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 return values 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 or return values.
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/LLVMContext.h"
28 #include "llvm/Module.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/CallSite.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/Transforms/Utils/Local.h"
34 #include "llvm/ADT/SmallVector.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/ADT/StringExtras.h"
41 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
42 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
45 /// DAE - The dead argument elimination pass.
47 class DAE : public ModulePass {
50 /// Struct that represents (part of) either a return value or a function
51 /// argument. Used so that arguments and return values can be used
54 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
60 /// Make RetOrArg comparable, so we can put it into a map.
61 bool operator<(const RetOrArg &O) const {
64 else if (Idx != O.Idx)
67 return IsArg < O.IsArg;
70 /// Make RetOrArg comparable, so we can easily iterate the multimap.
71 bool operator==(const RetOrArg &O) const {
72 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
75 std::string getDescription() const {
76 return std::string((IsArg ? "Argument #" : "Return value #"))
77 + utostr(Idx) + " of function " + F->getNameStr();
81 /// Liveness enum - During our initial pass over the program, we determine
82 /// that things are either alive or maybe alive. We don't mark anything
83 /// explicitly dead (even if we know they are), since anything not alive
84 /// with no registered uses (in Uses) will never be marked alive and will
85 /// thus become dead in the end.
86 enum Liveness { Live, MaybeLive };
88 /// Convenience wrapper
89 RetOrArg CreateRet(const Function *F, unsigned Idx) {
90 return RetOrArg(F, Idx, false);
92 /// Convenience wrapper
93 RetOrArg CreateArg(const Function *F, unsigned Idx) {
94 return RetOrArg(F, Idx, true);
97 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
98 /// This maps a return value or argument to any MaybeLive return values or
99 /// arguments it uses. This allows the MaybeLive values to be marked live
100 /// when any of its users is marked live.
101 /// For example (indices are left out for clarity):
102 /// - Uses[ret F] = ret G
103 /// This means that F calls G, and F returns the value returned by G.
104 /// - Uses[arg F] = ret G
105 /// This means that some function calls G and passes its result as an
107 /// - Uses[ret F] = arg F
108 /// This means that F returns one of its own arguments.
109 /// - Uses[arg F] = arg G
110 /// This means that G calls F and passes one of its own (G's) arguments
114 typedef std::set<RetOrArg> LiveSet;
115 typedef std::set<const Function*> LiveFuncSet;
117 /// This set contains all values that have been determined to be live.
119 /// This set contains all values that are cannot be changed in any way.
120 LiveFuncSet LiveFunctions;
122 typedef SmallVector<RetOrArg, 5> UseVector;
125 static char ID; // Pass identification, replacement for typeid
126 DAE() : ModulePass(&ID) {}
127 bool runOnModule(Module &M);
129 virtual bool ShouldHackArguments() const { return false; }
132 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
133 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
134 unsigned RetValNum = 0);
135 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses);
137 void SurveyFunction(Function &F);
138 void MarkValue(const RetOrArg &RA, Liveness L,
139 const UseVector &MaybeLiveUses);
140 void MarkLive(const RetOrArg &RA);
141 void MarkLive(const Function &F);
142 void PropagateLiveness(const RetOrArg &RA);
143 bool RemoveDeadStuffFromFunction(Function *F);
144 bool RemoveDeadParamsFromCallersOf(Function *F);
145 bool DeleteDeadVarargs(Function &Fn);
151 static RegisterPass<DAE>
152 X("deadargelim", "Dead Argument Elimination");
155 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
156 /// deletes arguments to functions which are external. This is only for use
158 struct DAH : public DAE {
160 virtual bool ShouldHackArguments() const { return true; }
165 static RegisterPass<DAH>
166 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
168 /// createDeadArgEliminationPass - This pass removes arguments from functions
169 /// which are not used by the body of the function.
171 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
172 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
174 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
175 /// llvm.vastart is never called, the varargs list is dead for the function.
176 bool DAE::DeleteDeadVarargs(Function &Fn) {
177 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
178 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
180 // Ensure that the function is only directly called.
181 if (Fn.hasAddressTaken())
184 // Okay, we know we can transform this function if safe. Scan its body
185 // looking for calls to llvm.vastart.
186 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
187 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
188 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
189 if (II->getIntrinsicID() == Intrinsic::vastart)
195 // If we get here, there are no calls to llvm.vastart in the function body,
196 // remove the "..." and adjust all the calls.
198 // Start by computing a new prototype for the function, which is the same as
199 // the old function, but doesn't have isVarArg set.
200 const FunctionType *FTy = Fn.getFunctionType();
202 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
203 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
205 unsigned NumArgs = Params.size();
207 // Create the new function body and insert it into the module...
208 Function *NF = Function::Create(NFTy, Fn.getLinkage());
209 NF->copyAttributesFrom(&Fn);
210 Fn.getParent()->getFunctionList().insert(&Fn, NF);
213 // Loop over all of the callers of the function, transforming the call sites
214 // to pass in a smaller number of arguments into the new function.
216 std::vector<Value*> Args;
217 while (!Fn.use_empty()) {
218 CallSite CS = CallSite::get(Fn.use_back());
219 Instruction *Call = CS.getInstruction();
221 // Pass all the same arguments.
222 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
224 // Drop any attributes that were on the vararg arguments.
225 AttrListPtr PAL = CS.getAttributes();
226 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
227 SmallVector<AttributeWithIndex, 8> AttributesVec;
228 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
229 AttributesVec.push_back(PAL.getSlot(i));
230 if (Attributes FnAttrs = PAL.getFnAttributes())
231 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
232 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
236 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
237 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
238 Args.begin(), Args.end(), "", Call);
239 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
240 cast<InvokeInst>(New)->setAttributes(PAL);
242 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
243 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
244 cast<CallInst>(New)->setAttributes(PAL);
245 if (cast<CallInst>(Call)->isTailCall())
246 cast<CallInst>(New)->setTailCall();
250 if (!Call->use_empty())
251 Call->replaceAllUsesWith(New);
255 // Finally, remove the old call from the program, reducing the use-count of
257 Call->eraseFromParent();
260 // Since we have now created the new function, splice the body of the old
261 // function right into the new function, leaving the old rotting hulk of the
263 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
265 // Loop over the argument list, transfering uses of the old arguments over to
266 // the new arguments, also transfering over the names as well. While we're at
267 // it, remove the dead arguments from the DeadArguments list.
269 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
270 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
271 // Move the name and users over to the new version.
272 I->replaceAllUsesWith(I2);
276 // Finally, nuke the old function.
277 Fn.eraseFromParent();
281 /// Convenience function that returns the number of return values. It returns 0
282 /// for void functions and 1 for functions not returning a struct. It returns
283 /// the number of struct elements for functions returning a struct.
284 static unsigned NumRetVals(const Function *F) {
285 if (F->getReturnType()->isVoidTy())
287 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
288 return STy->getNumElements();
293 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
294 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
296 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
297 // We're live if our use or its Function is already marked as live.
298 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
301 // We're maybe live otherwise, but remember that we must become live if
303 MaybeLiveUses.push_back(Use);
308 /// SurveyUse - This looks at a single use of an argument or return value
309 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
310 /// if it causes the used value to become MaybeLive.
312 /// RetValNum is the return value number to use when this use is used in a
313 /// return instruction. This is used in the recursion, you should always leave
315 DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
316 unsigned RetValNum) {
318 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
319 // The value is returned from a function. It's only live when the
320 // function's return value is live. We use RetValNum here, for the case
321 // that U is really a use of an insertvalue instruction that uses the
323 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
324 // We might be live, depending on the liveness of Use.
325 return MarkIfNotLive(Use, MaybeLiveUses);
327 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
328 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
330 // The use we are examining is inserted into an aggregate. Our liveness
331 // depends on all uses of that aggregate, but if it is used as a return
332 // value, only index at which we were inserted counts.
333 RetValNum = *IV->idx_begin();
335 // Note that if we are used as the aggregate operand to the insertvalue,
336 // we don't change RetValNum, but do survey all our uses.
338 Liveness Result = MaybeLive;
339 for (Value::use_iterator I = IV->use_begin(),
340 E = V->use_end(); I != E; ++I) {
341 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
347 CallSite CS = CallSite::get(V);
348 if (CS.getInstruction()) {
349 Function *F = CS.getCalledFunction();
351 // Used in a direct call.
353 // Find the argument number. We know for sure that this use is an
354 // argument, since if it was the function argument this would be an
355 // indirect call and the we know can't be looking at a value of the
356 // label type (for the invoke instruction).
357 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo());
359 if (ArgNo >= F->getFunctionType()->getNumParams())
360 // The value is passed in through a vararg! Must be live.
363 assert(CS.getArgument(ArgNo)
364 == CS.getInstruction()->getOperand(U.getOperandNo())
365 && "Argument is not where we expected it");
367 // Value passed to a normal call. It's only live when the corresponding
368 // argument to the called function turns out live.
369 RetOrArg Use = CreateArg(F, ArgNo);
370 return MarkIfNotLive(Use, MaybeLiveUses);
373 // Used in any other way? Value must be live.
377 /// SurveyUses - This looks at all the uses of the given value
378 /// Returns the Liveness deduced from the uses of this value.
380 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
381 /// the result is Live, MaybeLiveUses might be modified but its content should
382 /// be ignored (since it might not be complete).
383 DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) {
384 // Assume it's dead (which will only hold if there are no uses at all..).
385 Liveness Result = MaybeLive;
387 for (Value::use_iterator I = V->use_begin(),
388 E = V->use_end(); I != E; ++I) {
389 Result = SurveyUse(I, MaybeLiveUses);
396 // SurveyFunction - This performs the initial survey of the specified function,
397 // checking out whether or not it uses any of its incoming arguments or whether
398 // any callers use the return value. This fills in the LiveValues set and Uses
401 // We consider arguments of overridable functions to be intrinsically alive as
402 // well as arguments to functions which have their "address taken".
404 void DAE::SurveyFunction(Function &F) {
405 unsigned RetCount = NumRetVals(&F);
406 // Assume all return values are dead
407 typedef SmallVector<Liveness, 5> RetVals;
408 RetVals RetValLiveness(RetCount, MaybeLive);
410 typedef SmallVector<UseVector, 5> RetUses;
411 // These vectors map each return value to the uses that make it MaybeLive, so
412 // we can add those to the Uses map if the return value really turns out to be
413 // MaybeLive. Initialized to a list of RetCount empty lists.
414 RetUses MaybeLiveRetUses(RetCount);
416 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
417 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
418 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
419 != F.getFunctionType()->getReturnType()) {
420 // We don't support old style multiple return values.
425 if ((F.isDeclaration() || F.mayBeOverridden()) &&
426 (!ShouldHackArguments() || F.isIntrinsic())) {
429 } else if (!F.hasLocalLinkage()) {
430 DEBUG(dbgs() << "DAE - Intrinsically live return from " << F.getName()
432 // Mark the return values alive.
433 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
434 MarkLive(CreateRet(&F, i));
437 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
438 // Keep track of the number of live retvals, so we can skip checks once all
439 // of them turn out to be live.
440 unsigned NumLiveRetVals = 0;
441 const Type *STy = dyn_cast<StructType>(F.getReturnType());
442 // Loop all uses of the function.
443 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
444 // If the function is PASSED IN as an argument, its address has been
446 CallSite CS = CallSite::get(*I);
447 if (!CS.getInstruction() || !CS.isCallee(I)) {
452 // If this use is anything other than a call site, the function is alive.
453 Instruction *TheCall = CS.getInstruction();
454 if (!TheCall) { // Not a direct call site?
459 // If we end up here, we are looking at a direct call to our function.
461 // Now, check how our return value(s) is/are used in this caller. Don't
462 // bother checking return values if all of them are live already.
463 if (NumLiveRetVals != RetCount) {
465 // Check all uses of the return value.
466 for (Value::use_iterator I = TheCall->use_begin(),
467 E = TheCall->use_end(); I != E; ++I) {
468 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
469 if (Ext && Ext->hasIndices()) {
470 // This use uses a part of our return value, survey the uses of
471 // that part and store the results for this index only.
472 unsigned Idx = *Ext->idx_begin();
473 if (RetValLiveness[Idx] != Live) {
474 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
475 if (RetValLiveness[Idx] == Live)
479 // Used by something else than extractvalue. Mark all return
481 for (unsigned i = 0; i != RetCount; ++i )
482 RetValLiveness[i] = Live;
483 NumLiveRetVals = RetCount;
488 // Single return value
489 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
490 if (RetValLiveness[0] == Live)
491 NumLiveRetVals = RetCount;
496 // Now we've inspected all callers, record the liveness of our return values.
497 for (unsigned i = 0; i != RetCount; ++i)
498 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
500 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
502 // Now, check all of our arguments.
504 UseVector MaybeLiveArgUses;
505 for (Function::arg_iterator AI = F.arg_begin(),
506 E = F.arg_end(); AI != E; ++AI, ++i) {
507 // See what the effect of this use is (recording any uses that cause
508 // MaybeLive in MaybeLiveArgUses).
509 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
511 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
512 // Clear the vector again for the next iteration.
513 MaybeLiveArgUses.clear();
517 /// MarkValue - This function marks the liveness of RA depending on L. If L is
518 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
519 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
521 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
522 const UseVector &MaybeLiveUses) {
524 case Live: MarkLive(RA); break;
527 // Note any uses of this value, so this return value can be
528 // marked live whenever one of the uses becomes live.
529 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
530 UE = MaybeLiveUses.end(); UI != UE; ++UI)
531 Uses.insert(std::make_pair(*UI, RA));
537 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
538 /// changed in any way. Additionally,
539 /// mark any values that are used as this function's parameters or by its return
540 /// values (according to Uses) live as well.
541 void DAE::MarkLive(const Function &F) {
542 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
543 // Mark the function as live.
544 LiveFunctions.insert(&F);
545 // Mark all arguments as live.
546 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
547 PropagateLiveness(CreateArg(&F, i));
548 // Mark all return values as live.
549 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
550 PropagateLiveness(CreateRet(&F, i));
553 /// MarkLive - Mark the given return value or argument as live. Additionally,
554 /// mark any values that are used by this value (according to Uses) live as
556 void DAE::MarkLive(const RetOrArg &RA) {
557 if (LiveFunctions.count(RA.F))
558 return; // Function was already marked Live.
560 if (!LiveValues.insert(RA).second)
561 return; // We were already marked Live.
563 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
564 PropagateLiveness(RA);
567 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
568 /// to any other values it uses (according to Uses).
569 void DAE::PropagateLiveness(const RetOrArg &RA) {
570 // We don't use upper_bound (or equal_range) here, because our recursive call
571 // to ourselves is likely to cause the upper_bound (which is the first value
572 // not belonging to RA) to become erased and the iterator invalidated.
573 UseMap::iterator Begin = Uses.lower_bound(RA);
574 UseMap::iterator E = Uses.end();
576 for (I = Begin; I != E && I->first == RA; ++I)
579 // Erase RA from the Uses map (from the lower bound to wherever we ended up
581 Uses.erase(Begin, I);
584 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
585 // that are not in LiveValues. Transform the function and all of the callees of
586 // the function to not have these arguments and return values.
588 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
589 // Don't modify fully live functions
590 if (LiveFunctions.count(F))
593 // Start by computing a new prototype for the function, which is the same as
594 // the old function, but has fewer arguments and a different return type.
595 const FunctionType *FTy = F->getFunctionType();
596 std::vector<const Type*> Params;
598 // Set up to build a new list of parameter attributes.
599 SmallVector<AttributeWithIndex, 8> AttributesVec;
600 const AttrListPtr &PAL = F->getAttributes();
602 // The existing function return attributes.
603 Attributes RAttrs = PAL.getRetAttributes();
604 Attributes FnAttrs = PAL.getFnAttributes();
606 // Find out the new return value.
608 const Type *RetTy = FTy->getReturnType();
609 const Type *NRetTy = NULL;
610 unsigned RetCount = NumRetVals(F);
612 // -1 means unused, other numbers are the new index
613 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
614 std::vector<const Type*> RetTypes;
615 if (RetTy->isVoidTy()) {
618 const StructType *STy = dyn_cast<StructType>(RetTy);
620 // Look at each of the original return values individually.
621 for (unsigned i = 0; i != RetCount; ++i) {
622 RetOrArg Ret = CreateRet(F, i);
623 if (LiveValues.erase(Ret)) {
624 RetTypes.push_back(STy->getElementType(i));
625 NewRetIdxs[i] = RetTypes.size() - 1;
627 ++NumRetValsEliminated;
628 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
629 << F->getName() << "\n");
633 // We used to return a single value.
634 if (LiveValues.erase(CreateRet(F, 0))) {
635 RetTypes.push_back(RetTy);
638 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
640 ++NumRetValsEliminated;
642 if (RetTypes.size() > 1)
643 // More than one return type? Return a struct with them. Also, if we used
644 // to return a struct and didn't change the number of return values,
645 // return a struct again. This prevents changing {something} into
646 // something and {} into void.
647 // Make the new struct packed if we used to return a packed struct
649 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
650 else if (RetTypes.size() == 1)
651 // One return type? Just a simple value then, but only if we didn't use to
652 // return a struct with that simple value before.
653 NRetTy = RetTypes.front();
654 else if (RetTypes.size() == 0)
655 // No return types? Make it void, but only if we didn't use to return {}.
656 NRetTy = Type::getVoidTy(F->getContext());
659 assert(NRetTy && "No new return type found?");
661 // Remove any incompatible attributes, but only if we removed all return
662 // values. Otherwise, ensure that we don't have any conflicting attributes
663 // here. Currently, this should not be possible, but special handling might be
664 // required when new return value attributes are added.
665 if (NRetTy->isVoidTy())
666 RAttrs &= ~Attribute::typeIncompatible(NRetTy);
668 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
669 && "Return attributes no longer compatible?");
672 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
674 // Remember which arguments are still alive.
675 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
676 // Construct the new parameter list from non-dead arguments. Also construct
677 // a new set of parameter attributes to correspond. Skip the first parameter
678 // attribute, since that belongs to the return value.
680 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
682 RetOrArg Arg = CreateArg(F, i);
683 if (LiveValues.erase(Arg)) {
684 Params.push_back(I->getType());
687 // Get the original parameter attributes (skipping the first one, that is
688 // for the return value.
689 if (Attributes Attrs = PAL.getParamAttributes(i + 1))
690 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
692 ++NumArgumentsEliminated;
693 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
694 << ") from " << F->getName() << "\n");
698 if (FnAttrs != Attribute::None)
699 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
701 // Reconstruct the AttributesList based on the vector we constructed.
702 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
704 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
705 // have zero fixed arguments.
707 // Note that we apply this hack for a vararg fuction that does not have any
708 // arguments anymore, but did have them before (so don't bother fixing
709 // functions that were already broken wrt CWriter).
710 bool ExtraArgHack = false;
711 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) {
713 Params.push_back(Type::getInt32Ty(F->getContext()));
716 // Create the new function type based on the recomputed parameters.
717 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
723 // Create the new function body and insert it into the module...
724 Function *NF = Function::Create(NFTy, F->getLinkage());
725 NF->copyAttributesFrom(F);
726 NF->setAttributes(NewPAL);
727 // Insert the new function before the old function, so we won't be processing
729 F->getParent()->getFunctionList().insert(F, NF);
732 // Loop over all of the callers of the function, transforming the call sites
733 // to pass in a smaller number of arguments into the new function.
735 std::vector<Value*> Args;
736 while (!F->use_empty()) {
737 CallSite CS = CallSite::get(F->use_back());
738 Instruction *Call = CS.getInstruction();
740 AttributesVec.clear();
741 const AttrListPtr &CallPAL = CS.getAttributes();
743 // The call return attributes.
744 Attributes RAttrs = CallPAL.getRetAttributes();
745 Attributes FnAttrs = CallPAL.getFnAttributes();
746 // Adjust in case the function was changed to return void.
747 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
749 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
751 // Declare these outside of the loops, so we can reuse them for the second
752 // loop, which loops the varargs.
753 CallSite::arg_iterator I = CS.arg_begin();
755 // Loop over those operands, corresponding to the normal arguments to the
756 // original function, and add those that are still alive.
757 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
760 // Get original parameter attributes, but skip return attributes.
761 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
762 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
766 Args.push_back(UndefValue::get(Type::getInt32Ty(F->getContext())));
768 // Push any varargs arguments on the list. Don't forget their attributes.
769 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
771 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
772 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
775 if (FnAttrs != Attribute::None)
776 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
778 // Reconstruct the AttributesList based on the vector we constructed.
779 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
780 AttributesVec.end());
783 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
784 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
785 Args.begin(), Args.end(), "", Call);
786 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
787 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
789 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
790 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
791 cast<CallInst>(New)->setAttributes(NewCallPAL);
792 if (cast<CallInst>(Call)->isTailCall())
793 cast<CallInst>(New)->setTailCall();
797 if (!Call->use_empty()) {
798 if (New->getType() == Call->getType()) {
799 // Return type not changed? Just replace users then.
800 Call->replaceAllUsesWith(New);
802 } else if (New->getType()->isVoidTy()) {
803 // Our return value has uses, but they will get removed later on.
804 // Replace by null for now.
805 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
807 assert(isa<StructType>(RetTy) &&
808 "Return type changed, but not into a void. The old return type"
809 " must have been a struct!");
810 Instruction *InsertPt = Call;
811 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
812 BasicBlock::iterator IP = II->getNormalDest()->begin();
813 while (isa<PHINode>(IP)) ++IP;
817 // We used to return a struct. Instead of doing smart stuff with all the
818 // uses of this struct, we will just rebuild it using
819 // extract/insertvalue chaining and let instcombine clean that up.
821 // Start out building up our return value from undef
822 Value *RetVal = UndefValue::get(RetTy);
823 for (unsigned i = 0; i != RetCount; ++i)
824 if (NewRetIdxs[i] != -1) {
826 if (RetTypes.size() > 1)
827 // We are still returning a struct, so extract the value from our
829 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
832 // We are now returning a single element, so just insert that
834 // Insert the value at the old position
835 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
837 // Now, replace all uses of the old call instruction with the return
839 Call->replaceAllUsesWith(RetVal);
844 // Finally, remove the old call from the program, reducing the use-count of
846 Call->eraseFromParent();
849 // Since we have now created the new function, splice the body of the old
850 // function right into the new function, leaving the old rotting hulk of the
852 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
854 // Loop over the argument list, transfering uses of the old arguments over to
855 // the new arguments, also transfering over the names as well.
857 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
858 I2 = NF->arg_begin(); I != E; ++I, ++i)
860 // If this is a live argument, move the name and users over to the new
862 I->replaceAllUsesWith(I2);
866 // If this argument is dead, replace any uses of it with null constants
867 // (these are guaranteed to become unused later on).
868 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
871 // If we change the return value of the function we must rewrite any return
872 // instructions. Check this now.
873 if (F->getReturnType() != NF->getReturnType())
874 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
875 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
878 if (NFTy->getReturnType()->isVoidTy()) {
881 assert (isa<StructType>(RetTy));
882 // The original return value was a struct, insert
883 // extractvalue/insertvalue chains to extract only the values we need
884 // to return and insert them into our new result.
885 // This does generate messy code, but we'll let it to instcombine to
887 Value *OldRet = RI->getOperand(0);
888 // Start out building up our return value from undef
889 RetVal = UndefValue::get(NRetTy);
890 for (unsigned i = 0; i != RetCount; ++i)
891 if (NewRetIdxs[i] != -1) {
892 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
894 if (RetTypes.size() > 1) {
895 // We're still returning a struct, so reinsert the value into
896 // our new return value at the new index
898 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
901 // We are now only returning a simple value, so just return the
907 // Replace the return instruction with one returning the new return
908 // value (possibly 0 if we became void).
909 ReturnInst::Create(F->getContext(), RetVal, RI);
910 BB->getInstList().erase(RI);
913 // Now that the old function is dead, delete it.
914 F->eraseFromParent();
919 bool DAE::RemoveDeadParamsFromCallersOf(Function *F) {
920 // Don't modify fully live functions
921 if (LiveFunctions.count(F))
924 // Make a list of the dead arguments.
925 SmallVector<int, 10> ArgDead;
927 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
929 RetOrArg Arg = CreateArg(F, i);
930 if (!LiveValues.count(Arg))
931 ArgDead.push_back(i);
936 bool MadeChange = false;
937 for (Function::use_iterator I = F->use_begin(), E = F->use_end();
939 CallSite CS = CallSite::get(*I);
940 if (CS.getInstruction() && CS.isCallee(I)) {
941 for (unsigned i = 0, e = ArgDead.size(); i != e; ++i) {
942 Value *A = CS.getArgument(ArgDead[i]);
943 if (!isa<UndefValue>(A)) {
945 CS.setArgument(ArgDead[i], UndefValue::get(A->getType()));
946 RecursivelyDeleteTriviallyDeadInstructions(A);
955 bool DAE::runOnModule(Module &M) {
956 bool Changed = false;
958 // First pass: Do a simple check to see if any functions can have their "..."
959 // removed. We can do this if they never call va_start. This loop cannot be
960 // fused with the next loop, because deleting a function invalidates
961 // information computed while surveying other functions.
962 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
963 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
965 if (F.getFunctionType()->isVarArg())
966 Changed |= DeleteDeadVarargs(F);
969 // Second phase:loop through the module, determining which arguments are live.
970 // We assume all arguments are dead unless proven otherwise (allowing us to
971 // determine that dead arguments passed into recursive functions are dead).
973 DEBUG(dbgs() << "DAE - Determining liveness\n");
974 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
977 // Now, remove all dead arguments and return values from each function in
979 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
980 // Increment now, because the function will probably get removed (ie.
981 // replaced by a new one).
983 if (F->hasLocalLinkage())
984 Changed |= RemoveDeadStuffFromFunction(F);
986 Changed |= RemoveDeadParamsFromCallersOf(F);