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"
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 PAListPtr PAL = CS.getParamAttrs();
180 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
181 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
182 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
183 ParamAttrsVec.push_back(PAL.getSlot(i));
184 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
188 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
189 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
190 Args.begin(), Args.end(), "", Call);
191 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
192 cast<InvokeInst>(New)->setParamAttrs(PAL);
194 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
195 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
196 cast<CallInst>(New)->setParamAttrs(PAL);
197 if (cast<CallInst>(Call)->isTailCall())
198 cast<CallInst>(New)->setTailCall();
202 if (!Call->use_empty())
203 Call->replaceAllUsesWith(New);
207 // Finally, remove the old call from the program, reducing the use-count of
209 Call->eraseFromParent();
212 // Since we have now created the new function, splice the body of the old
213 // function right into the new function, leaving the old rotting hulk of the
215 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
217 // Loop over the argument list, transfering uses of the old arguments over to
218 // the new arguments, also transfering over the names as well. While we're at
219 // it, remove the dead arguments from the DeadArguments list.
221 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
222 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
223 // Move the name and users over to the new version.
224 I->replaceAllUsesWith(I2);
228 // Finally, nuke the old function.
229 Fn.eraseFromParent();
234 static inline bool CallPassesValueThoughVararg(Instruction *Call,
236 CallSite CS = CallSite::get(Call);
237 const Type *CalledValueTy = CS.getCalledValue()->getType();
238 const Type *FTy = cast<PointerType>(CalledValueTy)->getElementType();
239 unsigned NumFixedArgs = cast<FunctionType>(FTy)->getNumParams();
240 for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
241 AI != CS.arg_end(); ++AI)
242 if (AI->get() == Arg)
247 // getArgumentLiveness - Inspect an argument, determining if is known Live
248 // (used in a computation), MaybeLive (only passed as an argument to a call), or
250 DAE::Liveness DAE::getArgumentLiveness(const Argument &A) {
251 const Function *F = A.getParent();
253 // If this is the return value of a struct function, it's not really dead.
254 if (F->hasStructRetAttr() && &*(F->arg_begin()) == &A)
257 if (A.use_empty()) // First check, directly dead?
260 // Scan through all of the uses, looking for non-argument passing uses.
261 for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
262 // Return instructions do not immediately effect liveness.
263 if (isa<ReturnInst>(*I))
266 CallSite CS = CallSite::get(const_cast<User*>(*I));
267 if (!CS.getInstruction()) {
268 // If its used by something that is not a call or invoke, it's alive!
271 // If it's an indirect call, mark it alive...
272 Function *Callee = CS.getCalledFunction();
273 if (!Callee) return Live;
275 // Check to see if it's passed through a va_arg area: if so, we cannot
277 if (CallPassesValueThoughVararg(CS.getInstruction(), &A))
278 return Live; // If passed through va_arg area, we cannot remove it
281 return MaybeLive; // It must be used, but only as argument to a function
285 // SurveyFunction - This performs the initial survey of the specified function,
286 // checking out whether or not it uses any of its incoming arguments or whether
287 // any callers use the return value. This fills in the
288 // (Dead|MaybeLive|Live)(Arguments|RetVal) sets.
290 // We consider arguments of non-internal functions to be intrinsically alive as
291 // well as arguments to functions which have their "address taken".
293 void DAE::SurveyFunction(Function &F) {
294 bool FunctionIntrinsicallyLive = false;
295 Liveness RetValLiveness = F.getReturnType() == Type::VoidTy ? Live : Dead;
297 if (!F.hasInternalLinkage() &&
298 (!ShouldHackArguments() || F.isIntrinsic()))
299 FunctionIntrinsicallyLive = true;
301 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
302 // If this use is anything other than a call site, the function is alive.
303 CallSite CS = CallSite::get(*I);
304 Instruction *TheCall = CS.getInstruction();
305 if (!TheCall) { // Not a direct call site?
306 FunctionIntrinsicallyLive = true;
310 // Check to see if the return value is used...
311 if (RetValLiveness != Live)
312 for (Value::use_iterator I = TheCall->use_begin(),
313 E = TheCall->use_end(); I != E; ++I)
314 if (isa<ReturnInst>(cast<Instruction>(*I))) {
315 RetValLiveness = MaybeLive;
316 } else if (isa<CallInst>(cast<Instruction>(*I)) ||
317 isa<InvokeInst>(cast<Instruction>(*I))) {
318 if (CallPassesValueThoughVararg(cast<Instruction>(*I), TheCall) ||
319 !CallSite::get(cast<Instruction>(*I)).getCalledFunction()) {
320 RetValLiveness = Live;
323 RetValLiveness = MaybeLive;
326 RetValLiveness = Live;
330 // If the function is PASSED IN as an argument, its address has been taken
331 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
333 if (AI->get() == &F) {
334 FunctionIntrinsicallyLive = true;
337 if (FunctionIntrinsicallyLive) break;
340 if (FunctionIntrinsicallyLive) {
341 DOUT << " Intrinsically live fn: " << F.getName() << "\n";
342 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
344 LiveArguments.insert(AI);
345 LiveRetVal.insert(&F);
349 switch (RetValLiveness) {
350 case Live: LiveRetVal.insert(&F); break;
351 case MaybeLive: MaybeLiveRetVal.insert(&F); break;
352 case Dead: DeadRetVal.insert(&F); break;
355 DOUT << " Inspecting args for fn: " << F.getName() << "\n";
357 // If it is not intrinsically alive, we know that all users of the
358 // function are call sites. Mark all of the arguments live which are
359 // directly used, and keep track of all of the call sites of this function
360 // if there are any arguments we assume that are dead.
362 bool AnyMaybeLiveArgs = false;
363 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end();
365 switch (getArgumentLiveness(*AI)) {
367 DOUT << " Arg live by use: " << AI->getName() << "\n";
368 LiveArguments.insert(AI);
371 DOUT << " Arg definitely dead: " << AI->getName() <<"\n";
372 DeadArguments.insert(AI);
375 DOUT << " Arg only passed to calls: " << AI->getName() << "\n";
376 AnyMaybeLiveArgs = true;
377 MaybeLiveArguments.insert(AI);
381 // If there are any "MaybeLive" arguments, we need to check callees of
382 // this function when/if they become alive. Record which functions are
384 if (AnyMaybeLiveArgs || RetValLiveness == MaybeLive)
385 for (Value::use_iterator I = F.use_begin(), E = F.use_end();
387 if (AnyMaybeLiveArgs)
388 CallSites.insert(std::make_pair(&F, CallSite::get(*I)));
390 if (RetValLiveness == MaybeLive)
391 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
393 InstructionsToInspect.push_back(cast<Instruction>(*UI));
397 // isMaybeLiveArgumentNowLive - Check to see if Arg is alive. At this point, we
398 // know that the only uses of Arg are to be passed in as an argument to a
399 // function call or return. Check to see if the formal argument passed in is in
400 // the LiveArguments set. If so, return true.
402 bool DAE::isMaybeLiveArgumentNowLive(Argument *Arg) {
403 for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
404 if (isa<ReturnInst>(*I)) {
405 if (LiveRetVal.count(Arg->getParent())) return true;
409 CallSite CS = CallSite::get(*I);
411 // We know that this can only be used for direct calls...
412 Function *Callee = CS.getCalledFunction();
414 // Loop over all of the arguments (because Arg may be passed into the call
415 // multiple times) and check to see if any are now alive...
416 CallSite::arg_iterator CSAI = CS.arg_begin();
417 for (Function::arg_iterator AI = Callee->arg_begin(), E = Callee->arg_end();
418 AI != E; ++AI, ++CSAI)
419 // If this is the argument we are looking for, check to see if it's alive
420 if (*CSAI == Arg && LiveArguments.count(AI))
426 /// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
427 /// Mark it live in the specified sets and recursively mark arguments in callers
428 /// live that are needed to pass in a value.
430 void DAE::MarkArgumentLive(Argument *Arg) {
431 std::set<Argument*>::iterator It = MaybeLiveArguments.lower_bound(Arg);
432 if (It == MaybeLiveArguments.end() || *It != Arg) return;
434 DOUT << " MaybeLive argument now live: " << Arg->getName() <<"\n";
435 MaybeLiveArguments.erase(It);
436 LiveArguments.insert(Arg);
438 // Loop over all of the call sites of the function, making any arguments
439 // passed in to provide a value for this argument live as necessary.
441 Function *Fn = Arg->getParent();
442 unsigned ArgNo = std::distance(Fn->arg_begin(), Function::arg_iterator(Arg));
444 std::multimap<Function*, CallSite>::iterator I = CallSites.lower_bound(Fn);
445 for (; I != CallSites.end() && I->first == Fn; ++I) {
446 CallSite CS = I->second;
447 Value *ArgVal = *(CS.arg_begin()+ArgNo);
448 if (Argument *ActualArg = dyn_cast<Argument>(ArgVal)) {
449 MarkArgumentLive(ActualArg);
451 // If the value passed in at this call site is a return value computed by
452 // some other call site, make sure to mark the return value at the other
453 // call site as being needed.
454 CallSite ArgCS = CallSite::get(ArgVal);
455 if (ArgCS.getInstruction())
456 if (Function *Fn = ArgCS.getCalledFunction())
462 /// MarkArgumentLive - The MaybeLive return value for the specified function is
463 /// now known to be alive. Propagate this fact to the return instructions which
465 void DAE::MarkRetValLive(Function *F) {
466 assert(F && "Shame shame, we can't have null pointers here!");
468 // Check to see if we already knew it was live
469 std::set<Function*>::iterator I = MaybeLiveRetVal.lower_bound(F);
470 if (I == MaybeLiveRetVal.end() || *I != F) return; // It's already alive!
472 DOUT << " MaybeLive retval now live: " << F->getName() << "\n";
474 MaybeLiveRetVal.erase(I);
475 LiveRetVal.insert(F); // It is now known to be live!
477 // Loop over all of the functions, noticing that the return value is now live.
478 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
479 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
480 MarkReturnInstArgumentLive(RI);
483 void DAE::MarkReturnInstArgumentLive(ReturnInst *RI) {
484 Value *Op = RI->getOperand(0);
485 if (Argument *A = dyn_cast<Argument>(Op)) {
487 } else if (CallInst *CI = dyn_cast<CallInst>(Op)) {
488 if (Function *F = CI->getCalledFunction())
490 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Op)) {
491 if (Function *F = II->getCalledFunction())
496 // RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
497 // specified by the DeadArguments list. Transform the function and all of the
498 // callees of the function to not have these arguments.
500 void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
501 // Start by computing a new prototype for the function, which is the same as
502 // the old function, but has fewer arguments.
503 const FunctionType *FTy = F->getFunctionType();
504 std::vector<const Type*> Params;
506 // Set up to build a new list of parameter attributes
507 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
508 const PAListPtr &PAL = F->getParamAttrs();
510 // The existing function return attributes.
511 ParameterAttributes RAttrs = PAL.getParamAttrs(0);
513 // Make the function return void if the return value is dead.
514 const Type *RetTy = FTy->getReturnType();
515 if (DeadRetVal.count(F)) {
516 RetTy = Type::VoidTy;
517 RAttrs &= ~ParamAttr::typeIncompatible(RetTy);
522 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
524 // Construct the new parameter list from non-dead arguments. Also construct
525 // a new set of parameter attributes to correspond.
527 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
529 if (!DeadArguments.count(I)) {
530 Params.push_back(I->getType());
532 if (ParameterAttributes Attrs = PAL.getParamAttrs(index))
533 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
536 // Reconstruct the ParamAttrsList based on the vector we constructed.
537 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
539 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
540 // have zero fixed arguments.
542 bool ExtraArgHack = false;
543 if (Params.empty() && FTy->isVarArg()) {
545 Params.push_back(Type::Int32Ty);
548 // Create the new function type based on the recomputed parameters.
549 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
551 // Create the new function body and insert it into the module...
552 Function *NF = new Function(NFTy, F->getLinkage());
553 NF->setCallingConv(F->getCallingConv());
554 NF->setParamAttrs(NewPAL);
555 if (F->hasCollector())
556 NF->setCollector(F->getCollector());
557 F->getParent()->getFunctionList().insert(F, NF);
560 // Loop over all of the callers of the function, transforming the call sites
561 // to pass in a smaller number of arguments into the new function.
563 std::vector<Value*> Args;
564 while (!F->use_empty()) {
565 CallSite CS = CallSite::get(F->use_back());
566 Instruction *Call = CS.getInstruction();
567 ParamAttrsVec.clear();
568 const PAListPtr &CallPAL = CS.getParamAttrs();
570 // The call return attributes.
571 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0);
572 // Adjust in case the function was changed to return void.
573 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType());
575 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
577 // Loop over the operands, deleting dead ones...
578 CallSite::arg_iterator AI = CS.arg_begin();
580 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
581 I != E; ++I, ++AI, ++index)
582 if (!DeadArguments.count(I)) { // Remove operands for dead arguments
584 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(index))
585 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
589 Args.push_back(UndefValue::get(Type::Int32Ty));
591 // Push any varargs arguments on the list. Don't forget their attributes.
592 for (; AI != CS.arg_end(); ++AI) {
594 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(index++))
595 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
598 // Reconstruct the ParamAttrsList based on the vector we constructed.
599 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(),
600 ParamAttrsVec.end());
603 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
604 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
605 Args.begin(), Args.end(), "", Call);
606 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
607 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL);
609 New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
610 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
611 cast<CallInst>(New)->setParamAttrs(NewCallPAL);
612 if (cast<CallInst>(Call)->isTailCall())
613 cast<CallInst>(New)->setTailCall();
617 if (!Call->use_empty()) {
618 if (New->getType() == Type::VoidTy)
619 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
621 Call->replaceAllUsesWith(New);
626 // Finally, remove the old call from the program, reducing the use-count of
628 Call->getParent()->getInstList().erase(Call);
631 // Since we have now created the new function, splice the body of the old
632 // function right into the new function, leaving the old rotting hulk of the
634 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
636 // Loop over the argument list, transfering uses of the old arguments over to
637 // the new arguments, also transfering over the names as well. While we're at
638 // it, remove the dead arguments from the DeadArguments list.
640 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
641 I2 = NF->arg_begin();
643 if (!DeadArguments.count(I)) {
644 // If this is a live argument, move the name and users over to the new
646 I->replaceAllUsesWith(I2);
650 // If this argument is dead, replace any uses of it with null constants
651 // (these are guaranteed to only be operands to call instructions which
652 // will later be simplified).
653 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
654 DeadArguments.erase(I);
657 // If we change the return value of the function we must rewrite any return
658 // instructions. Check this now.
659 if (F->getReturnType() != NF->getReturnType())
660 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
661 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
662 new ReturnInst(0, RI);
663 BB->getInstList().erase(RI);
666 // Now that the old function is dead, delete it.
667 F->getParent()->getFunctionList().erase(F);
670 bool DAE::runOnModule(Module &M) {
671 bool Changed = false;
672 // First pass: Do a simple check to see if any functions can have their "..."
673 // removed. We can do this if they never call va_start. This loop cannot be
674 // fused with the next loop, because deleting a function invalidates
675 // information computed while surveying other functions.
676 DOUT << "DAE - Deleting dead varargs\n";
677 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
679 if (F.getFunctionType()->isVarArg())
680 Changed |= DeleteDeadVarargs(F);
683 // Second phase:loop through the module, determining which arguments are live.
684 // We assume all arguments are dead unless proven otherwise (allowing us to
685 // determine that dead arguments passed into recursive functions are dead).
687 DOUT << "DAE - Determining liveness\n";
688 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
691 // Loop over the instructions to inspect, propagating liveness among arguments
692 // and return values which are MaybeLive.
693 while (!InstructionsToInspect.empty()) {
694 Instruction *I = InstructionsToInspect.back();
695 InstructionsToInspect.pop_back();
697 if (ReturnInst *RI = dyn_cast<ReturnInst>(I)) {
698 // For return instructions, we just have to check to see if the return
699 // value for the current function is known now to be alive. If so, any
700 // arguments used by it are now alive, and any call instruction return
701 // value is alive as well.
702 if (LiveRetVal.count(RI->getParent()->getParent()))
703 MarkReturnInstArgumentLive(RI);
706 CallSite CS = CallSite::get(I);
707 assert(CS.getInstruction() && "Unknown instruction for the I2I list!");
709 Function *Callee = CS.getCalledFunction();
711 // If we found a call or invoke instruction on this list, that means that
712 // an argument of the function is a call instruction. If the argument is
713 // live, then the return value of the called instruction is now live.
715 CallSite::arg_iterator AI = CS.arg_begin(); // ActualIterator
716 for (Function::arg_iterator FI = Callee->arg_begin(),
717 E = Callee->arg_end(); FI != E; ++AI, ++FI) {
718 // If this argument is another call...
719 CallSite ArgCS = CallSite::get(*AI);
720 if (ArgCS.getInstruction() && LiveArguments.count(FI))
721 if (Function *Callee = ArgCS.getCalledFunction())
722 MarkRetValLive(Callee);
727 // Now we loop over all of the MaybeLive arguments, promoting them to be live
728 // arguments if one of the calls that uses the arguments to the calls they are
729 // passed into requires them to be live. Of course this could make other
730 // arguments live, so process callers recursively.
732 // Because elements can be removed from the MaybeLiveArguments set, copy it to
733 // a temporary vector.
735 std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
736 MaybeLiveArguments.end());
737 for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
738 Argument *MLA = TmpArgList[i];
739 if (MaybeLiveArguments.count(MLA) &&
740 isMaybeLiveArgumentNowLive(MLA))
741 MarkArgumentLive(MLA);
744 // Recover memory early...
747 // At this point, we know that all arguments in DeadArguments and
748 // MaybeLiveArguments are dead. If the two sets are empty, there is nothing
750 if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
751 MaybeLiveRetVal.empty() && DeadRetVal.empty())
754 // Otherwise, compact into one set, and start eliminating the arguments from
756 DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
757 MaybeLiveArguments.clear();
758 DeadRetVal.insert(MaybeLiveRetVal.begin(), MaybeLiveRetVal.end());
759 MaybeLiveRetVal.clear();
761 LiveArguments.clear();
764 NumArgumentsEliminated += DeadArguments.size();
765 NumRetValsEliminated += DeadRetVal.size();
766 while (!DeadArguments.empty())
767 RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent());
769 while (!DeadRetVal.empty())
770 RemoveDeadArgumentsFromFunction(*DeadRetVal.begin());