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");
43 STATISTIC(NumParametersEliminated, "Number of parameters replaced with undef");
46 /// DAE - The dead argument elimination pass.
48 class DAE : public ModulePass {
51 /// Struct that represents (part of) either a return value or a function
52 /// argument. Used so that arguments and return values can be used
55 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
61 /// Make RetOrArg comparable, so we can put it into a map.
62 bool operator<(const RetOrArg &O) const {
65 else if (Idx != O.Idx)
68 return IsArg < O.IsArg;
71 /// Make RetOrArg comparable, so we can easily iterate the multimap.
72 bool operator==(const RetOrArg &O) const {
73 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
76 std::string getDescription() const {
77 return std::string((IsArg ? "Argument #" : "Return value #"))
78 + utostr(Idx) + " of function " + F->getNameStr();
82 /// Liveness enum - During our initial pass over the program, we determine
83 /// that things are either alive or maybe alive. We don't mark anything
84 /// explicitly dead (even if we know they are), since anything not alive
85 /// with no registered uses (in Uses) will never be marked alive and will
86 /// thus become dead in the end.
87 enum Liveness { Live, MaybeLive };
89 /// Convenience wrapper
90 RetOrArg CreateRet(const Function *F, unsigned Idx) {
91 return RetOrArg(F, Idx, false);
93 /// Convenience wrapper
94 RetOrArg CreateArg(const Function *F, unsigned Idx) {
95 return RetOrArg(F, Idx, true);
98 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
99 /// This maps a return value or argument to any MaybeLive return values or
100 /// arguments it uses. This allows the MaybeLive values to be marked live
101 /// when any of its users is marked live.
102 /// For example (indices are left out for clarity):
103 /// - Uses[ret F] = ret G
104 /// This means that F calls G, and F returns the value returned by G.
105 /// - Uses[arg F] = ret G
106 /// This means that some function calls G and passes its result as an
108 /// - Uses[ret F] = arg F
109 /// This means that F returns one of its own arguments.
110 /// - Uses[arg F] = arg G
111 /// This means that G calls F and passes one of its own (G's) arguments
115 typedef std::set<RetOrArg> LiveSet;
116 typedef std::set<const Function*> LiveFuncSet;
118 /// This set contains all values that have been determined to be live.
120 /// This set contains all values that are cannot be changed in any way.
121 LiveFuncSet LiveFunctions;
123 typedef SmallVector<RetOrArg, 5> UseVector;
126 static char ID; // Pass identification, replacement for typeid
127 DAE() : ModulePass(&ID) {}
128 bool runOnModule(Module &M);
130 virtual bool ShouldHackArguments() const { return false; }
133 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
134 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
135 unsigned RetValNum = 0);
136 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
138 void SurveyFunction(const Function &F);
139 void MarkValue(const RetOrArg &RA, Liveness L,
140 const UseVector &MaybeLiveUses);
141 void MarkLive(const RetOrArg &RA);
142 void MarkLive(const Function &F);
143 void PropagateLiveness(const RetOrArg &RA);
144 bool RemoveDeadStuffFromFunction(Function *F);
145 bool RemoveDeadParamsFromCallersOf(Function *F);
146 bool DeleteDeadVarargs(Function &Fn);
152 static RegisterPass<DAE>
153 X("deadargelim", "Dead Argument Elimination");
156 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
157 /// deletes arguments to functions which are external. This is only for use
159 struct DAH : public DAE {
161 virtual bool ShouldHackArguments() const { return true; }
166 static RegisterPass<DAH>
167 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
169 /// createDeadArgEliminationPass - This pass removes arguments from functions
170 /// which are not used by the body of the function.
172 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
173 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
175 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
176 /// llvm.vastart is never called, the varargs list is dead for the function.
177 bool DAE::DeleteDeadVarargs(Function &Fn) {
178 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
179 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
181 // Ensure that the function is only directly called.
182 if (Fn.hasAddressTaken())
185 // Okay, we know we can transform this function if safe. Scan its body
186 // looking for calls to llvm.vastart.
187 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
188 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
189 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
190 if (II->getIntrinsicID() == Intrinsic::vastart)
196 // If we get here, there are no calls to llvm.vastart in the function body,
197 // remove the "..." and adjust all the calls.
199 // Start by computing a new prototype for the function, which is the same as
200 // the old function, but doesn't have isVarArg set.
201 const FunctionType *FTy = Fn.getFunctionType();
203 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
204 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
206 unsigned NumArgs = Params.size();
208 // Create the new function body and insert it into the module...
209 Function *NF = Function::Create(NFTy, Fn.getLinkage());
210 NF->copyAttributesFrom(&Fn);
211 Fn.getParent()->getFunctionList().insert(&Fn, NF);
214 // Loop over all of the callers of the function, transforming the call sites
215 // to pass in a smaller number of arguments into the new function.
217 std::vector<Value*> Args;
218 while (!Fn.use_empty()) {
219 CallSite CS = CallSite::get(Fn.use_back());
220 Instruction *Call = CS.getInstruction();
222 // Pass all the same arguments.
223 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
225 // Drop any attributes that were on the vararg arguments.
226 AttrListPtr PAL = CS.getAttributes();
227 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
228 SmallVector<AttributeWithIndex, 8> AttributesVec;
229 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
230 AttributesVec.push_back(PAL.getSlot(i));
231 if (Attributes FnAttrs = PAL.getFnAttributes())
232 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
233 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
237 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
238 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
239 Args.begin(), Args.end(), "", Call);
240 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
241 cast<InvokeInst>(New)->setAttributes(PAL);
243 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
244 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
245 cast<CallInst>(New)->setAttributes(PAL);
246 if (cast<CallInst>(Call)->isTailCall())
247 cast<CallInst>(New)->setTailCall();
251 if (!Call->use_empty())
252 Call->replaceAllUsesWith(New);
256 // Finally, remove the old call from the program, reducing the use-count of
258 Call->eraseFromParent();
261 // Since we have now created the new function, splice the body of the old
262 // function right into the new function, leaving the old rotting hulk of the
264 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
266 // Loop over the argument list, transfering uses of the old arguments over to
267 // the new arguments, also transfering over the names as well. While we're at
268 // it, remove the dead arguments from the DeadArguments list.
270 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
271 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
272 // Move the name and users over to the new version.
273 I->replaceAllUsesWith(I2);
277 // Finally, nuke the old function.
278 Fn.eraseFromParent();
282 /// Convenience function that returns the number of return values. It returns 0
283 /// for void functions and 1 for functions not returning a struct. It returns
284 /// the number of struct elements for functions returning a struct.
285 static unsigned NumRetVals(const Function *F) {
286 if (F->getReturnType()->isVoidTy())
288 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
289 return STy->getNumElements();
294 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
295 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
297 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
298 // We're live if our use or its Function is already marked as live.
299 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
302 // We're maybe live otherwise, but remember that we must become live if
304 MaybeLiveUses.push_back(Use);
309 /// SurveyUse - This looks at a single use of an argument or return value
310 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
311 /// if it causes the used value to become MaybeLive.
313 /// RetValNum is the return value number to use when this use is used in a
314 /// return instruction. This is used in the recursion, you should always leave
316 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
317 UseVector &MaybeLiveUses, unsigned RetValNum) {
319 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
320 // The value is returned from a function. It's only live when the
321 // function's return value is live. We use RetValNum here, for the case
322 // that U is really a use of an insertvalue instruction that uses the
324 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
325 // We might be live, depending on the liveness of Use.
326 return MarkIfNotLive(Use, MaybeLiveUses);
328 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
329 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
331 // The use we are examining is inserted into an aggregate. Our liveness
332 // depends on all uses of that aggregate, but if it is used as a return
333 // value, only index at which we were inserted counts.
334 RetValNum = *IV->idx_begin();
336 // Note that if we are used as the aggregate operand to the insertvalue,
337 // we don't change RetValNum, but do survey all our uses.
339 Liveness Result = MaybeLive;
340 for (Value::const_use_iterator I = IV->use_begin(),
341 E = V->use_end(); I != E; ++I) {
342 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
349 if (ImmutableCallSite CS = V) {
350 const Function *F = CS.getCalledFunction();
352 // Used in a direct call.
354 // Find the argument number. We know for sure that this use is an
355 // argument, since if it was the function argument this would be an
356 // indirect call and the we know can't be looking at a value of the
357 // label type (for the invoke instruction).
358 unsigned ArgNo = CS.getArgumentNo(U);
360 if (ArgNo >= F->getFunctionType()->getNumParams())
361 // The value is passed in through a vararg! Must be live.
364 assert(CS.getArgument(ArgNo)
365 == CS->getOperand(U.getOperandNo())
366 && "Argument is not where we expected it");
368 // Value passed to a normal call. It's only live when the corresponding
369 // argument to the called function turns out live.
370 RetOrArg Use = CreateArg(F, ArgNo);
371 return MarkIfNotLive(Use, MaybeLiveUses);
374 // Used in any other way? Value must be live.
378 /// SurveyUses - This looks at all the uses of the given value
379 /// Returns the Liveness deduced from the uses of this value.
381 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
382 /// the result is Live, MaybeLiveUses might be modified but its content should
383 /// be ignored (since it might not be complete).
384 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
385 // Assume it's dead (which will only hold if there are no uses at all..).
386 Liveness Result = MaybeLive;
388 for (Value::const_use_iterator I = V->use_begin(),
389 E = V->use_end(); I != E; ++I) {
390 Result = SurveyUse(I, MaybeLiveUses);
397 // SurveyFunction - This performs the initial survey of the specified function,
398 // checking out whether or not it uses any of its incoming arguments or whether
399 // any callers use the return value. This fills in the LiveValues set and Uses
402 // We consider arguments of non-internal functions to be intrinsically alive as
403 // well as arguments to functions which have their "address taken". Externally
404 // visible functions are assumed to only have their return values intrinsically
405 // alive, permitting removal of parameters to unused arguments in callers.
407 void DAE::SurveyFunction(const Function &F) {
408 unsigned RetCount = NumRetVals(&F);
409 // Assume all return values are dead
410 typedef SmallVector<Liveness, 5> RetVals;
411 RetVals RetValLiveness(RetCount, MaybeLive);
413 typedef SmallVector<UseVector, 5> RetUses;
414 // These vectors map each return value to the uses that make it MaybeLive, so
415 // we can add those to the Uses map if the return value really turns out to be
416 // MaybeLive. Initialized to a list of RetCount empty lists.
417 RetUses MaybeLiveRetUses(RetCount);
419 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
420 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
421 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
422 != F.getFunctionType()->getReturnType()) {
423 // We don't support old style multiple return values.
428 if (F.hasExternalLinkage() && !F.isDeclaration()) {
429 DEBUG(dbgs() << "DAE - Intrinsically live return from " << F.getName()
431 // Mark the return values alive.
432 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
433 MarkLive(CreateRet(&F, i));
434 } else if (!F.hasLocalLinkage() &&
435 (!ShouldHackArguments() || F.isIntrinsic())) {
440 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
441 // Keep track of the number of live retvals, so we can skip checks once all
442 // of them turn out to be live.
443 unsigned NumLiveRetVals = 0;
444 const Type *STy = dyn_cast<StructType>(F.getReturnType());
445 // Loop all uses of the function.
446 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
448 // If the function is PASSED IN as an argument, its address has been
450 ImmutableCallSite CS(*I);
451 if (!CS || !CS.isCallee(I)) {
456 // If this use is anything other than a call site, the function is alive.
457 const Instruction *TheCall = CS.getInstruction();
458 if (!TheCall) { // Not a direct call site?
463 // If we end up here, we are looking at a direct call to our function.
465 // Now, check how our return value(s) is/are used in this caller. Don't
466 // bother checking return values if all of them are live already.
467 if (NumLiveRetVals != RetCount) {
469 // Check all uses of the return value.
470 for (Value::const_use_iterator I = TheCall->use_begin(),
471 E = TheCall->use_end(); I != E; ++I) {
472 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
473 if (Ext && Ext->hasIndices()) {
474 // This use uses a part of our return value, survey the uses of
475 // that part and store the results for this index only.
476 unsigned Idx = *Ext->idx_begin();
477 if (RetValLiveness[Idx] != Live) {
478 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
479 if (RetValLiveness[Idx] == Live)
483 // Used by something else than extractvalue. Mark all return
485 for (unsigned i = 0; i != RetCount; ++i )
486 RetValLiveness[i] = Live;
487 NumLiveRetVals = RetCount;
492 // Single return value
493 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
494 if (RetValLiveness[0] == Live)
495 NumLiveRetVals = RetCount;
500 // Now we've inspected all callers, record the liveness of our return values.
501 for (unsigned i = 0; i != RetCount; ++i)
502 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
504 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
506 // Now, check all of our arguments.
508 UseVector MaybeLiveArgUses;
509 for (Function::const_arg_iterator AI = F.arg_begin(),
510 E = F.arg_end(); AI != E; ++AI, ++i) {
511 // See what the effect of this use is (recording any uses that cause
512 // MaybeLive in MaybeLiveArgUses).
513 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
515 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
516 // Clear the vector again for the next iteration.
517 MaybeLiveArgUses.clear();
521 /// MarkValue - This function marks the liveness of RA depending on L. If L is
522 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
523 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
525 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
526 const UseVector &MaybeLiveUses) {
528 case Live: MarkLive(RA); break;
531 // Note any uses of this value, so this return value can be
532 // marked live whenever one of the uses becomes live.
533 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
534 UE = MaybeLiveUses.end(); UI != UE; ++UI)
535 Uses.insert(std::make_pair(*UI, RA));
541 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
542 /// changed in any way. Additionally,
543 /// mark any values that are used as this function's parameters or by its return
544 /// values (according to Uses) live as well.
545 void DAE::MarkLive(const Function &F) {
546 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
547 // Mark the function as live.
548 LiveFunctions.insert(&F);
549 // Mark all arguments as live.
550 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
551 PropagateLiveness(CreateArg(&F, i));
552 // Mark all return values as live.
553 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
554 PropagateLiveness(CreateRet(&F, i));
557 /// MarkLive - Mark the given return value or argument as live. Additionally,
558 /// mark any values that are used by this value (according to Uses) live as
560 void DAE::MarkLive(const RetOrArg &RA) {
561 if (LiveFunctions.count(RA.F))
562 return; // Function was already marked Live.
564 if (!LiveValues.insert(RA).second)
565 return; // We were already marked Live.
567 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
568 PropagateLiveness(RA);
571 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
572 /// to any other values it uses (according to Uses).
573 void DAE::PropagateLiveness(const RetOrArg &RA) {
574 // We don't use upper_bound (or equal_range) here, because our recursive call
575 // to ourselves is likely to cause the upper_bound (which is the first value
576 // not belonging to RA) to become erased and the iterator invalidated.
577 UseMap::iterator Begin = Uses.lower_bound(RA);
578 UseMap::iterator E = Uses.end();
580 for (I = Begin; I != E && I->first == RA; ++I)
583 // Erase RA from the Uses map (from the lower bound to wherever we ended up
585 Uses.erase(Begin, I);
588 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
589 // that are not in LiveValues. Transform the function and all of the callees of
590 // the function to not have these arguments and return values.
592 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
593 // Don't modify fully live functions
594 if (LiveFunctions.count(F))
597 // Start by computing a new prototype for the function, which is the same as
598 // the old function, but has fewer arguments and a different return type.
599 const FunctionType *FTy = F->getFunctionType();
600 std::vector<const Type*> Params;
602 // Set up to build a new list of parameter attributes.
603 SmallVector<AttributeWithIndex, 8> AttributesVec;
604 const AttrListPtr &PAL = F->getAttributes();
606 // The existing function return attributes.
607 Attributes RAttrs = PAL.getRetAttributes();
608 Attributes FnAttrs = PAL.getFnAttributes();
610 // Find out the new return value.
612 const Type *RetTy = FTy->getReturnType();
613 const Type *NRetTy = NULL;
614 unsigned RetCount = NumRetVals(F);
616 // -1 means unused, other numbers are the new index
617 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
618 std::vector<const Type*> RetTypes;
619 if (RetTy->isVoidTy()) {
622 const StructType *STy = dyn_cast<StructType>(RetTy);
624 // Look at each of the original return values individually.
625 for (unsigned i = 0; i != RetCount; ++i) {
626 RetOrArg Ret = CreateRet(F, i);
627 if (LiveValues.erase(Ret)) {
628 RetTypes.push_back(STy->getElementType(i));
629 NewRetIdxs[i] = RetTypes.size() - 1;
631 ++NumRetValsEliminated;
632 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
633 << F->getName() << "\n");
637 // We used to return a single value.
638 if (LiveValues.erase(CreateRet(F, 0))) {
639 RetTypes.push_back(RetTy);
642 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
644 ++NumRetValsEliminated;
646 if (RetTypes.size() > 1)
647 // More than one return type? Return a struct with them. Also, if we used
648 // to return a struct and didn't change the number of return values,
649 // return a struct again. This prevents changing {something} into
650 // something and {} into void.
651 // Make the new struct packed if we used to return a packed struct
653 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
654 else if (RetTypes.size() == 1)
655 // One return type? Just a simple value then, but only if we didn't use to
656 // return a struct with that simple value before.
657 NRetTy = RetTypes.front();
658 else if (RetTypes.size() == 0)
659 // No return types? Make it void, but only if we didn't use to return {}.
660 NRetTy = Type::getVoidTy(F->getContext());
663 assert(NRetTy && "No new return type found?");
665 // Remove any incompatible attributes, but only if we removed all return
666 // values. Otherwise, ensure that we don't have any conflicting attributes
667 // here. Currently, this should not be possible, but special handling might be
668 // required when new return value attributes are added.
669 if (NRetTy->isVoidTy())
670 RAttrs &= ~Attribute::typeIncompatible(NRetTy);
672 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
673 && "Return attributes no longer compatible?");
676 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
678 // Remember which arguments are still alive.
679 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
680 // Construct the new parameter list from non-dead arguments. Also construct
681 // a new set of parameter attributes to correspond. Skip the first parameter
682 // attribute, since that belongs to the return value.
684 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
686 RetOrArg Arg = CreateArg(F, i);
687 if (LiveValues.erase(Arg)) {
688 Params.push_back(I->getType());
691 // Get the original parameter attributes (skipping the first one, that is
692 // for the return value.
693 if (Attributes Attrs = PAL.getParamAttributes(i + 1))
694 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
696 ++NumArgumentsEliminated;
697 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
698 << ") from " << F->getName() << "\n");
702 if (FnAttrs != Attribute::None)
703 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
705 // Reconstruct the AttributesList based on the vector we constructed.
706 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(),
707 AttributesVec.end());
709 // Create the new function type based on the recomputed parameters.
710 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
716 // Create the new function body and insert it into the module...
717 Function *NF = Function::Create(NFTy, F->getLinkage());
718 NF->copyAttributesFrom(F);
719 NF->setAttributes(NewPAL);
720 // Insert the new function before the old function, so we won't be processing
722 F->getParent()->getFunctionList().insert(F, NF);
725 // Loop over all of the callers of the function, transforming the call sites
726 // to pass in a smaller number of arguments into the new function.
728 std::vector<Value*> Args;
729 while (!F->use_empty()) {
730 CallSite CS = CallSite::get(F->use_back());
731 Instruction *Call = CS.getInstruction();
733 AttributesVec.clear();
734 const AttrListPtr &CallPAL = CS.getAttributes();
736 // The call return attributes.
737 Attributes RAttrs = CallPAL.getRetAttributes();
738 Attributes FnAttrs = CallPAL.getFnAttributes();
739 // Adjust in case the function was changed to return void.
740 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
742 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
744 // Declare these outside of the loops, so we can reuse them for the second
745 // loop, which loops the varargs.
746 CallSite::arg_iterator I = CS.arg_begin();
748 // Loop over those operands, corresponding to the normal arguments to the
749 // original function, and add those that are still alive.
750 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
753 // Get original parameter attributes, but skip return attributes.
754 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
755 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
758 // Push any varargs arguments on the list. Don't forget their attributes.
759 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
761 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
762 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
765 if (FnAttrs != Attribute::None)
766 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
768 // Reconstruct the AttributesList based on the vector we constructed.
769 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
770 AttributesVec.end());
773 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
774 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
775 Args.begin(), Args.end(), "", Call);
776 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
777 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
779 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
780 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
781 cast<CallInst>(New)->setAttributes(NewCallPAL);
782 if (cast<CallInst>(Call)->isTailCall())
783 cast<CallInst>(New)->setTailCall();
787 if (!Call->use_empty()) {
788 if (New->getType() == Call->getType()) {
789 // Return type not changed? Just replace users then.
790 Call->replaceAllUsesWith(New);
792 } else if (New->getType()->isVoidTy()) {
793 // Our return value has uses, but they will get removed later on.
794 // Replace by null for now.
795 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
797 assert(RetTy->isStructTy() &&
798 "Return type changed, but not into a void. The old return type"
799 " must have been a struct!");
800 Instruction *InsertPt = Call;
801 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
802 BasicBlock::iterator IP = II->getNormalDest()->begin();
803 while (isa<PHINode>(IP)) ++IP;
807 // We used to return a struct. Instead of doing smart stuff with all the
808 // uses of this struct, we will just rebuild it using
809 // extract/insertvalue chaining and let instcombine clean that up.
811 // Start out building up our return value from undef
812 Value *RetVal = UndefValue::get(RetTy);
813 for (unsigned i = 0; i != RetCount; ++i)
814 if (NewRetIdxs[i] != -1) {
816 if (RetTypes.size() > 1)
817 // We are still returning a struct, so extract the value from our
819 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
822 // We are now returning a single element, so just insert that
824 // Insert the value at the old position
825 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
827 // Now, replace all uses of the old call instruction with the return
829 Call->replaceAllUsesWith(RetVal);
834 // Finally, remove the old call from the program, reducing the use-count of
836 Call->eraseFromParent();
839 // Since we have now created the new function, splice the body of the old
840 // function right into the new function, leaving the old rotting hulk of the
842 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
844 // Loop over the argument list, transfering uses of the old arguments over to
845 // the new arguments, also transfering over the names as well.
847 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
848 I2 = NF->arg_begin(); I != E; ++I, ++i)
850 // If this is a live argument, move the name and users over to the new
852 I->replaceAllUsesWith(I2);
856 // If this argument is dead, replace any uses of it with null constants
857 // (these are guaranteed to become unused later on).
858 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
861 // If we change the return value of the function we must rewrite any return
862 // instructions. Check this now.
863 if (F->getReturnType() != NF->getReturnType())
864 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
865 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
868 if (NFTy->getReturnType()->isVoidTy()) {
871 assert (RetTy->isStructTy());
872 // The original return value was a struct, insert
873 // extractvalue/insertvalue chains to extract only the values we need
874 // to return and insert them into our new result.
875 // This does generate messy code, but we'll let it to instcombine to
877 Value *OldRet = RI->getOperand(0);
878 // Start out building up our return value from undef
879 RetVal = UndefValue::get(NRetTy);
880 for (unsigned i = 0; i != RetCount; ++i)
881 if (NewRetIdxs[i] != -1) {
882 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
884 if (RetTypes.size() > 1) {
885 // We're still returning a struct, so reinsert the value into
886 // our new return value at the new index
888 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
891 // We are now only returning a simple value, so just return the
897 // Replace the return instruction with one returning the new return
898 // value (possibly 0 if we became void).
899 ReturnInst::Create(F->getContext(), RetVal, RI);
900 BB->getInstList().erase(RI);
903 // Now that the old function is dead, delete it.
904 F->eraseFromParent();
909 bool DAE::RemoveDeadParamsFromCallersOf(Function *F) {
910 // Don't modify fully live functions
911 if (LiveFunctions.count(F))
914 // Make a list of the dead arguments.
915 SmallVector<int, 10> ArgDead;
917 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
919 RetOrArg Arg = CreateArg(F, i);
920 if (!LiveValues.count(Arg))
921 ArgDead.push_back(i);
926 bool MadeChange = false;
927 for (Function::use_iterator I = F->use_begin(), E = F->use_end();
929 CallSite CS = CallSite::get(*I);
930 if (CS.getInstruction() && CS.isCallee(I)) {
931 for (unsigned i = 0, e = ArgDead.size(); i != e; ++i) {
932 Value *A = CS.getArgument(ArgDead[i]);
933 if (!isa<UndefValue>(A)) {
934 ++NumParametersEliminated;
936 CS.setArgument(ArgDead[i], UndefValue::get(A->getType()));
937 RecursivelyDeleteTriviallyDeadInstructions(A);
946 bool DAE::runOnModule(Module &M) {
947 bool Changed = false;
949 // First pass: Do a simple check to see if any functions can have their "..."
950 // removed. We can do this if they never call va_start. This loop cannot be
951 // fused with the next loop, because deleting a function invalidates
952 // information computed while surveying other functions.
953 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
954 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
956 if (F.getFunctionType()->isVarArg())
957 Changed |= DeleteDeadVarargs(F);
960 // Second phase:loop through the module, determining which arguments are live.
961 // We assume all arguments are dead unless proven otherwise (allowing us to
962 // determine that dead arguments passed into recursive functions are dead).
964 DEBUG(dbgs() << "DAE - Determining liveness\n");
965 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
968 // Now, remove all dead arguments and return values from each function in
970 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
971 // Increment now, because the function will probably get removed (ie.
972 // replaced by a new one).
974 if (F->hasExternalLinkage() && !F->isDeclaration())
975 Changed |= RemoveDeadParamsFromCallersOf(F);
977 Changed |= RemoveDeadStuffFromFunction(F);