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/Support/CallSite.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/ADT/Statistic.h"
35 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
36 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
39 /// DAE - The dead argument elimination pass.
41 class DAE : public ModulePass {
42 /// Liveness enum - During our initial pass over the program, we determine
43 /// that things are either definately alive, definately dead, or in need of
44 /// interprocedural analysis (MaybeLive).
46 enum Liveness { Live, MaybeLive, Dead };
48 /// LiveArguments, MaybeLiveArguments, DeadArguments - These sets contain
49 /// all of the arguments in the program. The Dead set contains arguments
50 /// which are completely dead (never used in the function). The MaybeLive
51 /// set contains arguments which are only passed into other function calls,
52 /// thus may be live and may be dead. The Live set contains arguments which
53 /// are known to be alive.
55 std::set<Argument*> DeadArguments, MaybeLiveArguments, LiveArguments;
57 /// DeadRetVal, MaybeLiveRetVal, LifeRetVal - These sets contain all of the
58 /// functions in the program. The Dead set contains functions whose return
59 /// value is known to be dead. The MaybeLive set contains functions whose
60 /// return values are only used by return instructions, and the Live set
61 /// contains functions whose return values are used, functions that are
62 /// external, and functions that already return void.
64 std::set<Function*> DeadRetVal, MaybeLiveRetVal, LiveRetVal;
66 /// InstructionsToInspect - As we mark arguments and return values
67 /// MaybeLive, we keep track of which instructions could make the values
68 /// live here. Once the entire program has had the return value and
69 /// arguments analyzed, this set is scanned to promote the MaybeLive objects
70 /// to be Live if they really are used.
71 std::vector<Instruction*> InstructionsToInspect;
73 /// CallSites - Keep track of the call sites of functions that have
74 /// MaybeLive arguments or return values.
75 std::multimap<Function*, CallSite> CallSites;
78 bool runOnModule(Module &M);
80 virtual bool ShouldHackArguments() const { return false; }
83 Liveness getArgumentLiveness(const Argument &A);
84 bool isMaybeLiveArgumentNowLive(Argument *Arg);
86 bool DeleteDeadVarargs(Function &Fn);
87 void SurveyFunction(Function &Fn);
89 void MarkArgumentLive(Argument *Arg);
90 void MarkRetValLive(Function *F);
91 void MarkReturnInstArgumentLive(ReturnInst *RI);
93 void RemoveDeadArgumentsFromFunction(Function *F);
95 RegisterPass<DAE> X("deadargelim", "Dead Argument Elimination");
97 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
98 /// deletes arguments to functions which are external. This is only for use
100 struct DAH : public DAE {
101 virtual bool ShouldHackArguments() const { return true; }
103 RegisterPass<DAH> Y("deadarghaX0r",
104 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
107 /// createDeadArgEliminationPass - This pass removes arguments from functions
108 /// which are not used by the body of the function.
110 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
111 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
113 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
114 /// llvm.vastart is never called, the varargs list is dead for the function.
115 bool DAE::DeleteDeadVarargs(Function &Fn) {
116 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
117 if (Fn.isExternal() || !Fn.hasInternalLinkage()) return false;
119 // Ensure that the function is only directly called.
120 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) {
121 // If this use is anything other than a call site, give up.
122 CallSite CS = CallSite::get(*I);
123 Instruction *TheCall = CS.getInstruction();
124 if (!TheCall) return false; // Not a direct call site?
126 // The addr of this function is passed to the call.
127 if (I.getOperandNo() != 0) return false;
130 // Okay, we know we can transform this function if safe. Scan its body
131 // looking for calls to llvm.vastart.
132 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
133 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
134 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
135 if (II->getIntrinsicID() == Intrinsic::vastart)
141 // If we get here, there are no calls to llvm.vastart in the function body,
142 // remove the "..." and adjust all the calls.
144 // Start by computing a new prototype for the function, which is the same as
145 // the old function, but has fewer arguments.
146 const FunctionType *FTy = Fn.getFunctionType();
147 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
148 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
149 unsigned NumArgs = Params.size();
151 // Create the new function body and insert it into the module...
152 Function *NF = new Function(NFTy, Fn.getLinkage(), Fn.getName());
153 NF->setCallingConv(Fn.getCallingConv());
154 Fn.getParent()->getFunctionList().insert(&Fn, NF);
156 // Loop over all of the callers of the function, transforming the call sites
157 // to pass in a smaller number of arguments into the new function.
159 std::vector<Value*> Args;
160 while (!Fn.use_empty()) {
161 CallSite CS = CallSite::get(Fn.use_back());
162 Instruction *Call = CS.getInstruction();
164 // Loop over the operands, dropping extraneous ones at the end of the list.
165 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
168 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
169 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
171 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
173 New = new CallInst(NF, Args, "", Call);
174 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
175 if (cast<CallInst>(Call)->isTailCall())
176 cast<CallInst>(New)->setTailCall();
180 if (!Call->use_empty())
181 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
183 if (Call->hasName()) {
184 std::string Name = Call->getName();
189 // Finally, remove the old call from the program, reducing the use-count of
191 Call->getParent()->getInstList().erase(Call);
194 // Since we have now created the new function, splice the body of the old
195 // function right into the new function, leaving the old rotting hulk of the
197 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
199 // Loop over the argument list, transfering uses of the old arguments over to
200 // the new arguments, also transfering over the names as well. While we're at
201 // it, remove the dead arguments from the DeadArguments list.
203 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
204 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
205 // Move the name and users over to the new version.
206 I->replaceAllUsesWith(I2);
207 I2->setName(I->getName());
210 // Finally, nuke the old function.
211 Fn.eraseFromParent();
216 static inline bool CallPassesValueThoughVararg(Instruction *Call,
218 CallSite CS = CallSite::get(Call);
219 const Type *CalledValueTy = CS.getCalledValue()->getType();
220 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType();
221 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams();
222 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
223 AI != CS.arg_end(); ++AI)
224 if (AI->get() == Arg)
229 // getArgumentLiveness - Inspect an argument, determining if is known Live
230 // (used in a computation), MaybeLive (only passed as an argument to a call), or
232 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) {
233 // If this is the return value of a csret function, it's not really dead.
234 if (A.getParent()->getCallingConv() == CallingConv::CSRet &&
235 &*A.getParent()->arg_begin() == &A)
238 if (A.use_empty()) // First check, directly dead?
241 // Scan through all of the uses, looking for non-argument passing uses.
242 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
243 // Return instructions do not immediately effect liveness.
244 if (isa<ReturnInst>(*I))
247 CallSite CS = CallSite::get(const_cast<User*>(*I));
248 if (!CS.getInstruction()) {
249 // If its used by something that is not a call or invoke, it's alive!
252 // If it's an indirect call, mark it alive...
253 Function *Callee = CS.getCalledFunction();
254 if (!Callee) return Live;
256 // Check to see if it's passed through a va_arg area: if so, we cannot
258 if (CallPassesValueThoughVararg(CS.getInstruction(), &A))
259 return Live; // If passed through va_arg area, we cannot remove it
262 return MaybeLive; // It must be used, but only as argument to a function
266 // SurveyFunction - This performs the initial survey of the specified function,
267 // checking out whether or not it uses any of its incoming arguments or whether
268 // any callers use the return value. This fills in the
269 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets.
271 // We consider arguments of non-internal functions to be intrinsically alive as
272 // well as arguments to functions which have their "address taken".
274 void DAE::SurveyFunction(Function &F) {
275 bool FunctionIntrinsicallyLive = false;
276 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead;
278 if (!F.hasInternalLinkage() &&
279 (!ShouldHackArguments() || F.getIntrinsicID()))
280 FunctionIntrinsicallyLive = true;
282 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
283 // If this use is anything other than a call site, the function is alive.
284 CallSite CS = CallSite::get(*I);
285 Instruction *TheCall = CS.getInstruction();
286 if (!TheCall) { // Not a direct call site?
287 FunctionIntrinsicallyLive = true;
291 // Check to see if the return value is used...
292 if (RetValLiveness != Live)
293 for (Value::use_iterator I = TheCall->use_begin(),
294 E = TheCall->use_end(); I != E; ++I)
295 if (isa<ReturnInst>(cast<Instruction>(*I))) {
296 RetValLiveness = MaybeLive;
297 } else if (isa<CallInst>(cast<Instruction>(*I)) ||
298 isa<InvokeInst>(cast<Instruction>(*I))) {
299 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) ||
300 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) {
301 RetValLiveness = Live;
304 RetValLiveness = MaybeLive;
307 RetValLiveness = Live;
311 // If the function is PASSED IN as an argument, its address has been taken
312 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
314 if (AI->get() == &F) {
315 FunctionIntrinsicallyLive = true;
318 if (FunctionIntrinsicallyLive) break;
321 if (FunctionIntrinsicallyLive) {
322 DOUT << " Intrinsically live fn: " << F.getName() << "\n";
323 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
325 LiveArguments.insert(AI);
326 LiveRetVal.insert(&F);
330 switch (RetValLiveness) {
331 case Live: LiveRetVal.insert(&F); break;
332 case MaybeLive: MaybeLiveRetVal.insert(&F); break;
333 case Dead: DeadRetVal.insert(&F); break;
336 DOUT << " Inspecting args for fn: " << F.getName() << "\n";
338 // If it is not intrinsically alive, we know that all users of the
339 // function are call sites. Mark all of the arguments live which are
340 // directly used, and keep track of all of the call sites of this function
341 // if there are any arguments we assume that are dead.
343 bool AnyMaybeLiveArgs = false;
344 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
346 switch (getArgumentLiveness(*AI)) {
348 DOUT << " Arg live by use: " << AI->getName() << "\n";
349 LiveArguments.insert(AI);
352 DOUT << " Arg definitely dead: " << AI->getName() <<"\n";
353 DeadArguments.insert(AI);
356 DOUT << " Arg only passed to calls: " << AI->getName() << "\n";
357 AnyMaybeLiveArgs = true;
358 MaybeLiveArguments.insert(AI);
362 // If there are any "MaybeLive" arguments, we need to check callees of
363 // this function when/if they become alive. Record which functions are
365 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive)
366 for (Value::use_iterator I = F.use_begin(), E = F.use_end();
368 if (AnyMaybeLiveArgs)
369 CallSites.insert(std::make_pair(&F, CallSite::get(*I)));
371 if (RetValLiveness == MaybeLive)
372 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
374 InstructionsToInspect.push_back(cast<Instruction>(*UI));
378 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we
379 // know that the only uses of Arg are to be passed in as an argument to a
380 // function call or return. Check to see if the formal argument passed in is in
381 // the LiveArguments set. If so, return true.
383 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) {
384 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
385 if (isa<ReturnInst>(*I)) {
386 if (LiveRetVal.count(Arg->getParent())) return true;
390 CallSite CS = CallSite::get(*I);
392 // We know that this can only be used for direct calls...
393 Function *Callee = CS.getCalledFunction();
395 // Loop over all of the arguments (because Arg may be passed into the call
396 // multiple times) and check to see if any are now alive...
397 CallSite::arg_iterator CSAI = CS.arg_begin();
398 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end();
399 AI != E; ++AI, ++CSAI)
400 // If this is the argument we are looking for, check to see if it's alive
401 if (*CSAI == Arg && LiveArguments.count(AI))
407 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
408 /// Mark it live in the specified sets and recursively mark arguments in callers
409 /// live that are needed to pass in a value.
411 void DAE::MarkArgumentLive(Argument *Arg) {
412 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg);
413 if (It == MaybeLiveArguments.end() || *It != Arg) return;
415 DOUT << " MaybeLive argument now live: " << Arg->getName() <<"\n";
416 MaybeLiveArguments.erase(It);
417 LiveArguments.insert(Arg);
419 // Loop over all of the call sites of the function, making any arguments
420 // passed in to provide a value for this argument live as necessary.
422 Function *Fn = Arg->getParent();
423 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg));
425 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn);
426 for (; I != CallSites.end() && I->first == Fn; ++I) {
427 CallSite CS = I->second;
428 Value *ArgVal = *(CS.arg_begin()+ArgNo);
429 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) {
430 MarkArgumentLive(ActualArg);
432 // If the value passed in at this call site is a return value computed by
433 // some other call site, make sure to mark the return value at the other
434 // call site as being needed.
435 CallSite ArgCS = CallSite::get(ArgVal);
436 if (ArgCS.getInstruction())
437 if (Function *Fn = ArgCS.getCalledFunction())
443 /// MarkArgumentLive - The MaybeLive return value for the specified function is
444 /// now known to be alive. Propagate this fact to the return instructions which
446 void DAE::MarkRetValLive(Function *F) {
447 assert(F && "Shame shame, we can't have null pointers here!");
449 // Check to see if we already knew it was live
450 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F);
451 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive!
453 DOUT << " MaybeLive retval now live: " << F->getName() << "\n";
455 MaybeLiveRetVal.erase(I);
456 LiveRetVal.insert(F); // It is now known to be live!
458 // Loop over all of the functions, noticing that the return value is now live.
459 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
460 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
461 MarkReturnInstArgumentLive(RI);
464 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) {
465 Value *Op = RI->getOperand(0);
466 if (Argument *A = dyn_cast<Argument>(Op)) {
468 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) {
469 if (Function *F = CI->getCalledFunction())
471 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
472 if (Function *F = II->getCalledFunction())
477 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
478 // specified by the DeadArguments list. Transform the function and all of the
479 // callees of the function to not have these arguments.
481 void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
482 // Start by computing a new prototype for the function, which is the same as
483 // the old function, but has fewer arguments.
484 const FunctionType *FTy = F->getFunctionType();
485 std::vector<const Type*> Params;
487 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
488 if (!DeadArguments.count(I))
489 Params.push_back(I->getType());
491 const Type *RetTy = FTy->getReturnType();
492 if (DeadRetVal.count(F)) {
493 RetTy = Type::VoidTy;
497 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
498 // have zero fixed arguments.
500 bool ExtraArgHack = false;
501 if (Params.empty() && FTy->isVarArg()) {
503 Params.push_back(Type::Int32Ty);
506 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
508 // Create the new function body and insert it into the module...
509 Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
510 NF->setCallingConv(F->getCallingConv());
511 F->getParent()->getFunctionList().insert(F, NF);
513 // Loop over all of the callers of the function, transforming the call sites
514 // to pass in a smaller number of arguments into the new function.
516 std::vector<Value*> Args;
517 while (!F->use_empty()) {
518 CallSite CS = CallSite::get(F->use_back());
519 Instruction *Call = CS.getInstruction();
521 // Loop over the operands, deleting dead ones...
522 CallSite::arg_iterator AI = CS.arg_begin();
523 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
525 if (!DeadArguments.count(I)) // Remove operands for dead arguments
529 Args.push_back(UndefValue::get(Type::Int32Ty));
531 // Push any varargs arguments on the list
532 for (; AI != CS.arg_end(); ++AI)
536 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
537 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
539 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
541 New = new CallInst(NF, Args, "", Call);
542 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
543 if (cast<CallInst>(Call)->isTailCall())
544 cast<CallInst>(New)->setTailCall();
548 if (!Call->use_empty()) {
549 if (New->getType() == Type::VoidTy)
550 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
552 Call->replaceAllUsesWith(New);
553 std::string Name = Call->getName();
559 // Finally, remove the old call from the program, reducing the use-count of
561 Call->getParent()->getInstList().erase(Call);
564 // Since we have now created the new function, splice the body of the old
565 // function right into the new function, leaving the old rotting hulk of the
567 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
569 // Loop over the argument list, transfering uses of the old arguments over to
570 // the new arguments, also transfering over the names as well. While we're at
571 // it, remove the dead arguments from the DeadArguments list.
573 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
574 I2 = NF->arg_begin();
576 if (!DeadArguments.count(I)) {
577 // If this is a live argument, move the name and users over to the new
579 I->replaceAllUsesWith(I2);
580 I2->setName(I->getName());
583 // If this argument is dead, replace any uses of it with null constants
584 // (these are guaranteed to only be operands to call instructions which
585 // will later be simplified).
586 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
587 DeadArguments.erase(I);
590 // If we change the return value of the function we must rewrite any return
591 // instructions. Check this now.
592 if (F->getReturnType() != NF->getReturnType())
593 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
594 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
595 new ReturnInst(0, RI);
596 BB->getInstList().erase(RI);
599 // Now that the old function is dead, delete it.
600 F->getParent()->getFunctionList().erase(F);
603 bool DAE::runOnModule(Module &M) {
604 // First phase: loop through the module, determining which arguments are live.
605 // We assume all arguments are dead unless proven otherwise (allowing us to
606 // determine that dead arguments passed into recursive functions are dead).
608 DOUT << "DAE - Determining liveness\n";
609 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
611 if (F.getFunctionType()->isVarArg())
612 if (DeleteDeadVarargs(F))
618 // Loop over the instructions to inspect, propagating liveness among arguments
619 // and return values which are MaybeLive.
621 while (!InstructionsToInspect.empty()) {
622 Instruction *I = InstructionsToInspect.back();
623 InstructionsToInspect.pop_back();
625 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) {
626 // For return instructions, we just have to check to see if the return
627 // value for the current function is known now to be alive. If so, any
628 // arguments used by it are now alive, and any call instruction return
629 // value is alive as well.
630 if (LiveRetVal.count(RI->getParent()->getParent()))
631 MarkReturnInstArgumentLive(RI);
634 CallSite CS = CallSite::get(I);
635 assert(CS.getInstruction() && "Unknown instruction for the I2I list!");
637 Function *Callee = CS.getCalledFunction();
639 // If we found a call or invoke instruction on this list, that means that
640 // an argument of the function is a call instruction. If the argument is
641 // live, then the return value of the called instruction is now live.
643 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator
644 for (Function::arg_iterator FI = Callee->arg_begin(),
645 E = Callee->arg_end(); FI != E; ++AI, ++FI) {
646 // If this argument is another call...
647 CallSite ArgCS = CallSite::get(*AI);
648 if (ArgCS.getInstruction() && LiveArguments.count(FI))
649 if (Function *Callee = ArgCS.getCalledFunction())
650 MarkRetValLive(Callee);
655 // Now we loop over all of the MaybeLive arguments, promoting them to be live
656 // arguments if one of the calls that uses the arguments to the calls they are
657 // passed into requires them to be live. Of course this could make other
658 // arguments live, so process callers recursively.
660 // Because elements can be removed from the MaybeLiveArguments set, copy it to
661 // a temporary vector.
663 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
664 MaybeLiveArguments.end());
665 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
666 Argument *MLA = TmpArgList[i];
667 if (MaybeLiveArguments.count(MLA) &&
668 isMaybeLiveArgumentNowLive(MLA))
669 MarkArgumentLive(MLA);
672 // Recover memory early...
675 // At this point, we know that all arguments in DeadArguments and
676 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing
678 if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
679 MaybeLiveRetVal.empty() && DeadRetVal.empty())
682 // Otherwise, compact into one set, and start eliminating the arguments from
684 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
685 MaybeLiveArguments.clear();
686 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end());
687 MaybeLiveRetVal.clear();
689 LiveArguments.clear();
692 NumArgumentsEliminated += DeadArguments.size();
693 NumRetValsEliminated += DeadRetVal.size();
694 while (!DeadArguments.empty())
695 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent());
697 while (!DeadRetVal.empty())
698 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin());