DeadArgumentElimination.cpp revision d222f86d9d51a2d6299d43fb876099869430bf0f
1//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass deletes dead arguments from internal functions. Dead argument 11// elimination removes arguments which are directly dead, as well as arguments 12// only passed into function calls as dead arguments of other functions. This 13// pass also deletes dead return values in a similar way. 14// 15// This pass is often useful as a cleanup pass to run after aggressive 16// interprocedural passes, which add possibly-dead arguments or return values. 17// 18//===----------------------------------------------------------------------===// 19 20#define DEBUG_TYPE "deadargelim" 21#include "llvm/Transforms/IPO.h" 22#include "llvm/CallingConv.h" 23#include "llvm/Constant.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/Module.h" 28#include "llvm/Pass.h" 29#include "llvm/Support/CallSite.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/ADT/SmallVector.h" 32#include "llvm/ADT/Statistic.h" 33#include "llvm/ADT/StringExtras.h" 34#include "llvm/Support/Compiler.h" 35#include <map> 36#include <set> 37using namespace llvm; 38 39STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 40STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 41 42namespace { 43 /// DAE - The dead argument elimination pass. 44 /// 45 class VISIBILITY_HIDDEN DAE : public ModulePass { 46 public: 47 48 /// Struct that represents (part of) either a return value or a function 49 /// argument. Used so that arguments and return values can be used 50 /// interchangably. 51 struct RetOrArg { 52 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 53 IsArg(IsArg) {} 54 const Function *F; 55 unsigned Idx; 56 bool IsArg; 57 58 /// Make RetOrArg comparable, so we can put it into a map. 59 bool operator<(const RetOrArg &O) const { 60 if (F != O.F) 61 return F < O.F; 62 else if (Idx != O.Idx) 63 return Idx < O.Idx; 64 else 65 return IsArg < O.IsArg; 66 } 67 68 /// Make RetOrArg comparable, so we can easily iterate the multimap. 69 bool operator==(const RetOrArg &O) const { 70 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 71 } 72 73 std::string getDescription() const { 74 return std::string((IsArg ? "Argument #" : "Return value #")) 75 + utostr(Idx) + " of function " + F->getName(); 76 } 77 }; 78 79 /// Liveness enum - During our initial pass over the program, we determine 80 /// that things are either alive or maybe alive. We don't mark anything 81 /// explicitly dead (even if we know they are), since anything not alive 82 /// with no registered uses (in Uses) will never be marked alive and will 83 /// thus become dead in the end. 84 enum Liveness { Live, MaybeLive }; 85 86 /// Convenience wrapper 87 RetOrArg CreateRet(const Function *F, unsigned Idx) { 88 return RetOrArg(F, Idx, false); 89 } 90 /// Convenience wrapper 91 RetOrArg CreateArg(const Function *F, unsigned Idx) { 92 return RetOrArg(F, Idx, true); 93 } 94 95 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 96 /// This maps a return value or argument to any MaybeLive return values or 97 /// arguments it uses. This allows the MaybeLive values to be marked live 98 /// when any of its users is marked live. 99 /// For example (indices are left out for clarity): 100 /// - Uses[ret F] = ret G 101 /// This means that F calls G, and F returns the value returned by G. 102 /// - Uses[arg F] = ret G 103 /// This means that some function calls G and passes its result as an 104 /// argument to F. 105 /// - Uses[ret F] = arg F 106 /// This means that F returns one of its own arguments. 107 /// - Uses[arg F] = arg G 108 /// This means that G calls F and passes one of its own (G's) arguments 109 /// directly to F. 110 UseMap Uses; 111 112 typedef std::set<RetOrArg> LiveSet; 113 typedef std::set<const Function*> LiveFuncSet; 114 115 /// This set contains all values that have been determined to be live. 116 LiveSet LiveValues; 117 /// This set contains all values that are cannot be changed in any way. 118 LiveFuncSet LiveFunctions; 119 120 typedef SmallVector<RetOrArg, 5> UseVector; 121 122 public: 123 static char ID; // Pass identification, replacement for typeid 124 DAE() : ModulePass(&ID) {} 125 bool runOnModule(Module &M); 126 127 virtual bool ShouldHackArguments() const { return false; } 128 129 private: 130 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 131 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 132 unsigned RetValNum = 0); 133 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 134 135 void SurveyFunction(Function &F); 136 void MarkValue(const RetOrArg &RA, Liveness L, 137 const UseVector &MaybeLiveUses); 138 void MarkLive(const RetOrArg &RA); 139 void MarkLive(const Function &F); 140 void PropagateLiveness(const RetOrArg &RA); 141 bool RemoveDeadStuffFromFunction(Function *F); 142 bool DeleteDeadVarargs(Function &Fn); 143 }; 144} 145 146 147char DAE::ID = 0; 148static RegisterPass<DAE> 149X("deadargelim", "Dead Argument Elimination"); 150 151namespace { 152 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 153 /// deletes arguments to functions which are external. This is only for use 154 /// by bugpoint. 155 struct DAH : public DAE { 156 static char ID; 157 virtual bool ShouldHackArguments() const { return true; } 158 }; 159} 160 161char DAH::ID = 0; 162static RegisterPass<DAH> 163Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 164 165/// createDeadArgEliminationPass - This pass removes arguments from functions 166/// which are not used by the body of the function. 167/// 168ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 169ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 170 171/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 172/// llvm.vastart is never called, the varargs list is dead for the function. 173bool DAE::DeleteDeadVarargs(Function &Fn) { 174 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 175 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false; 176 177 // Ensure that the function is only directly called. 178 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) { 179 // If this use is anything other than a call site, give up. 180 CallSite CS = CallSite::get(*I); 181 Instruction *TheCall = CS.getInstruction(); 182 if (!TheCall) return false; // Not a direct call site? 183 184 // The addr of this function is passed to the call. 185 if (I.getOperandNo() != 0) return false; 186 } 187 188 // Okay, we know we can transform this function if safe. Scan its body 189 // looking for calls to llvm.vastart. 190 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 191 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 192 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 193 if (II->getIntrinsicID() == Intrinsic::vastart) 194 return false; 195 } 196 } 197 } 198 199 // If we get here, there are no calls to llvm.vastart in the function body, 200 // remove the "..." and adjust all the calls. 201 202 // Start by computing a new prototype for the function, which is the same as 203 // the old function, but doesn't have isVarArg set. 204 const FunctionType *FTy = Fn.getFunctionType(); 205 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 206 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false); 207 unsigned NumArgs = Params.size(); 208 209 // Create the new function body and insert it into the module... 210 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 211 NF->copyAttributesFrom(&Fn); 212 Fn.getParent()->getFunctionList().insert(&Fn, NF); 213 NF->takeName(&Fn); 214 215 // Loop over all of the callers of the function, transforming the call sites 216 // to pass in a smaller number of arguments into the new function. 217 // 218 std::vector<Value*> Args; 219 while (!Fn.use_empty()) { 220 CallSite CS = CallSite::get(Fn.use_back()); 221 Instruction *Call = CS.getInstruction(); 222 223 // Pass all the same arguments. 224 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 225 226 // Drop any attributes that were on the vararg arguments. 227 AttrListPtr PAL = CS.getAttributes(); 228 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 229 SmallVector<AttributeWithIndex, 8> AttributesVec; 230 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 231 AttributesVec.push_back(PAL.getSlot(i)); 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() == Type::VoidTy) 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 MaybeAlive. 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 non-internal 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.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 426 MarkLive(F); 427 return; 428 } 429 430 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 431 // Keep track of the number of live retvals, so we can skip checks once all 432 // of them turn out to be live. 433 unsigned NumLiveRetVals = 0; 434 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 435 // Loop all uses of the function. 436 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 437 // If the function is PASSED IN as an argument, its address has been 438 // taken. 439 if (I.getOperandNo() != 0) { 440 MarkLive(F); 441 return; 442 } 443 444 // If this use is anything other than a call site, the function is alive. 445 CallSite CS = CallSite::get(*I); 446 Instruction *TheCall = CS.getInstruction(); 447 if (!TheCall) { // Not a direct call site? 448 MarkLive(F); 449 return; 450 } 451 452 // If we end up here, we are looking at a direct call to our function. 453 454 // Now, check how our return value(s) is/are used in this caller. Don't 455 // bother checking return values if all of them are live already. 456 if (NumLiveRetVals != RetCount) { 457 if (STy) { 458 // Check all uses of the return value. 459 for (Value::use_iterator I = TheCall->use_begin(), 460 E = TheCall->use_end(); I != E; ++I) { 461 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 462 if (Ext && Ext->hasIndices()) { 463 // This use uses a part of our return value, survey the uses of 464 // that part and store the results for this index only. 465 unsigned Idx = *Ext->idx_begin(); 466 if (RetValLiveness[Idx] != Live) { 467 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 468 if (RetValLiveness[Idx] == Live) 469 NumLiveRetVals++; 470 } 471 } else { 472 // Used by something else than extractvalue. Mark all return 473 // values as live. 474 for (unsigned i = 0; i != RetCount; ++i ) 475 RetValLiveness[i] = Live; 476 NumLiveRetVals = RetCount; 477 break; 478 } 479 } 480 } else { 481 // Single return value 482 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 483 if (RetValLiveness[0] == Live) 484 NumLiveRetVals = RetCount; 485 } 486 } 487 } 488 489 // Now we've inspected all callers, record the liveness of our return values. 490 for (unsigned i = 0; i != RetCount; ++i) 491 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 492 493 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 494 495 // Now, check all of our arguments. 496 unsigned i = 0; 497 UseVector MaybeLiveArgUses; 498 for (Function::arg_iterator AI = F.arg_begin(), 499 E = F.arg_end(); AI != E; ++AI, ++i) { 500 // See what the effect of this use is (recording any uses that cause 501 // MaybeLive in MaybeLiveArgUses). 502 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 503 // Mark the result. 504 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 505 // Clear the vector again for the next iteration. 506 MaybeLiveArgUses.clear(); 507 } 508} 509 510/// MarkValue - This function marks the liveness of RA depending on L. If L is 511/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 512/// such that RA will be marked live if any use in MaybeLiveUses gets marked 513/// live later on. 514void DAE::MarkValue(const RetOrArg &RA, Liveness L, 515 const UseVector &MaybeLiveUses) { 516 switch (L) { 517 case Live: MarkLive(RA); break; 518 case MaybeLive: 519 { 520 // Note any uses of this value, so this return value can be 521 // marked live whenever one of the uses becomes live. 522 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 523 UE = MaybeLiveUses.end(); UI != UE; ++UI) 524 Uses.insert(std::make_pair(*UI, RA)); 525 break; 526 } 527 } 528} 529 530/// MarkLive - Mark the given Function as alive, meaning that it cannot be 531/// changed in any way. Additionally, 532/// mark any values that are used as this function's parameters or by its return 533/// values (according to Uses) live as well. 534void DAE::MarkLive(const Function &F) { 535 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 536 // Mark the function as live. 537 LiveFunctions.insert(&F); 538 // Mark all arguments as live. 539 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 540 PropagateLiveness(CreateArg(&F, i)); 541 // Mark all return values as live. 542 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 543 PropagateLiveness(CreateRet(&F, i)); 544} 545 546/// MarkLive - Mark the given return value or argument as live. Additionally, 547/// mark any values that are used by this value (according to Uses) live as 548/// well. 549void DAE::MarkLive(const RetOrArg &RA) { 550 if (LiveFunctions.count(RA.F)) 551 return; // Function was already marked Live. 552 553 if (!LiveValues.insert(RA).second) 554 return; // We were already marked Live. 555 556 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 557 PropagateLiveness(RA); 558} 559 560/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 561/// to any other values it uses (according to Uses). 562void DAE::PropagateLiveness(const RetOrArg &RA) { 563 // We don't use upper_bound (or equal_range) here, because our recursive call 564 // to ourselves is likely to cause the upper_bound (which is the first value 565 // not belonging to RA) to become erased and the iterator invalidated. 566 UseMap::iterator Begin = Uses.lower_bound(RA); 567 UseMap::iterator E = Uses.end(); 568 UseMap::iterator I; 569 for (I = Begin; I != E && I->first == RA; ++I) 570 MarkLive(I->second); 571 572 // Erase RA from the Uses map (from the lower bound to wherever we ended up 573 // after the loop). 574 Uses.erase(Begin, I); 575} 576 577// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 578// that are not in LiveValues. Transform the function and all of the callees of 579// the function to not have these arguments and return values. 580// 581bool DAE::RemoveDeadStuffFromFunction(Function *F) { 582 // Don't modify fully live functions 583 if (LiveFunctions.count(F)) 584 return false; 585 586 // Start by computing a new prototype for the function, which is the same as 587 // the old function, but has fewer arguments and a different return type. 588 const FunctionType *FTy = F->getFunctionType(); 589 std::vector<const Type*> Params; 590 591 // Set up to build a new list of parameter attributes. 592 SmallVector<AttributeWithIndex, 8> AttributesVec; 593 const AttrListPtr &PAL = F->getAttributes(); 594 595 // The existing function return attributes. 596 Attributes RAttrs = PAL.getAttributes(0); 597 598 599 // Find out the new return value. 600 601 const Type *RetTy = FTy->getReturnType(); 602 const Type *NRetTy = NULL; 603 unsigned RetCount = NumRetVals(F); 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 DOUT << "DAE - Removing return value " << i << " from " 621 << F->getNameStart() << "\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 DOUT << "DAE - Removing return value from " << F->getNameStart() 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(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.getAttributes(i + 1)) 682 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 683 } else { 684 ++NumArgumentsEliminated; 685 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 686 << ") from " << F->getNameStart() << "\n"; 687 } 688 } 689 690 // Reconstruct the AttributesList based on the vector we constructed. 691 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 692 693 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 694 // have zero fixed arguments. 695 // 696 // Note that we apply this hack for a vararg fuction that does not have any 697 // arguments anymore, but did have them before (so don't bother fixing 698 // functions that were already broken wrt CWriter). 699 bool ExtraArgHack = false; 700 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 701 ExtraArgHack = true; 702 Params.push_back(Type::Int32Ty); 703 } 704 705 // Create the new function type based on the recomputed parameters. 706 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 707 708 // No change? 709 if (NFTy == FTy) 710 return false; 711 712 // Create the new function body and insert it into the module... 713 Function *NF = Function::Create(NFTy, F->getLinkage()); 714 NF->copyAttributesFrom(F); 715 NF->setAttributes(NewPAL); 716 // Insert the new function before the old function, so we won't be processing 717 // it again. 718 F->getParent()->getFunctionList().insert(F, NF); 719 NF->takeName(F); 720 721 // Loop over all of the callers of the function, transforming the call sites 722 // to pass in a smaller number of arguments into the new function. 723 // 724 std::vector<Value*> Args; 725 while (!F->use_empty()) { 726 CallSite CS = CallSite::get(F->use_back()); 727 Instruction *Call = CS.getInstruction(); 728 729 AttributesVec.clear(); 730 const AttrListPtr &CallPAL = CS.getAttributes(); 731 732 // The call return attributes. 733 Attributes RAttrs = CallPAL.getAttributes(0); 734 // Adjust in case the function was changed to return void. 735 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 736 if (RAttrs) 737 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 738 739 // Declare these outside of the loops, so we can reuse them for the second 740 // loop, which loops the varargs. 741 CallSite::arg_iterator I = CS.arg_begin(); 742 unsigned i = 0; 743 // Loop over those operands, corresponding to the normal arguments to the 744 // original function, and add those that are still alive. 745 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 746 if (ArgAlive[i]) { 747 Args.push_back(*I); 748 // Get original parameter attributes, but skip return attributes. 749 if (Attributes Attrs = CallPAL.getAttributes(i + 1)) 750 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 751 } 752 753 if (ExtraArgHack) 754 Args.push_back(UndefValue::get(Type::Int32Ty)); 755 756 // Push any varargs arguments on the list. Don't forget their attributes. 757 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 758 Args.push_back(*I); 759 if (Attributes Attrs = CallPAL.getAttributes(i + 1)) 760 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 761 } 762 763 // Reconstruct the AttributesList based on the vector we constructed. 764 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 765 AttributesVec.end()); 766 767 Instruction *New; 768 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 769 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 770 Args.begin(), Args.end(), "", Call); 771 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 772 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 773 } else { 774 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 775 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 776 cast<CallInst>(New)->setAttributes(NewCallPAL); 777 if (cast<CallInst>(Call)->isTailCall()) 778 cast<CallInst>(New)->setTailCall(); 779 } 780 Args.clear(); 781 782 if (!Call->use_empty()) { 783 if (New->getType() == Call->getType()) { 784 // Return type not changed? Just replace users then. 785 Call->replaceAllUsesWith(New); 786 New->takeName(Call); 787 } else if (New->getType() == Type::VoidTy) { 788 // Our return value has uses, but they will get removed later on. 789 // Replace by null for now. 790 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 791 } else { 792 assert(isa<StructType>(RetTy) && "Return type changed, but not into a" 793 "void. The old return type must have" 794 "been a struct!"); 795 // We used to return a struct. Instead of doing smart stuff with all the 796 // uses of this struct, we will just rebuild it using 797 // extract/insertvalue chaining and let instcombine clean that up. 798 // 799 // Start out building up our return value from undef 800 Value *RetVal = llvm::UndefValue::get(RetTy); 801 for (unsigned i = 0; i != RetCount; ++i) 802 if (NewRetIdxs[i] != -1) { 803 Value *V; 804 if (RetTypes.size() > 1) 805 // We are still returning a struct, so extract the value from our 806 // return value 807 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", Call); 808 else 809 // We are now returning a single element, so just insert that 810 V = New; 811 // Insert the value at the old position 812 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", Call); 813 } 814 // Now, replace all uses of the old call instruction with the return 815 // struct we built 816 Call->replaceAllUsesWith(RetVal); 817 New->takeName(Call); 818 } 819 } 820 821 // Finally, remove the old call from the program, reducing the use-count of 822 // F. 823 Call->eraseFromParent(); 824 } 825 826 // Since we have now created the new function, splice the body of the old 827 // function right into the new function, leaving the old rotting hulk of the 828 // function empty. 829 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 830 831 // Loop over the argument list, transfering uses of the old arguments over to 832 // the new arguments, also transfering over the names as well. 833 i = 0; 834 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 835 I2 = NF->arg_begin(); I != E; ++I, ++i) 836 if (ArgAlive[i]) { 837 // If this is a live argument, move the name and users over to the new 838 // version. 839 I->replaceAllUsesWith(I2); 840 I2->takeName(I); 841 ++I2; 842 } else { 843 // If this argument is dead, replace any uses of it with null constants 844 // (these are guaranteed to become unused later on). 845 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 846 } 847 848 // If we change the return value of the function we must rewrite any return 849 // instructions. Check this now. 850 if (F->getReturnType() != NF->getReturnType()) 851 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 852 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 853 Value *RetVal; 854 855 if (NFTy->getReturnType() == Type::VoidTy) { 856 RetVal = 0; 857 } else { 858 assert (isa<StructType>(RetTy)); 859 // The original return value was a struct, insert 860 // extractvalue/insertvalue chains to extract only the values we need 861 // to return and insert them into our new result. 862 // This does generate messy code, but we'll let it to instcombine to 863 // clean that up. 864 Value *OldRet = RI->getOperand(0); 865 // Start out building up our return value from undef 866 RetVal = llvm::UndefValue::get(NRetTy); 867 for (unsigned i = 0; i != RetCount; ++i) 868 if (NewRetIdxs[i] != -1) { 869 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 870 "oldret", RI); 871 if (RetTypes.size() > 1) { 872 // We're still returning a struct, so reinsert the value into 873 // our new return value at the new index 874 875 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 876 "newret", RI); 877 } else { 878 // We are now only returning a simple value, so just return the 879 // extracted value. 880 RetVal = EV; 881 } 882 } 883 } 884 // Replace the return instruction with one returning the new return 885 // value (possibly 0 if we became void). 886 ReturnInst::Create(RetVal, RI); 887 BB->getInstList().erase(RI); 888 } 889 890 // Now that the old function is dead, delete it. 891 F->eraseFromParent(); 892 893 return true; 894} 895 896bool DAE::runOnModule(Module &M) { 897 bool Changed = false; 898 899 // First pass: Do a simple check to see if any functions can have their "..." 900 // removed. We can do this if they never call va_start. This loop cannot be 901 // fused with the next loop, because deleting a function invalidates 902 // information computed while surveying other functions. 903 DOUT << "DAE - Deleting dead varargs\n"; 904 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 905 Function &F = *I++; 906 if (F.getFunctionType()->isVarArg()) 907 Changed |= DeleteDeadVarargs(F); 908 } 909 910 // Second phase:loop through the module, determining which arguments are live. 911 // We assume all arguments are dead unless proven otherwise (allowing us to 912 // determine that dead arguments passed into recursive functions are dead). 913 // 914 DOUT << "DAE - Determining liveness\n"; 915 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 916 SurveyFunction(*I); 917 918 // Now, remove all dead arguments and return values from each function in 919 // turn 920 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 921 // Increment now, because the function will probably get removed (ie 922 // replaced by a new one). 923 Function *F = I++; 924 Changed |= RemoveDeadStuffFromFunction(F); 925 } 926 return Changed; 927} 928