DeadArgumentElimination.cpp revision ddd1a79b6d9dafc7ebafea252266438f2b7c876a
1//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass deletes dead arguments from internal functions. Dead argument 11// elimination removes arguments which are directly dead, as well as arguments 12// only passed into function calls as dead arguments of other functions. This 13// pass also deletes dead return values in a similar way. 14// 15// This pass is often useful as a cleanup pass to run after aggressive 16// interprocedural passes, which add possibly-dead arguments or return values. 17// 18//===----------------------------------------------------------------------===// 19 20#define DEBUG_TYPE "deadargelim" 21#include "llvm/Transforms/IPO.h" 22#include "llvm/CallingConv.h" 23#include "llvm/Constant.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/Module.h" 28#include "llvm/Pass.h" 29#include "llvm/Support/CallSite.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/ADT/SmallVector.h" 32#include "llvm/ADT/Statistic.h" 33#include "llvm/ADT/StringExtras.h" 34#include "llvm/Support/Compiler.h" 35#include <map> 36#include <set> 37using namespace llvm; 38 39STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); 40STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); 41 42namespace { 43 /// DAE - The dead argument elimination pass. 44 /// 45 class VISIBILITY_HIDDEN DAE : public ModulePass { 46 public: 47 48 /// Struct that represents (part of) either a return value or a function 49 /// argument. Used so that arguments and return values can be used 50 /// interchangably. Idx == -1 means the entire return value, while other 51 /// indices mean the corresponding element in the struct return type (if 52 /// any). 53 struct RetOrArg { 54 RetOrArg(const Function* F, signed Idx, bool IsArg) : F(F), Idx(Idx), 55 IsArg(IsArg) {} 56 const Function *F; 57 signed Idx; 58 bool IsArg; 59 60 /// Make RetOrArg comparable, so we can put it into a map. 61 bool operator<(const RetOrArg &O) const { 62 if (F != O.F) 63 return F < O.F; 64 else if (Idx != O.Idx) 65 return Idx < O.Idx; 66 else 67 return IsArg < O.IsArg; 68 } 69 70 /// Make RetOrArg comparable, so we can easily iterate the multimap. 71 bool operator==(const RetOrArg &O) const { 72 return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 73 } 74 75 std::string getDescription() const { 76 return std::string((!IsArg && Idx != -1 ? "partial " : "")) 77 + (IsArg ? "argument #" : "return value") 78 + (!IsArg && Idx == -1 ? "" : " #" + utostr(Idx)) 79 + " of function " + F->getName(); 80 } 81 }; 82 83 /// Liveness enum - During our initial pass over the program, we determine 84 /// that things are either alive or maybe alive. We don't mark anything 85 /// explicitly dead (even if we know they are), since anything not alive 86 /// with no registered uses (in Uses) will never be marked alive and will 87 /// thus become dead in the end. 88 enum Liveness { Live, MaybeLive }; 89 90 /// Convenience wrapper 91 RetOrArg CreateRet(const Function *F, signed Idx) { 92 return RetOrArg(F, Idx, false); 93 } 94 /// Convenience wrapper 95 RetOrArg CreateArg(const Function *F, signed Idx) { 96 return RetOrArg(F, Idx, true); 97 } 98 99 typedef std::multimap<RetOrArg, RetOrArg> UseMap; 100 /// This maps a return value or argument to any MaybeLive return values or 101 /// arguments it uses. This allows the MaybeLive values to be marked live 102 /// when any of its users is marked live. 103 /// For example (indices are left out for clarity): 104 /// - Uses[ret F] = ret G 105 /// This means that F calls G, and F returns the value returned by G. 106 /// - Uses[arg F] = ret G 107 /// This means that some function calls G and passes its result as an 108 /// argument to F. 109 /// - Uses[ret F] = arg F 110 /// This means that F returns one of its own arguments. 111 /// - Uses[arg F] = arg G 112 /// This means that G calls F and passes one of its own (G's) arguments 113 /// directly to F. 114 UseMap Uses; 115 116 typedef std::set<RetOrArg> LiveSet; 117 typedef std::set<const Function*> LiveFuncSet; 118 119 /// This set contains all values that have been determined to be live. 120 LiveSet LiveValues; 121 /// This set contains all values that are cannot be changed in any way. 122 LiveFuncSet LiveFunctions; 123 124 typedef SmallVector<RetOrArg, 5> UseVector; 125 126 public: 127 static char ID; // Pass identification, replacement for typeid 128 DAE() : ModulePass((intptr_t)&ID) {} 129 bool runOnModule(Module &M); 130 131 virtual bool ShouldHackArguments() const { return false; } 132 133 private: 134 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 135 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 136 signed RetValNum = -1); 137 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses); 138 139 void SurveyFunction(Function &F); 140 void MarkValue(const RetOrArg &RA, Liveness L, 141 const UseVector &MaybeLiveUses); 142 void MarkLive(const RetOrArg &RA); 143 void MarkLive(const Function &F); 144 void PropagateLiveness(const RetOrArg &RA); 145 bool RemoveDeadStuffFromFunction(Function *F); 146 bool DeleteDeadVarargs(Function &Fn); 147 }; 148} 149 150 151char DAE::ID = 0; 152static RegisterPass<DAE> 153X("deadargelim", "Dead Argument Elimination"); 154 155namespace { 156 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but 157 /// deletes arguments to functions which are external. This is only for use 158 /// by bugpoint. 159 struct DAH : public DAE { 160 static char ID; 161 virtual bool ShouldHackArguments() const { return true; } 162 }; 163} 164 165char DAH::ID = 0; 166static RegisterPass<DAH> 167Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)"); 168 169/// createDeadArgEliminationPass - This pass removes arguments from functions 170/// which are not used by the body of the function. 171/// 172ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } 173ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } 174 175/// DeleteDeadVarargs - If this is an function that takes a ... list, and if 176/// llvm.vastart is never called, the varargs list is dead for the function. 177bool DAE::DeleteDeadVarargs(Function &Fn) { 178 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); 179 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false; 180 181 // Ensure that the function is only directly called. 182 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) { 183 // If this use is anything other than a call site, give up. 184 CallSite CS = CallSite::get(*I); 185 Instruction *TheCall = CS.getInstruction(); 186 if (!TheCall) return false; // Not a direct call site? 187 188 // The addr of this function is passed to the call. 189 if (I.getOperandNo() != 0) return false; 190 } 191 192 // Okay, we know we can transform this function if safe. Scan its body 193 // looking for calls to llvm.vastart. 194 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) { 195 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 196 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 197 if (II->getIntrinsicID() == Intrinsic::vastart) 198 return false; 199 } 200 } 201 } 202 203 // If we get here, there are no calls to llvm.vastart in the function body, 204 // remove the "..." and adjust all the calls. 205 206 // Start by computing a new prototype for the function, which is the same as 207 // the old function, but doesn't have isVarArg set. 208 const FunctionType *FTy = Fn.getFunctionType(); 209 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end()); 210 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false); 211 unsigned NumArgs = Params.size(); 212 213 // Create the new function body and insert it into the module... 214 Function *NF = Function::Create(NFTy, Fn.getLinkage()); 215 NF->copyAttributesFrom(&Fn); 216 Fn.getParent()->getFunctionList().insert(&Fn, NF); 217 NF->takeName(&Fn); 218 219 // Loop over all of the callers of the function, transforming the call sites 220 // to pass in a smaller number of arguments into the new function. 221 // 222 std::vector<Value*> Args; 223 while (!Fn.use_empty()) { 224 CallSite CS = CallSite::get(Fn.use_back()); 225 Instruction *Call = CS.getInstruction(); 226 227 // Pass all the same arguments. 228 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs); 229 230 // Drop any attributes that were on the vararg arguments. 231 PAListPtr PAL = CS.getParamAttrs(); 232 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) { 233 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 234 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i) 235 ParamAttrsVec.push_back(PAL.getSlot(i)); 236 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()); 237 } 238 239 Instruction *New; 240 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 241 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 242 Args.begin(), Args.end(), "", Call); 243 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 244 cast<InvokeInst>(New)->setParamAttrs(PAL); 245 } else { 246 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 247 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 248 cast<CallInst>(New)->setParamAttrs(PAL); 249 if (cast<CallInst>(Call)->isTailCall()) 250 cast<CallInst>(New)->setTailCall(); 251 } 252 Args.clear(); 253 254 if (!Call->use_empty()) 255 Call->replaceAllUsesWith(New); 256 257 New->takeName(Call); 258 259 // Finally, remove the old call from the program, reducing the use-count of 260 // F. 261 Call->eraseFromParent(); 262 } 263 264 // Since we have now created the new function, splice the body of the old 265 // function right into the new function, leaving the old rotting hulk of the 266 // function empty. 267 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); 268 269 // Loop over the argument list, transfering uses of the old arguments over to 270 // the new arguments, also transfering over the names as well. While we're at 271 // it, remove the dead arguments from the DeadArguments list. 272 // 273 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), 274 I2 = NF->arg_begin(); I != E; ++I, ++I2) { 275 // Move the name and users over to the new version. 276 I->replaceAllUsesWith(I2); 277 I2->takeName(I); 278 } 279 280 // Finally, nuke the old function. 281 Fn.eraseFromParent(); 282 return true; 283} 284 285/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not 286/// live, it adds Use to the MaybeLiveUses argument. Returns the determined 287/// liveness of Use. 288DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) { 289 // We're live if our use or its Function is already marked as live. 290 if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) 291 return Live; 292 293 // We're maybe live otherwise, but remember that we must become live if 294 // Use becomes live. 295 MaybeLiveUses.push_back(Use); 296 return MaybeLive; 297} 298 299/// SurveyUse - This looks at a single use of an argument or return value 300/// and determines if it should be alive or not. Adds this use to MaybeLiveUses 301/// if it causes the used value to become MaybeAlive. 302/// 303/// RetValNum is the return value number to use when this use is used in a 304/// return instruction. This is used in the recursion, you should always leave 305/// it at -1. 306DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses, 307 signed RetValNum) { 308 Value *V = *U; 309 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) { 310 // The value is returned from a function. It's only live when the 311 // function's return value is live. We use RetValNum here, for the case 312 // that U is really a use of an insertvalue instruction that uses the 313 // orginal Use. 314 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum); 315 // We might be live, depending on the liveness of Use. 316 return MarkIfNotLive(Use, MaybeLiveUses); 317 } 318 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { 319 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex() 320 && IV->hasIndices()) 321 // The use we are examining is inserted into an aggregate. Our liveness 322 // depends on all uses of that aggregate, but if it is used as a return 323 // value, only index at which we were inserted counts. 324 RetValNum = *IV->idx_begin(); 325 326 // Note that if we are used as the aggregate operand to the insertvalue, 327 // we don't change RetValNum, but do survey all our uses. 328 329 Liveness Result = MaybeLive; 330 for (Value::use_iterator I = IV->use_begin(), 331 E = V->use_end(); I != E; ++I) { 332 Result = SurveyUse(I, MaybeLiveUses, RetValNum); 333 if (Result == Live) 334 break; 335 } 336 return Result; 337 } 338 CallSite CS = CallSite::get(V); 339 if (CS.getInstruction()) { 340 Function *F = CS.getCalledFunction(); 341 if (F) { 342 // Used in a direct call. 343 344 // Find the argument number. We know for sure that this use is an 345 // argument, since if it was the function argument this would be an 346 // indirect call and the we know can't be looking at a value of the 347 // label type (for the invoke instruction). 348 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo()); 349 350 if (ArgNo >= F->getFunctionType()->getNumParams()) 351 // The value is passed in through a vararg! Must be live. 352 return Live; 353 354 assert(CS.getArgument(ArgNo) 355 == CS.getInstruction()->getOperand(U.getOperandNo()) 356 && "Argument is not where we expected it"); 357 358 // Value passed to a normal call. It's only live when the corresponding 359 // argument to the called function turns out live. 360 RetOrArg Use = CreateArg(F, ArgNo); 361 return MarkIfNotLive(Use, MaybeLiveUses); 362 } 363 } 364 // Used in any other way? Value must be live. 365 return Live; 366} 367 368/// SurveyUses - This looks at all the uses of the given value 369/// Returns the Liveness deduced from the uses of this value. 370/// 371/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If 372/// the result is Live, MaybeLiveUses might be modified but its content should 373/// be ignored (since it might not be complete). 374DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) { 375 // Assume it's dead (which will only hold if there are no uses at all..). 376 Liveness Result = MaybeLive; 377 // Check each use. 378 for (Value::use_iterator I = V->use_begin(), 379 E = V->use_end(); I != E; ++I) { 380 Result = SurveyUse(I, MaybeLiveUses); 381 if (Result == Live) 382 break; 383 } 384 return Result; 385} 386 387// SurveyFunction - This performs the initial survey of the specified function, 388// checking out whether or not it uses any of its incoming arguments or whether 389// any callers use the return value. This fills in the LiveValues set and Uses 390// map. 391// 392// We consider arguments of non-internal functions to be intrinsically alive as 393// well as arguments to functions which have their "address taken". 394// 395void DAE::SurveyFunction(Function &F) { 396 const StructType *STy = dyn_cast<StructType>(F.getFunctionType()->getReturnType()); 397 // Store the number of partial return values, which we only have if the return 398 // type is a struct. 399 unsigned PartialRetVals = (STy ? STy->getNumElements() : 0); 400 // Assume all return values are dead 401 typedef SmallVector<Liveness, 5> RetVals; 402 // Allocate one slot for the entire return value (index 0) and one for each 403 // partial return value. 404 RetVals RetValLiveness(PartialRetVals + 1, MaybeLive); 405 406 typedef SmallVector<UseVector, 5> RetUses; 407 // These vectors map each return value to the uses that make it MaybeLive, so 408 // we can add those to the Uses map if the return value really turns out to be 409 // MaybeLive. 410 // Allocate one slot for the entire return value (index 0) and one for each 411 // partial return value. 412 RetUses MaybeLiveRetUses(PartialRetVals + 1); 413 414 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 415 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) 416 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() 417 != F.getFunctionType()->getReturnType()) { 418 // We don't support old style multiple return values. 419 MarkLive(F); 420 return; 421 } 422 423 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) { 424 MarkLive(F); 425 return; 426 } 427 428 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n"; 429 // Loop all uses of the function. 430 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) { 431 // If the function is PASSED IN as an argument, its address has been 432 // taken. 433 if (I.getOperandNo() != 0) { 434 MarkLive(F); 435 return; 436 } 437 438 // If this use is anything other than a call site, the function is alive. 439 CallSite CS = CallSite::get(*I); 440 Instruction *TheCall = CS.getInstruction(); 441 if (!TheCall) { // Not a direct call site? 442 MarkLive(F); 443 return; 444 } 445 446 // If we end up here, we are looking at a direct call to our function. 447 448 // Now, check how our return value(s) is/are used in this caller. Don't 449 // bother checking return values if the entire value is live already. 450 if (RetValLiveness[0] != Live) { 451 // Check all uses of the return value. 452 for (Value::use_iterator I = TheCall->use_begin(), 453 E = TheCall->use_end(); I != E; ++I) { 454 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I); 455 if (Ext && Ext->hasIndices()) { 456 // This use uses a part of our return value, survey the uses of 457 // that part and store the results for this index only. 458 unsigned Idx = *Ext->idx_begin(); 459 // + 1 to skip the "entire retval" index (0) 460 Liveness &IsLive = RetValLiveness[Idx + 1]; 461 if (IsLive != Live) { 462 // Don't bother checking if this retval was already live 463 // Survey all uses of the extractvalue 464 // + 1 to skip the "entire retval" index (0) 465 IsLive = SurveyUses(Ext, MaybeLiveRetUses[Idx + 1]); 466 } 467 } else { 468 // Survey this use 469 RetValLiveness[0] = SurveyUse(I, MaybeLiveRetUses[0]); 470 if (RetValLiveness[0] == Live) 471 break; 472 } 473 } 474 } 475 } 476 477 // Now we've inspected all callers, record the liveness of our return values. 478 MarkValue(CreateRet(&F, -1), RetValLiveness[0], MaybeLiveRetUses[0]); 479 if (RetValLiveness[0] != Live) 480 // If the entire retval (0) is Live, MarkValue will have marked all other retvals live 481 // as well, so we can skip this. 482 for (unsigned i = 0; i != PartialRetVals; ++i) 483 // + 1 to skip the "entire retval" index (0) 484 MarkValue(CreateRet(&F, i), RetValLiveness[i + 1], MaybeLiveRetUses[i + 1]); 485 486 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n"; 487 488 // Now, check all of our arguments. 489 unsigned i = 0; 490 UseVector MaybeLiveArgUses; 491 for (Function::arg_iterator AI = F.arg_begin(), 492 E = F.arg_end(); AI != E; ++AI, ++i) { 493 // See what the effect of this use is (recording any uses that cause 494 // MaybeLive in MaybeLiveArgUses). 495 Liveness Result = SurveyUses(AI, MaybeLiveArgUses); 496 // Mark the result. 497 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); 498 // Clear the vector again for the next iteration. 499 MaybeLiveArgUses.clear(); 500 } 501} 502 503/// MarkValue - This function marks the liveness of RA depending on L. If L is 504/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, 505/// such that RA will be marked live if any use in MaybeLiveUses gets marked 506/// live later on. 507void DAE::MarkValue(const RetOrArg &RA, Liveness L, 508 const UseVector &MaybeLiveUses) { 509 switch (L) { 510 case Live: MarkLive(RA); break; 511 case MaybeLive: 512 { 513 // Note any uses of this value, so this return value can be 514 // marked live whenever one of the uses becomes live. 515 for (UseVector::const_iterator UI = MaybeLiveUses.begin(), 516 UE = MaybeLiveUses.end(); UI != UE; ++UI) 517 Uses.insert(std::make_pair(*UI, RA)); 518 break; 519 } 520 } 521} 522 523/// MarkLive - Mark the given Function as alive, meaning that it cannot be 524/// changed in any way. Additionally, 525/// mark any values that are used as this function's parameters or by its return 526/// values (according to Uses) live as well. 527void DAE::MarkLive(const Function &F) { 528 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n"; 529 // Mark the function as live. 530 LiveFunctions.insert(&F); 531 // Mark all arguments as live. 532 for (unsigned i = 0, e = F.arg_size(); i != e; ++i) 533 PropagateLiveness(CreateArg(&F, i)); 534 // Mark all return values as live. 535 const Type *RTy = F.getFunctionType()->getReturnType(); 536 if (const StructType *STy = dyn_cast<StructType>(RTy)) 537 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 538 PropagateLiveness(CreateRet(&F, i)); 539 PropagateLiveness(CreateRet(&F, -1)); 540} 541 542/// MarkLive - Mark the given return value or argument as live. Additionally, 543/// mark any values that are used by this value (according to Uses) live as 544/// well. 545void DAE::MarkLive(const RetOrArg &RA) { 546 if (LiveFunctions.count(RA.F)) 547 return; // Function was already marked Live. 548 549 if (!LiveValues.insert(RA).second) 550 return; // We were already marked Live. 551 552 DOUT << "DAE - Marking " << RA.getDescription() << " live\n"; 553 PropagateLiveness(RA); 554 555 if (!RA.IsArg && RA.Idx == -1) { 556 // Entire return value live? 557 const Type *RTy = RA.F->getFunctionType()->getReturnType(); 558 if (const StructType *STy = dyn_cast<StructType>(RTy)) 559 // And the function returns a struct? 560 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 561 // Mark all partial return values live as well then 562 MarkLive(CreateRet(RA.F, i)); 563 } 564} 565 566/// PropagateLiveness - Given that RA is a live value, propagate it's liveness 567/// to any other values it uses (according to Uses). 568void DAE::PropagateLiveness(const RetOrArg &RA) { 569 // We don't use upper_bound (or equal_range) here, because our recursive call 570 // to ourselves is likely to cause the upper_bound (which is the first value 571 // not belonging to RA) to become erased and the iterator invalidated. 572 UseMap::iterator Begin = Uses.lower_bound(RA); 573 UseMap::iterator E = Uses.end(); 574 UseMap::iterator I; 575 for (I = Begin; I != E && I->first == RA; ++I) 576 MarkLive(I->second); 577 578 // Erase RA from the Uses map (from the lower bound to wherever we ended up 579 // after the loop). 580 Uses.erase(Begin, I); 581} 582 583// RemoveDeadStuffFromFunction - Remove any arguments and return values from F 584// that are not in LiveValues. Transform the function and all of the callees of 585// the function to not have these arguments and return values. 586// 587bool DAE::RemoveDeadStuffFromFunction(Function *F) { 588 // Don't modify fully live functions 589 if (LiveFunctions.count(F)) 590 return false; 591 592 // Start by computing a new prototype for the function, which is the same as 593 // the old function, but has fewer arguments and a different return type. 594 const FunctionType *FTy = F->getFunctionType(); 595 std::vector<const Type*> Params; 596 597 // Set up to build a new list of parameter attributes. 598 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec; 599 const PAListPtr &PAL = F->getParamAttrs(); 600 601 // The existing function return attributes. 602 ParameterAttributes RAttrs = PAL.getParamAttrs(0); 603 604 605 // Find out the new return value. 606 607 const Type *RetTy = FTy->getReturnType(); 608 const StructType *STy = dyn_cast<StructType>(RetTy); 609 const unsigned PartialRetVals = (STy ? STy->getNumElements() : 0); 610 const Type *NRetTy = NULL; 611 // -1 means unused, other numbers are the new index. Initialized to -1 for 612 // every partial return value we have. 613 SmallVector<int, 5> NewRetIdxs(PartialRetVals, -1); 614 std::vector<const Type*> RetTypes; 615 if (LiveValues.count(CreateRet(F, -1))) { 616 // If the entire return value is live, leave it unchanged. 617 NRetTy = RetTy; 618 } else { 619 if (STy) { 620 // Look at each of the partial return values individually. 621 for (unsigned i = 0; i != PartialRetVals; ++i) { 622 RetOrArg Ret = CreateRet(F, i); 623 if (LiveValues.erase(Ret)) { 624 RetTypes.push_back(STy->getElementType(i)); 625 NewRetIdxs[i] = RetTypes.size() - 1; 626 } else { 627 ++NumRetValsEliminated; 628 DOUT << "DAE - Removing return value " << i << " from " 629 << F->getNameStart() << "\n"; 630 // We remove the value by not adding anything to RetTypes. 631 } 632 } 633 } else if (RetTy != Type::VoidTy) { 634 // We used to return a single value, which is now dead (already checked in 635 // the if above) 636 DOUT << "DAE - Removing return value from " << F->getNameStart() 637 << "\n"; 638 ++NumRetValsEliminated; 639 // We remove the value by not adding anything to RetTypes. 640 } 641 642 if (RetTypes.size() > 1) 643 // More than one return type? Return a struct with them. 644 // Make the new struct packed if we used to return a packed struct 645 // already. 646 NRetTy = StructType::get(RetTypes, STy->isPacked()); 647 else if (RetTypes.size() == 1) 648 // One return type? Just a simple value then, but only if we didn't use to 649 // return a struct with that simple value before. 650 NRetTy = RetTypes.front(); 651 else if (RetTypes.size() == 0) 652 // No return types? Make it void. 653 NRetTy = Type::VoidTy; 654 } 655 656 assert(NRetTy && "No new return type found?"); 657 658 // Remove any incompatible attributes, but only if we removed all return 659 // values. Otherwise, ensure that we don't have any conflicting attributes 660 // here. Currently, this should not be possible, but special handling might be 661 // required when new return value attributes are added. 662 if (NRetTy == Type::VoidTy) 663 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy); 664 else 665 assert((RAttrs & ParamAttr::typeIncompatible(NRetTy)) == 0 666 && "Return attributes no longer compatible?"); 667 668 if (RAttrs) 669 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 670 671 // Remember which arguments are still alive. 672 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); 673 // Construct the new parameter list from non-dead arguments. Also construct 674 // a new set of parameter attributes to correspond. Skip the first parameter 675 // attribute, since that belongs to the return value. 676 unsigned i = 0; 677 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 678 I != E; ++I, ++i) { 679 RetOrArg Arg = CreateArg(F, i); 680 if (LiveValues.erase(Arg)) { 681 Params.push_back(I->getType()); 682 ArgAlive[i] = true; 683 684 // Get the original parameter attributes (skipping the first one, that is 685 // for the return value. 686 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1)) 687 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs)); 688 } else { 689 ++NumArgumentsEliminated; 690 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart() 691 << ") from " << F->getNameStart() << "\n"; 692 } 693 } 694 695 // Reconstruct the ParamAttrsList based on the vector we constructed. 696 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.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 = FunctionType::get(NRetTy, Params, FTy->isVarArg()); 712 713 // No change? 714 if (NFTy == FTy) 715 return false; 716 717 // Create the new function body and insert it into the module... 718 Function *NF = Function::Create(NFTy, F->getLinkage()); 719 NF->copyAttributesFrom(F); 720 NF->setParamAttrs(NewPAL); 721 // Insert the new function before the old function, so we won't be processing 722 // it again. 723 F->getParent()->getFunctionList().insert(F, NF); 724 NF->takeName(F); 725 726 // Loop over all of the callers of the function, transforming the call sites 727 // to pass in a smaller number of arguments into the new function. 728 // 729 std::vector<Value*> Args; 730 while (!F->use_empty()) { 731 CallSite CS = CallSite::get(F->use_back()); 732 Instruction *Call = CS.getInstruction(); 733 734 ParamAttrsVec.clear(); 735 const PAListPtr &CallPAL = CS.getParamAttrs(); 736 737 // The call return attributes. 738 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0); 739 // Adjust in case the function was changed to return void. 740 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType()); 741 if (RAttrs) 742 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs)); 743 744 // Declare these outside of the loops, so we can reuse them for the second 745 // loop, which loops the varargs. 746 CallSite::arg_iterator I = CS.arg_begin(); 747 unsigned i = 0; 748 // Loop over those operands, corresponding to the normal arguments to the 749 // original function, and add those that are still alive. 750 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) 751 if (ArgAlive[i]) { 752 Args.push_back(*I); 753 // Get original parameter attributes, but skip return attributes. 754 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 755 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 756 } 757 758 if (ExtraArgHack) 759 Args.push_back(UndefValue::get(Type::Int32Ty)); 760 761 // Push any varargs arguments on the list. Don't forget their attributes. 762 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { 763 Args.push_back(*I); 764 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1)) 765 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs)); 766 } 767 768 // Reconstruct the ParamAttrsList based on the vector we constructed. 769 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(), 770 ParamAttrsVec.end()); 771 772 Instruction *New; 773 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 774 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 775 Args.begin(), Args.end(), "", Call); 776 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 777 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL); 778 } else { 779 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 780 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 781 cast<CallInst>(New)->setParamAttrs(NewCallPAL); 782 if (cast<CallInst>(Call)->isTailCall()) 783 cast<CallInst>(New)->setTailCall(); 784 } 785 Args.clear(); 786 787 if (!Call->use_empty()) { 788 if (New->getType() == Call->getType()) { 789 // Return type not changed? Just replace users then. 790 Call->replaceAllUsesWith(New); 791 New->takeName(Call); 792 } else if (New->getType() == Type::VoidTy) { 793 // Our return value has uses, but they will get removed later on. 794 // Replace by null for now. 795 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType())); 796 } else { 797 assert(isa<StructType>(RetTy) && "Return type changed, but not into a" 798 "void. The old return type must have" 799 "been a struct!"); 800 // The original return value was a struct, update all uses (which are 801 // all extractvalue instructions, or uses that are unused themselves). 802 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end(); 803 I != E;) { 804 if (ExtractValueInst *EV = dyn_cast<ExtractValueInst>(*I)) { 805 // Increment now, since we're about to throw away this use. 806 ++I; 807 assert(EV->hasIndices() && "Return value used by extractvalue without" 808 "indices?"); 809 unsigned Idx = *EV->idx_begin(); 810 if (NewRetIdxs[Idx] != -1) { 811 if (RetTypes.size() > 1) { 812 // We're still returning a struct, create a new extractvalue 813 // instruction with the first index updated 814 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end()); 815 NewIdxs[0] = NewRetIdxs[Idx]; 816 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(), 817 NewIdxs.end(), "retval", 818 EV); 819 EV->replaceAllUsesWith(NEV); 820 EV->eraseFromParent(); 821 } else { 822 // We are now only returning a simple value, remove the 823 // extractvalue. 824 EV->replaceAllUsesWith(New); 825 EV->eraseFromParent(); 826 } 827 } else { 828 // Value unused, replace uses by null for now, they will get removed 829 // later on. 830 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType())); 831 EV->eraseFromParent(); 832 } 833 } else { 834 // Not an extractvalue, so this use will become dead soon. Just 835 // replace it with null. 836 I.getUse().set(Constant::getNullValue(I.getUse().get()->getType())); 837 } 838 } 839 New->takeName(Call); 840 } 841 } 842 843 // Finally, remove the old call from the program, reducing the use-count of 844 // F. 845 Call->eraseFromParent(); 846 } 847 848 // Since we have now created the new function, splice the body of the old 849 // function right into the new function, leaving the old rotting hulk of the 850 // function empty. 851 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 852 853 // Loop over the argument list, transfering uses of the old arguments over to 854 // the new arguments, also transfering over the names as well. 855 i = 0; 856 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 857 I2 = NF->arg_begin(); I != E; ++I, ++i) 858 if (ArgAlive[i]) { 859 // If this is a live argument, move the name and users over to the new 860 // version. 861 I->replaceAllUsesWith(I2); 862 I2->takeName(I); 863 ++I2; 864 } else { 865 // If this argument is dead, replace any uses of it with null constants 866 // (these are guaranteed to become unused later on). 867 I->replaceAllUsesWith(Constant::getNullValue(I->getType())); 868 } 869 870 // If we change the return value of the function we must rewrite any return 871 // instructions. Check this now. 872 if (F->getReturnType() != NF->getReturnType()) 873 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB) 874 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 875 Value *RetVal; 876 877 if (NFTy->getReturnType() == Type::VoidTy) { 878 RetVal = 0; 879 } else { 880 assert (isa<StructType>(RetTy)); 881 // The original return value was a struct, insert 882 // extractvalue/insertvalue chains to extract only the values we need 883 // to return and insert them into our new result. 884 // This does generate messy code, but we'll let it to instcombine to 885 // clean that up. 886 Value *OldRet = RI->getOperand(0); 887 // Start out building up our return value from undef 888 RetVal = llvm::UndefValue::get(NRetTy); 889 for (unsigned i = 0; i != PartialRetVals; ++i) 890 if (NewRetIdxs[i] != -1) { 891 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, 892 "oldret", RI); 893 if (RetTypes.size() > 1) { 894 // We're still returning a struct, so reinsert the value into 895 // our new return value at the new index 896 897 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], 898 "newret", RI); 899 } else { 900 // We are now only returning a simple value, so just return the 901 // extracted value. 902 RetVal = EV; 903 } 904 } 905 } 906 // Replace the return instruction with one returning the new return 907 // value (possibly 0 if we became void). 908 ReturnInst::Create(RetVal, RI); 909 BB->getInstList().erase(RI); 910 } 911 912 // Now that the old function is dead, delete it. 913 F->eraseFromParent(); 914 915 return true; 916} 917 918bool DAE::runOnModule(Module &M) { 919 bool Changed = false; 920 921 // First pass: Do a simple check to see if any functions can have their "..." 922 // removed. We can do this if they never call va_start. This loop cannot be 923 // fused with the next loop, because deleting a function invalidates 924 // information computed while surveying other functions. 925 DOUT << "DAE - Deleting dead varargs\n"; 926 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 927 Function &F = *I++; 928 if (F.getFunctionType()->isVarArg()) 929 Changed |= DeleteDeadVarargs(F); 930 } 931 932 // Second phase:loop through the module, determining which arguments are live. 933 // We assume all arguments are dead unless proven otherwise (allowing us to 934 // determine that dead arguments passed into recursive functions are dead). 935 // 936 DOUT << "DAE - Determining liveness\n"; 937 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 938 SurveyFunction(*I); 939 940 // Now, remove all dead arguments and return values from each function in 941 // turn 942 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { 943 // Increment now, because the function will probably get removed (ie 944 // replaced by a new one). 945 Function *F = I++; 946 Changed |= RemoveDeadStuffFromFunction(F); 947 } 948 return Changed; 949} 950