DeadArgumentElimination.cpp revision 5894c0b60ef75f382d64b268a5f1a0f2b0db840f
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"); 43STATISTIC(NumParametersEliminated, "Number of parameters replaced with undef"); 44 45namespace { 46 /// DAE - The dead argument elimination pass. 47 /// 48 class DAE : public ModulePass { 49 public: 50 51 /// Struct that represents (part of) either a return value or a function 52 /// argument. Used so that arguments and return values can be used 53 /// interchangably. 54 struct RetOrArg { 55 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 56 IsArg(IsArg) {} 57 const Function *F; 58 unsigned Idx; 59 bool IsArg; 60 61 /// Make RetOrArg comparable, so we can put it into a map. 62 bool operator<(const RetOrArg &O) const { 63 if (F != O.F) 64 return F < O.F; 65 else if (Idx != O.Idx) 66 return Idx < O.Idx; 67 else 68 return IsArg < O.IsArg; 69 } 70 71 /// Make RetOrArg comparable, so we can easily iterate the multimap. 72 bool operator==(const RetOrArg &O) const { 73 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 74 } 75 76 std::string getDescription() const { 77 return std::string((IsArg ? "Argument #" : "Return value #")) 78 + utostr(Idx) + " of function " + F->getNameStr(); 79 } 80 }; 81 82 /// Liveness enum - During our initial pass over the program, we determine 83 /// that things are either alive or maybe alive. We don't mark anything 84 /// explicitly dead (even if we know they are), since anything not alive 85 /// with no registered uses (in Uses) will never be marked alive and will 86 /// thus become dead in the end. 87 enum Liveness { Live, MaybeLive }; 88 89 /// Convenience wrapper 90 RetOrArg CreateRet(const Function *F, unsigned Idx) { 91 return RetOrArg(F, Idx, false); 92 } 93 /// Convenience wrapper 94 RetOrArg CreateArg(const Function *F, unsigned Idx) { 95 return RetOrArg(F, Idx, true); 96 } 97 98 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 99 /// This maps a return value or argument to any MaybeLive return values or 100 /// arguments it uses. This allows the MaybeLive values to be marked live 101 /// when any of its users is marked live. 102 /// For example (indices are left out for clarity): 103 /// - Uses[ret F] = ret G 104 /// This means that F calls G, and F returns the value returned by G. 105 /// - Uses[arg F] = ret G 106 /// This means that some function calls G and passes its result as an 107 /// argument to F. 108 /// - Uses[ret F] = arg F 109 /// This means that F returns one of its own arguments. 110 /// - Uses[arg F] = arg G 111 /// This means that G calls F and passes one of its own (G's) arguments 112 /// directly to F. 113 UseMap Uses; 114 115 typedef std::set<RetOrArg> LiveSet; 116 typedef std::set<const Function*> LiveFuncSet; 117 118 /// This set contains all values that have been determined to be live. 119 LiveSet LiveValues; 120 /// This set contains all values that are cannot be changed in any way. 121 LiveFuncSet LiveFunctions; 122 123 typedef SmallVector<RetOrArg, 5> UseVector; 124 125 public: 126 static char ID; // Pass identification, replacement for typeid 127 DAE() : ModulePass(&ID) {} 128 bool runOnModule(Module &M); 129 130 virtual bool ShouldHackArguments() const { return false; } 131 132 private: 133 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 134 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses, 135 unsigned RetValNum = 0); 136 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 137 138 void SurveyFunction(const Function &F); 139 void MarkValue(const RetOrArg &RA, Liveness L, 140 const UseVector &MaybeLiveUses); 141 void MarkLive(const RetOrArg &RA); 142 void MarkLive(const Function &F); 143 void PropagateLiveness(const RetOrArg &RA); 144 bool RemoveDeadStuffFromFunction(Function *F); 145 bool RemoveDeadParamsFromCallersOf(Function *F); 146 bool DeleteDeadVarargs(Function &Fn); 147 }; 148} 149 150 151char DAE::ID = 0; 152static RegisterPass<DAE> 153X("deadargelim", "Dead Argument Elimination"); 154 155namespace { 156 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 157 /// deletes arguments to functions which are external. This is only for use 158 /// by bugpoint. 159 struct DAH : public DAE { 160 static char ID; 161 virtual bool ShouldHackArguments() const { return true; } 162 }; 163} 164 165char DAH::ID = 0; 166static RegisterPass<DAH> 167Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 168 169/// createDeadArgEliminationPass - This pass removes arguments from functions 170/// which are not used by the body of the function. 171/// 172ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 173ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 174 175/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 176/// llvm.vastart is never called, the varargs list is dead for the function. 177bool DAE::DeleteDeadVarargs(Function &Fn) { 178 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 179 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 180 181 // Ensure that the function is only directly called. 182 if (Fn.hasAddressTaken()) 183 return false; 184 185 // Okay, we know we can transform this function if safe. Scan its body 186 // looking for calls to llvm.vastart. 187 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 188 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 189 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 190 if (II->getIntrinsicID() == Intrinsic::vastart) 191 return false; 192 } 193 } 194 } 195 196 // If we get here, there are no calls to llvm.vastart in the function body, 197 // remove the "..." and adjust all the calls. 198 199 // Start by computing a new prototype for the function, which is the same as 200 // the old function, but doesn't have isVarArg set. 201 const FunctionType *FTy = Fn.getFunctionType(); 202 203 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 204 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), 205 Params, false); 206 unsigned NumArgs = Params.size(); 207 208 // Create the new function body and insert it into the module... 209 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 210 NF->copyAttributesFrom(&Fn); 211 Fn.getParent()->getFunctionList().insert(&Fn, NF); 212 NF->takeName(&Fn); 213 214 // Loop over all of the callers of the function, transforming the call sites 215 // to pass in a smaller number of arguments into the new function. 216 // 217 std::vector<Value*> Args; 218 while (!Fn.use_empty()) { 219 CallSite CS = CallSite::get(Fn.use_back()); 220 Instruction *Call = CS.getInstruction(); 221 222 // Pass all the same arguments. 223 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 224 225 // Drop any attributes that were on the vararg arguments. 226 AttrListPtr PAL = CS.getAttributes(); 227 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 228 SmallVector<AttributeWithIndex, 8> AttributesVec; 229 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 230 AttributesVec.push_back(PAL.getSlot(i)); 231 if (Attributes FnAttrs = PAL.getFnAttributes()) 232 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 233 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 234 } 235 236 Instruction *New; 237 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 238 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 239 Args.begin(), Args.end(), "", Call); 240 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 241 cast<InvokeInst>(New)->setAttributes(PAL); 242 } else { 243 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 244 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 245 cast<CallInst>(New)->setAttributes(PAL); 246 if (cast<CallInst>(Call)->isTailCall()) 247 cast<CallInst>(New)->setTailCall(); 248 } 249 Args.clear(); 250 251 if (!Call->use_empty()) 252 Call->replaceAllUsesWith(New); 253 254 New->takeName(Call); 255 256 // Finally, remove the old call from the program, reducing the use-count of 257 // F. 258 Call->eraseFromParent(); 259 } 260 261 // Since we have now created the new function, splice the body of the old 262 // function right into the new function, leaving the old rotting hulk of the 263 // function empty. 264 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 265 266 // Loop over the argument list, transfering uses of the old arguments over to 267 // the new arguments, also transfering over the names as well. While we're at 268 // it, remove the dead arguments from the DeadArguments list. 269 // 270 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 271 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 272 // Move the name and users over to the new version. 273 I->replaceAllUsesWith(I2); 274 I2->takeName(I); 275 } 276 277 // Finally, nuke the old function. 278 Fn.eraseFromParent(); 279 return true; 280} 281 282/// Convenience function that returns the number of return values. It returns 0 283/// for void functions and 1 for functions not returning a struct. It returns 284/// the number of struct elements for functions returning a struct. 285static unsigned NumRetVals(const Function *F) { 286 if (F->getReturnType()->isVoidTy()) 287 return 0; 288 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 289 return STy->getNumElements(); 290 else 291 return 1; 292} 293 294/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 295/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 296/// liveness of Use. 297DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 298 // We're live if our use or its Function is already marked as live. 299 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 300 return Live; 301 302 // We're maybe live otherwise, but remember that we must become live if 303 // Use becomes live. 304 MaybeLiveUses.push_back(Use); 305 return MaybeLive; 306} 307 308 309/// SurveyUse - This looks at a single use of an argument or return value 310/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 311/// if it causes the used value to become MaybeLive. 312/// 313/// RetValNum is the return value number to use when this use is used in a 314/// return instruction. This is used in the recursion, you should always leave 315/// it at 0. 316DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U, 317 UseVector &MaybeLiveUses, unsigned RetValNum) { 318 const User *V = *U; 319 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 320 // The value is returned from a function. It's only live when the 321 // function's return value is live. We use RetValNum here, for the case 322 // that U is really a use of an insertvalue instruction that uses the 323 // orginal Use. 324 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 325 // We might be live, depending on the liveness of Use. 326 return MarkIfNotLive(Use, MaybeLiveUses); 327 } 328 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 329 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 330 && IV->hasIndices()) 331 // The use we are examining is inserted into an aggregate. Our liveness 332 // depends on all uses of that aggregate, but if it is used as a return 333 // value, only index at which we were inserted counts. 334 RetValNum = *IV->idx_begin(); 335 336 // Note that if we are used as the aggregate operand to the insertvalue, 337 // we don't change RetValNum, but do survey all our uses. 338 339 Liveness Result = MaybeLive; 340 for (Value::const_use_iterator I = IV->use_begin(), 341 E = V->use_end(); I != E; ++I) { 342 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 343 if (Result == Live) 344 break; 345 } 346 return Result; 347 } 348 349 if (ImmutableCallSite CS = V) { 350 const Function *F = CS.getCalledFunction(); 351 if (F) { 352 // Used in a direct call. 353 354 // Find the argument number. We know for sure that this use is an 355 // argument, since if it was the function argument this would be an 356 // indirect call and the we know can't be looking at a value of the 357 // label type (for the invoke instruction). 358 unsigned ArgNo = CS.getArgumentNo(U); 359 360 if (ArgNo >= F->getFunctionType()->getNumParams()) 361 // The value is passed in through a vararg! Must be live. 362 return Live; 363 364 assert(CS.getArgument(ArgNo) 365 == CS->getOperand(U.getOperandNo()) 366 && "Argument is not where we expected it"); 367 368 // Value passed to a normal call. It's only live when the corresponding 369 // argument to the called function turns out live. 370 RetOrArg Use = CreateArg(F, ArgNo); 371 return MarkIfNotLive(Use, MaybeLiveUses); 372 } 373 } 374 // Used in any other way? Value must be live. 375 return Live; 376} 377 378/// SurveyUses - This looks at all the uses of the given value 379/// Returns the Liveness deduced from the uses of this value. 380/// 381/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 382/// the result is Live, MaybeLiveUses might be modified but its content should 383/// be ignored (since it might not be complete). 384DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) { 385 // Assume it's dead (which will only hold if there are no uses at all..). 386 Liveness Result = MaybeLive; 387 // Check each use. 388 for (Value::const_use_iterator I = V->use_begin(), 389 E = V->use_end(); I != E; ++I) { 390 Result = SurveyUse(I, MaybeLiveUses); 391 if (Result == Live) 392 break; 393 } 394 return Result; 395} 396 397// SurveyFunction - This performs the initial survey of the specified function, 398// checking out whether or not it uses any of its incoming arguments or whether 399// any callers use the return value. This fills in the LiveValues set and Uses 400// map. 401// 402// We consider arguments of non-internal functions to be intrinsically alive as 403// well as arguments to functions which have their "address taken". Externally 404// visible functions are assumed to only have their return values intrinsically 405// alive, permitting removal of parameters to unused arguments in callers. 406// 407void DAE::SurveyFunction(const Function &F) { 408 unsigned RetCount = NumRetVals(&F); 409 // Assume all return values are dead 410 typedef SmallVector<Liveness, 5> RetVals; 411 RetVals RetValLiveness(RetCount, MaybeLive); 412 413 typedef SmallVector<UseVector, 5> RetUses; 414 // These vectors map each return value to the uses that make it MaybeLive, so 415 // we can add those to the Uses map if the return value really turns out to be 416 // MaybeLive. Initialized to a list of RetCount empty lists. 417 RetUses MaybeLiveRetUses(RetCount); 418 419 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 420 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 421 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 422 != F.getFunctionType()->getReturnType()) { 423 // We don't support old style multiple return values. 424 MarkLive(F); 425 return; 426 } 427 428 if (F.hasExternalLinkage() && !F.isDeclaration()) { 429 DEBUG(dbgs() << "DAE - Intrinsically live return from " << F.getName() 430 << "\n"); 431 // Mark the return values alive. 432 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 433 MarkLive(CreateRet(&F, i)); 434 } else if (!F.hasLocalLinkage() && 435 (!ShouldHackArguments() || F.isIntrinsic())) { 436 MarkLive(F); 437 return; 438 } 439 440 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n"); 441 // Keep track of the number of live retvals, so we can skip checks once all 442 // of them turn out to be live. 443 unsigned NumLiveRetVals = 0; 444 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 445 // Loop all uses of the function. 446 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end(); 447 I != E; ++I) { 448 // If the function is PASSED IN as an argument, its address has been 449 // taken. 450 ImmutableCallSite CS(*I); 451 if (!CS || !CS.isCallee(I)) { 452 MarkLive(F); 453 return; 454 } 455 456 // If this use is anything other than a call site, the function is alive. 457 const Instruction *TheCall = CS.getInstruction(); 458 if (!TheCall) { // Not a direct call site? 459 MarkLive(F); 460 return; 461 } 462 463 // If we end up here, we are looking at a direct call to our function. 464 465 // Now, check how our return value(s) is/are used in this caller. Don't 466 // bother checking return values if all of them are live already. 467 if (NumLiveRetVals != RetCount) { 468 if (STy) { 469 // Check all uses of the return value. 470 for (Value::const_use_iterator I = TheCall->use_begin(), 471 E = TheCall->use_end(); I != E; ++I) { 472 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 473 if (Ext && Ext->hasIndices()) { 474 // This use uses a part of our return value, survey the uses of 475 // that part and store the results for this index only. 476 unsigned Idx = *Ext->idx_begin(); 477 if (RetValLiveness[Idx] != Live) { 478 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 479 if (RetValLiveness[Idx] == Live) 480 NumLiveRetVals++; 481 } 482 } else { 483 // Used by something else than extractvalue. Mark all return 484 // values as live. 485 for (unsigned i = 0; i != RetCount; ++i ) 486 RetValLiveness[i] = Live; 487 NumLiveRetVals = RetCount; 488 break; 489 } 490 } 491 } else { 492 // Single return value 493 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 494 if (RetValLiveness[0] == Live) 495 NumLiveRetVals = RetCount; 496 } 497 } 498 } 499 500 // Now we've inspected all callers, record the liveness of our return values. 501 for (unsigned i = 0; i != RetCount; ++i) 502 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 503 504 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n"); 505 506 // Now, check all of our arguments. 507 unsigned i = 0; 508 UseVector MaybeLiveArgUses; 509 for (Function::const_arg_iterator AI = F.arg_begin(), 510 E = F.arg_end(); AI != E; ++AI, ++i) { 511 // See what the effect of this use is (recording any uses that cause 512 // MaybeLive in MaybeLiveArgUses). 513 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 514 // Mark the result. 515 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 516 // Clear the vector again for the next iteration. 517 MaybeLiveArgUses.clear(); 518 } 519} 520 521/// MarkValue - This function marks the liveness of RA depending on L. If L is 522/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 523/// such that RA will be marked live if any use in MaybeLiveUses gets marked 524/// live later on. 525void DAE::MarkValue(const RetOrArg &RA, Liveness L, 526 const UseVector &MaybeLiveUses) { 527 switch (L) { 528 case Live: MarkLive(RA); break; 529 case MaybeLive: 530 { 531 // Note any uses of this value, so this return value can be 532 // marked live whenever one of the uses becomes live. 533 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 534 UE = MaybeLiveUses.end(); UI != UE; ++UI) 535 Uses.insert(std::make_pair(*UI, RA)); 536 break; 537 } 538 } 539} 540 541/// MarkLive - Mark the given Function as alive, meaning that it cannot be 542/// changed in any way. Additionally, 543/// mark any values that are used as this function's parameters or by its return 544/// values (according to Uses) live as well. 545void DAE::MarkLive(const Function &F) { 546 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n"); 547 // Mark the function as live. 548 LiveFunctions.insert(&F); 549 // Mark all arguments as live. 550 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 551 PropagateLiveness(CreateArg(&F, i)); 552 // Mark all return values as live. 553 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 554 PropagateLiveness(CreateRet(&F, i)); 555} 556 557/// MarkLive - Mark the given return value or argument as live. Additionally, 558/// mark any values that are used by this value (according to Uses) live as 559/// well. 560void DAE::MarkLive(const RetOrArg &RA) { 561 if (LiveFunctions.count(RA.F)) 562 return; // Function was already marked Live. 563 564 if (!LiveValues.insert(RA).second) 565 return; // We were already marked Live. 566 567 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n"); 568 PropagateLiveness(RA); 569} 570 571/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 572/// to any other values it uses (according to Uses). 573void DAE::PropagateLiveness(const RetOrArg &RA) { 574 // We don't use upper_bound (or equal_range) here, because our recursive call 575 // to ourselves is likely to cause the upper_bound (which is the first value 576 // not belonging to RA) to become erased and the iterator invalidated. 577 UseMap::iterator Begin = Uses.lower_bound(RA); 578 UseMap::iterator E = Uses.end(); 579 UseMap::iterator I; 580 for (I = Begin; I != E && I->first == RA; ++I) 581 MarkLive(I->second); 582 583 // Erase RA from the Uses map (from the lower bound to wherever we ended up 584 // after the loop). 585 Uses.erase(Begin, I); 586} 587 588// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 589// that are not in LiveValues. Transform the function and all of the callees of 590// the function to not have these arguments and return values. 591// 592bool DAE::RemoveDeadStuffFromFunction(Function *F) { 593 // Don't modify fully live functions 594 if (LiveFunctions.count(F)) 595 return false; 596 597 // Start by computing a new prototype for the function, which is the same as 598 // the old function, but has fewer arguments and a different return type. 599 const FunctionType *FTy = F->getFunctionType(); 600 std::vector<const Type*> Params; 601 602 // Set up to build a new list of parameter attributes. 603 SmallVector<AttributeWithIndex, 8> AttributesVec; 604 const AttrListPtr &PAL = F->getAttributes(); 605 606 // The existing function return attributes. 607 Attributes RAttrs = PAL.getRetAttributes(); 608 Attributes FnAttrs = PAL.getFnAttributes(); 609 610 // Find out the new return value. 611 612 const Type *RetTy = FTy->getReturnType(); 613 const Type *NRetTy = NULL; 614 unsigned RetCount = NumRetVals(F); 615 616 // -1 means unused, other numbers are the new index 617 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 618 std::vector<const Type*> RetTypes; 619 if (RetTy->isVoidTy()) { 620 NRetTy = RetTy; 621 } else { 622 const StructType *STy = dyn_cast<StructType>(RetTy); 623 if (STy) 624 // Look at each of the original return values individually. 625 for (unsigned i = 0; i != RetCount; ++i) { 626 RetOrArg Ret = CreateRet(F, i); 627 if (LiveValues.erase(Ret)) { 628 RetTypes.push_back(STy->getElementType(i)); 629 NewRetIdxs[i] = RetTypes.size() - 1; 630 } else { 631 ++NumRetValsEliminated; 632 DEBUG(dbgs() << "DAE - Removing return value " << i << " from " 633 << F->getName() << "\n"); 634 } 635 } 636 else 637 // We used to return a single value. 638 if (LiveValues.erase(CreateRet(F, 0))) { 639 RetTypes.push_back(RetTy); 640 NewRetIdxs[0] = 0; 641 } else { 642 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName() 643 << "\n"); 644 ++NumRetValsEliminated; 645 } 646 if (RetTypes.size() > 1) 647 // More than one return type? Return a struct with them. Also, if we used 648 // to return a struct and didn't change the number of return values, 649 // return a struct again. This prevents changing {something} into 650 // something and {} into void. 651 // Make the new struct packed if we used to return a packed struct 652 // already. 653 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); 654 else if (RetTypes.size() == 1) 655 // One return type? Just a simple value then, but only if we didn't use to 656 // return a struct with that simple value before. 657 NRetTy = RetTypes.front(); 658 else if (RetTypes.size() == 0) 659 // No return types? Make it void, but only if we didn't use to return {}. 660 NRetTy = Type::getVoidTy(F->getContext()); 661 } 662 663 assert(NRetTy && "No new return type found?"); 664 665 // Remove any incompatible attributes, but only if we removed all return 666 // values. Otherwise, ensure that we don't have any conflicting attributes 667 // here. Currently, this should not be possible, but special handling might be 668 // required when new return value attributes are added. 669 if (NRetTy->isVoidTy()) 670 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 671 else 672 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 673 && "Return attributes no longer compatible?"); 674 675 if (RAttrs) 676 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 677 678 // Remember which arguments are still alive. 679 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 680 // Construct the new parameter list from non-dead arguments. Also construct 681 // a new set of parameter attributes to correspond. Skip the first parameter 682 // attribute, since that belongs to the return value. 683 unsigned i = 0; 684 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 685 I != E; ++I, ++i) { 686 RetOrArg Arg = CreateArg(F, i); 687 if (LiveValues.erase(Arg)) { 688 Params.push_back(I->getType()); 689 ArgAlive[i] = true; 690 691 // Get the original parameter attributes (skipping the first one, that is 692 // for the return value. 693 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 694 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 695 } else { 696 ++NumArgumentsEliminated; 697 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName() 698 << ") from " << F->getName() << "\n"); 699 } 700 } 701 702 if (FnAttrs != Attribute::None) 703 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 704 705 // Reconstruct the AttributesList based on the vector we constructed. 706 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), 707 AttributesVec.end()); 708 709 // Create the new function type based on the recomputed parameters. 710 FunctionType *NFTy = FunctionType::get(NRetTy, Params, 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 // 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()->isVoidTy()) { 793 // Our return value has uses, but they will get removed later on. 794 // Replace by null for now. 795 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 796 } else { 797 assert(RetTy->isStructTy() && 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 = UndefValue::get(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(Constant::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()->isVoidTy()) { 869 RetVal = 0; 870 } else { 871 assert (RetTy->isStructTy()); 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 = UndefValue::get(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(F->getContext(), 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::RemoveDeadParamsFromCallersOf(Function *F) { 910 // Don't modify fully live functions 911 if (LiveFunctions.count(F)) 912 return false; 913 914 // Make a list of the dead arguments. 915 SmallVector<int, 10> ArgDead; 916 unsigned i = 0; 917 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 918 I != E; ++I, ++i) { 919 RetOrArg Arg = CreateArg(F, i); 920 if (!LiveValues.count(Arg)) 921 ArgDead.push_back(i); 922 } 923 if (ArgDead.empty()) 924 return false; 925 926 bool MadeChange = false; 927 for (Function::use_iterator I = F->use_begin(), E = F->use_end(); 928 I != E; ++I) { 929 CallSite CS = CallSite::get(*I); 930 if (CS.getInstruction() && CS.isCallee(I)) { 931 for (unsigned i = 0, e = ArgDead.size(); i != e; ++i) { 932 Value *A = CS.getArgument(ArgDead[i]); 933 if (!isa<UndefValue>(A)) { 934 ++NumParametersEliminated; 935 MadeChange = true; 936 CS.setArgument(ArgDead[i], UndefValue::get(A->getType())); 937 RecursivelyDeleteTriviallyDeadInstructions(A); 938 } 939 } 940 } 941 } 942 943 return MadeChange; 944} 945 946bool DAE::runOnModule(Module &M) { 947 bool Changed = false; 948 949 // First pass: Do a simple check to see if any functions can have their "..." 950 // removed. We can do this if they never call va_start. This loop cannot be 951 // fused with the next loop, because deleting a function invalidates 952 // information computed while surveying other functions. 953 DEBUG(dbgs() << "DAE - Deleting dead varargs\n"); 954 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 955 Function &F = *I++; 956 if (F.getFunctionType()->isVarArg()) 957 Changed |= DeleteDeadVarargs(F); 958 } 959 960 // Second phase:loop through the module, determining which arguments are live. 961 // We assume all arguments are dead unless proven otherwise (allowing us to 962 // determine that dead arguments passed into recursive functions are dead). 963 // 964 DEBUG(dbgs() << "DAE - Determining liveness\n"); 965 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 966 SurveyFunction(*I); 967 968 // Now, remove all dead arguments and return values from each function in 969 // turn. 970 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 971 // Increment now, because the function will probably get removed (ie. 972 // replaced by a new one). 973 Function *F = I++; 974 if (F->hasExternalLinkage() && !F->isDeclaration()) 975 Changed |= RemoveDeadParamsFromCallersOf(F); 976 else 977 Changed |= RemoveDeadStuffFromFunction(F); 978 } 979 return Changed; 980} 981