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(char &ID) : ModulePass(ID) {}
128 static char ID; // Pass identification, replacement for typeid
129 DAE() : ModulePass(ID) {
130 initializeDAEPass(*PassRegistry::getPassRegistry());
133 bool runOnModule(Module &M);
135 virtual bool ShouldHackArguments() const { return false; }
138 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
139 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
140 unsigned RetValNum = 0);
141 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
143 void SurveyFunction(const Function &F);
144 void MarkValue(const RetOrArg &RA, Liveness L,
145 const UseVector &MaybeLiveUses);
146 void MarkLive(const RetOrArg &RA);
147 void MarkLive(const Function &F);
148 void PropagateLiveness(const RetOrArg &RA);
149 bool RemoveDeadStuffFromFunction(Function *F);
150 bool DeleteDeadVarargs(Function &Fn);
156 INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
159 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
160 /// deletes arguments to functions which are external. This is only for use
162 struct DAH : public DAE {
166 virtual bool ShouldHackArguments() const { return true; }
171 INITIALIZE_PASS(DAH, "deadarghaX0r",
172 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
175 /// createDeadArgEliminationPass - This pass removes arguments from functions
176 /// which are not used by the body of the function.
178 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
179 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
181 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
182 /// llvm.vastart is never called, the varargs list is dead for the function.
183 bool DAE::DeleteDeadVarargs(Function &Fn) {
184 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
185 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
187 // Ensure that the function is only directly called.
188 if (Fn.hasAddressTaken())
191 // Okay, we know we can transform this function if safe. Scan its body
192 // looking for calls to llvm.vastart.
193 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
194 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
195 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
196 if (II->getIntrinsicID() == Intrinsic::vastart)
202 // If we get here, there are no calls to llvm.vastart in the function body,
203 // remove the "..." and adjust all the calls.
205 // Start by computing a new prototype for the function, which is the same as
206 // the old function, but doesn't have isVarArg set.
207 const FunctionType *FTy = Fn.getFunctionType();
209 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
210 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
212 unsigned NumArgs = Params.size();
214 // Create the new function body and insert it into the module...
215 Function *NF = Function::Create(NFTy, Fn.getLinkage());
216 NF->copyAttributesFrom(&Fn);
217 Fn.getParent()->getFunctionList().insert(&Fn, NF);
220 // Loop over all of the callers of the function, transforming the call sites
221 // to pass in a smaller number of arguments into the new function.
223 std::vector<Value*> Args;
224 while (!Fn.use_empty()) {
225 CallSite CS(Fn.use_back());
226 Instruction *Call = CS.getInstruction();
228 // Pass all the same arguments.
229 Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
231 // Drop any attributes that were on the vararg arguments.
232 AttrListPtr PAL = CS.getAttributes();
233 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
234 SmallVector<AttributeWithIndex, 8> AttributesVec;
235 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
236 AttributesVec.push_back(PAL.getSlot(i));
237 if (Attributes FnAttrs = PAL.getFnAttributes())
238 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
239 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
243 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
244 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
245 Args.begin(), Args.end(), "", Call);
246 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
247 cast<InvokeInst>(New)->setAttributes(PAL);
249 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
250 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
251 cast<CallInst>(New)->setAttributes(PAL);
252 if (cast<CallInst>(Call)->isTailCall())
253 cast<CallInst>(New)->setTailCall();
255 New->setDebugLoc(Call->getDebugLoc());
259 if (!Call->use_empty())
260 Call->replaceAllUsesWith(New);
264 // Finally, remove the old call from the program, reducing the use-count of
266 Call->eraseFromParent();
269 // Since we have now created the new function, splice the body of the old
270 // function right into the new function, leaving the old rotting hulk of the
272 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
274 // Loop over the argument list, transfering uses of the old arguments over to
275 // the new arguments, also transfering over the names as well. While we're at
276 // it, remove the dead arguments from the DeadArguments list.
278 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
279 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
280 // Move the name and users over to the new version.
281 I->replaceAllUsesWith(I2);
285 // Finally, nuke the old function.
286 Fn.eraseFromParent();
290 /// Convenience function that returns the number of return values. It returns 0
291 /// for void functions and 1 for functions not returning a struct. It returns
292 /// the number of struct elements for functions returning a struct.
293 static unsigned NumRetVals(const Function *F) {
294 if (F->getReturnType()->isVoidTy())
296 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
297 return STy->getNumElements();
302 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
303 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
305 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
306 // We're live if our use or its Function is already marked as live.
307 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
310 // We're maybe live otherwise, but remember that we must become live if
312 MaybeLiveUses.push_back(Use);
317 /// SurveyUse - This looks at a single use of an argument or return value
318 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
319 /// if it causes the used value to become MaybeLive.
321 /// RetValNum is the return value number to use when this use is used in a
322 /// return instruction. This is used in the recursion, you should always leave
324 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
325 UseVector &MaybeLiveUses, unsigned RetValNum) {
327 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
328 // The value is returned from a function. It's only live when the
329 // function's return value is live. We use RetValNum here, for the case
330 // that U is really a use of an insertvalue instruction that uses the
332 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
333 // We might be live, depending on the liveness of Use.
334 return MarkIfNotLive(Use, MaybeLiveUses);
336 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
337 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
339 // The use we are examining is inserted into an aggregate. Our liveness
340 // depends on all uses of that aggregate, but if it is used as a return
341 // value, only index at which we were inserted counts.
342 RetValNum = *IV->idx_begin();
344 // Note that if we are used as the aggregate operand to the insertvalue,
345 // we don't change RetValNum, but do survey all our uses.
347 Liveness Result = MaybeLive;
348 for (Value::const_use_iterator I = IV->use_begin(),
349 E = V->use_end(); I != E; ++I) {
350 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
357 if (ImmutableCallSite CS = V) {
358 const Function *F = CS.getCalledFunction();
360 // Used in a direct call.
362 // Find the argument number. We know for sure that this use is an
363 // argument, since if it was the function argument this would be an
364 // indirect call and the we know can't be looking at a value of the
365 // label type (for the invoke instruction).
366 unsigned ArgNo = CS.getArgumentNo(U);
368 if (ArgNo >= F->getFunctionType()->getNumParams())
369 // The value is passed in through a vararg! Must be live.
372 assert(CS.getArgument(ArgNo)
373 == CS->getOperand(U.getOperandNo())
374 && "Argument is not where we expected it");
376 // Value passed to a normal call. It's only live when the corresponding
377 // argument to the called function turns out live.
378 RetOrArg Use = CreateArg(F, ArgNo);
379 return MarkIfNotLive(Use, MaybeLiveUses);
382 // Used in any other way? Value must be live.
386 /// SurveyUses - This looks at all the uses of the given value
387 /// Returns the Liveness deduced from the uses of this value.
389 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
390 /// the result is Live, MaybeLiveUses might be modified but its content should
391 /// be ignored (since it might not be complete).
392 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
393 // Assume it's dead (which will only hold if there are no uses at all..).
394 Liveness Result = MaybeLive;
396 for (Value::const_use_iterator I = V->use_begin(),
397 E = V->use_end(); I != E; ++I) {
398 Result = SurveyUse(I, MaybeLiveUses);
405 // SurveyFunction - This performs the initial survey of the specified function,
406 // checking out whether or not it uses any of its incoming arguments or whether
407 // any callers use the return value. This fills in the LiveValues set and Uses
410 // We consider arguments of non-internal functions to be intrinsically alive as
411 // well as arguments to functions which have their "address taken".
413 void DAE::SurveyFunction(const Function &F) {
414 unsigned RetCount = NumRetVals(&F);
415 // Assume all return values are dead
416 typedef SmallVector<Liveness, 5> RetVals;
417 RetVals RetValLiveness(RetCount, MaybeLive);
419 typedef SmallVector<UseVector, 5> RetUses;
420 // These vectors map each return value to the uses that make it MaybeLive, so
421 // we can add those to the Uses map if the return value really turns out to be
422 // MaybeLive. Initialized to a list of RetCount empty lists.
423 RetUses MaybeLiveRetUses(RetCount);
425 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
426 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
427 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
428 != F.getFunctionType()->getReturnType()) {
429 // We don't support old style multiple return values.
434 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
439 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
440 // Keep track of the number of live retvals, so we can skip checks once all
441 // of them turn out to be live.
442 unsigned NumLiveRetVals = 0;
443 const Type *STy = dyn_cast<StructType>(F.getReturnType());
444 // Loop all uses of the function.
445 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
447 // If the function is PASSED IN as an argument, its address has been
449 ImmutableCallSite CS(*I);
450 if (!CS || !CS.isCallee(I)) {
455 // If this use is anything other than a call site, the function is alive.
456 const Instruction *TheCall = CS.getInstruction();
457 if (!TheCall) { // Not a direct call site?
462 // If we end up here, we are looking at a direct call to our function.
464 // Now, check how our return value(s) is/are used in this caller. Don't
465 // bother checking return values if all of them are live already.
466 if (NumLiveRetVals != RetCount) {
468 // Check all uses of the return value.
469 for (Value::const_use_iterator I = TheCall->use_begin(),
470 E = TheCall->use_end(); I != E; ++I) {
471 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
472 if (Ext && Ext->hasIndices()) {
473 // This use uses a part of our return value, survey the uses of
474 // that part and store the results for this index only.
475 unsigned Idx = *Ext->idx_begin();
476 if (RetValLiveness[Idx] != Live) {
477 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
478 if (RetValLiveness[Idx] == Live)
482 // Used by something else than extractvalue. Mark all return
484 for (unsigned i = 0; i != RetCount; ++i )
485 RetValLiveness[i] = Live;
486 NumLiveRetVals = RetCount;
491 // Single return value
492 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
493 if (RetValLiveness[0] == Live)
494 NumLiveRetVals = RetCount;
499 // Now we've inspected all callers, record the liveness of our return values.
500 for (unsigned i = 0; i != RetCount; ++i)
501 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
503 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
505 // Now, check all of our arguments.
507 UseVector MaybeLiveArgUses;
508 for (Function::const_arg_iterator AI = F.arg_begin(),
509 E = F.arg_end(); AI != E; ++AI, ++i) {
510 // See what the effect of this use is (recording any uses that cause
511 // MaybeLive in MaybeLiveArgUses).
512 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
514 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
515 // Clear the vector again for the next iteration.
516 MaybeLiveArgUses.clear();
520 /// MarkValue - This function marks the liveness of RA depending on L. If L is
521 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
522 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
524 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
525 const UseVector &MaybeLiveUses) {
527 case Live: MarkLive(RA); break;
530 // Note any uses of this value, so this return value can be
531 // marked live whenever one of the uses becomes live.
532 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
533 UE = MaybeLiveUses.end(); UI != UE; ++UI)
534 Uses.insert(std::make_pair(*UI, RA));
540 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
541 /// changed in any way. Additionally,
542 /// mark any values that are used as this function's parameters or by its return
543 /// values (according to Uses) live as well.
544 void DAE::MarkLive(const Function &F) {
545 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
546 // Mark the function as live.
547 LiveFunctions.insert(&F);
548 // Mark all arguments as live.
549 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
550 PropagateLiveness(CreateArg(&F, i));
551 // Mark all return values as live.
552 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
553 PropagateLiveness(CreateRet(&F, i));
556 /// MarkLive - Mark the given return value or argument as live. Additionally,
557 /// mark any values that are used by this value (according to Uses) live as
559 void DAE::MarkLive(const RetOrArg &RA) {
560 if (LiveFunctions.count(RA.F))
561 return; // Function was already marked Live.
563 if (!LiveValues.insert(RA).second)
564 return; // We were already marked Live.
566 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
567 PropagateLiveness(RA);
570 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
571 /// to any other values it uses (according to Uses).
572 void DAE::PropagateLiveness(const RetOrArg &RA) {
573 // We don't use upper_bound (or equal_range) here, because our recursive call
574 // to ourselves is likely to cause the upper_bound (which is the first value
575 // not belonging to RA) to become erased and the iterator invalidated.
576 UseMap::iterator Begin = Uses.lower_bound(RA);
577 UseMap::iterator E = Uses.end();
579 for (I = Begin; I != E && I->first == RA; ++I)
582 // Erase RA from the Uses map (from the lower bound to wherever we ended up
584 Uses.erase(Begin, I);
587 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
588 // that are not in LiveValues. Transform the function and all of the callees of
589 // the function to not have these arguments and return values.
591 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
592 // Don't modify fully live functions
593 if (LiveFunctions.count(F))
596 // Start by computing a new prototype for the function, which is the same as
597 // the old function, but has fewer arguments and a different return type.
598 const FunctionType *FTy = F->getFunctionType();
599 std::vector<const Type*> Params;
601 // Set up to build a new list of parameter attributes.
602 SmallVector<AttributeWithIndex, 8> AttributesVec;
603 const AttrListPtr &PAL = F->getAttributes();
605 // The existing function return attributes.
606 Attributes RAttrs = PAL.getRetAttributes();
607 Attributes FnAttrs = PAL.getFnAttributes();
609 // Find out the new return value.
611 const Type *RetTy = FTy->getReturnType();
612 const Type *NRetTy = NULL;
613 unsigned RetCount = NumRetVals(F);
615 // -1 means unused, other numbers are the new index
616 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
617 std::vector<const Type*> RetTypes;
618 if (RetTy->isVoidTy()) {
621 const StructType *STy = dyn_cast<StructType>(RetTy);
623 // Look at each of the original return values individually.
624 for (unsigned i = 0; i != RetCount; ++i) {
625 RetOrArg Ret = CreateRet(F, i);
626 if (LiveValues.erase(Ret)) {
627 RetTypes.push_back(STy->getElementType(i));
628 NewRetIdxs[i] = RetTypes.size() - 1;
630 ++NumRetValsEliminated;
631 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
632 << F->getName() << "\n");
636 // We used to return a single value.
637 if (LiveValues.erase(CreateRet(F, 0))) {
638 RetTypes.push_back(RetTy);
641 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
643 ++NumRetValsEliminated;
645 if (RetTypes.size() > 1)
646 // More than one return type? Return a struct with them. Also, if we used
647 // to return a struct and didn't change the number of return values,
648 // return a struct again. This prevents changing {something} into
649 // something and {} into void.
650 // Make the new struct packed if we used to return a packed struct
652 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
653 else if (RetTypes.size() == 1)
654 // One return type? Just a simple value then, but only if we didn't use to
655 // return a struct with that simple value before.
656 NRetTy = RetTypes.front();
657 else if (RetTypes.size() == 0)
658 // No return types? Make it void, but only if we didn't use to return {}.
659 NRetTy = Type::getVoidTy(F->getContext());
662 assert(NRetTy && "No new return type found?");
664 // Remove any incompatible attributes, but only if we removed all return
665 // values. Otherwise, ensure that we don't have any conflicting attributes
666 // here. Currently, this should not be possible, but special handling might be
667 // required when new return value attributes are added.
668 if (NRetTy->isVoidTy())
669 RAttrs &= ~Attribute::typeIncompatible(NRetTy);
671 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
672 && "Return attributes no longer compatible?");
675 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
677 // Remember which arguments are still alive.
678 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
679 // Construct the new parameter list from non-dead arguments. Also construct
680 // a new set of parameter attributes to correspond. Skip the first parameter
681 // attribute, since that belongs to the return value.
683 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
685 RetOrArg Arg = CreateArg(F, i);
686 if (LiveValues.erase(Arg)) {
687 Params.push_back(I->getType());
690 // Get the original parameter attributes (skipping the first one, that is
691 // for the return value.
692 if (Attributes Attrs = PAL.getParamAttributes(i + 1))
693 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
695 ++NumArgumentsEliminated;
696 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
697 << ") from " << F->getName() << "\n");
701 if (FnAttrs != Attribute::None)
702 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
704 // Reconstruct the AttributesList based on the vector we constructed.
705 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(),
706 AttributesVec.end());
708 // Create the new function type based on the recomputed parameters.
709 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
715 // Create the new function body and insert it into the module...
716 Function *NF = Function::Create(NFTy, F->getLinkage());
717 NF->copyAttributesFrom(F);
718 NF->setAttributes(NewPAL);
719 // Insert the new function before the old function, so we won't be processing
721 F->getParent()->getFunctionList().insert(F, NF);
724 // Loop over all of the callers of the function, transforming the call sites
725 // to pass in a smaller number of arguments into the new function.
727 std::vector<Value*> Args;
728 while (!F->use_empty()) {
729 CallSite CS(F->use_back());
730 Instruction *Call = CS.getInstruction();
732 AttributesVec.clear();
733 const AttrListPtr &CallPAL = CS.getAttributes();
735 // The call return attributes.
736 Attributes RAttrs = CallPAL.getRetAttributes();
737 Attributes FnAttrs = CallPAL.getFnAttributes();
738 // Adjust in case the function was changed to return void.
739 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
741 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
743 // Declare these outside of the loops, so we can reuse them for the second
744 // loop, which loops the varargs.
745 CallSite::arg_iterator I = CS.arg_begin();
747 // Loop over those operands, corresponding to the normal arguments to the
748 // original function, and add those that are still alive.
749 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
752 // Get original parameter attributes, but skip return attributes.
753 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
754 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
757 // Push any varargs arguments on the list. Don't forget their attributes.
758 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
760 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
761 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
764 if (FnAttrs != Attribute::None)
765 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
767 // Reconstruct the AttributesList based on the vector we constructed.
768 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
769 AttributesVec.end());
772 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
773 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
774 Args.begin(), Args.end(), "", Call);
775 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
776 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
778 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
779 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
780 cast<CallInst>(New)->setAttributes(NewCallPAL);
781 if (cast<CallInst>(Call)->isTailCall())
782 cast<CallInst>(New)->setTailCall();
784 New->setDebugLoc(Call->getDebugLoc());
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 if (!Call->getType()->isX86_MMXTy())
797 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
799 assert(RetTy->isStructTy() &&
800 "Return type changed, but not into a void. The old return type"
801 " must have been a struct!");
802 Instruction *InsertPt = Call;
803 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
804 BasicBlock::iterator IP = II->getNormalDest()->begin();
805 while (isa<PHINode>(IP)) ++IP;
809 // We used to return a struct. Instead of doing smart stuff with all the
810 // uses of this struct, we will just rebuild it using
811 // extract/insertvalue chaining and let instcombine clean that up.
813 // Start out building up our return value from undef
814 Value *RetVal = UndefValue::get(RetTy);
815 for (unsigned i = 0; i != RetCount; ++i)
816 if (NewRetIdxs[i] != -1) {
818 if (RetTypes.size() > 1)
819 // We are still returning a struct, so extract the value from our
821 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
824 // We are now returning a single element, so just insert that
826 // Insert the value at the old position
827 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
829 // Now, replace all uses of the old call instruction with the return
831 Call->replaceAllUsesWith(RetVal);
836 // Finally, remove the old call from the program, reducing the use-count of
838 Call->eraseFromParent();
841 // Since we have now created the new function, splice the body of the old
842 // function right into the new function, leaving the old rotting hulk of the
844 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
846 // Loop over the argument list, transfering uses of the old arguments over to
847 // the new arguments, also transfering over the names as well.
849 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
850 I2 = NF->arg_begin(); I != E; ++I, ++i)
852 // If this is a live argument, move the name and users over to the new
854 I->replaceAllUsesWith(I2);
858 // If this argument is dead, replace any uses of it with null constants
859 // (these are guaranteed to become unused later on).
860 if (!I->getType()->isX86_MMXTy())
861 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
864 // If we change the return value of the function we must rewrite any return
865 // instructions. Check this now.
866 if (F->getReturnType() != NF->getReturnType())
867 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
868 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
871 if (NFTy->getReturnType()->isVoidTy()) {
874 assert (RetTy->isStructTy());
875 // The original return value was a struct, insert
876 // extractvalue/insertvalue chains to extract only the values we need
877 // to return and insert them into our new result.
878 // This does generate messy code, but we'll let it to instcombine to
880 Value *OldRet = RI->getOperand(0);
881 // Start out building up our return value from undef
882 RetVal = UndefValue::get(NRetTy);
883 for (unsigned i = 0; i != RetCount; ++i)
884 if (NewRetIdxs[i] != -1) {
885 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
887 if (RetTypes.size() > 1) {
888 // We're still returning a struct, so reinsert the value into
889 // our new return value at the new index
891 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
894 // We are now only returning a simple value, so just return the
900 // Replace the return instruction with one returning the new return
901 // value (possibly 0 if we became void).
902 ReturnInst::Create(F->getContext(), RetVal, RI);
903 BB->getInstList().erase(RI);
906 // Now that the old function is dead, delete it.
907 F->eraseFromParent();
912 bool DAE::runOnModule(Module &M) {
913 bool Changed = false;
915 // First pass: Do a simple check to see if any functions can have their "..."
916 // removed. We can do this if they never call va_start. This loop cannot be
917 // fused with the next loop, because deleting a function invalidates
918 // information computed while surveying other functions.
919 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
920 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
922 if (F.getFunctionType()->isVarArg())
923 Changed |= DeleteDeadVarargs(F);
926 // Second phase:loop through the module, determining which arguments are live.
927 // We assume all arguments are dead unless proven otherwise (allowing us to
928 // determine that dead arguments passed into recursive functions are dead).
930 DEBUG(dbgs() << "DAE - Determining liveness\n");
931 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
934 // Now, remove all dead arguments and return values from each function in
936 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
937 // Increment now, because the function will probably get removed (ie.
938 // replaced by a new one).
940 Changed |= RemoveDeadStuffFromFunction(F);