DeadArgumentElimination.cpp revision ca85d65277e7d07985712e49b267b34a65fe6aab
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/Support/Compiler.h" 34#include <map> 35#include <set> 36using namespace llvm; 37 38STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 39STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 40 41namespace { 42 /// DAE - The dead argument elimination pass. 43 /// 44 class VISIBILITY_HIDDEN DAE : public ModulePass { 45 public: 46 47 /// Struct that represent either a (part of a) return value or a function 48 /// argument. Used so that arguments and return values can be used 49 /// interchangably. 50 struct RetOrArg { 51 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx), IsArg(IsArg) {} 52 const Function *F; 53 unsigned Idx; 54 bool IsArg; 55 56 /// Make RetOrArg comparable, so we can put it into a map 57 bool operator<(const RetOrArg &O) const { 58 if (F != O.F) 59 return F < O.F; 60 else if (Idx != O.Idx) 61 return Idx < O.Idx; 62 else 63 return IsArg < O.IsArg; 64 } 65 }; 66 67 /// Liveness enum - During our initial pass over the program, we determine 68 /// that things are either definately alive, definately dead, or in need of 69 /// interprocedural analysis (MaybeLive). 70 /// 71 enum Liveness { Live, MaybeLive, Dead }; 72 73 /// Convenience wrapper 74 RetOrArg CreateRet(const Function *F, unsigned Idx) { return RetOrArg(F, Idx, false); } 75 /// Convenience wrapper 76 RetOrArg CreateArg(const Function *F, unsigned Idx) { return RetOrArg(F, Idx, true); } 77 78 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 79 /// This map maps a return value or argument to all return values or 80 /// arguments it uses. 81 /// For example (indices are left out for clarity): 82 /// - Uses[ret F] = ret G 83 /// This means that F calls G, and F returns the value returned by G. 84 /// - Uses[arg F] = ret G 85 /// This means that some function calls G and passes its result as an 86 /// argument to F. 87 /// - Uses[ret F] = arg F 88 /// This means that F returns one of its own arguments. 89 /// - Uses[arg F] = arg G 90 /// This means that G calls F and passes one of its own (G's) arguments 91 /// directly to F. 92 UseMap Uses; 93 94 typedef std::set<RetOrArg> LiveSet; 95 96 /// This set contains all values that have been determined to be live 97 LiveSet LiveValues; 98 99 typedef SmallVector<RetOrArg, 5> UseVector; 100 101 /// This is the set of functions that have been inspected. Since LiveValues 102 /// keeps a list of live values for inspected functions only, this way we 103 /// can prevent uninspected functions becoming completely dead. 104 std::set<Function*> InspectedFunctions; 105 106 public: 107 static char ID; // Pass identification, replacement for typeid 108 DAE() : ModulePass((intptr_t)&ID) {} 109 bool runOnModule(Module &M); 110 111 virtual bool ShouldHackArguments() const { return false; } 112 113 private: 114 Liveness IsMaybeLive(RetOrArg Use, UseVector &MaybeLiveUses); 115 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, unsigned RetValNum = 0); 116 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 117 118 void SurveyFunction(Function &F); 119 void MarkValue(const RetOrArg &RA, Liveness L, const UseVector &MaybeLiveUses); 120 void MarkLive(RetOrArg RA); 121 bool RemoveDeadStuffFromFunction(Function *F); 122 bool DeleteDeadVarargs(Function &Fn); 123 }; 124} 125 126 127char DAE::ID = 0; 128static RegisterPass<DAE> 129X("deadargelim", "Dead Argument Elimination"); 130 131namespace { 132 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 133 /// deletes arguments to functions which are external. This is only for use 134 /// by bugpoint. 135 struct DAH : public DAE { 136 static char ID; 137 virtual bool ShouldHackArguments() const { return true; } 138 }; 139} 140 141char DAH::ID = 0; 142static RegisterPass<DAH> 143Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 144 145/// createDeadArgEliminationPass - This pass removes arguments from functions 146/// which are not used by the body of the function. 147/// 148ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 149ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 150 151/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 152/// llvm.vastart is never called, the varargs list is dead for the function. 153bool DAE::DeleteDeadVarargs(Function &Fn) { 154 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 155 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false; 156 157 // Ensure that the function is only directly called. 158 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) { 159 // If this use is anything other than a call site, give up. 160 CallSite CS = CallSite::get(*I); 161 Instruction *TheCall = CS.getInstruction(); 162 if (!TheCall) return false; // Not a direct call site? 163 164 // The addr of this function is passed to the call. 165 if (I.getOperandNo() != 0) return false; 166 } 167 168 // Okay, we know we can transform this function if safe. Scan its body 169 // looking for calls to llvm.vastart. 170 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 171 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 172 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 173 if (II->getIntrinsicID() == Intrinsic::vastart) 174 return false; 175 } 176 } 177 } 178 179 // If we get here, there are no calls to llvm.vastart in the function body, 180 // remove the "..." and adjust all the calls. 181 182 // Start by computing a new prototype for the function, which is the same as 183 // the old function, but doesn't have isVarArg set. 184 const FunctionType *FTy = Fn.getFunctionType(); 185 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 186 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false); 187 unsigned NumArgs = Params.size(); 188 189 // Create the new function body and insert it into the module... 190 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 191 NF->copyAttributesFrom(&Fn); 192 Fn.getParent()->getFunctionList().insert(&Fn, NF); 193 NF->takeName(&Fn); 194 195 // Loop over all of the callers of the function, transforming the call sites 196 // to pass in a smaller number of arguments into the new function. 197 // 198 std::vector<Value*> Args; 199 while (!Fn.use_empty()) { 200 CallSite CS = CallSite::get(Fn.use_back()); 201 Instruction *Call = CS.getInstruction(); 202 203 // Pass all the same arguments. 204 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 205 206 // Drop any attributes that were on the vararg arguments. 207 PAListPtr PAL = CS.getParamAttrs(); 208 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 209 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 210 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 211 ParamAttrsVec.push_back(PAL.getSlot(i)); 212 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 213 } 214 215 Instruction *New; 216 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 217 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 218 Args.begin(), Args.end(), "", Call); 219 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 220 cast<InvokeInst>(New)->setParamAttrs(PAL); 221 } else { 222 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 223 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 224 cast<CallInst>(New)->setParamAttrs(PAL); 225 if (cast<CallInst>(Call)->isTailCall()) 226 cast<CallInst>(New)->setTailCall(); 227 } 228 Args.clear(); 229 230 if (!Call->use_empty()) 231 Call->replaceAllUsesWith(New); 232 233 New->takeName(Call); 234 235 // Finally, remove the old call from the program, reducing the use-count of 236 // F. 237 Call->eraseFromParent(); 238 } 239 240 // Since we have now created the new function, splice the body of the old 241 // function right into the new function, leaving the old rotting hulk of the 242 // function empty. 243 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 244 245 // Loop over the argument list, transfering uses of the old arguments over to 246 // the new arguments, also transfering over the names as well. While we're at 247 // it, remove the dead arguments from the DeadArguments list. 248 // 249 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 250 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 251 // Move the name and users over to the new version. 252 I->replaceAllUsesWith(I2); 253 I2->takeName(I); 254 } 255 256 // Finally, nuke the old function. 257 Fn.eraseFromParent(); 258 return true; 259} 260 261/// Convenience function that returns the number of return values. It returns 0 262/// for void functions and 1 for functions not returning a struct. It returns 263/// the number of struct elements for functions returning a struct. 264static unsigned NumRetVals(const Function *F) { 265 if (F->getReturnType() == Type::VoidTy) 266 return 0; 267 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) 268 return STy->getNumElements(); 269 else 270 return 1; 271} 272 273/// IsMaybeAlive - This checks Use for liveness. If Use is live, returns Live, 274/// else returns MaybeLive. Also, adds Use to MaybeLiveUses in the latter case. 275DAE::Liveness DAE::IsMaybeLive(RetOrArg Use, UseVector &MaybeLiveUses) { 276 // We're live if our use is already marked as live 277 if (LiveValues.count(Use)) 278 return Live; 279 280 // We're maybe live otherwise, but remember that we must become live if 281 // Use becomes live. 282 MaybeLiveUses.push_back(Use); 283 return MaybeLive; 284} 285 286 287/// SurveyUse - This looks at a single use of an argument or return value 288/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 289/// if it causes the used value to become MaybeAlive. 290/// 291/// RetValNum is the return value number to use when this use is used in a 292/// return instruction. This is used in the recursion, you should always leave 293/// it at 0. 294DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, unsigned RetValNum) { 295 Value *V = *U; 296 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 297 // The value is returned from another function. It's only live when the 298 // caller's return value is live 299 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 300 // We might be live, depending on the liveness of Use 301 return IsMaybeLive(Use, MaybeLiveUses); 302 } 303 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 304 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() && IV->hasIndices()) 305 // The use we are examining is inserted into an aggregate. Our liveness 306 // depends on all uses of that aggregate, but if it is used as a return 307 // value, only index at which we were inserted counts. 308 RetValNum = *IV->idx_begin(); 309 310 // Note that if we are used as the aggregate operand to the insertvalue, 311 // we don't change RetValNum, but do survey all our uses. 312 313 Liveness Result = Dead; 314 for (Value::use_iterator I = IV->use_begin(), 315 E = V->use_end(); I != E; ++I) { 316 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 317 if (Result == Live) 318 break; 319 } 320 return Result; 321 } 322 CallSite CS = CallSite::get(V); 323 if (CS.getInstruction()) { 324 Function *F = CS.getCalledFunction(); 325 if (F) { 326 // Used in a direct call 327 328 // Check for vararg. Do - 1 to skip the first operand to call (the 329 // function itself). 330 if (U.getOperandNo() - 1 >= F->getFunctionType()->getNumParams()) 331 // The value is passed in through a vararg! Must be live. 332 return Live; 333 334 // Value passed to a normal call. It's only live when the corresponding 335 // argument (operand number - 1 to skip the function pointer operand) to 336 // the called function turns out live 337 RetOrArg Use = CreateArg(F, U.getOperandNo() - 1); 338 return IsMaybeLive(Use, MaybeLiveUses); 339 } else { 340 // Used in any other way? Value must be live. 341 return Live; 342 } 343 } 344 // Used in any other way? Value must be live. 345 return Live; 346} 347 348/// SurveyUses - This looks at all the uses of the given return value 349/// (possibly a partial return value from a function returning a struct). 350/// Returns the Liveness deduced from the uses of this value. 351/// 352/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. 353DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 354 // Assume it's dead (which will only hold if there are no uses at all..) 355 Liveness Result = Dead; 356 // Check each use 357 for (Value::use_iterator I = V->use_begin(), 358 E = V->use_end(); I != E; ++I) { 359 Result = SurveyUse(I, MaybeLiveUses); 360 if (Result == Live) 361 break; 362 } 363 return Result; 364} 365 366// SurveyFunction - This performs the initial survey of the specified function, 367// checking out whether or not it uses any of its incoming arguments or whether 368// any callers use the return value. This fills in the 369// (Dead|MaybeLive|Live)(Arguments|RetVal) sets. 370// 371// We consider arguments of non-internal functions to be intrinsically alive as 372// well as arguments to functions which have their "address taken". 373// 374void DAE::SurveyFunction(Function &F) { 375 InspectedFunctions.insert(&F); 376 bool FunctionIntrinsicallyLive = false; 377 unsigned RetCount = NumRetVals(&F); 378 // Assume all return values are dead 379 typedef SmallVector<Liveness, 5> RetVals; 380 RetVals RetValLiveness(RetCount, Dead); 381 382 // These vectors maps each return value to the uses that make it MaybeLive, so 383 // we can add those to the MaybeLiveRetVals list if the return value 384 // really turns out to be MaybeLive. Initializes to RetCount empty vectors 385 typedef SmallVector<UseVector, 5> RetUses; 386 // Intialized to a list of RetCount empty lists 387 RetUses MaybeLiveRetUses(RetCount); 388 389 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 390 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 391 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() != F.getFunctionType()->getReturnType()) { 392 // We don't support old style multiple return values 393 FunctionIntrinsicallyLive = true; 394 break; 395 } 396 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) 397 FunctionIntrinsicallyLive = true; 398 if (!FunctionIntrinsicallyLive) { 399 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 400 // Keep track of the number of live retvals, so we can skip checks once all 401 // of them turn out to be live. 402 unsigned NumLiveRetVals = 0; 403 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 404 // Loop all uses of the function 405 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 406 // If the function is PASSED IN as an argument, its address has been taken 407 if (I.getOperandNo() != 0) { 408 FunctionIntrinsicallyLive = true; 409 break; 410 } 411 412 // If this use is anything other than a call site, the function is alive. 413 CallSite CS = CallSite::get(*I); 414 Instruction *TheCall = CS.getInstruction(); 415 if (!TheCall) { // Not a direct call site? 416 FunctionIntrinsicallyLive = true; 417 break; 418 } 419 420 // If we end up here, we are looking at a direct call to our function. 421 422 // Now, check how our return value(s) is/are used in this caller. Don't 423 // bother checking return values if all of them are live already 424 if (NumLiveRetVals != RetCount) { 425 if (STy) { 426 // Check all uses of the return value 427 for (Value::use_iterator I = TheCall->use_begin(), 428 E = TheCall->use_end(); I != E; ++I) { 429 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 430 if (Ext && Ext->hasIndices()) { 431 // This use uses a part of our return value, survey the uses of that 432 // part and store the results for this index only. 433 unsigned Idx = *Ext->idx_begin(); 434 if (RetValLiveness[Idx] != Live) { 435 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 436 if (RetValLiveness[Idx] == Live) 437 NumLiveRetVals++; 438 } 439 } else { 440 // Used by something else than extractvalue. Mark all 441 // return values as live. 442 for (unsigned i = 0; i != RetCount; ++i ) 443 RetValLiveness[i] = Live; 444 NumLiveRetVals = RetCount; 445 break; 446 } 447 } 448 } else { 449 // Single return value 450 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 451 if (RetValLiveness[0] == Live) 452 NumLiveRetVals = RetCount; 453 } 454 } 455 } 456 } 457 if (FunctionIntrinsicallyLive) { 458 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 459 // Mark all arguments as live 460 unsigned i = 0; 461 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); 462 AI != E; ++AI, ++i) 463 MarkLive(CreateArg(&F, i)); 464 // Mark all return values as live 465 i = 0; 466 for (unsigned i = 0, e = RetValLiveness.size(); i != e; ++i) 467 MarkLive(CreateRet(&F, i)); 468 return; 469 } 470 471 // Now we've inspected all callers, record the liveness of our return values. 472 for (unsigned i = 0, e = RetValLiveness.size(); i != e; ++i) { 473 RetOrArg Ret = CreateRet(&F, i); 474 // Mark the result down 475 MarkValue(Ret, RetValLiveness[i], MaybeLiveRetUses[i]); 476 } 477 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 478 479 // Now, check all of our arguments 480 unsigned i = 0; 481 UseVector MaybeLiveArgUses; 482 for (Function::arg_iterator AI = F.arg_begin(), 483 E = F.arg_end(); AI != E; ++AI, ++i) { 484 // See what the effect of this use is (recording any uses that cause 485 // MaybeLive in MaybeLiveArgUses) 486 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 487 RetOrArg Arg = CreateArg(&F, i); 488 // Mark the result down 489 MarkValue(Arg, Result, MaybeLiveArgUses); 490 // Clear the vector again for the next iteration 491 MaybeLiveArgUses.clear(); 492 } 493} 494 495/// MarkValue - This function marks the liveness of RA depending on L. If L is 496/// MaybeLive, it also records any uses in MaybeLiveUses such that RA will be 497/// marked live if any use in MaybeLiveUses gets marked live later on. 498void DAE::MarkValue(const RetOrArg &RA, Liveness L, const UseVector &MaybeLiveUses) { 499 switch (L) { 500 case Live: MarkLive(RA); break; 501 case MaybeLive: 502 { 503 // Note any uses of this value, so this return value can be 504 // marked live whenever one of the uses becomes live. 505 UseMap::iterator Where = Uses.begin(); 506 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 507 UE = MaybeLiveUses.end(); UI != UE; ++UI) 508 Where = Uses.insert(Where, UseMap::value_type(*UI, RA)); 509 break; 510 } 511 case Dead: break; 512 } 513} 514 515/// MarkLive - Mark the given return value or argument as live. Additionally, 516/// mark any values that are used by this value (according to Uses) live as 517/// well. 518void DAE::MarkLive(RetOrArg RA) { 519 if (!LiveValues.insert(RA).second) 520 return; // We were already marked Live 521 522 if (RA.IsArg) 523 DOUT << "DAE - Marking argument " << RA.Idx << " to function " << RA.F->getNameStart() << " live\n"; 524 else 525 DOUT << "DAE - Marking return value " << RA.Idx << " of function " << RA.F->getNameStart() << " live\n"; 526 527 std::pair<UseMap::iterator, UseMap::iterator> Range = Uses.equal_range(RA); 528 UseMap::iterator E = Range.second; 529 UseMap::iterator I = Range.first; 530 for (; I != E; ++I) 531 MarkLive(I->second); 532 // Erase RA from the Uses map (from the lower bound to wherever we ended up 533 // after the loop). 534 Uses.erase(Range.first, Range.second); 535} 536 537// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 538// that are not in LiveValues. This function is a noop for any Function created 539// by this function before, or any function that was not inspected for liveness. 540// specified by the DeadArguments list. Transform the function and all of the 541// callees of the function to not have these arguments. 542// 543bool DAE::RemoveDeadStuffFromFunction(Function *F) { 544 // Don't process functions we didn't inspect (such as external functions, or 545 // functions that we've newly created). 546 if (!InspectedFunctions.count(F)) 547 return false; 548 549 // Start by computing a new prototype for the function, which is the same as 550 // the old function, but has fewer arguments and a different return type. 551 const FunctionType *FTy = F->getFunctionType(); 552 std::vector<const Type*> Params; 553 554 // Set up to build a new list of parameter attributes 555 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 556 const PAListPtr &PAL = F->getParamAttrs(); 557 558 // The existing function return attributes. 559 ParameterAttributes RAttrs = PAL.getParamAttrs(0); 560 561 562 // Find out the new return value 563 564 const Type *RetTy = FTy->getReturnType(); 565 const Type *NRetTy; 566 unsigned RetCount = NumRetVals(F); 567 // -1 means unused, other numbers are the new index 568 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 569 std::vector<const Type*> RetTypes; 570 if (RetTy != Type::VoidTy) { 571 const StructType *STy = dyn_cast<StructType>(RetTy); 572 if (STy) 573 // Look at each of the original return values individually 574 for (unsigned i = 0; i != RetCount; ++i) { 575 RetOrArg Ret = CreateRet(F, i); 576 if (LiveValues.erase(Ret)) { 577 RetTypes.push_back(STy->getElementType(i)); 578 NewRetIdxs[i] = RetTypes.size() - 1; 579 } else { 580 ++NumRetValsEliminated; 581 DOUT << "DAE - Removing return value " << i << " from " << F->getNameStart() << "\n"; 582 } 583 } 584 else 585 // We used to return a single value 586 if (LiveValues.erase(CreateRet(F, 0))) { 587 RetTypes.push_back(RetTy); 588 NewRetIdxs[0] = 0; 589 } else { 590 DOUT << "DAE - Removing return value from " << F->getNameStart() << "\n"; 591 ++NumRetValsEliminated; 592 } 593 if (RetTypes.size() == 0) 594 // No return types? Make it void 595 NRetTy = Type::VoidTy; 596 else if (RetTypes.size() == 1) 597 // One return type? Just a simple value then 598 NRetTy = RetTypes.front(); 599 else 600 // More return types? Return a struct with them 601 NRetTy = StructType::get(RetTypes); 602 } else { 603 NRetTy = Type::VoidTy; 604 } 605 606 // Remove any incompatible attributes 607 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy); 608 if (RAttrs) 609 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 610 611 // Remember which arguments are still alive 612 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 613 // Construct the new parameter list from non-dead arguments. Also construct 614 // a new set of parameter attributes to correspond. Skip the first parameter 615 // attribute, since that belongs to the return value. 616 unsigned i = 0; 617 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 618 I != E; ++I, ++i) { 619 RetOrArg Arg = CreateArg(F, i); 620 if (LiveValues.erase(Arg)) { 621 Params.push_back(I->getType()); 622 ArgAlive[i] = true; 623 624 // Get the original parameter attributes (skipping the first one, that is 625 // for the return value 626 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1)) 627 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs)); 628 } else { 629 ++NumArgumentsEliminated; 630 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() << ") from " << F->getNameStart() << "\n"; 631 } 632 } 633 634 // Reconstruct the ParamAttrsList based on the vector we constructed. 635 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 636 637 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 638 // have zero fixed arguments. 639 // 640 bool ExtraArgHack = false; 641 if (Params.empty() && FTy->isVarArg()) { 642 ExtraArgHack = true; 643 Params.push_back(Type::Int32Ty); 644 } 645 646 // Create the new function type based on the recomputed parameters. 647 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 648 649 // No change? 650 if (NFTy == FTy) 651 return false; 652 653 // Create the new function body and insert it into the module... 654 Function *NF = Function::Create(NFTy, F->getLinkage()); 655 NF->copyAttributesFrom(F); 656 NF->setParamAttrs(NewPAL); 657 F->getParent()->getFunctionList().insert(F, NF); 658 NF->takeName(F); 659 660 // Loop over all of the callers of the function, transforming the call sites 661 // to pass in a smaller number of arguments into the new function. 662 // 663 std::vector<Value*> Args; 664 while (!F->use_empty()) { 665 CallSite CS = CallSite::get(F->use_back()); 666 Instruction *Call = CS.getInstruction(); 667 ParamAttrsVec.clear(); 668 const PAListPtr &CallPAL = CS.getParamAttrs(); 669 670 // The call return attributes. 671 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0); 672 // Adjust in case the function was changed to return void. 673 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType()); 674 if (RAttrs) 675 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 676 677 // Declare these outside of the loops, so we can reuse them for the second 678 // loop, which loops the varargs 679 CallSite::arg_iterator I = CS.arg_begin(); 680 unsigned i = 0; 681 // Loop over those operands, corresponding to the normal arguments to the 682 // original function, and add those that are still alive. 683 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 684 if (ArgAlive[i]) { 685 Args.push_back(*I); 686 // Get original parameter attributes, but skip return attributes 687 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 688 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 689 } 690 691 if (ExtraArgHack) 692 Args.push_back(UndefValue::get(Type::Int32Ty)); 693 694 // Push any varargs arguments on the list. Don't forget their attributes. 695 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 696 Args.push_back(*I); 697 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 698 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 699 } 700 701 // Reconstruct the ParamAttrsList based on the vector we constructed. 702 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(), 703 ParamAttrsVec.end()); 704 705 Instruction *New; 706 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 707 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 708 Args.begin(), Args.end(), "", Call); 709 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 710 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL); 711 } else { 712 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 713 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 714 cast<CallInst>(New)->setParamAttrs(NewCallPAL); 715 if (cast<CallInst>(Call)->isTailCall()) 716 cast<CallInst>(New)->setTailCall(); 717 } 718 Args.clear(); 719 720 if (!Call->use_empty()) { 721 if (New->getType() == Type::VoidTy) 722 // Our return value was unused, replace by null for now, uses will get 723 // removed later on 724 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 725 else if (isa<StructType>(RetTy)) { 726 // The original return value was a struct, update all uses (which are 727 // all extractvalue instructions). 728 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end(); 729 I != E;) { 730 assert(isa<ExtractValueInst>(*I) && "Return value not only used by extractvalue?"); 731 ExtractValueInst *EV = cast<ExtractValueInst>(*I); 732 // Increment now, since we're about to throw away this use. 733 ++I; 734 assert(EV->hasIndices() && "Return value used by extractvalue without indices?"); 735 unsigned Idx = *EV->idx_begin(); 736 if (NewRetIdxs[Idx] != -1) { 737 if (RetTypes.size() > 1) { 738 // We're still returning a struct, create a new extractvalue 739 // instruction with the first index updated 740 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end()); 741 NewIdxs[0] = NewRetIdxs[Idx]; 742 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(), NewIdxs.end(), "retval", EV); 743 EV->replaceAllUsesWith(NEV); 744 EV->eraseFromParent(); 745 } else { 746 // We are now only returning a simple value, remove the 747 // extractvalue 748 EV->replaceAllUsesWith(New); 749 EV->eraseFromParent(); 750 } 751 } else { 752 // Value unused, replace uses by null for now, they will get removed 753 // later on 754 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType())); 755 EV->eraseFromParent(); 756 } 757 } 758 New->takeName(Call); 759 } else { 760 // The original function had a single return value 761 Call->replaceAllUsesWith(New); 762 New->takeName(Call); 763 } 764 } 765 766 // Finally, remove the old call from the program, reducing the use-count of 767 // F. 768 Call->eraseFromParent(); 769 } 770 771 // Since we have now created the new function, splice the body of the old 772 // function right into the new function, leaving the old rotting hulk of the 773 // function empty. 774 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 775 776 // Loop over the argument list, transfering uses of the old arguments over to 777 // the new arguments, also transfering over the names as well. 778 i = 0; 779 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 780 I2 = NF->arg_begin(); I != E; ++I, ++i) 781 if (ArgAlive[i]) { 782 // If this is a live argument, move the name and users over to the new 783 // version. 784 I->replaceAllUsesWith(I2); 785 I2->takeName(I); 786 ++I2; 787 } else { 788 // If this argument is dead, replace any uses of it with null constants 789 // (these are guaranteed to become unused later on) 790 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 791 } 792 793 // If we change the return value of the function we must rewrite any return 794 // instructions. Check this now. 795 if (F->getReturnType() != NF->getReturnType()) 796 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 797 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 798 Value *RetVal; 799 800 if (NFTy->getReturnType() == Type::VoidTy) { 801 RetVal = 0; 802 } else { 803 assert (isa<StructType>(RetTy)); 804 // The original return value was a struct, insert 805 // extractvalue/insertvalue chains to extract only the values we need 806 // to return and insert them into our new result. 807 // This does generate messy code, but we'll let it to instcombine to 808 // clean that up 809 Value *OldRet = RI->getOperand(0); 810 // Start out building up our return value from undef 811 RetVal = llvm::UndefValue::get(NRetTy); 812 for (unsigned i = 0; i != RetCount; ++i) 813 if (NewRetIdxs[i] != -1) { 814 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, "newret", RI); 815 if (RetTypes.size() > 1) { 816 // We're still returning a struct, so reinsert the value into 817 // our new return value at the new index 818 819 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], "oldret"); 820 } else { 821 // We are now only returning a simple value, so just return the 822 // extracted value 823 RetVal = EV; 824 } 825 } 826 } 827 // Replace the return instruction with one returning the new return 828 // value (possibly 0 if we became void). 829 ReturnInst::Create(RetVal, RI); 830 BB->getInstList().erase(RI); 831 } 832 833 // Now that the old function is dead, delete it. 834 F->eraseFromParent(); 835 836 return true; 837} 838 839bool DAE::runOnModule(Module &M) { 840 bool Changed = false; 841 // First pass: Do a simple check to see if any functions can have their "..." 842 // removed. We can do this if they never call va_start. This loop cannot be 843 // fused with the next loop, because deleting a function invalidates 844 // information computed while surveying other functions. 845 DOUT << "DAE - Deleting dead varargs\n"; 846 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 847 Function &F = *I++; 848 if (F.getFunctionType()->isVarArg()) 849 Changed |= DeleteDeadVarargs(F); 850 } 851 852 // Second phase:loop through the module, determining which arguments are live. 853 // We assume all arguments are dead unless proven otherwise (allowing us to 854 // determine that dead arguments passed into recursive functions are dead). 855 // 856 DOUT << "DAE - Determining liveness\n"; 857 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 858 SurveyFunction(*I); 859 860 // Now, remove all dead arguments and return values from each function in 861 // turn 862 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 863 // Increment now, because the function will probably get removed (ie 864 // replaced by a new one) 865 Function *F = I++; 866 Changed |= RemoveDeadStuffFromFunction(F); 867 } 868 869 return Changed; 870} 871