DeadArgumentElimination.cpp revision c95e44b4e0f7aa7a32be2f3649decf2ec006a503
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 /// Make RetOrArg comparable, so we can easily iterate the multimap 67 bool operator==(const RetOrArg &O) const { 68 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 69 } 70 }; 71 72 /// Liveness enum - During our initial pass over the program, we determine 73 /// that things are either definately alive, definately dead, or in need of 74 /// interprocedural analysis (MaybeLive). 75 /// 76 enum Liveness { Live, MaybeLive, Dead }; 77 78 /// Convenience wrapper 79 RetOrArg CreateRet(const Function *F, unsigned Idx) { return RetOrArg(F, Idx, false); } 80 /// Convenience wrapper 81 RetOrArg CreateArg(const Function *F, unsigned Idx) { return RetOrArg(F, Idx, true); } 82 83 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 84 /// This map maps a return value or argument to all return values or 85 /// arguments it uses. 86 /// For example (indices are left out for clarity): 87 /// - Uses[ret F] = ret G 88 /// This means that F calls G, and F returns the value returned by G. 89 /// - Uses[arg F] = ret G 90 /// This means that some function calls G and passes its result as an 91 /// argument to F. 92 /// - Uses[ret F] = arg F 93 /// This means that F returns one of its own arguments. 94 /// - Uses[arg F] = arg G 95 /// This means that G calls F and passes one of its own (G's) arguments 96 /// directly to F. 97 UseMap Uses; 98 99 typedef std::set<RetOrArg> LiveSet; 100 101 /// This set contains all values that have been determined to be live 102 LiveSet LiveValues; 103 104 typedef SmallVector<RetOrArg, 5> UseVector; 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 bool FunctionIntrinsicallyLive = false; 376 unsigned RetCount = NumRetVals(&F); 377 // Assume all return values are dead 378 typedef SmallVector<Liveness, 5> RetVals; 379 RetVals RetValLiveness(RetCount, Dead); 380 381 // These vectors maps each return value to the uses that make it MaybeLive, so 382 // we can add those to the MaybeLiveRetVals list if the return value 383 // really turns out to be MaybeLive. Initializes to RetCount empty vectors 384 typedef SmallVector<UseVector, 5> RetUses; 385 // Intialized to a list of RetCount empty lists 386 RetUses MaybeLiveRetUses(RetCount); 387 388 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 389 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 390 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() != F.getFunctionType()->getReturnType()) { 391 // We don't support old style multiple return values 392 FunctionIntrinsicallyLive = true; 393 break; 394 } 395 396 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) 397 FunctionIntrinsicallyLive = true; 398 399 if (!FunctionIntrinsicallyLive) { 400 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 401 // Keep track of the number of live retvals, so we can skip checks once all 402 // of them turn out to be live. 403 unsigned NumLiveRetVals = 0; 404 const Type *STy = dyn_cast<StructType>(F.getReturnType()); 405 // Loop all uses of the function 406 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 407 // If the function is PASSED IN as an argument, its address has been taken 408 if (I.getOperandNo() != 0) { 409 FunctionIntrinsicallyLive = true; 410 break; 411 } 412 413 // If this use is anything other than a call site, the function is alive. 414 CallSite CS = CallSite::get(*I); 415 Instruction *TheCall = CS.getInstruction(); 416 if (!TheCall) { // Not a direct call site? 417 FunctionIntrinsicallyLive = true; 418 break; 419 } 420 421 // If we end up here, we are looking at a direct call to our function. 422 423 // Now, check how our return value(s) is/are used in this caller. Don't 424 // bother checking return values if all of them are live already 425 if (NumLiveRetVals != RetCount) { 426 if (STy) { 427 // Check all uses of the return value 428 for (Value::use_iterator I = TheCall->use_begin(), 429 E = TheCall->use_end(); I != E; ++I) { 430 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 431 if (Ext && Ext->hasIndices()) { 432 // This use uses a part of our return value, survey the uses of that 433 // part and store the results for this index only. 434 unsigned Idx = *Ext->idx_begin(); 435 if (RetValLiveness[Idx] != Live) { 436 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); 437 if (RetValLiveness[Idx] == Live) 438 NumLiveRetVals++; 439 } 440 } else { 441 // Used by something else than extractvalue. Mark all 442 // return values as live. 443 for (unsigned i = 0; i != RetCount; ++i ) 444 RetValLiveness[i] = Live; 445 NumLiveRetVals = RetCount; 446 break; 447 } 448 } 449 } else { 450 // Single return value 451 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]); 452 if (RetValLiveness[0] == Live) 453 NumLiveRetVals = RetCount; 454 } 455 } 456 } 457 } 458 if (FunctionIntrinsicallyLive) { 459 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 460 // Mark all arguments as live 461 unsigned i = 0; 462 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); 463 AI != E; ++AI, ++i) 464 MarkLive(CreateArg(&F, i)); 465 // Mark all return values as live 466 i = 0; 467 for (unsigned i = 0, e = RetValLiveness.size(); i != e; ++i) 468 MarkLive(CreateRet(&F, i)); 469 return; 470 } 471 472 // Now we've inspected all callers, record the liveness of our return values. 473 for (unsigned i = 0, e = RetValLiveness.size(); i != e; ++i) { 474 RetOrArg Ret = CreateRet(&F, i); 475 // Mark the result down 476 MarkValue(Ret, RetValLiveness[i], MaybeLiveRetUses[i]); 477 } 478 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 479 480 // Now, check all of our arguments 481 unsigned i = 0; 482 UseVector MaybeLiveArgUses; 483 for (Function::arg_iterator AI = F.arg_begin(), 484 E = F.arg_end(); AI != E; ++AI, ++i) { 485 // See what the effect of this use is (recording any uses that cause 486 // MaybeLive in MaybeLiveArgUses) 487 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 488 RetOrArg Arg = CreateArg(&F, i); 489 // Mark the result down 490 MarkValue(Arg, Result, MaybeLiveArgUses); 491 // Clear the vector again for the next iteration 492 MaybeLiveArgUses.clear(); 493 } 494} 495 496/// MarkValue - This function marks the liveness of RA depending on L. If L is 497/// MaybeLive, it also records any uses in MaybeLiveUses such that RA will be 498/// marked live if any use in MaybeLiveUses gets marked live later on. 499void DAE::MarkValue(const RetOrArg &RA, Liveness L, const UseVector &MaybeLiveUses) { 500 switch (L) { 501 case Live: MarkLive(RA); break; 502 case MaybeLive: 503 { 504 // Note any uses of this value, so this return value can be 505 // marked live whenever one of the uses becomes live. 506 UseMap::iterator Where = Uses.begin(); 507 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 508 UE = MaybeLiveUses.end(); UI != UE; ++UI) 509 Where = Uses.insert(Where, UseMap::value_type(*UI, RA)); 510 break; 511 } 512 case Dead: break; 513 } 514} 515 516/// MarkLive - Mark the given return value or argument as live. Additionally, 517/// mark any values that are used by this value (according to Uses) live as 518/// well. 519void DAE::MarkLive(RetOrArg RA) { 520 if (!LiveValues.insert(RA).second) 521 return; // We were already marked Live 522 523 if (RA.IsArg) 524 DOUT << "DAE - Marking argument " << RA.Idx << " to function " << RA.F->getNameStart() << " live\n"; 525 else 526 DOUT << "DAE - Marking return value " << RA.Idx << " of function " << RA.F->getNameStart() << " live\n"; 527 528 // We don't use upper_bound (or equal_range) here, because our recursive call 529 // to ourselves is likely to mark the upper_bound (which is the first value 530 // not belonging to RA) to become erased and the iterator invalidated. 531 UseMap::iterator Begin = Uses.lower_bound(RA); 532 UseMap::iterator E = Uses.end(); 533 UseMap::iterator I; 534 for (I = Begin; I != E && I->first == RA; ++I) 535 MarkLive(I->second); 536 537 // Erase RA from the Uses map (from the lower bound to wherever we ended up 538 // after the loop). 539 Uses.erase(Begin, I); 540} 541 542// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 543// that are not in LiveValues. This function is a noop for any Function created 544// by this function before, or any function that was not inspected for liveness. 545// specified by the DeadArguments list. Transform the function and all of the 546// callees of the function to not have these arguments. 547// 548bool DAE::RemoveDeadStuffFromFunction(Function *F) { 549 // Quick exit path for external functions 550 if (!F->hasInternalLinkage() && (!ShouldHackArguments() || F->isIntrinsic())) 551 return false; 552 553 // Start by computing a new prototype for the function, which is the same as 554 // the old function, but has fewer arguments and a different return type. 555 const FunctionType *FTy = F->getFunctionType(); 556 std::vector<const Type*> Params; 557 558 // Set up to build a new list of parameter attributes 559 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 560 const PAListPtr &PAL = F->getParamAttrs(); 561 562 // The existing function return attributes. 563 ParameterAttributes RAttrs = PAL.getParamAttrs(0); 564 565 566 // Find out the new return value 567 568 const Type *RetTy = FTy->getReturnType(); 569 const Type *NRetTy; 570 unsigned RetCount = NumRetVals(F); 571 // -1 means unused, other numbers are the new index 572 SmallVector<int, 5> NewRetIdxs(RetCount, -1); 573 std::vector<const Type*> RetTypes; 574 if (RetTy != Type::VoidTy) { 575 const StructType *STy = dyn_cast<StructType>(RetTy); 576 if (STy) 577 // Look at each of the original return values individually 578 for (unsigned i = 0; i != RetCount; ++i) { 579 RetOrArg Ret = CreateRet(F, i); 580 if (LiveValues.erase(Ret)) { 581 RetTypes.push_back(STy->getElementType(i)); 582 NewRetIdxs[i] = RetTypes.size() - 1; 583 } else { 584 ++NumRetValsEliminated; 585 DOUT << "DAE - Removing return value " << i << " from " << F->getNameStart() << "\n"; 586 } 587 } 588 else 589 // We used to return a single value 590 if (LiveValues.erase(CreateRet(F, 0))) { 591 RetTypes.push_back(RetTy); 592 NewRetIdxs[0] = 0; 593 } else { 594 DOUT << "DAE - Removing return value from " << F->getNameStart() << "\n"; 595 ++NumRetValsEliminated; 596 } 597 if (RetTypes.size() == 0) 598 // No return types? Make it void 599 NRetTy = Type::VoidTy; 600 else if (RetTypes.size() == 1) 601 // One return type? Just a simple value then 602 NRetTy = RetTypes.front(); 603 else 604 // More return types? Return a struct with them 605 NRetTy = StructType::get(RetTypes); 606 } else { 607 NRetTy = Type::VoidTy; 608 } 609 610 // Remove any incompatible attributes 611 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy); 612 if (RAttrs) 613 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 614 615 // Remember which arguments are still alive 616 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 617 // Construct the new parameter list from non-dead arguments. Also construct 618 // a new set of parameter attributes to correspond. Skip the first parameter 619 // attribute, since that belongs to the return value. 620 unsigned i = 0; 621 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 622 I != E; ++I, ++i) { 623 RetOrArg Arg = CreateArg(F, i); 624 if (LiveValues.erase(Arg)) { 625 Params.push_back(I->getType()); 626 ArgAlive[i] = true; 627 628 // Get the original parameter attributes (skipping the first one, that is 629 // for the return value 630 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1)) 631 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs)); 632 } else { 633 ++NumArgumentsEliminated; 634 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() << ") from " << F->getNameStart() << "\n"; 635 } 636 } 637 638 // Reconstruct the ParamAttrsList based on the vector we constructed. 639 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 640 641 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 642 // have zero fixed arguments. 643 // 644 // Not that we apply this hack for a vararg fuction that does not have any 645 // arguments anymore, but did have them before (so don't bother fixing 646 // functions that were already broken wrt CWriter). 647 bool ExtraArgHack = false; 648 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) { 649 ExtraArgHack = true; 650 Params.push_back(Type::Int32Ty); 651 } 652 653 // Create the new function type based on the recomputed parameters. 654 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 655 656 // No change? 657 if (NFTy == FTy) 658 return false; 659 660 // Create the new function body and insert it into the module... 661 Function *NF = Function::Create(NFTy, F->getLinkage()); 662 NF->copyAttributesFrom(F); 663 NF->setParamAttrs(NewPAL); 664 // Insert the new function before the old function, so we won't be processing 665 // it again 666 F->getParent()->getFunctionList().insert(F, NF); 667 NF->takeName(F); 668 669 // Loop over all of the callers of the function, transforming the call sites 670 // to pass in a smaller number of arguments into the new function. 671 // 672 std::vector<Value*> Args; 673 while (!F->use_empty()) { 674 CallSite CS = CallSite::get(F->use_back()); 675 Instruction *Call = CS.getInstruction(); 676 if (!Call) { 677 DOUT << "Old: " << *FTy << "\n"; 678 DOUT << "New: " << *NFTy << "\n"; 679 } 680 681 ParamAttrsVec.clear(); 682 const PAListPtr &CallPAL = CS.getParamAttrs(); 683 684 // The call return attributes. 685 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0); 686 // Adjust in case the function was changed to return void. 687 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType()); 688 if (RAttrs) 689 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 690 691 // Declare these outside of the loops, so we can reuse them for the second 692 // loop, which loops the varargs 693 CallSite::arg_iterator I = CS.arg_begin(); 694 unsigned i = 0; 695 // Loop over those operands, corresponding to the normal arguments to the 696 // original function, and add those that are still alive. 697 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 698 if (ArgAlive[i]) { 699 Args.push_back(*I); 700 // Get original parameter attributes, but skip return attributes 701 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 702 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 703 } 704 705 if (ExtraArgHack) 706 Args.push_back(UndefValue::get(Type::Int32Ty)); 707 708 // Push any varargs arguments on the list. Don't forget their attributes. 709 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 710 Args.push_back(*I); 711 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 712 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 713 } 714 715 // Reconstruct the ParamAttrsList based on the vector we constructed. 716 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(), 717 ParamAttrsVec.end()); 718 719 Instruction *New; 720 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 721 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 722 Args.begin(), Args.end(), "", Call); 723 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 724 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL); 725 } else { 726 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 727 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 728 cast<CallInst>(New)->setParamAttrs(NewCallPAL); 729 if (cast<CallInst>(Call)->isTailCall()) 730 cast<CallInst>(New)->setTailCall(); 731 } 732 Args.clear(); 733 734 if (!Call->use_empty()) { 735 if (New->getType() == Type::VoidTy) 736 // Our return value was unused, replace by null for now, uses will get 737 // removed later on 738 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 739 else if (isa<StructType>(RetTy)) { 740 // The original return value was a struct, update all uses (which are 741 // all extractvalue instructions). 742 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end(); 743 I != E;) { 744 assert(isa<ExtractValueInst>(*I) && "Return value not only used by extractvalue?"); 745 ExtractValueInst *EV = cast<ExtractValueInst>(*I); 746 // Increment now, since we're about to throw away this use. 747 ++I; 748 assert(EV->hasIndices() && "Return value used by extractvalue without indices?"); 749 unsigned Idx = *EV->idx_begin(); 750 if (NewRetIdxs[Idx] != -1) { 751 if (RetTypes.size() > 1) { 752 // We're still returning a struct, create a new extractvalue 753 // instruction with the first index updated 754 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end()); 755 NewIdxs[0] = NewRetIdxs[Idx]; 756 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(), NewIdxs.end(), "retval", EV); 757 EV->replaceAllUsesWith(NEV); 758 EV->eraseFromParent(); 759 } else { 760 // We are now only returning a simple value, remove the 761 // extractvalue 762 EV->replaceAllUsesWith(New); 763 EV->eraseFromParent(); 764 } 765 } else { 766 // Value unused, replace uses by null for now, they will get removed 767 // later on 768 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType())); 769 EV->eraseFromParent(); 770 } 771 } 772 New->takeName(Call); 773 } else { 774 // The original function had a single return value 775 Call->replaceAllUsesWith(New); 776 New->takeName(Call); 777 } 778 } 779 780 // Finally, remove the old call from the program, reducing the use-count of 781 // F. 782 Call->eraseFromParent(); 783 } 784 785 // Since we have now created the new function, splice the body of the old 786 // function right into the new function, leaving the old rotting hulk of the 787 // function empty. 788 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 789 790 // Loop over the argument list, transfering uses of the old arguments over to 791 // the new arguments, also transfering over the names as well. 792 i = 0; 793 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 794 I2 = NF->arg_begin(); I != E; ++I, ++i) 795 if (ArgAlive[i]) { 796 // If this is a live argument, move the name and users over to the new 797 // version. 798 I->replaceAllUsesWith(I2); 799 I2->takeName(I); 800 ++I2; 801 } else { 802 // If this argument is dead, replace any uses of it with null constants 803 // (these are guaranteed to become unused later on) 804 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 805 } 806 807 // If we change the return value of the function we must rewrite any return 808 // instructions. Check this now. 809 if (F->getReturnType() != NF->getReturnType()) 810 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 811 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 812 Value *RetVal; 813 814 if (NFTy->getReturnType() == Type::VoidTy) { 815 RetVal = 0; 816 } else { 817 assert (isa<StructType>(RetTy)); 818 // The original return value was a struct, insert 819 // extractvalue/insertvalue chains to extract only the values we need 820 // to return and insert them into our new result. 821 // This does generate messy code, but we'll let it to instcombine to 822 // clean that up 823 Value *OldRet = RI->getOperand(0); 824 // Start out building up our return value from undef 825 RetVal = llvm::UndefValue::get(NRetTy); 826 for (unsigned i = 0; i != RetCount; ++i) 827 if (NewRetIdxs[i] != -1) { 828 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, "newret", RI); 829 if (RetTypes.size() > 1) { 830 // We're still returning a struct, so reinsert the value into 831 // our new return value at the new index 832 833 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], "oldret"); 834 } else { 835 // We are now only returning a simple value, so just return the 836 // extracted value 837 RetVal = EV; 838 } 839 } 840 } 841 // Replace the return instruction with one returning the new return 842 // value (possibly 0 if we became void). 843 ReturnInst::Create(RetVal, RI); 844 BB->getInstList().erase(RI); 845 } 846 847 // Now that the old function is dead, delete it. 848 F->eraseFromParent(); 849 850 return true; 851} 852 853bool DAE::runOnModule(Module &M) { 854 bool Changed = false; 855 // First pass: Do a simple check to see if any functions can have their "..." 856 // removed. We can do this if they never call va_start. This loop cannot be 857 // fused with the next loop, because deleting a function invalidates 858 // information computed while surveying other functions. 859 DOUT << "DAE - Deleting dead varargs\n"; 860 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 861 Function &F = *I++; 862 if (F.getFunctionType()->isVarArg()) 863 Changed |= DeleteDeadVarargs(F); 864 } 865 866 // Second phase:loop through the module, determining which arguments are live. 867 // We assume all arguments are dead unless proven otherwise (allowing us to 868 // determine that dead arguments passed into recursive functions are dead). 869 // 870 DOUT << "DAE - Determining liveness\n"; 871 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 872 SurveyFunction(*I); 873 874 // Now, remove all dead arguments and return values from each function in 875 // turn 876 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 877 // Increment now, because the function will probably get removed (ie 878 // replaced by a new one) 879 Function *F = I++; 880 Changed |= RemoveDeadStuffFromFunction(F); 881 } 882 883 return Changed; 884} 885