DeadArgumentElimination.cpp revision d7f2a6cb3fbc012763adb42fd967f6fefbb22a37
1//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass deletes dead arguments from internal functions. Dead argument 11// elimination removes arguments which are directly dead, as well as arguments 12// only passed into function calls as dead arguments of other functions. This 13// pass also deletes dead return values in a similar way. 14// 15// This pass is often useful as a cleanup pass to run after aggressive 16// interprocedural passes, which add possibly-dead arguments or return values. 17// 18//===----------------------------------------------------------------------===// 19 20#define DEBUG_TYPE "deadargelim" 21#include "llvm/Transforms/IPO.h" 22#include "llvm/CallingConv.h" 23#include "llvm/Constant.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/LLVMContext.h" 28#include "llvm/Module.h" 29#include "llvm/Pass.h" 30#include "llvm/Support/CallSite.h" 31#include "llvm/Support/Debug.h" 32#include "llvm/Support/raw_ostream.h" 33#include "llvm/ADT/SmallVector.h" 34#include "llvm/ADT/Statistic.h" 35#include "llvm/ADT/StringExtras.h" 36#include "llvm/Support/Compiler.h" 37#include <map> 38#include <set> 39using namespace llvm; 40 41STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 42STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 43 44namespace { 45 /// DAE - The dead argument elimination pass. 46 /// 47 class VISIBILITY_HIDDEN DAE : public ModulePass { 48 public: 49 50 /// Struct that represents (part of) either a return value or a function 51 /// argument. Used so that arguments and return values can be used 52 /// interchangably. 53 struct RetOrArg { 54 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 55 IsArg(IsArg) {} 56 const Function *F; 57 unsigned Idx; 58 bool IsArg; 59 60 /// Make RetOrArg comparable, so we can put it into a map. 61 bool operator<(const RetOrArg &O) const { 62 if (F != O.F) 63 return F < O.F; 64 else if (Idx != O.Idx) 65 return Idx < O.Idx; 66 else 67 return IsArg < O.IsArg; 68 } 69 70 /// Make RetOrArg comparable, so we can easily iterate the multimap. 71 bool operator==(const RetOrArg &O) const { 72 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 73 } 74 75 std::string getDescription() const { 76 return std::string((IsArg ? "Argument #" : "Return value #")) 77 + utostr(Idx) + " of function " + F->getNameStr(); 78 } 79 }; 80 81 /// Liveness enum - During our initial pass over the program, we determine 82 /// that things are either alive or maybe alive. We don't mark anything 83 /// explicitly dead (even if we know they are), since anything not alive 84 /// with no registered uses (in Uses) will never be marked alive and will 85 /// thus become dead in the end. 86 enum Liveness { Live, MaybeLive }; 87 88 /// Convenience wrapper 89 RetOrArg CreateRet(const Function *F, unsigned Idx) { 90 return RetOrArg(F, Idx, false); 91 } 92 /// Convenience wrapper 93 RetOrArg CreateArg(const Function *F, unsigned Idx) { 94 return RetOrArg(F, Idx, true); 95 } 96 97 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 98 /// This maps a return value or argument to any MaybeLive return values or 99 /// arguments it uses. This allows the MaybeLive values to be marked live 100 /// when any of its users is marked live. 101 /// For example (indices are left out for clarity): 102 /// - Uses[ret F] = ret G 103 /// This means that F calls G, and F returns the value returned by G. 104 /// - Uses[arg F] = ret G 105 /// This means that some function calls G and passes its result as an 106 /// argument to F. 107 /// - Uses[ret F] = arg F 108 /// This means that F returns one of its own arguments. 109 /// - Uses[arg F] = arg G 110 /// This means that G calls F and passes one of its own (G's) arguments 111 /// directly to F. 112 UseMap Uses; 113 114 typedef std::set<RetOrArg> LiveSet; 115 typedef std::set<const Function*> LiveFuncSet; 116 117 /// This set contains all values that have been determined to be live. 118 LiveSet LiveValues; 119 /// This set contains all values that are cannot be changed in any way. 120 LiveFuncSet LiveFunctions; 121 122 typedef SmallVector<RetOrArg, 5> UseVector; 123 124 public: 125 static char ID; // Pass identification, replacement for typeid 126 DAE() : ModulePass(&ID) {} 127 bool runOnModule(Module &M); 128 129 virtual bool ShouldHackArguments() const { return false; } 130 131 private: 132 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 133 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 134 unsigned RetValNum = 0); 135 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 136 137 void SurveyFunction(Function &F); 138 void MarkValue(const RetOrArg &RA, Liveness L, 139 const UseVector &MaybeLiveUses); 140 void MarkLive(const RetOrArg &RA); 141 void MarkLive(const Function &F); 142 void PropagateLiveness(const RetOrArg &RA); 143 bool RemoveDeadStuffFromFunction(Function *F); 144 bool DeleteDeadVarargs(Function &Fn); 145 }; 146} 147 148 149char DAE::ID = 0; 150static RegisterPass<DAE> 151X("deadargelim", "Dead Argument Elimination"); 152 153namespace { 154 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 155 /// deletes arguments to functions which are external. This is only for use 156 /// by bugpoint. 157 struct DAH : public DAE { 158 static char ID; 159 virtual bool ShouldHackArguments() const { return true; } 160 }; 161} 162 163char DAH::ID = 0; 164static RegisterPass<DAH> 165Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 166 167/// createDeadArgEliminationPass - This pass removes arguments from functions 168/// which are not used by the body of the function. 169/// 170ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 171ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 172 173/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 174/// llvm.vastart is never called, the varargs list is dead for the function. 175bool DAE::DeleteDeadVarargs(Function &Fn) { 176 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 177 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 178 179 // Ensure that the function is only directly called. 180 if (Fn.hasAddressTaken()) 181 return false; 182 183 // Okay, we know we can transform this function if safe. Scan its body 184 // looking for calls to llvm.vastart. 185 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 186 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 187 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 188 if (II->getIntrinsicID() == Intrinsic::vastart) 189 return false; 190 } 191 } 192 } 193 194 // If we get here, there are no calls to llvm.vastart in the function body, 195 // remove the "..." and adjust all the calls. 196 197 // Start by computing a new prototype for the function, which is the same as 198 // the old function, but doesn't have isVarArg set. 199 const FunctionType *FTy = Fn.getFunctionType(); 200 201 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 202 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 203 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 AttrListPtr PAL = CS.getAttributes(); 225 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 226 SmallVector<AttributeWithIndex, 8> AttributesVec; 227 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 228 AttributesVec.push_back(PAL.getSlot(i)); 229 if (Attributes FnAttrs = PAL.getFnAttributes()) 230 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 231 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 232 } 233 234 Instruction *New; 235 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 236 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 237 Args.begin(), Args.end(), "", Call); 238 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 239 cast<InvokeInst>(New)->setAttributes(PAL); 240 } else { 241 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 242 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 243 cast<CallInst>(New)->setAttributes(PAL); 244 if (cast<CallInst>(Call)->isTailCall()) 245 cast<CallInst>(New)->setTailCall(); 246 } 247 Args.clear(); 248 249 if (!Call->use_empty()) 250 Call->replaceAllUsesWith(New); 251 252 New->takeName(Call); 253 254 // Finally, remove the old call from the program, reducing the use-count of 255 // F. 256 Call->eraseFromParent(); 257 } 258 259 // Since we have now created the new function, splice the body of the old 260 // function right into the new function, leaving the old rotting hulk of the 261 // function empty. 262 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 263 264 // Loop over the argument list, transfering uses of the old arguments over to 265 // the new arguments, also transfering over the names as well. While we're at 266 // it, remove the dead arguments from the DeadArguments list. 267 // 268 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 269 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 270 // Move the name and users over to the new version. 271 I->replaceAllUsesWith(I2); 272 I2->takeName(I); 273 } 274 275 // Finally, nuke the old function. 276 Fn.eraseFromParent(); 277 return true; 278} 279 280/// Convenience function that returns the number of return values. It returns 0 281/// for void functions and 1 for functions not returning a struct. It returns 282/// the number of struct elements for functions returning a struct. 283static unsigned NumRetVals(const Function *F) { 284 if (F->getReturnType() == Type::VoidTy) 285 return 0; 286 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 287 return STy->getNumElements(); 288 else 289 return 1; 290} 291 292/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 293/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 294/// liveness of Use. 295DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 296 // We're live if our use or its Function is already marked as live. 297 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 298 return Live; 299 300 // We're maybe live otherwise, but remember that we must become live if 301 // Use becomes live. 302 MaybeLiveUses.push_back(Use); 303 return MaybeLive; 304} 305 306 307/// SurveyUse - This looks at a single use of an argument or return value 308/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 309/// if it causes the used value to become MaybeAlive. 310/// 311/// RetValNum is the return value number to use when this use is used in a 312/// return instruction. This is used in the recursion, you should always leave 313/// it at 0. 314DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 315 unsigned RetValNum) { 316 Value *V = *U; 317 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 318 // The value is returned from a function. It's only live when the 319 // function's return value is live. We use RetValNum here, for the case 320 // that U is really a use of an insertvalue instruction that uses the 321 // orginal Use. 322 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 323 // We might be live, depending on the liveness of Use. 324 return MarkIfNotLive(Use, MaybeLiveUses); 325 } 326 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 327 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 328 && IV->hasIndices()) 329 // The use we are examining is inserted into an aggregate. Our liveness 330 // depends on all uses of that aggregate, but if it is used as a return 331 // value, only index at which we were inserted counts. 332 RetValNum = *IV->idx_begin(); 333 334 // Note that if we are used as the aggregate operand to the insertvalue, 335 // we don't change RetValNum, but do survey all our uses. 336 337 Liveness Result = MaybeLive; 338 for (Value::use_iterator I = IV->use_begin(), 339 E = V->use_end(); I != E; ++I) { 340 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 341 if (Result == Live) 342 break; 343 } 344 return Result; 345 } 346 CallSite CS = CallSite::get(V); 347 if (CS.getInstruction()) { 348 Function *F = CS.getCalledFunction(); 349 if (F) { 350 // Used in a direct call. 351 352 // Find the argument number. We know for sure that this use is an 353 // argument, since if it was the function argument this would be an 354 // indirect call and the we know can't be looking at a value of the 355 // label type (for the invoke instruction). 356 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 357 358 if (ArgNo >= F->getFunctionType()->getNumParams()) 359 // The value is passed in through a vararg! Must be live. 360 return Live; 361 362 assert(CS.getArgument(ArgNo) 363 == CS.getInstruction()->getOperand(U.getOperandNo()) 364 && "Argument is not where we expected it"); 365 366 // Value passed to a normal call. It's only live when the corresponding 367 // argument to the called function turns out live. 368 RetOrArg Use = CreateArg(F, ArgNo); 369 return MarkIfNotLive(Use, MaybeLiveUses); 370 } 371 } 372 // Used in any other way? Value must be live. 373 return Live; 374} 375 376/// SurveyUses - This looks at all the uses of the given value 377/// Returns the Liveness deduced from the uses of this value. 378/// 379/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 380/// the result is Live, MaybeLiveUses might be modified but its content should 381/// be ignored (since it might not be complete). 382DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 383 // Assume it's dead (which will only hold if there are no uses at all..). 384 Liveness Result = MaybeLive; 385 // Check each use. 386 for (Value::use_iterator I = V->use_begin(), 387 E = V->use_end(); I != E; ++I) { 388 Result = SurveyUse(I, MaybeLiveUses); 389 if (Result == Live) 390 break; 391 } 392 return Result; 393} 394 395// SurveyFunction - This performs the initial survey of the specified function, 396// checking out whether or not it uses any of its incoming arguments or whether 397// any callers use the return value. This fills in the LiveValues set and Uses 398// map. 399// 400// We consider arguments of non-internal functions to be intrinsically alive as 401// well as arguments to functions which have their "address taken". 402// 403void DAE::SurveyFunction(Function &F) { 404 unsigned RetCount = NumRetVals(&F); 405 // Assume all return values are dead 406 typedef SmallVector<Liveness, 5> RetVals; 407 RetVals RetValLiveness(RetCount, MaybeLive); 408 409 typedef SmallVector<UseVector, 5> RetUses; 410 // These vectors map each return value to the uses that make it MaybeLive, so 411 // we can add those to the Uses map if the return value really turns out to be 412 // MaybeLive. Initialized to a list of RetCount empty lists. 413 RetUses MaybeLiveRetUses(RetCount); 414 415 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 416 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 417 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 418 != F.getFunctionType()->getReturnType()) { 419 // We don't support old style multiple return values. 420 MarkLive(F); 421 return; 422 } 423 424 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 425 MarkLive(F); 426 return; 427 } 428 429 DEBUG(errs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 430 // Keep track of the number of live retvals, so we can skip checks once all 431 // of them turn out to be live. 432 unsigned NumLiveRetVals = 0; 433 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 434 // Loop all uses of the function. 435 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 436 // If the function is PASSED IN as an argument, its address has been 437 // taken. 438 CallSite CS = CallSite::get(*I); 439 if (!CS.getInstruction() || !CS.isCallee(I)) { 440 MarkLive(F); 441 return; 442 } 443 444 // If this use is anything other than a call site, the function is alive. 445 Instruction *TheCall = CS.getInstruction(); 446 if (!TheCall) { // Not a direct call site? 447 MarkLive(F); 448 return; 449 } 450 451 // If we end up here, we are looking at a direct call to our function. 452 453 // Now, check how our return value(s) is/are used in this caller. Don't 454 // bother checking return values if all of them are live already. 455 if (NumLiveRetVals != RetCount) { 456 if (STy) { 457 // Check all uses of the return value. 458 for (Value::use_iterator I = TheCall->use_begin(), 459 E = TheCall->use_end(); I != E; ++I) { 460 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 461 if (Ext && Ext->hasIndices()) { 462 // This use uses a part of our return value, survey the uses of 463 // that part and store the results for this index only. 464 unsigned Idx = *Ext->idx_begin(); 465 if (RetValLiveness[Idx] != Live) { 466 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 467 if (RetValLiveness[Idx] == Live) 468 NumLiveRetVals++; 469 } 470 } else { 471 // Used by something else than extractvalue. Mark all return 472 // values as live. 473 for (unsigned i = 0; i != RetCount; ++i ) 474 RetValLiveness[i] = Live; 475 NumLiveRetVals = RetCount; 476 break; 477 } 478 } 479 } else { 480 // Single return value 481 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 482 if (RetValLiveness[0] == Live) 483 NumLiveRetVals = RetCount; 484 } 485 } 486 } 487 488 // Now we've inspected all callers, record the liveness of our return values. 489 for (unsigned i = 0; i != RetCount; ++i) 490 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 491 492 DEBUG(errs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 493 494 // Now, check all of our arguments. 495 unsigned i = 0; 496 UseVector MaybeLiveArgUses; 497 for (Function::arg_iterator AI = F.arg_begin(), 498 E = F.arg_end(); AI != E; ++AI, ++i) { 499 // See what the effect of this use is (recording any uses that cause 500 // MaybeLive in MaybeLiveArgUses). 501 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 502 // Mark the result. 503 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 504 // Clear the vector again for the next iteration. 505 MaybeLiveArgUses.clear(); 506 } 507} 508 509/// MarkValue - This function marks the liveness of RA depending on L. If L is 510/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 511/// such that RA will be marked live if any use in MaybeLiveUses gets marked 512/// live later on. 513void DAE::MarkValue(const RetOrArg &RA, Liveness L, 514 const UseVector &MaybeLiveUses) { 515 switch (L) { 516 case Live: MarkLive(RA); break; 517 case MaybeLive: 518 { 519 // Note any uses of this value, so this return value can be 520 // marked live whenever one of the uses becomes live. 521 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 522 UE = MaybeLiveUses.end(); UI != UE; ++UI) 523 Uses.insert(std::make_pair(*UI, RA)); 524 break; 525 } 526 } 527} 528 529/// MarkLive - Mark the given Function as alive, meaning that it cannot be 530/// changed in any way. Additionally, 531/// mark any values that are used as this function's parameters or by its return 532/// values (according to Uses) live as well. 533void DAE::MarkLive(const Function &F) { 534 DEBUG(errs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 535 // Mark the function as live. 536 LiveFunctions.insert(&F); 537 // Mark all arguments as live. 538 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 539 PropagateLiveness(CreateArg(&F, i)); 540 // Mark all return values as live. 541 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 542 PropagateLiveness(CreateRet(&F, i)); 543} 544 545/// MarkLive - Mark the given return value or argument as live. Additionally, 546/// mark any values that are used by this value (according to Uses) live as 547/// well. 548void DAE::MarkLive(const RetOrArg &RA) { 549 if (LiveFunctions.count(RA.F)) 550 return; // Function was already marked Live. 551 552 if (!LiveValues.insert(RA).second) 553 return; // We were already marked Live. 554 555 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 556 PropagateLiveness(RA); 557} 558 559/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 560/// to any other values it uses (according to Uses). 561void DAE::PropagateLiveness(const RetOrArg &RA) { 562 // We don't use upper_bound (or equal_range) here, because our recursive call 563 // to ourselves is likely to cause the upper_bound (which is the first value 564 // not belonging to RA) to become erased and the iterator invalidated. 565 UseMap::iterator Begin = Uses.lower_bound(RA); 566 UseMap::iterator E = Uses.end(); 567 UseMap::iterator I; 568 for (I = Begin; I != E && I->first == RA; ++I) 569 MarkLive(I->second); 570 571 // Erase RA from the Uses map (from the lower bound to wherever we ended up 572 // after the loop). 573 Uses.erase(Begin, I); 574} 575 576// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 577// that are not in LiveValues. Transform the function and all of the callees of 578// the function to not have these arguments and return values. 579// 580bool DAE::RemoveDeadStuffFromFunction(Function *F) { 581 // Don't modify fully live functions 582 if (LiveFunctions.count(F)) 583 return false; 584 585 // Start by computing a new prototype for the function, which is the same as 586 // the old function, but has fewer arguments and a different return type. 587 const FunctionType *FTy = F->getFunctionType(); 588 std::vector<const Type*> Params; 589 590 // Set up to build a new list of parameter attributes. 591 SmallVector<AttributeWithIndex, 8> AttributesVec; 592 const AttrListPtr &PAL = F->getAttributes(); 593 594 // The existing function return attributes. 595 Attributes RAttrs = PAL.getRetAttributes(); 596 Attributes FnAttrs = PAL.getFnAttributes(); 597 598 // Find out the new return value. 599 600 const Type *RetTy = FTy->getReturnType(); 601 const Type *NRetTy = NULL; 602 unsigned RetCount = NumRetVals(F); 603 604 // -1 means unused, other numbers are the new index 605 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 606 std::vector<const Type*> RetTypes; 607 if (RetTy == Type::VoidTy) { 608 NRetTy = Type::VoidTy; 609 } else { 610 const StructType *STy = dyn_cast<StructType>(RetTy); 611 if (STy) 612 // Look at each of the original return values individually. 613 for (unsigned i = 0; i != RetCount; ++i) { 614 RetOrArg Ret = CreateRet(F, i); 615 if (LiveValues.erase(Ret)) { 616 RetTypes.push_back(STy->getElementType(i)); 617 NewRetIdxs[i] = RetTypes.size() - 1; 618 } else { 619 ++NumRetValsEliminated; 620 DEBUG(errs() << "DAE - Removing return value " << i << " from " 621 << F->getName() << "\n"); 622 } 623 } 624 else 625 // We used to return a single value. 626 if (LiveValues.erase(CreateRet(F, 0))) { 627 RetTypes.push_back(RetTy); 628 NewRetIdxs[0] = 0; 629 } else { 630 DEBUG(errs() << "DAE - Removing return value from " << F->getName() 631 << "\n"); 632 ++NumRetValsEliminated; 633 } 634 if (RetTypes.size() > 1) 635 // More than one return type? Return a struct with them. Also, if we used 636 // to return a struct and didn't change the number of return values, 637 // return a struct again. This prevents changing {something} into 638 // something and {} into void. 639 // Make the new struct packed if we used to return a packed struct 640 // already. 641 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 642 else if (RetTypes.size() == 1) 643 // One return type? Just a simple value then, but only if we didn't use to 644 // return a struct with that simple value before. 645 NRetTy = RetTypes.front(); 646 else if (RetTypes.size() == 0) 647 // No return types? Make it void, but only if we didn't use to return {}. 648 NRetTy = Type::VoidTy; 649 } 650 651 assert(NRetTy && "No new return type found?"); 652 653 // Remove any incompatible attributes, but only if we removed all return 654 // values. Otherwise, ensure that we don't have any conflicting attributes 655 // here. Currently, this should not be possible, but special handling might be 656 // required when new return value attributes are added. 657 if (NRetTy == Type::VoidTy) 658 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 659 else 660 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 661 && "Return attributes no longer compatible?"); 662 663 if (RAttrs) 664 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 665 666 // Remember which arguments are still alive. 667 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 668 // Construct the new parameter list from non-dead arguments. Also construct 669 // a new set of parameter attributes to correspond. Skip the first parameter 670 // attribute, since that belongs to the return value. 671 unsigned i = 0; 672 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 673 I != E; ++I, ++i) { 674 RetOrArg Arg = CreateArg(F, i); 675 if (LiveValues.erase(Arg)) { 676 Params.push_back(I->getType()); 677 ArgAlive[i] = true; 678 679 // Get the original parameter attributes (skipping the first one, that is 680 // for the return value. 681 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 682 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 683 } else { 684 ++NumArgumentsEliminated; 685 DEBUG(errs() << "DAE - Removing argument " << i << " (" << I->getName() 686 << ") from " << F->getName() << "\n"); 687 } 688 } 689 690 if (FnAttrs != Attribute::None) 691 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 692 693 // Reconstruct the AttributesList based on the vector we constructed. 694 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 695 696 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 697 // have zero fixed arguments. 698 // 699 // Note that we apply this hack for a vararg fuction that does not have any 700 // arguments anymore, but did have them before (so don't bother fixing 701 // functions that were already broken wrt CWriter). 702 bool ExtraArgHack = false; 703 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 704 ExtraArgHack = true; 705 Params.push_back(Type::Int32Ty); 706 } 707 708 // Create the new function type based on the recomputed parameters. 709 FunctionType *NFTy = FunctionType::get(NRetTy, Params, 710 FTy->isVarArg()); 711 712 // No change? 713 if (NFTy == FTy) 714 return false; 715 716 // Create the new function body and insert it into the module... 717 Function *NF = Function::Create(NFTy, F->getLinkage()); 718 NF->copyAttributesFrom(F); 719 NF->setAttributes(NewPAL); 720 // Insert the new function before the old function, so we won't be processing 721 // it again. 722 F->getParent()->getFunctionList().insert(F, NF); 723 NF->takeName(F); 724 725 // Loop over all of the callers of the function, transforming the call sites 726 // to pass in a smaller number of arguments into the new function. 727 // 728 std::vector<Value*> Args; 729 while (!F->use_empty()) { 730 CallSite CS = CallSite::get(F->use_back()); 731 Instruction *Call = CS.getInstruction(); 732 733 AttributesVec.clear(); 734 const AttrListPtr &CallPAL = CS.getAttributes(); 735 736 // The call return attributes. 737 Attributes RAttrs = CallPAL.getRetAttributes(); 738 Attributes FnAttrs = CallPAL.getFnAttributes(); 739 // Adjust in case the function was changed to return void. 740 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 741 if (RAttrs) 742 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 743 744 // Declare these outside of the loops, so we can reuse them for the second 745 // loop, which loops the varargs. 746 CallSite::arg_iterator I = CS.arg_begin(); 747 unsigned i = 0; 748 // Loop over those operands, corresponding to the normal arguments to the 749 // original function, and add those that are still alive. 750 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 751 if (ArgAlive[i]) { 752 Args.push_back(*I); 753 // Get original parameter attributes, but skip return attributes. 754 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 755 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 756 } 757 758 if (ExtraArgHack) 759 Args.push_back(UndefValue::get(Type::Int32Ty)); 760 761 // Push any varargs arguments on the list. Don't forget their attributes. 762 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 763 Args.push_back(*I); 764 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 765 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 766 } 767 768 if (FnAttrs != Attribute::None) 769 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 770 771 // Reconstruct the AttributesList based on the vector we constructed. 772 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 773 AttributesVec.end()); 774 775 Instruction *New; 776 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 777 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 778 Args.begin(), Args.end(), "", Call); 779 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 780 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 781 } else { 782 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 783 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 784 cast<CallInst>(New)->setAttributes(NewCallPAL); 785 if (cast<CallInst>(Call)->isTailCall()) 786 cast<CallInst>(New)->setTailCall(); 787 } 788 Args.clear(); 789 790 if (!Call->use_empty()) { 791 if (New->getType() == Call->getType()) { 792 // Return type not changed? Just replace users then. 793 Call->replaceAllUsesWith(New); 794 New->takeName(Call); 795 } else if (New->getType() == Type::VoidTy) { 796 // Our return value has uses, but they will get removed later on. 797 // Replace by null for now. 798 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 799 } else { 800 assert(isa<StructType>(RetTy) && 801 "Return type changed, but not into a void. The old return type" 802 " must have been a struct!"); 803 Instruction *InsertPt = Call; 804 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 805 BasicBlock::iterator IP = II->getNormalDest()->begin(); 806 while (isa<PHINode>(IP)) ++IP; 807 InsertPt = IP; 808 } 809 810 // We used to return a struct. Instead of doing smart stuff with all the 811 // uses of this struct, we will just rebuild it using 812 // extract/insertvalue chaining and let instcombine clean that up. 813 // 814 // Start out building up our return value from undef 815 Value *RetVal = UndefValue::get(RetTy); 816 for (unsigned i = 0; i != RetCount; ++i) 817 if (NewRetIdxs[i] != -1) { 818 Value *V; 819 if (RetTypes.size() > 1) 820 // We are still returning a struct, so extract the value from our 821 // return value 822 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 823 InsertPt); 824 else 825 // We are now returning a single element, so just insert that 826 V = New; 827 // Insert the value at the old position 828 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 829 } 830 // Now, replace all uses of the old call instruction with the return 831 // struct we built 832 Call->replaceAllUsesWith(RetVal); 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 = 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