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/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);
178 // Drop any attributes that were on the vararg arguments.
179 const ParamAttrsList *PAL = CS.getParamAttrs();
180 if (PAL && PAL->getParamIndex(PAL->size() - 1) > NumArgs) {
181 ParamAttrsVector ParamAttrsVec;
182 for (unsigned i = 0; PAL->getParamIndex(i) <= NumArgs; ++i) {
183 ParamAttrsWithIndex PAWI;
184 PAWI = ParamAttrsWithIndex::get(PAL->getParamIndex(i),
185 PAL->getParamAttrsAtIndex(i));
186 ParamAttrsVec.push_back(PAWI);
188 PAL = ParamAttrsList::get(ParamAttrsVec);
192 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
193 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
194 Args.begin(), Args.end(), "", Call);
195 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
196 cast<InvokeInst>(New)->setParamAttrs(PAL);
198 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
199 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
200 cast<CallInst>(New)->setParamAttrs(PAL);
201 if (cast<CallInst>(Call)->isTailCall())
202 cast<CallInst>(New)->setTailCall();
206 if (!Call->use_empty())
207 Call->replaceAllUsesWith(New);
211 // Finally, remove the old call from the program, reducing the use-count of
213 Call->eraseFromParent();
216 // Since we have now created the new function, splice the body of the old
217 // function right into the new function, leaving the old rotting hulk of the
219 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
221 // Loop over the argument list, transfering uses of the old arguments over to
222 // the new arguments, also transfering over the names as well. While we're at
223 // it, remove the dead arguments from the DeadArguments list.
225 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
226 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
227 // Move the name and users over to the new version.
228 I->replaceAllUsesWith(I2);
232 // Finally, nuke the old function.
233 Fn.eraseFromParent();
238 static inline bool CallPassesValueThoughVararg(Instruction *Call,
240 CallSite CS = CallSite::get(Call);
241 const Type *CalledValueTy = CS.getCalledValue()->getType();
242 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType();
243 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams();
244 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
245 AI != CS.arg_end(); ++AI)
246 if (AI->get() == Arg)
251 // getArgumentLiveness - Inspect an argument, determining if is known Live
252 // (used in a computation), MaybeLive (only passed as an argument to a call), or
254 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) {
255 const Function *F = A.getParent();
257 // If this is the return value of a struct function, it's not really dead.
258 if (F->isStructReturn() && &*(F->arg_begin()) == &A)
261 if (A.use_empty()) // First check, directly dead?
264 // Scan through all of the uses, looking for non-argument passing uses.
265 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
266 // Return instructions do not immediately effect liveness.
267 if (isa<ReturnInst>(*I))
270 CallSite CS = CallSite::get(const_cast<User*>(*I));
271 if (!CS.getInstruction()) {
272 // If its used by something that is not a call or invoke, it's alive!
275 // If it's an indirect call, mark it alive...
276 Function *Callee = CS.getCalledFunction();
277 if (!Callee) return Live;
279 // Check to see if it's passed through a va_arg area: if so, we cannot
281 if (CallPassesValueThoughVararg(CS.getInstruction(), &A))
282 return Live; // If passed through va_arg area, we cannot remove it
285 return MaybeLive; // It must be used, but only as argument to a function
289 // SurveyFunction - This performs the initial survey of the specified function,
290 // checking out whether or not it uses any of its incoming arguments or whether
291 // any callers use the return value. This fills in the
292 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets.
294 // We consider arguments of non-internal functions to be intrinsically alive as
295 // well as arguments to functions which have their "address taken".
297 void DAE::SurveyFunction(Function &F) {
298 bool FunctionIntrinsicallyLive = false;
299 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead;
301 if (!F.hasInternalLinkage() &&
302 (!ShouldHackArguments() || F.isIntrinsic()))
303 FunctionIntrinsicallyLive = true;
305 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
306 // If this use is anything other than a call site, the function is alive.
307 CallSite CS = CallSite::get(*I);
308 Instruction *TheCall = CS.getInstruction();
309 if (!TheCall) { // Not a direct call site?
310 FunctionIntrinsicallyLive = true;
314 // Check to see if the return value is used...
315 if (RetValLiveness != Live)
316 for (Value::use_iterator I = TheCall->use_begin(),
317 E = TheCall->use_end(); I != E; ++I)
318 if (isa<ReturnInst>(cast<Instruction>(*I))) {
319 RetValLiveness = MaybeLive;
320 } else if (isa<CallInst>(cast<Instruction>(*I)) ||
321 isa<InvokeInst>(cast<Instruction>(*I))) {
322 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) ||
323 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) {
324 RetValLiveness = Live;
327 RetValLiveness = MaybeLive;
330 RetValLiveness = Live;
334 // If the function is PASSED IN as an argument, its address has been taken
335 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
337 if (AI->get() == &F) {
338 FunctionIntrinsicallyLive = true;
341 if (FunctionIntrinsicallyLive) break;
344 if (FunctionIntrinsicallyLive) {
345 DOUT << " Intrinsically live fn: " << F.getName() << "\n";
346 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
348 LiveArguments.insert(AI);
349 LiveRetVal.insert(&F);
353 switch (RetValLiveness) {
354 case Live: LiveRetVal.insert(&F); break;
355 case MaybeLive: MaybeLiveRetVal.insert(&F); break;
356 case Dead: DeadRetVal.insert(&F); break;
359 DOUT << " Inspecting args for fn: " << F.getName() << "\n";
361 // If it is not intrinsically alive, we know that all users of the
362 // function are call sites. Mark all of the arguments live which are
363 // directly used, and keep track of all of the call sites of this function
364 // if there are any arguments we assume that are dead.
366 bool AnyMaybeLiveArgs = false;
367 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
369 switch (getArgumentLiveness(*AI)) {
371 DOUT << " Arg live by use: " << AI->getName() << "\n";
372 LiveArguments.insert(AI);
375 DOUT << " Arg definitely dead: " << AI->getName() <<"\n";
376 DeadArguments.insert(AI);
379 DOUT << " Arg only passed to calls: " << AI->getName() << "\n";
380 AnyMaybeLiveArgs = true;
381 MaybeLiveArguments.insert(AI);
385 // If there are any "MaybeLive" arguments, we need to check callees of
386 // this function when/if they become alive. Record which functions are
388 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive)
389 for (Value::use_iterator I = F.use_begin(), E = F.use_end();
391 if (AnyMaybeLiveArgs)
392 CallSites.insert(std::make_pair(&F, CallSite::get(*I)));
394 if (RetValLiveness == MaybeLive)
395 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
397 InstructionsToInspect.push_back(cast<Instruction>(*UI));
401 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we
402 // know that the only uses of Arg are to be passed in as an argument to a
403 // function call or return. Check to see if the formal argument passed in is in
404 // the LiveArguments set. If so, return true.
406 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) {
407 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
408 if (isa<ReturnInst>(*I)) {
409 if (LiveRetVal.count(Arg->getParent())) return true;
413 CallSite CS = CallSite::get(*I);
415 // We know that this can only be used for direct calls...
416 Function *Callee = CS.getCalledFunction();
418 // Loop over all of the arguments (because Arg may be passed into the call
419 // multiple times) and check to see if any are now alive...
420 CallSite::arg_iterator CSAI = CS.arg_begin();
421 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end();
422 AI != E; ++AI, ++CSAI)
423 // If this is the argument we are looking for, check to see if it's alive
424 if (*CSAI == Arg && LiveArguments.count(AI))
430 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
431 /// Mark it live in the specified sets and recursively mark arguments in callers
432 /// live that are needed to pass in a value.
434 void DAE::MarkArgumentLive(Argument *Arg) {
435 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg);
436 if (It == MaybeLiveArguments.end() || *It != Arg) return;
438 DOUT << " MaybeLive argument now live: " << Arg->getName() <<"\n";
439 MaybeLiveArguments.erase(It);
440 LiveArguments.insert(Arg);
442 // Loop over all of the call sites of the function, making any arguments
443 // passed in to provide a value for this argument live as necessary.
445 Function *Fn = Arg->getParent();
446 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg));
448 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn);
449 for (; I != CallSites.end() && I->first == Fn; ++I) {
450 CallSite CS = I->second;
451 Value *ArgVal = *(CS.arg_begin()+ArgNo);
452 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) {
453 MarkArgumentLive(ActualArg);
455 // If the value passed in at this call site is a return value computed by
456 // some other call site, make sure to mark the return value at the other
457 // call site as being needed.
458 CallSite ArgCS = CallSite::get(ArgVal);
459 if (ArgCS.getInstruction())
460 if (Function *Fn = ArgCS.getCalledFunction())
466 /// MarkArgumentLive - The MaybeLive return value for the specified function is
467 /// now known to be alive. Propagate this fact to the return instructions which
469 void DAE::MarkRetValLive(Function *F) {
470 assert(F && "Shame shame, we can't have null pointers here!");
472 // Check to see if we already knew it was live
473 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F);
474 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive!
476 DOUT << " MaybeLive retval now live: " << F->getName() << "\n";
478 MaybeLiveRetVal.erase(I);
479 LiveRetVal.insert(F); // It is now known to be live!
481 // Loop over all of the functions, noticing that the return value is now live.
482 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
483 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
484 MarkReturnInstArgumentLive(RI);
487 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) {
488 Value *Op = RI->getOperand(0);
489 if (Argument *A = dyn_cast<Argument>(Op)) {
491 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) {
492 if (Function *F = CI->getCalledFunction())
494 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
495 if (Function *F = II->getCalledFunction())
500 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
501 // specified by the DeadArguments list. Transform the function and all of the
502 // callees of the function to not have these arguments.
504 void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
505 // Start by computing a new prototype for the function, which is the same as
506 // the old function, but has fewer arguments.
507 const FunctionType *FTy = F->getFunctionType();
508 std::vector<const Type*> Params;
510 // Set up to build a new list of parameter attributes
511 ParamAttrsVector ParamAttrsVec;
512 const ParamAttrsList *PAL = F->getParamAttrs();
514 // The existing function return attributes.
515 uint16_t RAttrs = PAL ? PAL->getParamAttrs(0) : 0;
517 // Make the function return void if the return value is dead.
518 const Type *RetTy = FTy->getReturnType();
519 if (DeadRetVal.count(F)) {
520 RetTy = Type::VoidTy;
521 RAttrs &= ~ParamAttr::typeIncompatible(RetTy);
526 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
528 // Construct the new parameter list from non-dead arguments. Also construct
529 // a new set of parameter attributes to correspond.
531 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
533 if (!DeadArguments.count(I)) {
534 Params.push_back(I->getType());
535 uint16_t Attrs = PAL ? PAL->getParamAttrs(index) : 0;
537 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
540 // Reconstruct the ParamAttrsList based on the vector we constructed.
541 PAL = ParamAttrsList::get(ParamAttrsVec);
543 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
544 // have zero fixed arguments.
546 bool ExtraArgHack = false;
547 if (Params.empty() && FTy->isVarArg()) {
549 Params.push_back(Type::Int32Ty);
552 // Create the new function type based on the recomputed parameters.
553 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
555 // Create the new function body and insert it into the module...
556 Function *NF = new Function(NFTy, F->getLinkage());
557 NF->setCallingConv(F->getCallingConv());
558 NF->setParamAttrs(PAL);
559 if (F->hasCollector())
560 NF->setCollector(F->getCollector());
561 F->getParent()->getFunctionList().insert(F, NF);
564 // Loop over all of the callers of the function, transforming the call sites
565 // to pass in a smaller number of arguments into the new function.
567 std::vector<Value*> Args;
568 while (!F->use_empty()) {
569 CallSite CS = CallSite::get(F->use_back());
570 Instruction *Call = CS.getInstruction();
571 ParamAttrsVec.clear();
572 PAL = CS.getParamAttrs();
574 // The call return attributes.
575 uint16_t RAttrs = PAL ? PAL->getParamAttrs(0) : 0;
576 // Adjust in case the function was changed to return void.
577 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType());
579 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
581 // Loop over the operands, deleting dead ones...
582 CallSite::arg_iterator AI = CS.arg_begin();
584 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
585 I != E; ++I, ++AI, ++index)
586 if (!DeadArguments.count(I)) { // Remove operands for dead arguments
588 uint16_t Attrs = PAL ? PAL->getParamAttrs(index) : 0;
590 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
594 Args.push_back(UndefValue::get(Type::Int32Ty));
596 // Push any varargs arguments on the list. Don't forget their attributes.
597 for (; AI != CS.arg_end(); ++AI) {
599 uint16_t Attrs = PAL ? PAL->getParamAttrs(index++) : 0;
601 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
604 // Reconstruct the ParamAttrsList based on the vector we constructed.
605 PAL = ParamAttrsList::get(ParamAttrsVec);
608 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
609 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
610 Args.begin(), Args.end(), "", Call);
611 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
612 cast<InvokeInst>(New)->setParamAttrs(PAL);
614 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
615 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
616 cast<CallInst>(New)->setParamAttrs(PAL);
617 if (cast<CallInst>(Call)->isTailCall())
618 cast<CallInst>(New)->setTailCall();
622 if (!Call->use_empty()) {
623 if (New->getType() == Type::VoidTy)
624 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
626 Call->replaceAllUsesWith(New);
631 // Finally, remove the old call from the program, reducing the use-count of
633 Call->getParent()->getInstList().erase(Call);
636 // Since we have now created the new function, splice the body of the old
637 // function right into the new function, leaving the old rotting hulk of the
639 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
641 // Loop over the argument list, transfering uses of the old arguments over to
642 // the new arguments, also transfering over the names as well. While we're at
643 // it, remove the dead arguments from the DeadArguments list.
645 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
646 I2 = NF->arg_begin();
648 if (!DeadArguments.count(I)) {
649 // If this is a live argument, move the name and users over to the new
651 I->replaceAllUsesWith(I2);
655 // If this argument is dead, replace any uses of it with null constants
656 // (these are guaranteed to only be operands to call instructions which
657 // will later be simplified).
658 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
659 DeadArguments.erase(I);
662 // If we change the return value of the function we must rewrite any return
663 // instructions. Check this now.
664 if (F->getReturnType() != NF->getReturnType())
665 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
666 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
667 new ReturnInst(0, RI);
668 BB->getInstList().erase(RI);
671 // Now that the old function is dead, delete it.
672 F->getParent()->getFunctionList().erase(F);
675 bool DAE::runOnModule(Module &M) {
676 bool Changed = false;
677 // First pass: Do a simple check to see if any functions can have their "..."
678 // removed. We can do this if they never call va_start. This loop cannot be
679 // fused with the next loop, because deleting a function invalidates
680 // information computed while surveying other functions.
681 DOUT << "DAE - Deleting dead varargs\n";
682 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
684 if (F.getFunctionType()->isVarArg())
685 Changed |= DeleteDeadVarargs(F);
688 // Second phase:loop through the module, determining which arguments are live.
689 // We assume all arguments are dead unless proven otherwise (allowing us to
690 // determine that dead arguments passed into recursive functions are dead).
692 DOUT << "DAE - Determining liveness\n";
693 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
696 // Loop over the instructions to inspect, propagating liveness among arguments
697 // and return values which are MaybeLive.
698 while (!InstructionsToInspect.empty()) {
699 Instruction *I = InstructionsToInspect.back();
700 InstructionsToInspect.pop_back();
702 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) {
703 // For return instructions, we just have to check to see if the return
704 // value for the current function is known now to be alive. If so, any
705 // arguments used by it are now alive, and any call instruction return
706 // value is alive as well.
707 if (LiveRetVal.count(RI->getParent()->getParent()))
708 MarkReturnInstArgumentLive(RI);
711 CallSite CS = CallSite::get(I);
712 assert(CS.getInstruction() && "Unknown instruction for the I2I list!");
714 Function *Callee = CS.getCalledFunction();
716 // If we found a call or invoke instruction on this list, that means that
717 // an argument of the function is a call instruction. If the argument is
718 // live, then the return value of the called instruction is now live.
720 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator
721 for (Function::arg_iterator FI = Callee->arg_begin(),
722 E = Callee->arg_end(); FI != E; ++AI, ++FI) {
723 // If this argument is another call...
724 CallSite ArgCS = CallSite::get(*AI);
725 if (ArgCS.getInstruction() && LiveArguments.count(FI))
726 if (Function *Callee = ArgCS.getCalledFunction())
727 MarkRetValLive(Callee);
732 // Now we loop over all of the MaybeLive arguments, promoting them to be live
733 // arguments if one of the calls that uses the arguments to the calls they are
734 // passed into requires them to be live. Of course this could make other
735 // arguments live, so process callers recursively.
737 // Because elements can be removed from the MaybeLiveArguments set, copy it to
738 // a temporary vector.
740 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
741 MaybeLiveArguments.end());
742 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
743 Argument *MLA = TmpArgList[i];
744 if (MaybeLiveArguments.count(MLA) &&
745 isMaybeLiveArgumentNowLive(MLA))
746 MarkArgumentLive(MLA);
749 // Recover memory early...
752 // At this point, we know that all arguments in DeadArguments and
753 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing
755 if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
756 MaybeLiveRetVal.empty() && DeadRetVal.empty())
759 // Otherwise, compact into one set, and start eliminating the arguments from
761 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
762 MaybeLiveArguments.clear();
763 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end());
764 MaybeLiveRetVal.clear();
766 LiveArguments.clear();
769 NumArgumentsEliminated += DeadArguments.size();
770 NumRetValsEliminated += DeadRetVal.size();
771 while (!DeadArguments.empty())
772 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent());
774 while (!DeadRetVal.empty())
775 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin());