1 //===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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 arguments in a similar way.
15 // This pass is often useful as a cleanup pass to run after aggressive
16 // interprocedural passes, which add possibly-dead arguments.
18 //===----------------------------------------------------------------------===//
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/ParameterAttributes.h"
30 #include "llvm/Support/CallSite.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Support/Compiler.h"
37 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
38 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
41 /// DAE - The dead argument elimination pass.
43 class VISIBILITY_HIDDEN DAE : public ModulePass {
44 /// Liveness enum - During our initial pass over the program, we determine
45 /// that things are either definately alive, definately dead, or in need of
46 /// interprocedural analysis (MaybeLive).
48 enum Liveness { Live, MaybeLive, Dead };
50 /// LiveArguments, MaybeLiveArguments, DeadArguments - These sets contain
51 /// all of the arguments in the program. The Dead set contains arguments
52 /// which are completely dead (never used in the function). The MaybeLive
53 /// set contains arguments which are only passed into other function calls,
54 /// thus may be live and may be dead. The Live set contains arguments which
55 /// are known to be alive.
57 std::set<Argument*> DeadArguments, MaybeLiveArguments, LiveArguments;
59 /// DeadRetVal, MaybeLiveRetVal, LifeRetVal - These sets contain all of the
60 /// functions in the program. The Dead set contains functions whose return
61 /// value is known to be dead. The MaybeLive set contains functions whose
62 /// return values are only used by return instructions, and the Live set
63 /// contains functions whose return values are used, functions that are
64 /// external, and functions that already return void.
66 std::set<Function*> DeadRetVal, MaybeLiveRetVal, LiveRetVal;
68 /// InstructionsToInspect - As we mark arguments and return values
69 /// MaybeLive, we keep track of which instructions could make the values
70 /// live here. Once the entire program has had the return value and
71 /// arguments analyzed, this set is scanned to promote the MaybeLive objects
72 /// to be Live if they really are used.
73 std::vector<Instruction*> InstructionsToInspect;
75 /// CallSites - Keep track of the call sites of functions that have
76 /// MaybeLive arguments or return values.
77 std::multimap<Function*, CallSite> CallSites;
80 static char ID; // Pass identification, replacement for typeid
81 DAE() : ModulePass((intptr_t)&ID) {}
82 bool runOnModule(Module &M);
84 virtual bool ShouldHackArguments() const { return false; }
87 Liveness getArgumentLiveness(const Argument &A);
88 bool isMaybeLiveArgumentNowLive(Argument *Arg);
90 bool DeleteDeadVarargs(Function &Fn);
91 void SurveyFunction(Function &Fn);
93 void MarkArgumentLive(Argument *Arg);
94 void MarkRetValLive(Function *F);
95 void MarkReturnInstArgumentLive(ReturnInst *RI);
97 void RemoveDeadArgumentsFromFunction(Function *F);
100 RegisterPass<DAE> X("deadargelim", "Dead Argument Elimination");
102 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
103 /// deletes arguments to functions which are external. This is only for use
105 struct DAH : public DAE {
107 virtual bool ShouldHackArguments() const { return true; }
110 RegisterPass<DAH> Y("deadarghaX0r",
111 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
114 /// createDeadArgEliminationPass - This pass removes arguments from functions
115 /// which are not used by the body of the function.
117 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
118 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
120 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
121 /// llvm.vastart is never called, the varargs list is dead for the function.
122 bool DAE::DeleteDeadVarargs(Function &Fn) {
123 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
124 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false;
126 // Ensure that the function is only directly called.
127 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) {
128 // If this use is anything other than a call site, give up.
129 CallSite CS = CallSite::get(*I);
130 Instruction *TheCall = CS.getInstruction();
131 if (!TheCall) return false; // Not a direct call site?
133 // The addr of this function is passed to the call.
134 if (I.getOperandNo() != 0) return false;
137 // Okay, we know we can transform this function if safe. Scan its body
138 // looking for calls to llvm.vastart.
139 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
140 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
141 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
142 if (II->getIntrinsicID() == Intrinsic::vastart)
148 // If we get here, there are no calls to llvm.vastart in the function body,
149 // remove the "..." and adjust all the calls.
151 // Start by computing a new prototype for the function, which is the same as
152 // the old function, but has fewer arguments.
153 const FunctionType *FTy = Fn.getFunctionType();
154 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
155 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
156 unsigned NumArgs = Params.size();
158 // Create the new function body and insert it into the module...
159 Function *NF = new Function(NFTy, Fn.getLinkage());
160 NF->setCallingConv(Fn.getCallingConv());
161 NF->setParamAttrs(Fn.getParamAttrs());
162 if (Fn.hasCollector())
163 NF->setCollector(Fn.getCollector());
164 Fn.getParent()->getFunctionList().insert(&Fn, NF);
167 // Loop over all of the callers of the function, transforming the call sites
168 // to pass in a smaller number of arguments into the new function.
170 std::vector<Value*> Args;
171 while (!Fn.use_empty()) {
172 CallSite CS = CallSite::get(Fn.use_back());
173 Instruction *Call = CS.getInstruction();
175 // Pass all the same arguments.
176 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
179 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
180 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
181 Args.begin(), Args.end(), "", Call);
182 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
183 cast<InvokeInst>(New)->setParamAttrs(CS.getParamAttrs());
185 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
186 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
187 cast<CallInst>(New)->setParamAttrs(CS.getParamAttrs());
188 if (cast<CallInst>(Call)->isTailCall())
189 cast<CallInst>(New)->setTailCall();
193 if (!Call->use_empty())
194 Call->replaceAllUsesWith(New);
198 // Finally, remove the old call from the program, reducing the use-count of
200 Call->eraseFromParent();
203 // Since we have now created the new function, splice the body of the old
204 // function right into the new function, leaving the old rotting hulk of the
206 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
208 // Loop over the argument list, transfering uses of the old arguments over to
209 // the new arguments, also transfering over the names as well. While we're at
210 // it, remove the dead arguments from the DeadArguments list.
212 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
213 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
214 // Move the name and users over to the new version.
215 I->replaceAllUsesWith(I2);
219 // Finally, nuke the old function.
220 Fn.eraseFromParent();
225 static inline bool CallPassesValueThoughVararg(Instruction *Call,
227 CallSite CS = CallSite::get(Call);
228 const Type *CalledValueTy = CS.getCalledValue()->getType();
229 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType();
230 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams();
231 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
232 AI != CS.arg_end(); ++AI)
233 if (AI->get() == Arg)
238 // getArgumentLiveness - Inspect an argument, determining if is known Live
239 // (used in a computation), MaybeLive (only passed as an argument to a call), or
241 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) {
242 const Function *F = A.getParent();
244 // If this is the return value of a struct function, it's not really dead.
245 if (F->isStructReturn() && &*(F->arg_begin()) == &A)
248 if (A.use_empty()) // First check, directly dead?
251 // Scan through all of the uses, looking for non-argument passing uses.
252 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
253 // Return instructions do not immediately effect liveness.
254 if (isa<ReturnInst>(*I))
257 CallSite CS = CallSite::get(const_cast<User*>(*I));
258 if (!CS.getInstruction()) {
259 // If its used by something that is not a call or invoke, it's alive!
262 // If it's an indirect call, mark it alive...
263 Function *Callee = CS.getCalledFunction();
264 if (!Callee) return Live;
266 // Check to see if it's passed through a va_arg area: if so, we cannot
268 if (CallPassesValueThoughVararg(CS.getInstruction(), &A))
269 return Live; // If passed through va_arg area, we cannot remove it
272 return MaybeLive; // It must be used, but only as argument to a function
276 // SurveyFunction - This performs the initial survey of the specified function,
277 // checking out whether or not it uses any of its incoming arguments or whether
278 // any callers use the return value. This fills in the
279 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets.
281 // We consider arguments of non-internal functions to be intrinsically alive as
282 // well as arguments to functions which have their "address taken".
284 void DAE::SurveyFunction(Function &F) {
285 bool FunctionIntrinsicallyLive = false;
286 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead;
288 if (!F.hasInternalLinkage() &&
289 (!ShouldHackArguments() || F.isIntrinsic()))
290 FunctionIntrinsicallyLive = true;
292 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
293 // If this use is anything other than a call site, the function is alive.
294 CallSite CS = CallSite::get(*I);
295 Instruction *TheCall = CS.getInstruction();
296 if (!TheCall) { // Not a direct call site?
297 FunctionIntrinsicallyLive = true;
301 // Check to see if the return value is used...
302 if (RetValLiveness != Live)
303 for (Value::use_iterator I = TheCall->use_begin(),
304 E = TheCall->use_end(); I != E; ++I)
305 if (isa<ReturnInst>(cast<Instruction>(*I))) {
306 RetValLiveness = MaybeLive;
307 } else if (isa<CallInst>(cast<Instruction>(*I)) ||
308 isa<InvokeInst>(cast<Instruction>(*I))) {
309 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) ||
310 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) {
311 RetValLiveness = Live;
314 RetValLiveness = MaybeLive;
317 RetValLiveness = Live;
321 // If the function is PASSED IN as an argument, its address has been taken
322 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
324 if (AI->get() == &F) {
325 FunctionIntrinsicallyLive = true;
328 if (FunctionIntrinsicallyLive) break;
331 if (FunctionIntrinsicallyLive) {
332 DOUT << " Intrinsically live fn: " << F.getName() << "\n";
333 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
335 LiveArguments.insert(AI);
336 LiveRetVal.insert(&F);
340 switch (RetValLiveness) {
341 case Live: LiveRetVal.insert(&F); break;
342 case MaybeLive: MaybeLiveRetVal.insert(&F); break;
343 case Dead: DeadRetVal.insert(&F); break;
346 DOUT << " Inspecting args for fn: " << F.getName() << "\n";
348 // If it is not intrinsically alive, we know that all users of the
349 // function are call sites. Mark all of the arguments live which are
350 // directly used, and keep track of all of the call sites of this function
351 // if there are any arguments we assume that are dead.
353 bool AnyMaybeLiveArgs = false;
354 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
356 switch (getArgumentLiveness(*AI)) {
358 DOUT << " Arg live by use: " << AI->getName() << "\n";
359 LiveArguments.insert(AI);
362 DOUT << " Arg definitely dead: " << AI->getName() <<"\n";
363 DeadArguments.insert(AI);
366 DOUT << " Arg only passed to calls: " << AI->getName() << "\n";
367 AnyMaybeLiveArgs = true;
368 MaybeLiveArguments.insert(AI);
372 // If there are any "MaybeLive" arguments, we need to check callees of
373 // this function when/if they become alive. Record which functions are
375 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive)
376 for (Value::use_iterator I = F.use_begin(), E = F.use_end();
378 if (AnyMaybeLiveArgs)
379 CallSites.insert(std::make_pair(&F, CallSite::get(*I)));
381 if (RetValLiveness == MaybeLive)
382 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
384 InstructionsToInspect.push_back(cast<Instruction>(*UI));
388 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we
389 // know that the only uses of Arg are to be passed in as an argument to a
390 // function call or return. Check to see if the formal argument passed in is in
391 // the LiveArguments set. If so, return true.
393 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) {
394 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
395 if (isa<ReturnInst>(*I)) {
396 if (LiveRetVal.count(Arg->getParent())) return true;
400 CallSite CS = CallSite::get(*I);
402 // We know that this can only be used for direct calls...
403 Function *Callee = CS.getCalledFunction();
405 // Loop over all of the arguments (because Arg may be passed into the call
406 // multiple times) and check to see if any are now alive...
407 CallSite::arg_iterator CSAI = CS.arg_begin();
408 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end();
409 AI != E; ++AI, ++CSAI)
410 // If this is the argument we are looking for, check to see if it's alive
411 if (*CSAI == Arg && LiveArguments.count(AI))
417 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
418 /// Mark it live in the specified sets and recursively mark arguments in callers
419 /// live that are needed to pass in a value.
421 void DAE::MarkArgumentLive(Argument *Arg) {
422 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg);
423 if (It == MaybeLiveArguments.end() || *It != Arg) return;
425 DOUT << " MaybeLive argument now live: " << Arg->getName() <<"\n";
426 MaybeLiveArguments.erase(It);
427 LiveArguments.insert(Arg);
429 // Loop over all of the call sites of the function, making any arguments
430 // passed in to provide a value for this argument live as necessary.
432 Function *Fn = Arg->getParent();
433 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg));
435 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn);
436 for (; I != CallSites.end() && I->first == Fn; ++I) {
437 CallSite CS = I->second;
438 Value *ArgVal = *(CS.arg_begin()+ArgNo);
439 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) {
440 MarkArgumentLive(ActualArg);
442 // If the value passed in at this call site is a return value computed by
443 // some other call site, make sure to mark the return value at the other
444 // call site as being needed.
445 CallSite ArgCS = CallSite::get(ArgVal);
446 if (ArgCS.getInstruction())
447 if (Function *Fn = ArgCS.getCalledFunction())
453 /// MarkArgumentLive - The MaybeLive return value for the specified function is
454 /// now known to be alive. Propagate this fact to the return instructions which
456 void DAE::MarkRetValLive(Function *F) {
457 assert(F && "Shame shame, we can't have null pointers here!");
459 // Check to see if we already knew it was live
460 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F);
461 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive!
463 DOUT << " MaybeLive retval now live: " << F->getName() << "\n";
465 MaybeLiveRetVal.erase(I);
466 LiveRetVal.insert(F); // It is now known to be live!
468 // Loop over all of the functions, noticing that the return value is now live.
469 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
470 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
471 MarkReturnInstArgumentLive(RI);
474 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) {
475 Value *Op = RI->getOperand(0);
476 if (Argument *A = dyn_cast<Argument>(Op)) {
478 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) {
479 if (Function *F = CI->getCalledFunction())
481 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
482 if (Function *F = II->getCalledFunction())
487 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
488 // specified by the DeadArguments list. Transform the function and all of the
489 // callees of the function to not have these arguments.
491 void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
492 // Start by computing a new prototype for the function, which is the same as
493 // the old function, but has fewer arguments.
494 const FunctionType *FTy = F->getFunctionType();
495 std::vector<const Type*> Params;
497 // Set up to build a new list of parameter attributes
498 ParamAttrsVector ParamAttrsVec;
499 const ParamAttrsList *PAL = F->getParamAttrs();
501 // The existing function return attributes.
502 uint16_t RAttrs = PAL ? PAL->getParamAttrs(0) : 0;
504 // Make the function return void if the return value is dead.
505 const Type *RetTy = FTy->getReturnType();
506 if (DeadRetVal.count(F)) {
507 RetTy = Type::VoidTy;
508 RAttrs &= ~ParamAttr::VoidTypeIncompatible;
513 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
515 // Construct the new parameter list from non-dead arguments. Also construct
516 // a new set of parameter attributes to correspond.
518 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
520 if (!DeadArguments.count(I)) {
521 Params.push_back(I->getType());
522 uint16_t Attrs = PAL ? PAL->getParamAttrs(index) : 0;
524 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
527 // Reconstruct the ParamAttrsList based on the vector we constructed.
528 PAL = ParamAttrsList::get(ParamAttrsVec);
530 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
531 // have zero fixed arguments.
533 bool ExtraArgHack = false;
534 if (Params.empty() && FTy->isVarArg()) {
536 Params.push_back(Type::Int32Ty);
539 // Create the new function type based on the recomputed parameters.
540 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
542 // Create the new function body and insert it into the module...
543 Function *NF = new Function(NFTy, F->getLinkage());
544 NF->setCallingConv(F->getCallingConv());
545 NF->setParamAttrs(PAL);
546 if (F->hasCollector())
547 NF->setCollector(F->getCollector());
548 F->getParent()->getFunctionList().insert(F, NF);
551 // Loop over all of the callers of the function, transforming the call sites
552 // to pass in a smaller number of arguments into the new function.
554 std::vector<Value*> Args;
555 while (!F->use_empty()) {
556 CallSite CS = CallSite::get(F->use_back());
557 Instruction *Call = CS.getInstruction();
558 ParamAttrsVec.clear();
559 PAL = CS.getParamAttrs();
561 // The call return attributes.
562 uint16_t RAttrs = PAL ? PAL->getParamAttrs(0) : 0;
563 // Adjust in case the function was changed to return void.
564 if (NF->getReturnType() == Type::VoidTy)
565 RAttrs &= ~ParamAttr::VoidTypeIncompatible;
567 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
569 // Loop over the operands, deleting dead ones...
570 CallSite::arg_iterator AI = CS.arg_begin();
572 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
573 I != E; ++I, ++AI, ++index)
574 if (!DeadArguments.count(I)) { // Remove operands for dead arguments
576 uint16_t Attrs = PAL ? PAL->getParamAttrs(index) : 0;
578 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
581 // Reconstruct the ParamAttrsList based on the vector we constructed.
582 PAL = ParamAttrsList::get(ParamAttrsVec);
585 Args.push_back(UndefValue::get(Type::Int32Ty));
587 // Push any varargs arguments on the list
588 for (; AI != CS.arg_end(); ++AI)
592 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
593 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
594 Args.begin(), Args.end(), "", Call);
595 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
596 cast<InvokeInst>(New)->setParamAttrs(PAL);
598 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
599 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
600 cast<CallInst>(New)->setParamAttrs(PAL);
601 if (cast<CallInst>(Call)->isTailCall())
602 cast<CallInst>(New)->setTailCall();
606 if (!Call->use_empty()) {
607 if (New->getType() == Type::VoidTy)
608 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
610 Call->replaceAllUsesWith(New);
615 // Finally, remove the old call from the program, reducing the use-count of
617 Call->getParent()->getInstList().erase(Call);
620 // Since we have now created the new function, splice the body of the old
621 // function right into the new function, leaving the old rotting hulk of the
623 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
625 // Loop over the argument list, transfering uses of the old arguments over to
626 // the new arguments, also transfering over the names as well. While we're at
627 // it, remove the dead arguments from the DeadArguments list.
629 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
630 I2 = NF->arg_begin();
632 if (!DeadArguments.count(I)) {
633 // If this is a live argument, move the name and users over to the new
635 I->replaceAllUsesWith(I2);
639 // If this argument is dead, replace any uses of it with null constants
640 // (these are guaranteed to only be operands to call instructions which
641 // will later be simplified).
642 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
643 DeadArguments.erase(I);
646 // If we change the return value of the function we must rewrite any return
647 // instructions. Check this now.
648 if (F->getReturnType() != NF->getReturnType())
649 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
650 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
651 new ReturnInst(0, RI);
652 BB->getInstList().erase(RI);
655 // Now that the old function is dead, delete it.
656 F->getParent()->getFunctionList().erase(F);
659 bool DAE::runOnModule(Module &M) {
660 bool Changed = false;
661 // First pass: Do a simple check to see if any functions can have their "..."
662 // removed. We can do this if they never call va_start. This loop cannot be
663 // fused with the next loop, because deleting a function invalidates
664 // information computed while surveying other functions.
665 DOUT << "DAE - Deleting dead varargs\n";
666 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
668 if (F.getFunctionType()->isVarArg())
669 Changed |= DeleteDeadVarargs(F);
672 // Second phase:loop through the module, determining which arguments are live.
673 // We assume all arguments are dead unless proven otherwise (allowing us to
674 // determine that dead arguments passed into recursive functions are dead).
676 DOUT << "DAE - Determining liveness\n";
677 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
680 // Loop over the instructions to inspect, propagating liveness among arguments
681 // and return values which are MaybeLive.
682 while (!InstructionsToInspect.empty()) {
683 Instruction *I = InstructionsToInspect.back();
684 InstructionsToInspect.pop_back();
686 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) {
687 // For return instructions, we just have to check to see if the return
688 // value for the current function is known now to be alive. If so, any
689 // arguments used by it are now alive, and any call instruction return
690 // value is alive as well.
691 if (LiveRetVal.count(RI->getParent()->getParent()))
692 MarkReturnInstArgumentLive(RI);
695 CallSite CS = CallSite::get(I);
696 assert(CS.getInstruction() && "Unknown instruction for the I2I list!");
698 Function *Callee = CS.getCalledFunction();
700 // If we found a call or invoke instruction on this list, that means that
701 // an argument of the function is a call instruction. If the argument is
702 // live, then the return value of the called instruction is now live.
704 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator
705 for (Function::arg_iterator FI = Callee->arg_begin(),
706 E = Callee->arg_end(); FI != E; ++AI, ++FI) {
707 // If this argument is another call...
708 CallSite ArgCS = CallSite::get(*AI);
709 if (ArgCS.getInstruction() && LiveArguments.count(FI))
710 if (Function *Callee = ArgCS.getCalledFunction())
711 MarkRetValLive(Callee);
716 // Now we loop over all of the MaybeLive arguments, promoting them to be live
717 // arguments if one of the calls that uses the arguments to the calls they are
718 // passed into requires them to be live. Of course this could make other
719 // arguments live, so process callers recursively.
721 // Because elements can be removed from the MaybeLiveArguments set, copy it to
722 // a temporary vector.
724 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
725 MaybeLiveArguments.end());
726 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
727 Argument *MLA = TmpArgList[i];
728 if (MaybeLiveArguments.count(MLA) &&
729 isMaybeLiveArgumentNowLive(MLA))
730 MarkArgumentLive(MLA);
733 // Recover memory early...
736 // At this point, we know that all arguments in DeadArguments and
737 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing
739 if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
740 MaybeLiveRetVal.empty() && DeadRetVal.empty())
743 // Otherwise, compact into one set, and start eliminating the arguments from
745 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
746 MaybeLiveArguments.clear();
747 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end());
748 MaybeLiveRetVal.clear();
750 LiveArguments.clear();
753 NumArgumentsEliminated += DeadArguments.size();
754 NumRetValsEliminated += DeadRetVal.size();
755 while (!DeadArguments.empty())
756 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent());
758 while (!DeadRetVal.empty())
759 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin());