DeadArgumentElimination.cpp revision dbeecede809c1bffb016e48674622c5e8cb75a0c
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/Transforms/Utils/Local.h" 34#include "llvm/ADT/SmallVector.h" 35#include "llvm/ADT/Statistic.h" 36#include "llvm/ADT/StringExtras.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 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 RemoveDeadParamsFromCallersOf(Function *F); 145 bool DeleteDeadVarargs(Function &Fn); 146 }; 147} 148 149 150char DAE::ID = 0; 151static RegisterPass<DAE> 152X("deadargelim", "Dead Argument Elimination"); 153 154namespace { 155 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 156 /// deletes arguments to functions which are external. This is only for use 157 /// by bugpoint. 158 struct DAH : public DAE { 159 static char ID; 160 virtual bool ShouldHackArguments() const { return true; } 161 }; 162} 163 164char DAH::ID = 0; 165static RegisterPass<DAH> 166Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 167 168/// createDeadArgEliminationPass - This pass removes arguments from functions 169/// which are not used by the body of the function. 170/// 171ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 172ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 173 174/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 175/// llvm.vastart is never called, the varargs list is dead for the function. 176bool DAE::DeleteDeadVarargs(Function &Fn) { 177 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 178 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 179 180 // Ensure that the function is only directly called. 181 if (Fn.hasAddressTaken()) 182 return false; 183 184 // Okay, we know we can transform this function if safe. Scan its body 185 // looking for calls to llvm.vastart. 186 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 187 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 188 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 189 if (II->getIntrinsicID() == Intrinsic::vastart) 190 return false; 191 } 192 } 193 } 194 195 // If we get here, there are no calls to llvm.vastart in the function body, 196 // remove the "..." and adjust all the calls. 197 198 // Start by computing a new prototype for the function, which is the same as 199 // the old function, but doesn't have isVarArg set. 200 const FunctionType *FTy = Fn.getFunctionType(); 201 202 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 203 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 204 Params, false); 205 unsigned NumArgs = Params.size(); 206 207 // Create the new function body and insert it into the module... 208 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 209 NF->copyAttributesFrom(&Fn); 210 Fn.getParent()->getFunctionList().insert(&Fn, NF); 211 NF->takeName(&Fn); 212 213 // Loop over all of the callers of the function, transforming the call sites 214 // to pass in a smaller number of arguments into the new function. 215 // 216 std::vector<Value*> Args; 217 while (!Fn.use_empty()) { 218 CallSite CS = CallSite::get(Fn.use_back()); 219 Instruction *Call = CS.getInstruction(); 220 221 // Pass all the same arguments. 222 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 223 224 // Drop any attributes that were on the vararg arguments. 225 AttrListPtr PAL = CS.getAttributes(); 226 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 227 SmallVector<AttributeWithIndex, 8> AttributesVec; 228 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 229 AttributesVec.push_back(PAL.getSlot(i)); 230 if (Attributes FnAttrs = PAL.getFnAttributes()) 231 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 232 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 233 } 234 235 Instruction *New; 236 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 237 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 238 Args.begin(), Args.end(), "", Call); 239 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 240 cast<InvokeInst>(New)->setAttributes(PAL); 241 } else { 242 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 243 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 244 cast<CallInst>(New)->setAttributes(PAL); 245 if (cast<CallInst>(Call)->isTailCall()) 246 cast<CallInst>(New)->setTailCall(); 247 } 248 Args.clear(); 249 250 if (!Call->use_empty()) 251 Call->replaceAllUsesWith(New); 252 253 New->takeName(Call); 254 255 // Finally, remove the old call from the program, reducing the use-count of 256 // F. 257 Call->eraseFromParent(); 258 } 259 260 // Since we have now created the new function, splice the body of the old 261 // function right into the new function, leaving the old rotting hulk of the 262 // function empty. 263 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 264 265 // Loop over the argument list, transfering uses of the old arguments over to 266 // the new arguments, also transfering over the names as well. While we're at 267 // it, remove the dead arguments from the DeadArguments list. 268 // 269 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 270 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 271 // Move the name and users over to the new version. 272 I->replaceAllUsesWith(I2); 273 I2->takeName(I); 274 } 275 276 // Finally, nuke the old function. 277 Fn.eraseFromParent(); 278 return true; 279} 280 281/// Convenience function that returns the number of return values. It returns 0 282/// for void functions and 1 for functions not returning a struct. It returns 283/// the number of struct elements for functions returning a struct. 284static unsigned NumRetVals(const Function *F) { 285 if (F->getReturnType()->isVoidTy()) 286 return 0; 287 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 288 return STy->getNumElements(); 289 else 290 return 1; 291} 292 293/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 294/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 295/// liveness of Use. 296DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 297 // We're live if our use or its Function is already marked as live. 298 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 299 return Live; 300 301 // We're maybe live otherwise, but remember that we must become live if 302 // Use becomes live. 303 MaybeLiveUses.push_back(Use); 304 return MaybeLive; 305} 306 307 308/// SurveyUse - This looks at a single use of an argument or return value 309/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 310/// if it causes the used value to become MaybeLive. 311/// 312/// RetValNum is the return value number to use when this use is used in a 313/// return instruction. This is used in the recursion, you should always leave 314/// it at 0. 315DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 316 unsigned RetValNum) { 317 Value *V = *U; 318 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 319 // The value is returned from a function. It's only live when the 320 // function's return value is live. We use RetValNum here, for the case 321 // that U is really a use of an insertvalue instruction that uses the 322 // orginal Use. 323 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 324 // We might be live, depending on the liveness of Use. 325 return MarkIfNotLive(Use, MaybeLiveUses); 326 } 327 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 328 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 329 && IV->hasIndices()) 330 // The use we are examining is inserted into an aggregate. Our liveness 331 // depends on all uses of that aggregate, but if it is used as a return 332 // value, only index at which we were inserted counts. 333 RetValNum = *IV->idx_begin(); 334 335 // Note that if we are used as the aggregate operand to the insertvalue, 336 // we don't change RetValNum, but do survey all our uses. 337 338 Liveness Result = MaybeLive; 339 for (Value::use_iterator I = IV->use_begin(), 340 E = V->use_end(); I != E; ++I) { 341 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 342 if (Result == Live) 343 break; 344 } 345 return Result; 346 } 347 CallSite CS = CallSite::get(V); 348 if (CS.getInstruction()) { 349 Function *F = CS.getCalledFunction(); 350 if (F) { 351 // Used in a direct call. 352 353 // Find the argument number. We know for sure that this use is an 354 // argument, since if it was the function argument this would be an 355 // indirect call and the we know can't be looking at a value of the 356 // label type (for the invoke instruction). 357 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 358 359 if (ArgNo >= F->getFunctionType()->getNumParams()) 360 // The value is passed in through a vararg! Must be live. 361 return Live; 362 363 assert(CS.getArgument(ArgNo) 364 == CS.getInstruction()->getOperand(U.getOperandNo()) 365 && "Argument is not where we expected it"); 366 367 // Value passed to a normal call. It's only live when the corresponding 368 // argument to the called function turns out live. 369 RetOrArg Use = CreateArg(F, ArgNo); 370 return MarkIfNotLive(Use, MaybeLiveUses); 371 } 372 } 373 // Used in any other way? Value must be live. 374 return Live; 375} 376 377/// SurveyUses - This looks at all the uses of the given value 378/// Returns the Liveness deduced from the uses of this value. 379/// 380/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 381/// the result is Live, MaybeLiveUses might be modified but its content should 382/// be ignored (since it might not be complete). 383DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 384 // Assume it's dead (which will only hold if there are no uses at all..). 385 Liveness Result = MaybeLive; 386 // Check each use. 387 for (Value::use_iterator I = V->use_begin(), 388 E = V->use_end(); I != E; ++I) { 389 Result = SurveyUse(I, MaybeLiveUses); 390 if (Result == Live) 391 break; 392 } 393 return Result; 394} 395 396// SurveyFunction - This performs the initial survey of the specified function, 397// checking out whether or not it uses any of its incoming arguments or whether 398// any callers use the return value. This fills in the LiveValues set and Uses 399// map. 400// 401// We consider arguments of overridable functions to be intrinsically alive as 402// well as arguments to functions which have their "address taken". 403// 404void DAE::SurveyFunction(Function &F) { 405 unsigned RetCount = NumRetVals(&F); 406 // Assume all return values are dead 407 typedef SmallVector<Liveness, 5> RetVals; 408 RetVals RetValLiveness(RetCount, MaybeLive); 409 410 typedef SmallVector<UseVector, 5> RetUses; 411 // These vectors map each return value to the uses that make it MaybeLive, so 412 // we can add those to the Uses map if the return value really turns out to be 413 // MaybeLive. Initialized to a list of RetCount empty lists. 414 RetUses MaybeLiveRetUses(RetCount); 415 416 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 417 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 418 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 419 != F.getFunctionType()->getReturnType()) { 420 // We don't support old style multiple return values. 421 MarkLive(F); 422 return; 423 } 424 425 if ((F.isDeclaration() || F.mayBeOverridden()) && 426 (!ShouldHackArguments() || F.isIntrinsic())) { 427 MarkLive(F); 428 return; 429 } else if (!F.hasLocalLinkage()) { 430 DEBUG(dbgs() << "DAE - Intrinsically live return from " << F.getName() 431 << "\n"); 432 // Mark the return values alive. 433 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 434 MarkLive(CreateRet(&F, i)); 435 } 436 437 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 438 // Keep track of the number of live retvals, so we can skip checks once all 439 // of them turn out to be live. 440 unsigned NumLiveRetVals = 0; 441 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 442 // Loop all uses of the function. 443 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 444 // If the function is PASSED IN as an argument, its address has been 445 // taken. 446 CallSite CS = CallSite::get(*I); 447 if (!CS.getInstruction() || !CS.isCallee(I)) { 448 MarkLive(F); 449 return; 450 } 451 452 // If this use is anything other than a call site, the function is alive. 453 Instruction *TheCall = CS.getInstruction(); 454 if (!TheCall) { // Not a direct call site? 455 MarkLive(F); 456 return; 457 } 458 459 // If we end up here, we are looking at a direct call to our function. 460 461 // Now, check how our return value(s) is/are used in this caller. Don't 462 // bother checking return values if all of them are live already. 463 if (NumLiveRetVals != RetCount) { 464 if (STy) { 465 // Check all uses of the return value. 466 for (Value::use_iterator I = TheCall->use_begin(), 467 E = TheCall->use_end(); I != E; ++I) { 468 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 469 if (Ext && Ext->hasIndices()) { 470 // This use uses a part of our return value, survey the uses of 471 // that part and store the results for this index only. 472 unsigned Idx = *Ext->idx_begin(); 473 if (RetValLiveness[Idx] != Live) { 474 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 475 if (RetValLiveness[Idx] == Live) 476 NumLiveRetVals++; 477 } 478 } else { 479 // Used by something else than extractvalue. Mark all return 480 // values as live. 481 for (unsigned i = 0; i != RetCount; ++i ) 482 RetValLiveness[i] = Live; 483 NumLiveRetVals = RetCount; 484 break; 485 } 486 } 487 } else { 488 // Single return value 489 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 490 if (RetValLiveness[0] == Live) 491 NumLiveRetVals = RetCount; 492 } 493 } 494 } 495 496 // Now we've inspected all callers, record the liveness of our return values. 497 for (unsigned i = 0; i != RetCount; ++i) 498 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 499 500 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 501 502 // Now, check all of our arguments. 503 unsigned i = 0; 504 UseVector MaybeLiveArgUses; 505 for (Function::arg_iterator AI = F.arg_begin(), 506 E = F.arg_end(); AI != E; ++AI, ++i) { 507 // See what the effect of this use is (recording any uses that cause 508 // MaybeLive in MaybeLiveArgUses). 509 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 510 // Mark the result. 511 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 512 // Clear the vector again for the next iteration. 513 MaybeLiveArgUses.clear(); 514 } 515} 516 517/// MarkValue - This function marks the liveness of RA depending on L. If L is 518/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 519/// such that RA will be marked live if any use in MaybeLiveUses gets marked 520/// live later on. 521void DAE::MarkValue(const RetOrArg &RA, Liveness L, 522 const UseVector &MaybeLiveUses) { 523 switch (L) { 524 case Live: MarkLive(RA); break; 525 case MaybeLive: 526 { 527 // Note any uses of this value, so this return value can be 528 // marked live whenever one of the uses becomes live. 529 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 530 UE = MaybeLiveUses.end(); UI != UE; ++UI) 531 Uses.insert(std::make_pair(*UI, RA)); 532 break; 533 } 534 } 535} 536 537/// MarkLive - Mark the given Function as alive, meaning that it cannot be 538/// changed in any way. Additionally, 539/// mark any values that are used as this function's parameters or by its return 540/// values (according to Uses) live as well. 541void DAE::MarkLive(const Function &F) { 542 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 543 // Mark the function as live. 544 LiveFunctions.insert(&F); 545 // Mark all arguments as live. 546 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 547 PropagateLiveness(CreateArg(&F, i)); 548 // Mark all return values as live. 549 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 550 PropagateLiveness(CreateRet(&F, i)); 551} 552 553/// MarkLive - Mark the given return value or argument as live. Additionally, 554/// mark any values that are used by this value (according to Uses) live as 555/// well. 556void DAE::MarkLive(const RetOrArg &RA) { 557 if (LiveFunctions.count(RA.F)) 558 return; // Function was already marked Live. 559 560 if (!LiveValues.insert(RA).second) 561 return; // We were already marked Live. 562 563 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 564 PropagateLiveness(RA); 565} 566 567/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 568/// to any other values it uses (according to Uses). 569void DAE::PropagateLiveness(const RetOrArg &RA) { 570 // We don't use upper_bound (or equal_range) here, because our recursive call 571 // to ourselves is likely to cause the upper_bound (which is the first value 572 // not belonging to RA) to become erased and the iterator invalidated. 573 UseMap::iterator Begin = Uses.lower_bound(RA); 574 UseMap::iterator E = Uses.end(); 575 UseMap::iterator I; 576 for (I = Begin; I != E && I->first == RA; ++I) 577 MarkLive(I->second); 578 579 // Erase RA from the Uses map (from the lower bound to wherever we ended up 580 // after the loop). 581 Uses.erase(Begin, I); 582} 583 584// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 585// that are not in LiveValues. Transform the function and all of the callees of 586// the function to not have these arguments and return values. 587// 588bool DAE::RemoveDeadStuffFromFunction(Function *F) { 589 // Don't modify fully live functions 590 if (LiveFunctions.count(F)) 591 return false; 592 593 // Start by computing a new prototype for the function, which is the same as 594 // the old function, but has fewer arguments and a different return type. 595 const FunctionType *FTy = F->getFunctionType(); 596 std::vector<const Type*> Params; 597 598 // Set up to build a new list of parameter attributes. 599 SmallVector<AttributeWithIndex, 8> AttributesVec; 600 const AttrListPtr &PAL = F->getAttributes(); 601 602 // The existing function return attributes. 603 Attributes RAttrs = PAL.getRetAttributes(); 604 Attributes FnAttrs = PAL.getFnAttributes(); 605 606 // Find out the new return value. 607 608 const Type *RetTy = FTy->getReturnType(); 609 const Type *NRetTy = NULL; 610 unsigned RetCount = NumRetVals(F); 611 612 // -1 means unused, other numbers are the new index 613 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 614 std::vector<const Type*> RetTypes; 615 if (RetTy->isVoidTy()) { 616 NRetTy = RetTy; 617 } else { 618 const StructType *STy = dyn_cast<StructType>(RetTy); 619 if (STy) 620 // Look at each of the original return values individually. 621 for (unsigned i = 0; i != RetCount; ++i) { 622 RetOrArg Ret = CreateRet(F, i); 623 if (LiveValues.erase(Ret)) { 624 RetTypes.push_back(STy->getElementType(i)); 625 NewRetIdxs[i] = RetTypes.size() - 1; 626 } else { 627 ++NumRetValsEliminated; 628 DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 629 << F->getName() << "\n"); 630 } 631 } 632 else 633 // We used to return a single value. 634 if (LiveValues.erase(CreateRet(F, 0))) { 635 RetTypes.push_back(RetTy); 636 NewRetIdxs[0] = 0; 637 } else { 638 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 639 << "\n"); 640 ++NumRetValsEliminated; 641 } 642 if (RetTypes.size() > 1) 643 // More than one return type? Return a struct with them. Also, if we used 644 // to return a struct and didn't change the number of return values, 645 // return a struct again. This prevents changing {something} into 646 // something and {} into void. 647 // Make the new struct packed if we used to return a packed struct 648 // already. 649 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 650 else if (RetTypes.size() == 1) 651 // One return type? Just a simple value then, but only if we didn't use to 652 // return a struct with that simple value before. 653 NRetTy = RetTypes.front(); 654 else if (RetTypes.size() == 0) 655 // No return types? Make it void, but only if we didn't use to return {}. 656 NRetTy = Type::getVoidTy(F->getContext()); 657 } 658 659 assert(NRetTy && "No new return type found?"); 660 661 // Remove any incompatible attributes, but only if we removed all return 662 // values. Otherwise, ensure that we don't have any conflicting attributes 663 // here. Currently, this should not be possible, but special handling might be 664 // required when new return value attributes are added. 665 if (NRetTy->isVoidTy()) 666 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 667 else 668 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 669 && "Return attributes no longer compatible?"); 670 671 if (RAttrs) 672 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 673 674 // Remember which arguments are still alive. 675 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 676 // Construct the new parameter list from non-dead arguments. Also construct 677 // a new set of parameter attributes to correspond. Skip the first parameter 678 // attribute, since that belongs to the return value. 679 unsigned i = 0; 680 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 681 I != E; ++I, ++i) { 682 RetOrArg Arg = CreateArg(F, i); 683 if (LiveValues.erase(Arg)) { 684 Params.push_back(I->getType()); 685 ArgAlive[i] = true; 686 687 // Get the original parameter attributes (skipping the first one, that is 688 // for the return value. 689 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 690 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 691 } else { 692 ++NumArgumentsEliminated; 693 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 694 << ") from " << F->getName() << "\n"); 695 } 696 } 697 698 if (FnAttrs != Attribute::None) 699 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 700 701 // Reconstruct the AttributesList based on the vector we constructed. 702 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 703 704 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 705 // have zero fixed arguments. 706 // 707 // Note that we apply this hack for a vararg fuction that does not have any 708 // arguments anymore, but did have them before (so don't bother fixing 709 // functions that were already broken wrt CWriter). 710 bool ExtraArgHack = false; 711 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 712 ExtraArgHack = true; 713 Params.push_back(Type::getInt32Ty(F->getContext())); 714 } 715 716 // Create the new function type based on the recomputed parameters. 717 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 718 719 // No change? 720 if (NFTy == FTy) 721 return false; 722 723 // Create the new function body and insert it into the module... 724 Function *NF = Function::Create(NFTy, F->getLinkage()); 725 NF->copyAttributesFrom(F); 726 NF->setAttributes(NewPAL); 727 // Insert the new function before the old function, so we won't be processing 728 // it again. 729 F->getParent()->getFunctionList().insert(F, NF); 730 NF->takeName(F); 731 732 // Loop over all of the callers of the function, transforming the call sites 733 // to pass in a smaller number of arguments into the new function. 734 // 735 std::vector<Value*> Args; 736 while (!F->use_empty()) { 737 CallSite CS = CallSite::get(F->use_back()); 738 Instruction *Call = CS.getInstruction(); 739 740 AttributesVec.clear(); 741 const AttrListPtr &CallPAL = CS.getAttributes(); 742 743 // The call return attributes. 744 Attributes RAttrs = CallPAL.getRetAttributes(); 745 Attributes FnAttrs = CallPAL.getFnAttributes(); 746 // Adjust in case the function was changed to return void. 747 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 748 if (RAttrs) 749 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 750 751 // Declare these outside of the loops, so we can reuse them for the second 752 // loop, which loops the varargs. 753 CallSite::arg_iterator I = CS.arg_begin(); 754 unsigned i = 0; 755 // Loop over those operands, corresponding to the normal arguments to the 756 // original function, and add those that are still alive. 757 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 758 if (ArgAlive[i]) { 759 Args.push_back(*I); 760 // Get original parameter attributes, but skip return attributes. 761 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 762 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 763 } 764 765 if (ExtraArgHack) 766 Args.push_back(UndefValue::get(Type::getInt32Ty(F->getContext()))); 767 768 // Push any varargs arguments on the list. Don't forget their attributes. 769 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 770 Args.push_back(*I); 771 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 772 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 773 } 774 775 if (FnAttrs != Attribute::None) 776 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 777 778 // Reconstruct the AttributesList based on the vector we constructed. 779 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 780 AttributesVec.end()); 781 782 Instruction *New; 783 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 784 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 785 Args.begin(), Args.end(), "", Call); 786 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 787 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 788 } else { 789 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 790 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 791 cast<CallInst>(New)->setAttributes(NewCallPAL); 792 if (cast<CallInst>(Call)->isTailCall()) 793 cast<CallInst>(New)->setTailCall(); 794 } 795 Args.clear(); 796 797 if (!Call->use_empty()) { 798 if (New->getType() == Call->getType()) { 799 // Return type not changed? Just replace users then. 800 Call->replaceAllUsesWith(New); 801 New->takeName(Call); 802 } else if (New->getType()->isVoidTy()) { 803 // Our return value has uses, but they will get removed later on. 804 // Replace by null for now. 805 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 806 } else { 807 assert(isa<StructType>(RetTy) && 808 "Return type changed, but not into a void. The old return type" 809 " must have been a struct!"); 810 Instruction *InsertPt = Call; 811 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 812 BasicBlock::iterator IP = II->getNormalDest()->begin(); 813 while (isa<PHINode>(IP)) ++IP; 814 InsertPt = IP; 815 } 816 817 // We used to return a struct. Instead of doing smart stuff with all the 818 // uses of this struct, we will just rebuild it using 819 // extract/insertvalue chaining and let instcombine clean that up. 820 // 821 // Start out building up our return value from undef 822 Value *RetVal = UndefValue::get(RetTy); 823 for (unsigned i = 0; i != RetCount; ++i) 824 if (NewRetIdxs[i] != -1) { 825 Value *V; 826 if (RetTypes.size() > 1) 827 // We are still returning a struct, so extract the value from our 828 // return value 829 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 830 InsertPt); 831 else 832 // We are now returning a single element, so just insert that 833 V = New; 834 // Insert the value at the old position 835 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 836 } 837 // Now, replace all uses of the old call instruction with the return 838 // struct we built 839 Call->replaceAllUsesWith(RetVal); 840 New->takeName(Call); 841 } 842 } 843 844 // Finally, remove the old call from the program, reducing the use-count of 845 // F. 846 Call->eraseFromParent(); 847 } 848 849 // Since we have now created the new function, splice the body of the old 850 // function right into the new function, leaving the old rotting hulk of the 851 // function empty. 852 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 853 854 // Loop over the argument list, transfering uses of the old arguments over to 855 // the new arguments, also transfering over the names as well. 856 i = 0; 857 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 858 I2 = NF->arg_begin(); I != E; ++I, ++i) 859 if (ArgAlive[i]) { 860 // If this is a live argument, move the name and users over to the new 861 // version. 862 I->replaceAllUsesWith(I2); 863 I2->takeName(I); 864 ++I2; 865 } else { 866 // If this argument is dead, replace any uses of it with null constants 867 // (these are guaranteed to become unused later on). 868 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 869 } 870 871 // If we change the return value of the function we must rewrite any return 872 // instructions. Check this now. 873 if (F->getReturnType() != NF->getReturnType()) 874 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 875 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 876 Value *RetVal; 877 878 if (NFTy->getReturnType()->isVoidTy()) { 879 RetVal = 0; 880 } else { 881 assert (isa<StructType>(RetTy)); 882 // The original return value was a struct, insert 883 // extractvalue/insertvalue chains to extract only the values we need 884 // to return and insert them into our new result. 885 // This does generate messy code, but we'll let it to instcombine to 886 // clean that up. 887 Value *OldRet = RI->getOperand(0); 888 // Start out building up our return value from undef 889 RetVal = UndefValue::get(NRetTy); 890 for (unsigned i = 0; i != RetCount; ++i) 891 if (NewRetIdxs[i] != -1) { 892 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 893 "oldret", RI); 894 if (RetTypes.size() > 1) { 895 // We're still returning a struct, so reinsert the value into 896 // our new return value at the new index 897 898 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 899 "newret", RI); 900 } else { 901 // We are now only returning a simple value, so just return the 902 // extracted value. 903 RetVal = EV; 904 } 905 } 906 } 907 // Replace the return instruction with one returning the new return 908 // value (possibly 0 if we became void). 909 ReturnInst::Create(F->getContext(), RetVal, RI); 910 BB->getInstList().erase(RI); 911 } 912 913 // Now that the old function is dead, delete it. 914 F->eraseFromParent(); 915 916 return true; 917} 918 919bool DAE::RemoveDeadParamsFromCallersOf(Function *F) { 920 // Don't modify fully live functions 921 if (LiveFunctions.count(F)) 922 return false; 923 924 // Make a list of the dead arguments. 925 SmallVector<int, 10> ArgDead; 926 unsigned i = 0; 927 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 928 I != E; ++I, ++i) { 929 RetOrArg Arg = CreateArg(F, i); 930 if (!LiveValues.count(Arg)) 931 ArgDead.push_back(i); 932 } 933 if (ArgDead.empty()) 934 return false; 935 936 bool MadeChange = false; 937 for (Function::use_iterator I = F->use_begin(), E = F->use_end(); 938 I != E; ++I) { 939 CallSite CS = CallSite::get(*I); 940 if (CS.getInstruction() && CS.isCallee(I)) { 941 for (unsigned i = 0, e = ArgDead.size(); i != e; ++i) { 942 Value *A = CS.getArgument(ArgDead[i]); 943 if (!isa<UndefValue>(A)) { 944 MadeChange = true; 945 CS.setArgument(ArgDead[i], UndefValue::get(A->getType())); 946 RecursivelyDeleteTriviallyDeadInstructions(A); 947 } 948 } 949 } 950 } 951 952 return MadeChange; 953} 954 955bool DAE::runOnModule(Module &M) { 956 bool Changed = false; 957 958 // First pass: Do a simple check to see if any functions can have their "..." 959 // removed. We can do this if they never call va_start. This loop cannot be 960 // fused with the next loop, because deleting a function invalidates 961 // information computed while surveying other functions. 962 DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 963 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 964 Function &F = *I++; 965 if (F.getFunctionType()->isVarArg()) 966 Changed |= DeleteDeadVarargs(F); 967 } 968 969 // Second phase:loop through the module, determining which arguments are live. 970 // We assume all arguments are dead unless proven otherwise (allowing us to 971 // determine that dead arguments passed into recursive functions are dead). 972 // 973 DEBUG(dbgs() << "DAE - Determining liveness\n"); 974 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 975 SurveyFunction(*I); 976 977 // Now, remove all dead arguments and return values from each function in 978 // turn. 979 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 980 // Increment now, because the function will probably get removed (ie. 981 // replaced by a new one). 982 Function *F = I++; 983 if (F->hasLocalLinkage()) 984 Changed |= RemoveDeadStuffFromFunction(F); 985 else 986 Changed |= RemoveDeadParamsFromCallersOf(F); 987 } 988 return Changed; 989} 990