1 //===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Support/Compiler.h"
38 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
39 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
42 /// DAE - The dead argument elimination pass.
44 class VISIBILITY_HIDDEN DAE : public ModulePass {
45 /// Liveness enum - During our initial pass over the program, we determine
46 /// that things are either definately alive, definately dead, or in need of
47 /// interprocedural analysis (MaybeLive).
49 enum Liveness { Live, MaybeLive, Dead };
51 /// LiveArguments, MaybeLiveArguments, DeadArguments - These sets contain
52 /// all of the arguments in the program. The Dead set contains arguments
53 /// which are completely dead (never used in the function). The MaybeLive
54 /// set contains arguments which are only passed into other function calls,
55 /// thus may be live and may be dead. The Live set contains arguments which
56 /// are known to be alive.
58 std::set<Argument*> DeadArguments, MaybeLiveArguments, LiveArguments;
60 /// DeadRetVal, MaybeLiveRetVal, LifeRetVal - These sets contain all of the
61 /// functions in the program. The Dead set contains functions whose return
62 /// value is known to be dead. The MaybeLive set contains functions whose
63 /// return values are only used by return instructions, and the Live set
64 /// contains functions whose return values are used, functions that are
65 /// external, and functions that already return void.
67 std::set<Function*> DeadRetVal, MaybeLiveRetVal, LiveRetVal;
69 /// InstructionsToInspect - As we mark arguments and return values
70 /// MaybeLive, we keep track of which instructions could make the values
71 /// live here. Once the entire program has had the return value and
72 /// arguments analyzed, this set is scanned to promote the MaybeLive objects
73 /// to be Live if they really are used.
74 std::vector<Instruction*> InstructionsToInspect;
76 /// CallSites - Keep track of the call sites of functions that have
77 /// MaybeLive arguments or return values.
78 std::multimap<Function*, CallSite> CallSites;
81 static char ID; // Pass identification, replacement for typeid
82 DAE() : ModulePass((intptr_t)&ID) {}
83 bool runOnModule(Module &M);
85 virtual bool ShouldHackArguments() const { return false; }
88 Liveness getArgumentLiveness(const Argument &A);
89 bool isMaybeLiveArgumentNowLive(Argument *Arg);
91 bool DeleteDeadVarargs(Function &Fn);
92 void SurveyFunction(Function &Fn);
94 void MarkArgumentLive(Argument *Arg);
95 void MarkRetValLive(Function *F);
96 void MarkReturnInstArgumentLive(ReturnInst *RI);
98 void RemoveDeadArgumentsFromFunction(Function *F);
101 RegisterPass<DAE> X("deadargelim", "Dead Argument Elimination");
103 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
104 /// deletes arguments to functions which are external. This is only for use
106 struct DAH : public DAE {
108 virtual bool ShouldHackArguments() const { return true; }
111 RegisterPass<DAH> Y("deadarghaX0r",
112 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
115 /// createDeadArgEliminationPass - This pass removes arguments from functions
116 /// which are not used by the body of the function.
118 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
119 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
121 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
122 /// llvm.vastart is never called, the varargs list is dead for the function.
123 bool DAE::DeleteDeadVarargs(Function &Fn) {
124 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
125 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false;
127 // Ensure that the function is only directly called.
128 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) {
129 // If this use is anything other than a call site, give up.
130 CallSite CS = CallSite::get(*I);
131 Instruction *TheCall = CS.getInstruction();
132 if (!TheCall) return false; // Not a direct call site?
134 // The addr of this function is passed to the call.
135 if (I.getOperandNo() != 0) return false;
138 // Okay, we know we can transform this function if safe. Scan its body
139 // looking for calls to llvm.vastart.
140 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
141 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
142 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
143 if (II->getIntrinsicID() == Intrinsic::vastart)
149 // If we get here, there are no calls to llvm.vastart in the function body,
150 // remove the "..." and adjust all the calls.
152 // Start by computing a new prototype for the function, which is the same as
153 // the old function, but has fewer arguments.
154 const FunctionType *FTy = Fn.getFunctionType();
155 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
156 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
157 unsigned NumArgs = Params.size();
159 // Create the new function body and insert it into the module...
160 Function *NF = Function::Create(NFTy, Fn.getLinkage());
161 NF->setCallingConv(Fn.getCallingConv());
162 NF->setParamAttrs(Fn.getParamAttrs());
163 if (Fn.hasCollector())
164 NF->setCollector(Fn.getCollector());
165 Fn.getParent()->getFunctionList().insert(&Fn, NF);
168 // Loop over all of the callers of the function, transforming the call sites
169 // to pass in a smaller number of arguments into the new function.
171 std::vector<Value*> Args;
172 while (!Fn.use_empty()) {
173 CallSite CS = CallSite::get(Fn.use_back());
174 Instruction *Call = CS.getInstruction();
176 // Pass all the same arguments.
177 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
179 // Drop any attributes that were on the vararg arguments.
180 PAListPtr PAL = CS.getParamAttrs();
181 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
182 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
183 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
184 ParamAttrsVec.push_back(PAL.getSlot(i));
185 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
189 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
190 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
191 Args.begin(), Args.end(), "", Call);
192 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
193 cast<InvokeInst>(New)->setParamAttrs(PAL);
195 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
196 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
197 cast<CallInst>(New)->setParamAttrs(PAL);
198 if (cast<CallInst>(Call)->isTailCall())
199 cast<CallInst>(New)->setTailCall();
203 if (!Call->use_empty())
204 Call->replaceAllUsesWith(New);
208 // Finally, remove the old call from the program, reducing the use-count of
210 Call->eraseFromParent();
213 // Since we have now created the new function, splice the body of the old
214 // function right into the new function, leaving the old rotting hulk of the
216 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
218 // Loop over the argument list, transfering uses of the old arguments over to
219 // the new arguments, also transfering over the names as well. While we're at
220 // it, remove the dead arguments from the DeadArguments list.
222 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
223 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
224 // Move the name and users over to the new version.
225 I->replaceAllUsesWith(I2);
229 // Finally, nuke the old function.
230 Fn.eraseFromParent();
235 static inline bool CallPassesValueThoughVararg(Instruction *Call,
237 CallSite CS = CallSite::get(Call);
238 const Type *CalledValueTy = CS.getCalledValue()->getType();
239 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType();
240 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams();
241 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
242 AI != CS.arg_end(); ++AI)
243 if (AI->get() == Arg)
248 // getArgumentLiveness - Inspect an argument, determining if is known Live
249 // (used in a computation), MaybeLive (only passed as an argument to a call), or
251 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) {
252 const Function *F = A.getParent();
254 // If this is the return value of a struct function, it's not really dead.
255 if (F->hasStructRetAttr() && &*(F->arg_begin()) == &A)
258 if (A.use_empty()) // First check, directly dead?
261 // Scan through all of the uses, looking for non-argument passing uses.
262 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
263 // Return instructions do not immediately effect liveness.
264 if (isa<ReturnInst>(*I))
267 CallSite CS = CallSite::get(const_cast<User*>(*I));
268 if (!CS.getInstruction()) {
269 // If its used by something that is not a call or invoke, it's alive!
272 // If it's an indirect call, mark it alive...
273 Function *Callee = CS.getCalledFunction();
274 if (!Callee) return Live;
276 // Check to see if it's passed through a va_arg area: if so, we cannot
278 if (CallPassesValueThoughVararg(CS.getInstruction(), &A))
279 return Live; // If passed through va_arg area, we cannot remove it
282 return MaybeLive; // It must be used, but only as argument to a function
286 // SurveyFunction - This performs the initial survey of the specified function,
287 // checking out whether or not it uses any of its incoming arguments or whether
288 // any callers use the return value. This fills in the
289 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets.
291 // We consider arguments of non-internal functions to be intrinsically alive as
292 // well as arguments to functions which have their "address taken".
294 void DAE::SurveyFunction(Function &F) {
295 bool FunctionIntrinsicallyLive = false;
296 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead;
298 if (!F.hasInternalLinkage() &&
299 (!ShouldHackArguments() || F.isIntrinsic()))
300 FunctionIntrinsicallyLive = true;
302 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
303 // If this use is anything other than a call site, the function is alive.
304 CallSite CS = CallSite::get(*I);
305 Instruction *TheCall = CS.getInstruction();
306 if (!TheCall) { // Not a direct call site?
307 FunctionIntrinsicallyLive = true;
311 // Check to see if the return value is used...
312 if (RetValLiveness != Live)
313 for (Value::use_iterator I = TheCall->use_begin(),
314 E = TheCall->use_end(); I != E; ++I)
315 if (isa<ReturnInst>(cast<Instruction>(*I))) {
316 RetValLiveness = MaybeLive;
317 } else if (isa<CallInst>(cast<Instruction>(*I)) ||
318 isa<InvokeInst>(cast<Instruction>(*I))) {
319 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) ||
320 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) {
321 RetValLiveness = Live;
324 RetValLiveness = MaybeLive;
327 RetValLiveness = Live;
331 // If the function is PASSED IN as an argument, its address has been taken
332 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
334 if (AI->get() == &F) {
335 FunctionIntrinsicallyLive = true;
338 if (FunctionIntrinsicallyLive) break;
341 if (FunctionIntrinsicallyLive) {
342 DOUT << " Intrinsically live fn: " << F.getName() << "\n";
343 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
345 LiveArguments.insert(AI);
346 LiveRetVal.insert(&F);
350 switch (RetValLiveness) {
351 case Live: LiveRetVal.insert(&F); break;
352 case MaybeLive: MaybeLiveRetVal.insert(&F); break;
353 case Dead: DeadRetVal.insert(&F); break;
356 DOUT << " Inspecting args for fn: " << F.getName() << "\n";
358 // If it is not intrinsically alive, we know that all users of the
359 // function are call sites. Mark all of the arguments live which are
360 // directly used, and keep track of all of the call sites of this function
361 // if there are any arguments we assume that are dead.
363 bool AnyMaybeLiveArgs = false;
364 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
366 switch (getArgumentLiveness(*AI)) {
368 DOUT << " Arg live by use: " << AI->getName() << "\n";
369 LiveArguments.insert(AI);
372 DOUT << " Arg definitely dead: " << AI->getName() <<"\n";
373 DeadArguments.insert(AI);
376 DOUT << " Arg only passed to calls: " << AI->getName() << "\n";
377 AnyMaybeLiveArgs = true;
378 MaybeLiveArguments.insert(AI);
382 // If there are any "MaybeLive" arguments, we need to check callees of
383 // this function when/if they become alive. Record which functions are
385 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive)
386 for (Value::use_iterator I = F.use_begin(), E = F.use_end();
388 if (AnyMaybeLiveArgs)
389 CallSites.insert(std::make_pair(&F, CallSite::get(*I)));
391 if (RetValLiveness == MaybeLive)
392 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
394 InstructionsToInspect.push_back(cast<Instruction>(*UI));
398 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we
399 // know that the only uses of Arg are to be passed in as an argument to a
400 // function call or return. Check to see if the formal argument passed in is in
401 // the LiveArguments set. If so, return true.
403 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) {
404 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
405 if (isa<ReturnInst>(*I)) {
406 if (LiveRetVal.count(Arg->getParent())) return true;
410 CallSite CS = CallSite::get(*I);
412 // We know that this can only be used for direct calls...
413 Function *Callee = CS.getCalledFunction();
415 // Loop over all of the arguments (because Arg may be passed into the call
416 // multiple times) and check to see if any are now alive...
417 CallSite::arg_iterator CSAI = CS.arg_begin();
418 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end();
419 AI != E; ++AI, ++CSAI)
420 // If this is the argument we are looking for, check to see if it's alive
421 if (*CSAI == Arg && LiveArguments.count(AI))
427 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
428 /// Mark it live in the specified sets and recursively mark arguments in callers
429 /// live that are needed to pass in a value.
431 void DAE::MarkArgumentLive(Argument *Arg) {
432 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg);
433 if (It == MaybeLiveArguments.end() || *It != Arg) return;
435 DOUT << " MaybeLive argument now live: " << Arg->getName() <<"\n";
436 MaybeLiveArguments.erase(It);
437 LiveArguments.insert(Arg);
439 // Loop over all of the call sites of the function, making any arguments
440 // passed in to provide a value for this argument live as necessary.
442 Function *Fn = Arg->getParent();
443 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg));
445 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn);
446 for (; I != CallSites.end() && I->first == Fn; ++I) {
447 CallSite CS = I->second;
448 Value *ArgVal = *(CS.arg_begin()+ArgNo);
449 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) {
450 MarkArgumentLive(ActualArg);
452 // If the value passed in at this call site is a return value computed by
453 // some other call site, make sure to mark the return value at the other
454 // call site as being needed.
455 CallSite ArgCS = CallSite::get(ArgVal);
456 if (ArgCS.getInstruction())
457 if (Function *Fn = ArgCS.getCalledFunction())
463 /// MarkArgumentLive - The MaybeLive return value for the specified function is
464 /// now known to be alive. Propagate this fact to the return instructions which
466 void DAE::MarkRetValLive(Function *F) {
467 assert(F && "Shame shame, we can't have null pointers here!");
469 // Check to see if we already knew it was live
470 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F);
471 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive!
473 DOUT << " MaybeLive retval now live: " << F->getName() << "\n";
475 MaybeLiveRetVal.erase(I);
476 LiveRetVal.insert(F); // It is now known to be live!
478 // Loop over all of the functions, noticing that the return value is now live.
479 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
480 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
481 MarkReturnInstArgumentLive(RI);
484 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) {
485 Value *Op = RI->getOperand(0);
486 if (Argument *A = dyn_cast<Argument>(Op)) {
488 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) {
489 if (Function *F = CI->getCalledFunction())
491 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
492 if (Function *F = II->getCalledFunction())
497 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
498 // specified by the DeadArguments list. Transform the function and all of the
499 // callees of the function to not have these arguments.
501 void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
502 // Start by computing a new prototype for the function, which is the same as
503 // the old function, but has fewer arguments.
504 const FunctionType *FTy = F->getFunctionType();
505 std::vector<const Type*> Params;
507 // Set up to build a new list of parameter attributes
508 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
509 const PAListPtr &PAL = F->getParamAttrs();
511 // The existing function return attributes.
512 ParameterAttributes RAttrs = PAL.getParamAttrs(0);
514 // Make the function return void if the return value is dead.
515 const Type *RetTy = FTy->getReturnType();
516 if (DeadRetVal.count(F)) {
517 RetTy = Type::VoidTy;
518 RAttrs &= ~ParamAttr::typeIncompatible(RetTy);
523 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
525 // Construct the new parameter list from non-dead arguments. Also construct
526 // a new set of parameter attributes to correspond.
528 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
530 if (!DeadArguments.count(I)) {
531 Params.push_back(I->getType());
533 if (ParameterAttributes Attrs = PAL.getParamAttrs(index))
534 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
537 // Reconstruct the ParamAttrsList based on the vector we constructed.
538 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
540 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
541 // have zero fixed arguments.
543 bool ExtraArgHack = false;
544 if (Params.empty() && FTy->isVarArg()) {
546 Params.push_back(Type::Int32Ty);
549 // Create the new function type based on the recomputed parameters.
550 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
552 // Create the new function body and insert it into the module...
553 Function *NF = Function::Create(NFTy, F->getLinkage());
554 NF->setCallingConv(F->getCallingConv());
555 NF->setParamAttrs(NewPAL);
556 if (F->hasCollector())
557 NF->setCollector(F->getCollector());
558 F->getParent()->getFunctionList().insert(F, NF);
561 // Loop over all of the callers of the function, transforming the call sites
562 // to pass in a smaller number of arguments into the new function.
564 std::vector<Value*> Args;
565 while (!F->use_empty()) {
566 CallSite CS = CallSite::get(F->use_back());
567 Instruction *Call = CS.getInstruction();
568 ParamAttrsVec.clear();
569 const PAListPtr &CallPAL = CS.getParamAttrs();
571 // The call return attributes.
572 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0);
573 // Adjust in case the function was changed to return void.
574 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType());
576 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
578 // Loop over the operands, deleting dead ones...
579 CallSite::arg_iterator AI = CS.arg_begin();
581 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
582 I != E; ++I, ++AI, ++index)
583 if (!DeadArguments.count(I)) { // Remove operands for dead arguments
585 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(index))
586 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
590 Args.push_back(UndefValue::get(Type::Int32Ty));
592 // Push any varargs arguments on the list. Don't forget their attributes.
593 for (; AI != CS.arg_end(); ++AI) {
595 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(index++))
596 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
599 // Reconstruct the ParamAttrsList based on the vector we constructed.
600 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(),
601 ParamAttrsVec.end());
604 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
605 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
606 Args.begin(), Args.end(), "", Call);
607 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
608 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL);
610 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
611 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
612 cast<CallInst>(New)->setParamAttrs(NewCallPAL);
613 if (cast<CallInst>(Call)->isTailCall())
614 cast<CallInst>(New)->setTailCall();
618 if (!Call->use_empty()) {
619 if (New->getType() == Type::VoidTy)
620 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
622 Call->replaceAllUsesWith(New);
627 // Finally, remove the old call from the program, reducing the use-count of
629 Call->getParent()->getInstList().erase(Call);
632 // Since we have now created the new function, splice the body of the old
633 // function right into the new function, leaving the old rotting hulk of the
635 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
637 // Loop over the argument list, transfering uses of the old arguments over to
638 // the new arguments, also transfering over the names as well. While we're at
639 // it, remove the dead arguments from the DeadArguments list.
641 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
642 I2 = NF->arg_begin();
644 if (!DeadArguments.count(I)) {
645 // If this is a live argument, move the name and users over to the new
647 I->replaceAllUsesWith(I2);
651 // If this argument is dead, replace any uses of it with null constants
652 // (these are guaranteed to only be operands to call instructions which
653 // will later be simplified).
654 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
655 DeadArguments.erase(I);
658 // If we change the return value of the function we must rewrite any return
659 // instructions. Check this now.
660 if (F->getReturnType() != NF->getReturnType())
661 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
662 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
663 ReturnInst::Create(0, RI);
664 BB->getInstList().erase(RI);
667 // Now that the old function is dead, delete it.
668 F->getParent()->getFunctionList().erase(F);
671 bool DAE::runOnModule(Module &M) {
672 bool Changed = false;
673 // First pass: Do a simple check to see if any functions can have their "..."
674 // removed. We can do this if they never call va_start. This loop cannot be
675 // fused with the next loop, because deleting a function invalidates
676 // information computed while surveying other functions.
677 DOUT << "DAE - Deleting dead varargs\n";
678 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
680 if (F.getFunctionType()->isVarArg())
681 Changed |= DeleteDeadVarargs(F);
684 // Second phase:loop through the module, determining which arguments are live.
685 // We assume all arguments are dead unless proven otherwise (allowing us to
686 // determine that dead arguments passed into recursive functions are dead).
688 DOUT << "DAE - Determining liveness\n";
689 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
692 // Loop over the instructions to inspect, propagating liveness among arguments
693 // and return values which are MaybeLive.
694 while (!InstructionsToInspect.empty()) {
695 Instruction *I = InstructionsToInspect.back();
696 InstructionsToInspect.pop_back();
698 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) {
699 // For return instructions, we just have to check to see if the return
700 // value for the current function is known now to be alive. If so, any
701 // arguments used by it are now alive, and any call instruction return
702 // value is alive as well.
703 if (LiveRetVal.count(RI->getParent()->getParent()))
704 MarkReturnInstArgumentLive(RI);
707 CallSite CS = CallSite::get(I);
708 assert(CS.getInstruction() && "Unknown instruction for the I2I list!");
710 Function *Callee = CS.getCalledFunction();
712 // If we found a call or invoke instruction on this list, that means that
713 // an argument of the function is a call instruction. If the argument is
714 // live, then the return value of the called instruction is now live.
716 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator
717 for (Function::arg_iterator FI = Callee->arg_begin(),
718 E = Callee->arg_end(); FI != E; ++AI, ++FI) {
719 // If this argument is another call...
720 CallSite ArgCS = CallSite::get(*AI);
721 if (ArgCS.getInstruction() && LiveArguments.count(FI))
722 if (Function *Callee = ArgCS.getCalledFunction())
723 MarkRetValLive(Callee);
728 // Now we loop over all of the MaybeLive arguments, promoting them to be live
729 // arguments if one of the calls that uses the arguments to the calls they are
730 // passed into requires them to be live. Of course this could make other
731 // arguments live, so process callers recursively.
733 // Because elements can be removed from the MaybeLiveArguments set, copy it to
734 // a temporary vector.
736 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
737 MaybeLiveArguments.end());
738 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
739 Argument *MLA = TmpArgList[i];
740 if (MaybeLiveArguments.count(MLA) &&
741 isMaybeLiveArgumentNowLive(MLA))
742 MarkArgumentLive(MLA);
745 // Recover memory early...
748 // At this point, we know that all arguments in DeadArguments and
749 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing
751 if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
752 MaybeLiveRetVal.empty() && DeadRetVal.empty())
755 // Otherwise, compact into one set, and start eliminating the arguments from
757 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
758 MaybeLiveArguments.clear();
759 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end());
760 MaybeLiveRetVal.clear();
762 LiveArguments.clear();
765 NumArgumentsEliminated += DeadArguments.size();
766 NumRetValsEliminated += DeadRetVal.size();
767 while (!DeadArguments.empty())
768 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent());
770 while (!DeadRetVal.empty())
771 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin());