DeadArgumentElimination.cpp revision f6ccee5a9d2b9573f679bca6266ade3eb8cd3f88
1//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass deletes dead arguments from internal functions. Dead argument 11// elimination removes arguments which are directly dead, as well as arguments 12// only passed into function calls as dead arguments of other functions. This 13// pass also deletes dead return values in a similar way. 14// 15// This pass is often useful as a cleanup pass to run after aggressive 16// interprocedural passes, which add possibly-dead arguments or return values. 17// 18//===----------------------------------------------------------------------===// 19 20#define DEBUG_TYPE "deadargelim" 21#include "llvm/Transforms/IPO.h" 22#include "llvm/CallingConv.h" 23#include "llvm/Constant.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/LLVMContext.h" 28#include "llvm/Module.h" 29#include "llvm/Pass.h" 30#include "llvm/Support/CallSite.h" 31#include "llvm/Support/Debug.h" 32#include "llvm/ADT/SmallVector.h" 33#include "llvm/ADT/Statistic.h" 34#include "llvm/ADT/StringExtras.h" 35#include "llvm/Support/Compiler.h" 36#include <map> 37#include <set> 38using namespace llvm; 39 40STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 41STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 42 43namespace { 44 /// DAE - The dead argument elimination pass. 45 /// 46 class VISIBILITY_HIDDEN DAE : public ModulePass { 47 public: 48 49 /// Struct that represents (part of) either a return value or a function 50 /// argument. Used so that arguments and return values can be used 51 /// interchangably. 52 struct RetOrArg { 53 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), 54 IsArg(IsArg) {} 55 const Function *F; 56 unsigned Idx; 57 bool IsArg; 58 59 /// Make RetOrArg comparable, so we can put it into a map. 60 bool operator<(const RetOrArg &O) const { 61 if (F != O.F) 62 return F < O.F; 63 else if (Idx != O.Idx) 64 return Idx < O.Idx; 65 else 66 return IsArg < O.IsArg; 67 } 68 69 /// Make RetOrArg comparable, so we can easily iterate the multimap. 70 bool operator==(const RetOrArg &O) const { 71 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 72 } 73 74 std::string getDescription() const { 75 return std::string((IsArg ? "Argument #" : "Return value #")) 76 + utostr(Idx) + " of function " + F->getNameStr(); 77 } 78 }; 79 80 /// Liveness enum - During our initial pass over the program, we determine 81 /// that things are either alive or maybe alive. We don't mark anything 82 /// explicitly dead (even if we know they are), since anything not alive 83 /// with no registered uses (in Uses) will never be marked alive and will 84 /// thus become dead in the end. 85 enum Liveness { Live, MaybeLive }; 86 87 /// Convenience wrapper 88 RetOrArg CreateRet(const Function *F, unsigned Idx) { 89 return RetOrArg(F, Idx, false); 90 } 91 /// Convenience wrapper 92 RetOrArg CreateArg(const Function *F, unsigned Idx) { 93 return RetOrArg(F, Idx, true); 94 } 95 96 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 97 /// This maps a return value or argument to any MaybeLive return values or 98 /// arguments it uses. This allows the MaybeLive values to be marked live 99 /// when any of its users is marked live. 100 /// For example (indices are left out for clarity): 101 /// - Uses[ret F] = ret G 102 /// This means that F calls G, and F returns the value returned by G. 103 /// - Uses[arg F] = ret G 104 /// This means that some function calls G and passes its result as an 105 /// argument to F. 106 /// - Uses[ret F] = arg F 107 /// This means that F returns one of its own arguments. 108 /// - Uses[arg F] = arg G 109 /// This means that G calls F and passes one of its own (G's) arguments 110 /// directly to F. 111 UseMap Uses; 112 113 typedef std::set<RetOrArg> LiveSet; 114 typedef std::set<const Function*> LiveFuncSet; 115 116 /// This set contains all values that have been determined to be live. 117 LiveSet LiveValues; 118 /// This set contains all values that are cannot be changed in any way. 119 LiveFuncSet LiveFunctions; 120 121 typedef SmallVector<RetOrArg, 5> UseVector; 122 123 public: 124 static char ID; // Pass identification, replacement for typeid 125 DAE() : ModulePass(&ID) {} 126 bool runOnModule(Module &M); 127 128 virtual bool ShouldHackArguments() const { return false; } 129 130 private: 131 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 132 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 133 unsigned RetValNum = 0); 134 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 135 136 void SurveyFunction(Function &F); 137 void MarkValue(const RetOrArg &RA, Liveness L, 138 const UseVector &MaybeLiveUses); 139 void MarkLive(const RetOrArg &RA); 140 void MarkLive(const Function &F); 141 void PropagateLiveness(const RetOrArg &RA); 142 bool RemoveDeadStuffFromFunction(Function *F); 143 bool DeleteDeadVarargs(Function &Fn); 144 }; 145} 146 147 148char DAE::ID = 0; 149static RegisterPass<DAE> 150X("deadargelim", "Dead Argument Elimination"); 151 152namespace { 153 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 154 /// deletes arguments to functions which are external. This is only for use 155 /// by bugpoint. 156 struct DAH : public DAE { 157 static char ID; 158 virtual bool ShouldHackArguments() const { return true; } 159 }; 160} 161 162char DAH::ID = 0; 163static RegisterPass<DAH> 164Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 165 166/// createDeadArgEliminationPass - This pass removes arguments from functions 167/// which are not used by the body of the function. 168/// 169ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 170ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 171 172/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 173/// llvm.vastart is never called, the varargs list is dead for the function. 174bool DAE::DeleteDeadVarargs(Function &Fn) { 175 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 176 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; 177 178 // Ensure that the function is only directly called. 179 if (Fn.hasAddressTaken()) 180 return false; 181 182 // Okay, we know we can transform this function if safe. Scan its body 183 // looking for calls to llvm.vastart. 184 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 185 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 186 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 187 if (II->getIntrinsicID() == Intrinsic::vastart) 188 return false; 189 } 190 } 191 } 192 193 // If we get here, there are no calls to llvm.vastart in the function body, 194 // remove the "..." and adjust all the calls. 195 196 // Start by computing a new prototype for the function, which is the same as 197 // the old function, but doesn't have isVarArg set. 198 const FunctionType *FTy = Fn.getFunctionType(); 199 LLVMContext &Context = FTy->getContext(); 200 201 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 202 FunctionType *NFTy = Context.getFunctionType(FTy->getReturnType(), 203 Params, false); 204 unsigned NumArgs = Params.size(); 205 206 // Create the new function body and insert it into the module... 207 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 208 NF->copyAttributesFrom(&Fn); 209 Fn.getParent()->getFunctionList().insert(&Fn, NF); 210 NF->takeName(&Fn); 211 212 // Loop over all of the callers of the function, transforming the call sites 213 // to pass in a smaller number of arguments into the new function. 214 // 215 std::vector<Value*> Args; 216 while (!Fn.use_empty()) { 217 CallSite CS = CallSite::get(Fn.use_back()); 218 Instruction *Call = CS.getInstruction(); 219 220 // Pass all the same arguments. 221 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 222 223 // Drop any attributes that were on the vararg arguments. 224 AttrListPtr PAL = CS.getAttributes(); 225 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 226 SmallVector<AttributeWithIndex, 8> AttributesVec; 227 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 228 AttributesVec.push_back(PAL.getSlot(i)); 229 if (Attributes FnAttrs = PAL.getFnAttributes()) 230 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 231 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 232 } 233 234 Instruction *New; 235 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 236 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 237 Args.begin(), Args.end(), "", Call); 238 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 239 cast<InvokeInst>(New)->setAttributes(PAL); 240 } else { 241 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 242 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 243 cast<CallInst>(New)->setAttributes(PAL); 244 if (cast<CallInst>(Call)->isTailCall()) 245 cast<CallInst>(New)->setTailCall(); 246 } 247 Args.clear(); 248 249 if (!Call->use_empty()) 250 Call->replaceAllUsesWith(New); 251 252 New->takeName(Call); 253 254 // Finally, remove the old call from the program, reducing the use-count of 255 // F. 256 Call->eraseFromParent(); 257 } 258 259 // Since we have now created the new function, splice the body of the old 260 // function right into the new function, leaving the old rotting hulk of the 261 // function empty. 262 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 263 264 // Loop over the argument list, transfering uses of the old arguments over to 265 // the new arguments, also transfering over the names as well. While we're at 266 // it, remove the dead arguments from the DeadArguments list. 267 // 268 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 269 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 270 // Move the name and users over to the new version. 271 I->replaceAllUsesWith(I2); 272 I2->takeName(I); 273 } 274 275 // Finally, nuke the old function. 276 Fn.eraseFromParent(); 277 return true; 278} 279 280/// Convenience function that returns the number of return values. It returns 0 281/// for void functions and 1 for functions not returning a struct. It returns 282/// the number of struct elements for functions returning a struct. 283static unsigned NumRetVals(const Function *F) { 284 if (F->getReturnType() == Type::VoidTy) 285 return 0; 286 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 287 return STy->getNumElements(); 288 else 289 return 1; 290} 291 292/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 293/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 294/// liveness of Use. 295DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 296 // We're live if our use or its Function is already marked as live. 297 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 298 return Live; 299 300 // We're maybe live otherwise, but remember that we must become live if 301 // Use becomes live. 302 MaybeLiveUses.push_back(Use); 303 return MaybeLive; 304} 305 306 307/// SurveyUse - This looks at a single use of an argument or return value 308/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 309/// if it causes the used value to become MaybeAlive. 310/// 311/// RetValNum is the return value number to use when this use is used in a 312/// return instruction. This is used in the recursion, you should always leave 313/// it at 0. 314DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 315 unsigned RetValNum) { 316 Value *V = *U; 317 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 318 // The value is returned from a function. It's only live when the 319 // function's return value is live. We use RetValNum here, for the case 320 // that U is really a use of an insertvalue instruction that uses the 321 // orginal Use. 322 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 323 // We might be live, depending on the liveness of Use. 324 return MarkIfNotLive(Use, MaybeLiveUses); 325 } 326 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 327 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 328 && IV->hasIndices()) 329 // The use we are examining is inserted into an aggregate. Our liveness 330 // depends on all uses of that aggregate, but if it is used as a return 331 // value, only index at which we were inserted counts. 332 RetValNum = *IV->idx_begin(); 333 334 // Note that if we are used as the aggregate operand to the insertvalue, 335 // we don't change RetValNum, but do survey all our uses. 336 337 Liveness Result = MaybeLive; 338 for (Value::use_iterator I = IV->use_begin(), 339 E = V->use_end(); I != E; ++I) { 340 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 341 if (Result == Live) 342 break; 343 } 344 return Result; 345 } 346 CallSite CS = CallSite::get(V); 347 if (CS.getInstruction()) { 348 Function *F = CS.getCalledFunction(); 349 if (F) { 350 // Used in a direct call. 351 352 // Find the argument number. We know for sure that this use is an 353 // argument, since if it was the function argument this would be an 354 // indirect call and the we know can't be looking at a value of the 355 // label type (for the invoke instruction). 356 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 357 358 if (ArgNo >= F->getFunctionType()->getNumParams()) 359 // The value is passed in through a vararg! Must be live. 360 return Live; 361 362 assert(CS.getArgument(ArgNo) 363 == CS.getInstruction()->getOperand(U.getOperandNo()) 364 && "Argument is not where we expected it"); 365 366 // Value passed to a normal call. It's only live when the corresponding 367 // argument to the called function turns out live. 368 RetOrArg Use = CreateArg(F, ArgNo); 369 return MarkIfNotLive(Use, MaybeLiveUses); 370 } 371 } 372 // Used in any other way? Value must be live. 373 return Live; 374} 375 376/// SurveyUses - This looks at all the uses of the given value 377/// Returns the Liveness deduced from the uses of this value. 378/// 379/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 380/// the result is Live, MaybeLiveUses might be modified but its content should 381/// be ignored (since it might not be complete). 382DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 383 // Assume it's dead (which will only hold if there are no uses at all..). 384 Liveness Result = MaybeLive; 385 // Check each use. 386 for (Value::use_iterator I = V->use_begin(), 387 E = V->use_end(); I != E; ++I) { 388 Result = SurveyUse(I, MaybeLiveUses); 389 if (Result == Live) 390 break; 391 } 392 return Result; 393} 394 395// SurveyFunction - This performs the initial survey of the specified function, 396// checking out whether or not it uses any of its incoming arguments or whether 397// any callers use the return value. This fills in the LiveValues set and Uses 398// map. 399// 400// We consider arguments of non-internal functions to be intrinsically alive as 401// well as arguments to functions which have their "address taken". 402// 403void DAE::SurveyFunction(Function &F) { 404 unsigned RetCount = NumRetVals(&F); 405 // Assume all return values are dead 406 typedef SmallVector<Liveness, 5> RetVals; 407 RetVals RetValLiveness(RetCount, MaybeLive); 408 409 typedef SmallVector<UseVector, 5> RetUses; 410 // These vectors map each return value to the uses that make it MaybeLive, so 411 // we can add those to the Uses map if the return value really turns out to be 412 // MaybeLive. Initialized to a list of RetCount empty lists. 413 RetUses MaybeLiveRetUses(RetCount); 414 415 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 416 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 417 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 418 != F.getFunctionType()->getReturnType()) { 419 // We don't support old style multiple return values. 420 MarkLive(F); 421 return; 422 } 423 424 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 425 MarkLive(F); 426 return; 427 } 428 429 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 430 // Keep track of the number of live retvals, so we can skip checks once all 431 // of them turn out to be live. 432 unsigned NumLiveRetVals = 0; 433 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 434 // Loop all uses of the function. 435 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 436 // If the function is PASSED IN as an argument, its address has been 437 // taken. 438 CallSite CS = CallSite::get(*I); 439 if (!CS.getInstruction() || !CS.isCallee(I)) { 440 MarkLive(F); 441 return; 442 } 443 444 // If this use is anything other than a call site, the function is alive. 445 Instruction *TheCall = CS.getInstruction(); 446 if (!TheCall) { // Not a direct call site? 447 MarkLive(F); 448 return; 449 } 450 451 // If we end up here, we are looking at a direct call to our function. 452 453 // Now, check how our return value(s) is/are used in this caller. Don't 454 // bother checking return values if all of them are live already. 455 if (NumLiveRetVals != RetCount) { 456 if (STy) { 457 // Check all uses of the return value. 458 for (Value::use_iterator I = TheCall->use_begin(), 459 E = TheCall->use_end(); I != E; ++I) { 460 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 461 if (Ext && Ext->hasIndices()) { 462 // This use uses a part of our return value, survey the uses of 463 // that part and store the results for this index only. 464 unsigned Idx = *Ext->idx_begin(); 465 if (RetValLiveness[Idx] != Live) { 466 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 467 if (RetValLiveness[Idx] == Live) 468 NumLiveRetVals++; 469 } 470 } else { 471 // Used by something else than extractvalue. Mark all return 472 // values as live. 473 for (unsigned i = 0; i != RetCount; ++i ) 474 RetValLiveness[i] = Live; 475 NumLiveRetVals = RetCount; 476 break; 477 } 478 } 479 } else { 480 // Single return value 481 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 482 if (RetValLiveness[0] == Live) 483 NumLiveRetVals = RetCount; 484 } 485 } 486 } 487 488 // Now we've inspected all callers, record the liveness of our return values. 489 for (unsigned i = 0; i != RetCount; ++i) 490 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); 491 492 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 493 494 // Now, check all of our arguments. 495 unsigned i = 0; 496 UseVector MaybeLiveArgUses; 497 for (Function::arg_iterator AI = F.arg_begin(), 498 E = F.arg_end(); AI != E; ++AI, ++i) { 499 // See what the effect of this use is (recording any uses that cause 500 // MaybeLive in MaybeLiveArgUses). 501 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 502 // Mark the result. 503 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 504 // Clear the vector again for the next iteration. 505 MaybeLiveArgUses.clear(); 506 } 507} 508 509/// MarkValue - This function marks the liveness of RA depending on L. If L is 510/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 511/// such that RA will be marked live if any use in MaybeLiveUses gets marked 512/// live later on. 513void DAE::MarkValue(const RetOrArg &RA, Liveness L, 514 const UseVector &MaybeLiveUses) { 515 switch (L) { 516 case Live: MarkLive(RA); break; 517 case MaybeLive: 518 { 519 // Note any uses of this value, so this return value can be 520 // marked live whenever one of the uses becomes live. 521 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 522 UE = MaybeLiveUses.end(); UI != UE; ++UI) 523 Uses.insert(std::make_pair(*UI, RA)); 524 break; 525 } 526 } 527} 528 529/// MarkLive - Mark the given Function as alive, meaning that it cannot be 530/// changed in any way. Additionally, 531/// mark any values that are used as this function's parameters or by its return 532/// values (according to Uses) live as well. 533void DAE::MarkLive(const Function &F) { 534 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 535 // Mark the function as live. 536 LiveFunctions.insert(&F); 537 // Mark all arguments as live. 538 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 539 PropagateLiveness(CreateArg(&F, i)); 540 // Mark all return values as live. 541 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) 542 PropagateLiveness(CreateRet(&F, i)); 543} 544 545/// MarkLive - Mark the given return value or argument as live. Additionally, 546/// mark any values that are used by this value (according to Uses) live as 547/// well. 548void DAE::MarkLive(const RetOrArg &RA) { 549 if (LiveFunctions.count(RA.F)) 550 return; // Function was already marked Live. 551 552 if (!LiveValues.insert(RA).second) 553 return; // We were already marked Live. 554 555 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 556 PropagateLiveness(RA); 557} 558 559/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 560/// to any other values it uses (according to Uses). 561void DAE::PropagateLiveness(const RetOrArg &RA) { 562 // We don't use upper_bound (or equal_range) here, because our recursive call 563 // to ourselves is likely to cause the upper_bound (which is the first value 564 // not belonging to RA) to become erased and the iterator invalidated. 565 UseMap::iterator Begin = Uses.lower_bound(RA); 566 UseMap::iterator E = Uses.end(); 567 UseMap::iterator I; 568 for (I = Begin; I != E && I->first == RA; ++I) 569 MarkLive(I->second); 570 571 // Erase RA from the Uses map (from the lower bound to wherever we ended up 572 // after the loop). 573 Uses.erase(Begin, I); 574} 575 576// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 577// that are not in LiveValues. Transform the function and all of the callees of 578// the function to not have these arguments and return values. 579// 580bool DAE::RemoveDeadStuffFromFunction(Function *F) { 581 // Don't modify fully live functions 582 if (LiveFunctions.count(F)) 583 return false; 584 585 // Start by computing a new prototype for the function, which is the same as 586 // the old function, but has fewer arguments and a different return type. 587 const FunctionType *FTy = F->getFunctionType(); 588 std::vector<const Type*> Params; 589 590 // Set up to build a new list of parameter attributes. 591 SmallVector<AttributeWithIndex, 8> AttributesVec; 592 const AttrListPtr &PAL = F->getAttributes(); 593 594 // The existing function return attributes. 595 Attributes RAttrs = PAL.getRetAttributes(); 596 Attributes FnAttrs = PAL.getFnAttributes(); 597 598 // Find out the new return value. 599 600 const Type *RetTy = FTy->getReturnType(); 601 const Type *NRetTy = NULL; 602 unsigned RetCount = NumRetVals(F); 603 604 LLVMContext &Context = RetTy->getContext(); 605 606 // -1 means unused, other numbers are the new index 607 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 608 std::vector<const Type*> RetTypes; 609 if (RetTy == Type::VoidTy) { 610 NRetTy = Type::VoidTy; 611 } else { 612 const StructType *STy = dyn_cast<StructType>(RetTy); 613 if (STy) 614 // Look at each of the original return values individually. 615 for (unsigned i = 0; i != RetCount; ++i) { 616 RetOrArg Ret = CreateRet(F, i); 617 if (LiveValues.erase(Ret)) { 618 RetTypes.push_back(STy->getElementType(i)); 619 NewRetIdxs[i] = RetTypes.size() - 1; 620 } else { 621 ++NumRetValsEliminated; 622 DOUT << "DAE - Removing return value " << i << " from " 623 << F->getNameStart() << "\n"; 624 } 625 } 626 else 627 // We used to return a single value. 628 if (LiveValues.erase(CreateRet(F, 0))) { 629 RetTypes.push_back(RetTy); 630 NewRetIdxs[0] = 0; 631 } else { 632 DOUT << "DAE - Removing return value from " << F->getNameStart() 633 << "\n"; 634 ++NumRetValsEliminated; 635 } 636 if (RetTypes.size() > 1) 637 // More than one return type? Return a struct with them. Also, if we used 638 // to return a struct and didn't change the number of return values, 639 // return a struct again. This prevents changing {something} into 640 // something and {} into void. 641 // Make the new struct packed if we used to return a packed struct 642 // already. 643 NRetTy = Context.getStructType(RetTypes, STy->isPacked()); 644 else if (RetTypes.size() == 1) 645 // One return type? Just a simple value then, but only if we didn't use to 646 // return a struct with that simple value before. 647 NRetTy = RetTypes.front(); 648 else if (RetTypes.size() == 0) 649 // No return types? Make it void, but only if we didn't use to return {}. 650 NRetTy = Type::VoidTy; 651 } 652 653 assert(NRetTy && "No new return type found?"); 654 655 // Remove any incompatible attributes, but only if we removed all return 656 // values. Otherwise, ensure that we don't have any conflicting attributes 657 // here. Currently, this should not be possible, but special handling might be 658 // required when new return value attributes are added. 659 if (NRetTy == Type::VoidTy) 660 RAttrs &= ~Attribute::typeIncompatible(NRetTy); 661 else 662 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0 663 && "Return attributes no longer compatible?"); 664 665 if (RAttrs) 666 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 667 668 // Remember which arguments are still alive. 669 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 670 // Construct the new parameter list from non-dead arguments. Also construct 671 // a new set of parameter attributes to correspond. Skip the first parameter 672 // attribute, since that belongs to the return value. 673 unsigned i = 0; 674 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 675 I != E; ++I, ++i) { 676 RetOrArg Arg = CreateArg(F, i); 677 if (LiveValues.erase(Arg)) { 678 Params.push_back(I->getType()); 679 ArgAlive[i] = true; 680 681 // Get the original parameter attributes (skipping the first one, that is 682 // for the return value. 683 if (Attributes Attrs = PAL.getParamAttributes(i + 1)) 684 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs)); 685 } else { 686 ++NumArgumentsEliminated; 687 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 688 << ") from " << F->getNameStart() << "\n"; 689 } 690 } 691 692 if (FnAttrs != Attribute::None) 693 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 694 695 // Reconstruct the AttributesList based on the vector we constructed. 696 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end()); 697 698 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 699 // have zero fixed arguments. 700 // 701 // Note that we apply this hack for a vararg fuction that does not have any 702 // arguments anymore, but did have them before (so don't bother fixing 703 // functions that were already broken wrt CWriter). 704 bool ExtraArgHack = false; 705 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 706 ExtraArgHack = true; 707 Params.push_back(Type::Int32Ty); 708 } 709 710 // Create the new function type based on the recomputed parameters. 711 FunctionType *NFTy = Context.getFunctionType(NRetTy, Params, 712 FTy->isVarArg()); 713 714 // No change? 715 if (NFTy == FTy) 716 return false; 717 718 // Create the new function body and insert it into the module... 719 Function *NF = Function::Create(NFTy, F->getLinkage()); 720 NF->copyAttributesFrom(F); 721 NF->setAttributes(NewPAL); 722 // Insert the new function before the old function, so we won't be processing 723 // it again. 724 F->getParent()->getFunctionList().insert(F, NF); 725 NF->takeName(F); 726 727 // Loop over all of the callers of the function, transforming the call sites 728 // to pass in a smaller number of arguments into the new function. 729 // 730 std::vector<Value*> Args; 731 while (!F->use_empty()) { 732 CallSite CS = CallSite::get(F->use_back()); 733 Instruction *Call = CS.getInstruction(); 734 735 AttributesVec.clear(); 736 const AttrListPtr &CallPAL = CS.getAttributes(); 737 738 // The call return attributes. 739 Attributes RAttrs = CallPAL.getRetAttributes(); 740 Attributes FnAttrs = CallPAL.getFnAttributes(); 741 // Adjust in case the function was changed to return void. 742 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType()); 743 if (RAttrs) 744 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs)); 745 746 // Declare these outside of the loops, so we can reuse them for the second 747 // loop, which loops the varargs. 748 CallSite::arg_iterator I = CS.arg_begin(); 749 unsigned i = 0; 750 // Loop over those operands, corresponding to the normal arguments to the 751 // original function, and add those that are still alive. 752 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 753 if (ArgAlive[i]) { 754 Args.push_back(*I); 755 // Get original parameter attributes, but skip return attributes. 756 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 757 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 758 } 759 760 if (ExtraArgHack) 761 Args.push_back(Context.getUndef(Type::Int32Ty)); 762 763 // Push any varargs arguments on the list. Don't forget their attributes. 764 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 765 Args.push_back(*I); 766 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1)) 767 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 768 } 769 770 if (FnAttrs != Attribute::None) 771 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs)); 772 773 // Reconstruct the AttributesList based on the vector we constructed. 774 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(), 775 AttributesVec.end()); 776 777 Instruction *New; 778 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 779 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 780 Args.begin(), Args.end(), "", Call); 781 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 782 cast<InvokeInst>(New)->setAttributes(NewCallPAL); 783 } else { 784 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 785 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 786 cast<CallInst>(New)->setAttributes(NewCallPAL); 787 if (cast<CallInst>(Call)->isTailCall()) 788 cast<CallInst>(New)->setTailCall(); 789 } 790 Args.clear(); 791 792 if (!Call->use_empty()) { 793 if (New->getType() == Call->getType()) { 794 // Return type not changed? Just replace users then. 795 Call->replaceAllUsesWith(New); 796 New->takeName(Call); 797 } else if (New->getType() == Type::VoidTy) { 798 // Our return value has uses, but they will get removed later on. 799 // Replace by null for now. 800 Call->replaceAllUsesWith(Context.getNullValue(Call->getType())); 801 } else { 802 assert(isa<StructType>(RetTy) && 803 "Return type changed, but not into a void. The old return type" 804 " must have been a struct!"); 805 Instruction *InsertPt = Call; 806 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 807 BasicBlock::iterator IP = II->getNormalDest()->begin(); 808 while (isa<PHINode>(IP)) ++IP; 809 InsertPt = IP; 810 } 811 812 // We used to return a struct. Instead of doing smart stuff with all the 813 // uses of this struct, we will just rebuild it using 814 // extract/insertvalue chaining and let instcombine clean that up. 815 // 816 // Start out building up our return value from undef 817 Value *RetVal = Context.getUndef(RetTy); 818 for (unsigned i = 0; i != RetCount; ++i) 819 if (NewRetIdxs[i] != -1) { 820 Value *V; 821 if (RetTypes.size() > 1) 822 // We are still returning a struct, so extract the value from our 823 // return value 824 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", 825 InsertPt); 826 else 827 // We are now returning a single element, so just insert that 828 V = New; 829 // Insert the value at the old position 830 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); 831 } 832 // Now, replace all uses of the old call instruction with the return 833 // struct we built 834 Call->replaceAllUsesWith(RetVal); 835 New->takeName(Call); 836 } 837 } 838 839 // Finally, remove the old call from the program, reducing the use-count of 840 // F. 841 Call->eraseFromParent(); 842 } 843 844 // Since we have now created the new function, splice the body of the old 845 // function right into the new function, leaving the old rotting hulk of the 846 // function empty. 847 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 848 849 // Loop over the argument list, transfering uses of the old arguments over to 850 // the new arguments, also transfering over the names as well. 851 i = 0; 852 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 853 I2 = NF->arg_begin(); I != E; ++I, ++i) 854 if (ArgAlive[i]) { 855 // If this is a live argument, move the name and users over to the new 856 // version. 857 I->replaceAllUsesWith(I2); 858 I2->takeName(I); 859 ++I2; 860 } else { 861 // If this argument is dead, replace any uses of it with null constants 862 // (these are guaranteed to become unused later on). 863 I->replaceAllUsesWith(Context.getNullValue(I->getType())); 864 } 865 866 // If we change the return value of the function we must rewrite any return 867 // instructions. Check this now. 868 if (F->getReturnType() != NF->getReturnType()) 869 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 870 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 871 Value *RetVal; 872 873 if (NFTy->getReturnType() == Type::VoidTy) { 874 RetVal = 0; 875 } else { 876 assert (isa<StructType>(RetTy)); 877 // The original return value was a struct, insert 878 // extractvalue/insertvalue chains to extract only the values we need 879 // to return and insert them into our new result. 880 // This does generate messy code, but we'll let it to instcombine to 881 // clean that up. 882 Value *OldRet = RI->getOperand(0); 883 // Start out building up our return value from undef 884 RetVal = Context.getUndef(NRetTy); 885 for (unsigned i = 0; i != RetCount; ++i) 886 if (NewRetIdxs[i] != -1) { 887 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 888 "oldret", RI); 889 if (RetTypes.size() > 1) { 890 // We're still returning a struct, so reinsert the value into 891 // our new return value at the new index 892 893 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 894 "newret", RI); 895 } else { 896 // We are now only returning a simple value, so just return the 897 // extracted value. 898 RetVal = EV; 899 } 900 } 901 } 902 // Replace the return instruction with one returning the new return 903 // value (possibly 0 if we became void). 904 ReturnInst::Create(RetVal, RI); 905 BB->getInstList().erase(RI); 906 } 907 908 // Now that the old function is dead, delete it. 909 F->eraseFromParent(); 910 911 return true; 912} 913 914bool DAE::runOnModule(Module &M) { 915 bool Changed = false; 916 917 // First pass: Do a simple check to see if any functions can have their "..." 918 // removed. We can do this if they never call va_start. This loop cannot be 919 // fused with the next loop, because deleting a function invalidates 920 // information computed while surveying other functions. 921 DOUT << "DAE - Deleting dead varargs\n"; 922 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 923 Function &F = *I++; 924 if (F.getFunctionType()->isVarArg()) 925 Changed |= DeleteDeadVarargs(F); 926 } 927 928 // Second phase:loop through the module, determining which arguments are live. 929 // We assume all arguments are dead unless proven otherwise (allowing us to 930 // determine that dead arguments passed into recursive functions are dead). 931 // 932 DOUT << "DAE - Determining liveness\n"; 933 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 934 SurveyFunction(*I); 935 936 // Now, remove all dead arguments and return values from each function in 937 // turn 938 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 939 // Increment now, because the function will probably get removed (ie 940 // replaced by a new one). 941 Function *F = I++; 942 Changed |= RemoveDeadStuffFromFunction(F); 943 } 944 return Changed; 945} 946