctions.count(RA.F)) 548 return; // Function was already marked Live. 549 550 if (!LiveValues.insert(RA).second) 551 return; // We were already marked Live. 552 553 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 554 PropagateLiveness(RA); 555} 556 557/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 558/// to any other values it uses (according to Uses). 559void DAE::PropagateLiveness(const RetOrArg &RA) { 560 // We don't use upper_bound (or equal_range) here, because our recursive call 561 // to ourselves is likely to cause the upper_bound (which is the first value 562 // not belonging to RA) to become erased and the iterator invalidated. 563 UseMap::iterator Begin = Uses.lower_bound(RA); 564 UseMap::iterator E = Uses.end(); 565 UseMap::iterator I; 566 for (I = Begin; I != E && I->first == RA; ++I) 567 MarkLive(I->second); 568 569 // Erase RA from the Uses map (from the lower bound to wherever we ended up 570 // after the loop). 571 Uses.erase(Begin, I); 572} 573 574// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 575// that are not in LiveValues. Transform the function and all of the callees of 576// the function to not have these arguments and return values. 577// 578bool DAE::RemoveDeadStuffFromFunction(Function *F) { 579 // Don't modify fully live functions 580 if (LiveFunctions.count(F)) 581 return false; 582 583 // Start by computing a new prototype for the function, which is the same as 584 // the old function, but has fewer arguments and a different return type. 585 const FunctionType *FTy = F->getFunctionType(); 586 std::vector<const Type*> Params; 587 588 // Set up to build a new list of parameter attributes. 589 SmallVector<AttributeWithIndex, 8> AttributesVec; 590 const AttrListPtr &PAL = F->getAttributes(); 591 592 // The existing function return attributes. 593 Attributes RAttrs = PAL.getRetAttributes(); 594 Attributes FnAttrs = PAL.getFnAttributes(); 595 596 // Find out the new return value. 597 598 const Type *RetTy = FTy->getReturnType(); 599 const Type *NRetTy = NULL; 600 unsigned RetCount = NumRetVals(F); 601 // -1 means unused, other numbers are the new index 602 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 603 std::vector<const Type*> RetTypes; 604 if (RetTy == Type::VoidTy) { 605 NRetTy = Type::VoidTy; 606 } else { 607 const StructType *STy = dyn_cast<StructType>(RetTy); 608 if (STy) 609 // Look at each of the original return values individually. 610 for (unsigned i = 0; i != RetCount; ++i) { 611 RetOrArg Ret = CreateRet(F, i); 612 if (LiveValues.erase(Ret)) { 613 RetTypes.push_back(STy->getElementType(i)); 614 NewRetIdxs[i] = RetTypes.size() - 1; 615 } else { 616 ++NumRetValsEliminated; 617 DOUT << "DAE - Removing return value " << i << " from " 618 << F->getNameStart() << "\n"; 619 } 620 } 621 else 622 // We used to return a single value. 623 if (LiveValues.erase(CreateRet(F, 0))) { 624 RetTypes.push_back(RetTy); 625 NewRetIdxs[0] = 0; 626 } else { 627 DOUT << "DAE - Removing return value from " << F->getNameStart() 628 << "\n"; 629 ++NumRetValsEliminated; 630 } 631 if (RetTypes.size() > 1) 632 // More than one return type? Return a struct with them. Also, if we used 633 // to return a struct and didn't change the number of return values, 634 // return a struct again. This prevents changing {something} into 635 // something and {} into void. 636 // Make the new struct packed if we used to return a packed struct 637 // already. 638 NRetTy = Context->getStructType(RetTypes, STy->isPacked()); 639 else if (RetTypes.size() == 1) 640 // One return type? Just a simple value then, but only if we didn't use to 641 // return a struct with that simple value before. 642 NRetTy = RetTypes.front(); 643 else if (RetTypes.size() == 0) 644 // No return types? Make it void, but only if we didn't use to return {}. 645 NRetTy = Type::VoidTy; 646 } 647 648 assert(NRetTy && "No new return type found?"); 649 650 // Remove any incompatible attributes, but only if we removed all return 651 // values. Otherwise, ensure that we don't have any conflicting attributes 652 // here. Currently, this should not be possible, but special handling might be 653 // required when new return value attributes are added. 654 if (NRetTy == Type::VoidTy) 655 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 656 else 657 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 658 && "Return attributes no longer compatible?"); 659 660 if (RAttrs) 661 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 662 663 // Remember which arguments are still alive. 664 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 665 // Construct the new parameter list from non-dead arguments. Also construct 666 // a new set of parameter attributes to correspond. Skip the first parameter 667 // attribute, since that belongs to the return value. 668 unsigned i = 0; 669 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 670 I != E; ++I, ++i) { 671 RetOrArg Arg = CreateArg(F, i); 672 if (LiveValues.erase(Arg)) { 673 Params.push_back(I->getType()); 674 ArgAlive[i] = true; 675 676 // Get the original parameter attributes (skipping the first one, that is 677 // for the return value. 678 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 679 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 680 } else { 681 ++NumArgumentsEliminated; 682 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 683 << ") from " << F->getNameStart() << "\n"; 684 } 685 } 686 687 if (FnAttrs != Attribute::None) 688 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 689 690 // Reconstruct the AttributesList based on the vector we constructed. 691 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 692 693 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 694 // have zero fixed arguments. 695 // 696 // Note that we apply this hack for a vararg fuction that does not have any 697 // arguments anymore, but did have them before (so don't bother fixing 698 // functions that were already broken wrt CWriter). 699 bool ExtraArgHack = false; 700 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 701 ExtraArgHack = true; 702 Params.push_back(Type::Int32Ty); 703 } 704 705 // Create the new function type based on the recomputed parameters. 706 FunctionType *NFTy = Context->getFunctionType(NRetTy, Params, 707 FTy->isVarArg()); 708 709 // No change? 710 if (NFTy == FTy) 711 return false; 712 713 // Create the new function body and insert it into the module... 714 Function *NF = Function::Create(NFTy, F->getLinkage()); 715 NF->copyAttributesFrom(F); 716 NF->setAttributes(NewPAL); 717 // Insert the new function before the old function, so we won't be processing 718 // it again. 719 F->getParent()->getFunctionList().insert(F, NF); 720 NF->takeName(F); 721 722 // Loop over all of the callers of the function, transforming the call sites 723 // to pass in a smaller number of arguments into the new function. 724 // 725 std::vector<Value*> Args; 726 while (!F->use_empty()) { 727 CallSite CS = CallSite::get(F->use_back()); 728 Instruction *Call = CS.getInstruction(); 729 730 AttributesVec.clear(); 731 const AttrListPtr &CallPAL = CS.getAttributes(); 732 733 // The call return attributes. 734 Attributes RAttrs = CallPAL.getRetAttributes(); 735 Attributes FnAttrs = CallPAL.getFnAttributes(); 736 // Adjust in case the function was changed to return void. 737 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 738 if (RAttrs) 739 AttributesVec.push_back(AttributeWithIndex::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 (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 752 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 753 } 754 755 if (ExtraArgHack) 756 Args.push_back(Context->getUndef(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 (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 762 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 763 } 764 765 if (FnAttrs != Attribute::None) 766 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 767 768 // Reconstruct the AttributesList based on the vector we constructed. 769 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 770 AttributesVec.end()); 771 772 Instruction *New; 773 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 774 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 775 Args.begin(), Args.end(), "", Call); 776 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 777 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 778 } else { 779 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 780 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 781 cast<CallInst>(New)->setAttributes(NewCallPAL); 782 if (cast<CallInst>(Call)->isTailCall()) 783 cast<CallInst>(New)->setTailCall(); 784 } 785 Args.clear(); 786 787 if (!Call->use_empty()) { 788 if (New->getType() == Call->getType()) { 789 // Return type not changed? Just replace users then. 790 Call->replaceAllUsesWith(New); 791 New->takeName(Call); 792 } else if (New->getType() == Type::VoidTy) { 793 // Our return value has uses, but they will get removed later on. 794 // Replace by null for now. 795 Call->replaceAllUsesWith(Context->getNullValue(Call->getType())); 796 } else { 797 assert(isa<StructType>(RetTy) && 798 "Return type changed, but not into a void. The old return type" 799 " must have been a struct!"); 800 Instruction *InsertPt = Call; 801 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 802 BasicBlock::iterator IP = II->getNormalDest()->begin(); 803 while (isa<PHINode>(IP)) ++IP; 804 InsertPt = IP; 805 } 806 807 // We used to return a struct. Instead of doing smart stuff with all the 808 // uses of this struct, we will just rebuild it using 809 // extract/insertvalue chaining and let instcombine clean that up. 810 // 811 // Start out building up our return value from undef 812 Value *RetVal = Context->getUndef(RetTy); 813 for (unsigned i = 0; i != RetCount; ++i) 814 if (NewRetIdxs[i] != -1) { 815 Value *V; 816 if (RetTypes.size() > 1) 817 // We are still returning a struct, so extract the value from our 818 // return value 819 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 820 InsertPt); 821 else 822 // We are now returning a single element, so just insert that 823 V = New; 824 // Insert the value at the old position 825 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 826 } 827 // Now, replace all uses of the old call instruction with the return 828 // struct we built 829 Call->replaceAllUsesWith(RetVal); 830 New->takeName(Call); 831 } 832 } 833 834 // Finally, remove the old call from the program, reducing the use-count of 835 // F. 836 Call->eraseFromParent(); 837 } 838 839 // Since we have now created the new function, splice the body of the old 840 // function right into the new function, leaving the old rotting hulk of the 841 // function empty. 842 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 843 844 // Loop over the argument list, transfering uses of the old arguments over to 845 // the new arguments, also transfering over the names as well. 846 i = 0; 847 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 848 I2 = NF->arg_begin(); I != E; ++I, ++i) 849 if (ArgAlive[i]) { 850 // If this is a live argument, move the name and users over to the new 851 // version. 852 I->replaceAllUsesWith(I2); 853 I2->takeName(I); 854 ++I2; 855 } else { 856 // If this argument is dead, replace any uses of it with null constants 857 // (these are guaranteed to become unused later on). 858 I->replaceAllUsesWith(Context->getNullValue(I->getType())); 859 } 860 861 // If we change the return value of the function we must rewrite any return 862 // instructions. Check this now. 863 if (F->getReturnType() != NF->getReturnType()) 864 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 865 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 866 Value *RetVal; 867 868 if (NFTy->getReturnType() == Type::VoidTy) { 869 RetVal = 0; 870 } else { 871 assert (isa<StructType>(RetTy)); 872 // The original return value was a struct, insert 873 // extractvalue/insertvalue chains to extract only the values we need 874 // to return and insert them into our new result. 875 // This does generate messy code, but we'll let it to instcombine to 876 // clean that up. 877 Value *OldRet = RI->getOperand(0); 878 // Start out building up our return value from undef 879 RetVal = Context->getUndef(NRetTy); 880 for (unsigned i = 0; i != RetCount; ++i) 881 if (NewRetIdxs[i] != -1) { 882 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 883 "oldret", RI); 884 if (RetTypes.size() > 1) { 885 // We're still returning a struct, so reinsert the value into 886 // our new return value at the new index 887 888 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 889 "newret", RI); 890 } else { 891 // We are now only returning a simple value, so just return the 892 // extracted value. 893 RetVal = EV; 894 } 895 } 896 } 897 // Replace the return instruction with one returning the new return 898 // value (possibly 0 if we became void). 899 ReturnInst::Create(RetVal, RI); 900 BB->getInstList().erase(RI); 901 } 902 903 // Now that the old function is dead, delete it. 904 F->eraseFromParent(); 905 906 return true; 907} 908 909bool DAE::runOnModule(Module &M) { 910 bool Changed = false; 911 912 // First pass: Do a simple check to see if any functions can have their "..." 913 // removed. We can do this if they never call va_start. This loop cannot be 914 // fused with the next loop, because deleting a function invalidates 915 // information computed while surveying other functions. 916 DOUT << "DAE - Deleting dead varargs\n"; 917 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 918 Function &F = *I++; 919 if (F.getFunctionType()->isVarArg()) 920 Changed |= DeleteDeadVarargs(F); 921 } 922 923 // Second phase:loop through the module, determining which arguments are live. 924 // We assume all arguments are dead unless proven otherwise (allowing us to 925 // determine that dead arguments passed into recursive functions are dead). 926 // 927 DOUT << "DAE - Determining liveness\n"; 928 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 929 SurveyFunction(*I); 930 931 // Now, remove all dead arguments and return values from each function in 932 // turn 933 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 934 // Increment now, because the function will probably get removed (ie 935 // replaced by a new one). 936 Function *F = I++; 937 Changed |= RemoveDeadStuffFromFunction(F); 938 } 939 return Changed; 940} 941