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/ADT/SmallVector.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/ADT/StringExtras.h"
40 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
41 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
44 /// DAE - The dead argument elimination pass.
46 class DAE : public ModulePass {
49 /// Struct that represents (part of) either a return value or a function
50 /// argument. Used so that arguments and return values can be used
53 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
59 /// Make RetOrArg comparable, so we can put it into a map.
60 bool operator<(const RetOrArg &O) const {
63 else if (Idx != O.Idx)
66 return IsArg < O.IsArg;
69 /// Make RetOrArg comparable, so we can easily iterate the multimap.
70 bool operator==(const RetOrArg &O) const {
71 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
74 std::string getDescription() const {
75 return std::string((IsArg ? "Argument #" : "Return value #"))
76 + utostr(Idx) + " of function " + F->getNameStr();
80 /// Liveness enum - During our initial pass over the program, we determine
81 /// that things are either alive or maybe alive. We don't mark anything
82 /// explicitly dead (even if we know they are), since anything not alive
83 /// with no registered uses (in Uses) will never be marked alive and will
84 /// thus become dead in the end.
85 enum Liveness { Live, MaybeLive };
87 /// Convenience wrapper
88 RetOrArg CreateRet(const Function *F, unsigned Idx) {
89 return RetOrArg(F, Idx, false);
91 /// Convenience wrapper
92 RetOrArg CreateArg(const Function *F, unsigned Idx) {
93 return RetOrArg(F, Idx, true);
96 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
97 /// This maps a return value or argument to any MaybeLive return values or
98 /// arguments it uses. This allows the MaybeLive values to be marked live
99 /// when any of its users is marked live.
100 /// For example (indices are left out for clarity):
101 /// - Uses[ret F] = ret G
102 /// This means that F calls G, and F returns the value returned by G.
103 /// - Uses[arg F] = ret G
104 /// This means that some function calls G and passes its result as an
106 /// - Uses[ret F] = arg F
107 /// This means that F returns one of its own arguments.
108 /// - Uses[arg F] = arg G
109 /// This means that G calls F and passes one of its own (G's) arguments
113 typedef std::set<RetOrArg> LiveSet;
114 typedef std::set<const Function*> LiveFuncSet;
116 /// This set contains all values that have been determined to be live.
118 /// This set contains all values that are cannot be changed in any way.
119 LiveFuncSet LiveFunctions;
121 typedef SmallVector<RetOrArg, 5> UseVector;
124 // DAH uses this to specify a different ID.
125 explicit DAE(void *ID) : ModulePass(ID) {}
128 static char ID; // Pass identification, replacement for typeid
129 DAE() : ModulePass(&ID) {}
131 bool runOnModule(Module &M);
133 virtual bool ShouldHackArguments() const { return false; }
136 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
137 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
138 unsigned RetValNum = 0);
139 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
141 void SurveyFunction(const Function &F);
142 void MarkValue(const RetOrArg &RA, Liveness L,
143 const UseVector &MaybeLiveUses);
144 void MarkLive(const RetOrArg &RA);
145 void MarkLive(const Function &F);
146 void PropagateLiveness(const RetOrArg &RA);
147 bool RemoveDeadStuffFromFunction(Function *F);
148 bool DeleteDeadVarargs(Function &Fn);
154 static RegisterPass<DAE>
155 X("deadargelim", "Dead Argument Elimination");
158 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
159 /// deletes arguments to functions which are external. This is only for use
161 struct DAH : public DAE {
165 virtual bool ShouldHackArguments() const { return true; }
170 static RegisterPass<DAH>
171 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
173 /// createDeadArgEliminationPass - This pass removes arguments from functions
174 /// which are not used by the body of the function.
176 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
177 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
179 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
180 /// llvm.vastart is never called, the varargs list is dead for the function.
181 bool DAE::DeleteDeadVarargs(Function &Fn) {
182 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
183 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
185 // Ensure that the function is only directly called.
186 if (Fn.hasAddressTaken())
189 // Okay, we know we can transform this function if safe. Scan its body
190 // looking for calls to llvm.vastart.
191 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
192 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
193 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
194 if (II->getIntrinsicID() == Intrinsic::vastart)
200 // If we get here, there are no calls to llvm.vastart in the function body,
201 // remove the "..." and adjust all the calls.
203 // Start by computing a new prototype for the function, which is the same as
204 // the old function, but doesn't have isVarArg set.
205 const FunctionType *FTy = Fn.getFunctionType();
207 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
208 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
210 unsigned NumArgs = Params.size();
212 // Create the new function body and insert it into the module...
213 Function *NF = Function::Create(NFTy, Fn.getLinkage());
214 NF->copyAttributesFrom(&Fn);
215 Fn.getParent()->getFunctionList().insert(&Fn, NF);
218 // Loop over all of the callers of the function, transforming the call sites
219 // to pass in a smaller number of arguments into the new function.
221 std::vector<Value*> Args;
222 while (!Fn.use_empty()) {
223 CallSite CS = CallSite::get(Fn.use_back());
224 Instruction *Call = CS.getInstruction();
226 // Pass all the same arguments.
227 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
229 // Drop any attributes that were on the vararg arguments.
230 AttrListPtr PAL = CS.getAttributes();
231 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
232 SmallVector<AttributeWithIndex, 8> AttributesVec;
233 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
234 AttributesVec.push_back(PAL.getSlot(i));
235 if (Attributes FnAttrs = PAL.getFnAttributes())
236 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
237 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
241 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
242 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
243 Args.begin(), Args.end(), "", Call);
244 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
245 cast<InvokeInst>(New)->setAttributes(PAL);
247 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
248 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
249 cast<CallInst>(New)->setAttributes(PAL);
250 if (cast<CallInst>(Call)->isTailCall())
251 cast<CallInst>(New)->setTailCall();
253 if (MDNode *N = Call->getDbgMetadata())
254 New->setDbgMetadata(N);
258 if (!Call->use_empty())
259 Call->replaceAllUsesWith(New);
263 // Finally, remove the old call from the program, reducing the use-count of
265 Call->eraseFromParent();
268 // Since we have now created the new function, splice the body of the old
269 // function right into the new function, leaving the old rotting hulk of the
271 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
273 // Loop over the argument list, transfering uses of the old arguments over to
274 // the new arguments, also transfering over the names as well. While we're at
275 // it, remove the dead arguments from the DeadArguments list.
277 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
278 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
279 // Move the name and users over to the new version.
280 I->replaceAllUsesWith(I2);
284 // Finally, nuke the old function.
285 Fn.eraseFromParent();
289 /// Convenience function that returns the number of return values. It returns 0
290 /// for void functions and 1 for functions not returning a struct. It returns
291 /// the number of struct elements for functions returning a struct.
292 static unsigned NumRetVals(const Function *F) {
293 if (F->getReturnType()->isVoidTy())
295 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
296 return STy->getNumElements();
301 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
302 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
304 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
305 // We're live if our use or its Function is already marked as live.
306 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
309 // We're maybe live otherwise, but remember that we must become live if
311 MaybeLiveUses.push_back(Use);
316 /// SurveyUse - This looks at a single use of an argument or return value
317 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
318 /// if it causes the used value to become MaybeLive.
320 /// RetValNum is the return value number to use when this use is used in a
321 /// return instruction. This is used in the recursion, you should always leave
323 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
324 UseVector &MaybeLiveUses, unsigned RetValNum) {
326 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
327 // The value is returned from a function. It's only live when the
328 // function's return value is live. We use RetValNum here, for the case
329 // that U is really a use of an insertvalue instruction that uses the
331 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
332 // We might be live, depending on the liveness of Use.
333 return MarkIfNotLive(Use, MaybeLiveUses);
335 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
336 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
338 // The use we are examining is inserted into an aggregate. Our liveness
339 // depends on all uses of that aggregate, but if it is used as a return
340 // value, only index at which we were inserted counts.
341 RetValNum = *IV->idx_begin();
343 // Note that if we are used as the aggregate operand to the insertvalue,
344 // we don't change RetValNum, but do survey all our uses.
346 Liveness Result = MaybeLive;
347 for (Value::const_use_iterator I = IV->use_begin(),
348 E = V->use_end(); I != E; ++I) {
349 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
356 if (ImmutableCallSite CS = V) {
357 const Function *F = CS.getCalledFunction();
359 // Used in a direct call.
361 // Find the argument number. We know for sure that this use is an
362 // argument, since if it was the function argument this would be an
363 // indirect call and the we know can't be looking at a value of the
364 // label type (for the invoke instruction).
365 unsigned ArgNo = CS.getArgumentNo(U);
367 if (ArgNo >= F->getFunctionType()->getNumParams())
368 // The value is passed in through a vararg! Must be live.
371 assert(CS.getArgument(ArgNo)
372 == CS->getOperand(U.getOperandNo())
373 && "Argument is not where we expected it");
375 // Value passed to a normal call. It's only live when the corresponding
376 // argument to the called function turns out live.
377 RetOrArg Use = CreateArg(F, ArgNo);
378 return MarkIfNotLive(Use, MaybeLiveUses);
381 // Used in any other way? Value must be live.
385 /// SurveyUses - This looks at all the uses of the given value
386 /// Returns the Liveness deduced from the uses of this value.
388 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
389 /// the result is Live, MaybeLiveUses might be modified but its content should
390 /// be ignored (since it might not be complete).
391 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
392 // Assume it's dead (which will only hold if there are no uses at all..).
393 Liveness Result = MaybeLive;
395 for (Value::const_use_iterator I = V->use_begin(),
396 E = V->use_end(); I != E; ++I) {
397 Result = SurveyUse(I, MaybeLiveUses);
404 // SurveyFunction - This performs the initial survey of the specified function,
405 // checking out whether or not it uses any of its incoming arguments or whether
406 // any callers use the return value. This fills in the LiveValues set and Uses
409 // We consider arguments of non-internal functions to be intrinsically alive as
410 // well as arguments to functions which have their "address taken".
412 void DAE::SurveyFunction(const Function &F) {
413 unsigned RetCount = NumRetVals(&F);
414 // Assume all return values are dead
415 typedef SmallVector<Liveness, 5> RetVals;
416 RetVals RetValLiveness(RetCount, MaybeLive);
418 typedef SmallVector<UseVector, 5> RetUses;
419 // These vectors map each return value to the uses that make it MaybeLive, so
420 // we can add those to the Uses map if the return value really turns out to be
421 // MaybeLive. Initialized to a list of RetCount empty lists.
422 RetUses MaybeLiveRetUses(RetCount);
424 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
425 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
426 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
427 != F.getFunctionType()->getReturnType()) {
428 // We don't support old style multiple return values.
433 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
438 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
439 // Keep track of the number of live retvals, so we can skip checks once all
440 // of them turn out to be live.
441 unsigned NumLiveRetVals = 0;
442 const Type *STy = dyn_cast<StructType>(F.getReturnType());
443 // Loop all uses of the function.
444 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
446 // If the function is PASSED IN as an argument, its address has been
448 ImmutableCallSite CS(*I);
449 if (!CS || !CS.isCallee(I)) {
454 // If this use is anything other than a call site, the function is alive.
455 const Instruction *TheCall = CS.getInstruction();
456 if (!TheCall) { // Not a direct call site?
461 // If we end up here, we are looking at a direct call to our function.
463 // Now, check how our return value(s) is/are used in this caller. Don't
464 // bother checking return values if all of them are live already.
465 if (NumLiveRetVals != RetCount) {
467 // Check all uses of the return value.
468 for (Value::const_use_iterator I = TheCall->use_begin(),
469 E = TheCall->use_end(); I != E; ++I) {
470 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
471 if (Ext && Ext->hasIndices()) {
472 // This use uses a part of our return value, survey the uses of
473 // that part and store the results for this index only.
474 unsigned Idx = *Ext->idx_begin();
475 if (RetValLiveness[Idx] != Live) {
476 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
477 if (RetValLiveness[Idx] == Live)
481 // Used by something else than extractvalue. Mark all return
483 for (unsigned i = 0; i != RetCount; ++i )
484 RetValLiveness[i] = Live;
485 NumLiveRetVals = RetCount;
490 // Single return value
491 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
492 if (RetValLiveness[0] == Live)
493 NumLiveRetVals = RetCount;
498 // Now we've inspected all callers, record the liveness of our return values.
499 for (unsigned i = 0; i != RetCount; ++i)
500 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
502 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
504 // Now, check all of our arguments.
506 UseVector MaybeLiveArgUses;
507 for (Function::const_arg_iterator AI = F.arg_begin(),
508 E = F.arg_end(); AI != E; ++AI, ++i) {
509 // See what the effect of this use is (recording any uses that cause
510 // MaybeLive in MaybeLiveArgUses).
511 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
513 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
514 // Clear the vector again for the next iteration.
515 MaybeLiveArgUses.clear();
519 /// MarkValue - This function marks the liveness of RA depending on L. If L is
520 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
521 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
523 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
524 const UseVector &MaybeLiveUses) {
526 case Live: MarkLive(RA); break;
529 // Note any uses of this value, so this return value can be
530 // marked live whenever one of the uses becomes live.
531 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
532 UE = MaybeLiveUses.end(); UI != UE; ++UI)
533 Uses.insert(std::make_pair(*UI, RA));
539 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
540 /// changed in any way. Additionally,
541 /// mark any values that are used as this function's parameters or by its return
542 /// values (according to Uses) live as well.
543 void DAE::MarkLive(const Function &F) {
544 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
545 // Mark the function as live.
546 LiveFunctions.insert(&F);
547 // Mark all arguments as live.
548 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
549 PropagateLiveness(CreateArg(&F, i));
550 // Mark all return values as live.
551 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
552 PropagateLiveness(CreateRet(&F, i));
555 /// MarkLive - Mark the given return value or argument as live. Additionally,
556 /// mark any values that are used by this value (according to Uses) live as
558 void DAE::MarkLive(const RetOrArg &RA) {
559 if (LiveFunctions.count(RA.F))
560 return; // Function was already marked Live.
562 if (!LiveValues.insert(RA).second)
563 return; // We were already marked Live.
565 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
566 PropagateLiveness(RA);
569 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
570 /// to any other values it uses (according to Uses).
571 void DAE::PropagateLiveness(const RetOrArg &RA) {
572 // We don't use upper_bound (or equal_range) here, because our recursive call
573 // to ourselves is likely to cause the upper_bound (which is the first value
574 // not belonging to RA) to become erased and the iterator invalidated.
575 UseMap::iterator Begin = Uses.lower_bound(RA);
576 UseMap::iterator E = Uses.end();
578 for (I = Begin; I != E && I->first == RA; ++I)
581 // Erase RA from the Uses map (from the lower bound to wherever we ended up
583 Uses.erase(Begin, I);
586 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
587 // that are not in LiveValues. Transform the function and all of the callees of
588 // the function to not have these arguments and return values.
590 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
591 // Don't modify fully live functions
592 if (LiveFunctions.count(F))
595 // Start by computing a new prototype for the function, which is the same as
596 // the old function, but has fewer arguments and a different return type.
597 const FunctionType *FTy = F->getFunctionType();
598 std::vector<const Type*> Params;
600 // Set up to build a new list of parameter attributes.
601 SmallVector<AttributeWithIndex, 8> AttributesVec;
602 const AttrListPtr &PAL = F->getAttributes();
604 // The existing function return attributes.
605 Attributes RAttrs = PAL.getRetAttributes();
606 Attributes FnAttrs = PAL.getFnAttributes();
608 // Find out the new return value.
610 const Type *RetTy = FTy->getReturnType();
611 const Type *NRetTy = NULL;
612 unsigned RetCount = NumRetVals(F);
614 // -1 means unused, other numbers are the new index
615 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
616 std::vector<const Type*> RetTypes;
617 if (RetTy->isVoidTy()) {
620 const StructType *STy = dyn_cast<StructType>(RetTy);
622 // Look at each of the original return values individually.
623 for (unsigned i = 0; i != RetCount; ++i) {
624 RetOrArg Ret = CreateRet(F, i);
625 if (LiveValues.erase(Ret)) {
626 RetTypes.push_back(STy->getElementType(i));
627 NewRetIdxs[i] = RetTypes.size() - 1;
629 ++NumRetValsEliminated;
630 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
631 << F->getName() << "\n");
635 // We used to return a single value.
636 if (LiveValues.erase(CreateRet(F, 0))) {
637 RetTypes.push_back(RetTy);
640 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
642 ++NumRetValsEliminated;
644 if (RetTypes.size() > 1)
645 // More than one return type? Return a struct with them. Also, if we used
646 // to return a struct and didn't change the number of return values,
647 // return a struct again. This prevents changing {something} into
648 // something and {} into void.
649 // Make the new struct packed if we used to return a packed struct
651 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
652 else if (RetTypes.size() == 1)
653 // One return type? Just a simple value then, but only if we didn't use to
654 // return a struct with that simple value before.
655 NRetTy = RetTypes.front();
656 else if (RetTypes.size() == 0)
657 // No return types? Make it void, but only if we didn't use to return {}.
658 NRetTy = Type::getVoidTy(F->getContext());
661 assert(NRetTy && "No new return type found?");
663 // Remove any incompatible attributes, but only if we removed all return
664 // values. Otherwise, ensure that we don't have any conflicting attributes
665 // here. Currently, this should not be possible, but special handling might be
666 // required when new return value attributes are added.
667 if (NRetTy->isVoidTy())
668 RAttrs &= ~Attribute::typeIncompatible(NRetTy);
670 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
671 && "Return attributes no longer compatible?");
674 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
676 // Remember which arguments are still alive.
677 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
678 // Construct the new parameter list from non-dead arguments. Also construct
679 // a new set of parameter attributes to correspond. Skip the first parameter
680 // attribute, since that belongs to the return value.
682 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
684 RetOrArg Arg = CreateArg(F, i);
685 if (LiveValues.erase(Arg)) {
686 Params.push_back(I->getType());
689 // Get the original parameter attributes (skipping the first one, that is
690 // for the return value.
691 if (Attributes Attrs = PAL.getParamAttributes(i + 1))
692 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
694 ++NumArgumentsEliminated;
695 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
696 << ") from " << F->getName() << "\n");
700 if (FnAttrs != Attribute::None)
701 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
703 // Reconstruct the AttributesList based on the vector we constructed.
704 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(),
705 AttributesVec.end());
707 // Create the new function type based on the recomputed parameters.
708 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
714 // Create the new function body and insert it into the module...
715 Function *NF = Function::Create(NFTy, F->getLinkage());
716 NF->copyAttributesFrom(F);
717 NF->setAttributes(NewPAL);
718 // Insert the new function before the old function, so we won't be processing
720 F->getParent()->getFunctionList().insert(F, NF);
723 // Loop over all of the callers of the function, transforming the call sites
724 // to pass in a smaller number of arguments into the new function.
726 std::vector<Value*> Args;
727 while (!F->use_empty()) {
728 CallSite CS = CallSite::get(F->use_back());
729 Instruction *Call = CS.getInstruction();
731 AttributesVec.clear();
732 const AttrListPtr &CallPAL = CS.getAttributes();
734 // The call return attributes.
735 Attributes RAttrs = CallPAL.getRetAttributes();
736 Attributes FnAttrs = CallPAL.getFnAttributes();
737 // Adjust in case the function was changed to return void.
738 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
740 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
742 // Declare these outside of the loops, so we can reuse them for the second
743 // loop, which loops the varargs.
744 CallSite::arg_iterator I = CS.arg_begin();
746 // Loop over those operands, corresponding to the normal arguments to the
747 // original function, and add those that are still alive.
748 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
751 // Get original parameter attributes, but skip return attributes.
752 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
753 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
756 // Push any varargs arguments on the list. Don't forget their attributes.
757 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
759 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
760 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
763 if (FnAttrs != Attribute::None)
764 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
766 // Reconstruct the AttributesList based on the vector we constructed.
767 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
768 AttributesVec.end());
771 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
772 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
773 Args.begin(), Args.end(), "", Call);
774 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
775 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
777 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
778 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
779 cast<CallInst>(New)->setAttributes(NewCallPAL);
780 if (cast<CallInst>(Call)->isTailCall())
781 cast<CallInst>(New)->setTailCall();
783 if (MDNode *N = Call->getDbgMetadata())
784 New->setDbgMetadata(N);
788 if (!Call->use_empty()) {
789 if (New->getType() == Call->getType()) {
790 // Return type not changed? Just replace users then.
791 Call->replaceAllUsesWith(New);
793 } else if (New->getType()->isVoidTy()) {
794 // Our return value has uses, but they will get removed later on.
795 // Replace by null for now.
796 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
798 assert(RetTy->isStructTy() &&
799 "Return type changed, but not into a void. The old return type"
800 " must have been a struct!");
801 Instruction *InsertPt = Call;
802 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
803 BasicBlock::iterator IP = II->getNormalDest()->begin();
804 while (isa<PHINode>(IP)) ++IP;
808 // We used to return a struct. Instead of doing smart stuff with all the
809 // uses of this struct, we will just rebuild it using
810 // extract/insertvalue chaining and let instcombine clean that up.
812 // Start out building up our return value from undef
813 Value *RetVal = UndefValue::get(RetTy);
814 for (unsigned i = 0; i != RetCount; ++i)
815 if (NewRetIdxs[i] != -1) {
817 if (RetTypes.size() > 1)
818 // We are still returning a struct, so extract the value from our
820 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
823 // We are now returning a single element, so just insert that
825 // Insert the value at the old position
826 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
828 // Now, replace all uses of the old call instruction with the return
830 Call->replaceAllUsesWith(RetVal);
835 // Finally, remove the old call from the program, reducing the use-count of
837 Call->eraseFromParent();
840 // Since we have now created the new function, splice the body of the old
841 // function right into the new function, leaving the old rotting hulk of the
843 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
845 // Loop over the argument list, transfering uses of the old arguments over to
846 // the new arguments, also transfering over the names as well.
848 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
849 I2 = NF->arg_begin(); I != E; ++I, ++i)
851 // If this is a live argument, move the name and users over to the new
853 I->replaceAllUsesWith(I2);
857 // If this argument is dead, replace any uses of it with null constants
858 // (these are guaranteed to become unused later on).
859 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
862 // If we change the return value of the function we must rewrite any return
863 // instructions. Check this now.
864 if (F->getReturnType() != NF->getReturnType())
865 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
866 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
869 if (NFTy->getReturnType()->isVoidTy()) {
872 assert (RetTy->isStructTy());
873 // The original return value was a struct, insert
874 // extractvalue/insertvalue chains to extract only the values we need
875 // to return and insert them into our new result.
876 // This does generate messy code, but we'll let it to instcombine to
878 Value *OldRet = RI->getOperand(0);
879 // Start out building up our return value from undef
880 RetVal = UndefValue::get(NRetTy);
881 for (unsigned i = 0; i != RetCount; ++i)
882 if (NewRetIdxs[i] != -1) {
883 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
885 if (RetTypes.size() > 1) {
886 // We're still returning a struct, so reinsert the value into
887 // our new return value at the new index
889 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
892 // We are now only returning a simple value, so just return the
898 // Replace the return instruction with one returning the new return
899 // value (possibly 0 if we became void).
900 ReturnInst::Create(F->getContext(), RetVal, RI);
901 BB->getInstList().erase(RI);
904 // Now that the old function is dead, delete it.
905 F->eraseFromParent();
910 bool DAE::runOnModule(Module &M) {
911 bool Changed = false;
913 // First pass: Do a simple check to see if any functions can have their "..."
914 // removed. We can do this if they never call va_start. This loop cannot be
915 // fused with the next loop, because deleting a function invalidates
916 // information computed while surveying other functions.
917 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
918 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
920 if (F.getFunctionType()->isVarArg())
921 Changed |= DeleteDeadVarargs(F);
924 // Second phase:loop through the module, determining which arguments are live.
925 // We assume all arguments are dead unless proven otherwise (allowing us to
926 // determine that dead arguments passed into recursive functions are dead).
928 DEBUG(dbgs() << "DAE - Determining liveness\n");
929 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
932 // Now, remove all dead arguments and return values from each function in
934 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
935 // Increment now, because the function will probably get removed (ie.
936 // replaced by a new one).
938 Changed |= RemoveDeadStuffFromFunction(F);