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/Module.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Support/CallSite.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/ADT/StringExtras.h"
34 #include "llvm/Support/Compiler.h"
39 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
40 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
43 /// DAE - The dead argument elimination pass.
45 class VISIBILITY_HIDDEN DAE : public ModulePass {
48 /// Struct that represents (part of) either a return value or a function
49 /// argument. Used so that arguments and return values can be used
52 RetOrArg(const Function* F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
58 /// Make RetOrArg comparable, so we can put it into a map.
59 bool operator<(const RetOrArg &O) const {
62 else if (Idx != O.Idx)
65 return IsArg < O.IsArg;
68 /// Make RetOrArg comparable, so we can easily iterate the multimap.
69 bool operator==(const RetOrArg &O) const {
70 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
73 std::string getDescription() const {
74 return std::string((IsArg ? "Argument #" : "Return value #"))
75 + utostr(Idx) + " of function " + F->getName();
79 /// Liveness enum - During our initial pass over the program, we determine
80 /// that things are either alive or maybe alive. We don't mark anything
81 /// explicitly dead (even if we know they are), since anything not alive
82 /// with no registered uses (in Uses) will never be marked alive and will
83 /// thus become dead in the end.
84 enum Liveness { Live, MaybeLive };
86 /// Convenience wrapper
87 RetOrArg CreateRet(const Function *F, unsigned Idx) {
88 return RetOrArg(F, Idx, false);
90 /// Convenience wrapper
91 RetOrArg CreateArg(const Function *F, unsigned Idx) {
92 return RetOrArg(F, Idx, true);
95 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
96 /// This maps a return value or argument to any MaybeLive return values or
97 /// arguments it uses. This allows the MaybeLive values to be marked live
98 /// when any of its users is marked live.
99 /// For example (indices are left out for clarity):
100 /// - Uses[ret F] = ret G
101 /// This means that F calls G, and F returns the value returned by G.
102 /// - Uses[arg F] = ret G
103 /// This means that some function calls G and passes its result as an
105 /// - Uses[ret F] = arg F
106 /// This means that F returns one of its own arguments.
107 /// - Uses[arg F] = arg G
108 /// This means that G calls F and passes one of its own (G's) arguments
112 typedef std::set<RetOrArg> LiveSet;
113 typedef std::set<const Function*> LiveFuncSet;
115 /// This set contains all values that have been determined to be live.
117 /// This set contains all values that are cannot be changed in any way.
118 LiveFuncSet LiveFunctions;
120 typedef SmallVector<RetOrArg, 5> UseVector;
123 static char ID; // Pass identification, replacement for typeid
124 DAE() : ModulePass(&ID) {}
125 bool runOnModule(Module &M);
127 virtual bool ShouldHackArguments() const { return false; }
130 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
131 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
132 unsigned RetValNum = 0);
133 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses);
135 void SurveyFunction(Function &F);
136 void MarkValue(const RetOrArg &RA, Liveness L,
137 const UseVector &MaybeLiveUses);
138 void MarkLive(const RetOrArg &RA);
139 void MarkLive(const Function &F);
140 void PropagateLiveness(const RetOrArg &RA);
141 bool RemoveDeadStuffFromFunction(Function *F);
142 bool DeleteDeadVarargs(Function &Fn);
148 static RegisterPass<DAE>
149 X("deadargelim", "Dead Argument Elimination");
152 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
153 /// deletes arguments to functions which are external. This is only for use
155 struct DAH : public DAE {
157 virtual bool ShouldHackArguments() const { return true; }
162 static RegisterPass<DAH>
163 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
165 /// createDeadArgEliminationPass - This pass removes arguments from functions
166 /// which are not used by the body of the function.
168 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
169 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
171 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
172 /// llvm.vastart is never called, the varargs list is dead for the function.
173 bool DAE::DeleteDeadVarargs(Function &Fn) {
174 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
175 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
177 // Ensure that the function is only directly called.
178 if (Fn.hasAddressTaken())
181 // Okay, we know we can transform this function if safe. Scan its body
182 // looking for calls to llvm.vastart.
183 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
184 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
185 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
186 if (II->getIntrinsicID() == Intrinsic::vastart)
192 // If we get here, there are no calls to llvm.vastart in the function body,
193 // remove the "..." and adjust all the calls.
195 // Start by computing a new prototype for the function, which is the same as
196 // the old function, but doesn't have isVarArg set.
197 const FunctionType *FTy = Fn.getFunctionType();
198 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
199 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
200 unsigned NumArgs = Params.size();
202 // Create the new function body and insert it into the module...
203 Function *NF = Function::Create(NFTy, Fn.getLinkage());
204 NF->copyAttributesFrom(&Fn);
205 Fn.getParent()->getFunctionList().insert(&Fn, NF);
208 // Loop over all of the callers of the function, transforming the call sites
209 // to pass in a smaller number of arguments into the new function.
211 std::vector<Value*> Args;
212 while (!Fn.use_empty()) {
213 CallSite CS = CallSite::get(Fn.use_back());
214 Instruction *Call = CS.getInstruction();
216 // Pass all the same arguments.
217 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
219 // Drop any attributes that were on the vararg arguments.
220 AttrListPtr PAL = CS.getAttributes();
221 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
222 SmallVector<AttributeWithIndex, 8> AttributesVec;
223 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
224 AttributesVec.push_back(PAL.getSlot(i));
225 if (Attributes FnAttrs = PAL.getFnAttributes())
226 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
227 PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
231 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
232 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
233 Args.begin(), Args.end(), "", Call);
234 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
235 cast<InvokeInst>(New)->setAttributes(PAL);
237 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
238 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
239 cast<CallInst>(New)->setAttributes(PAL);
240 if (cast<CallInst>(Call)->isTailCall())
241 cast<CallInst>(New)->setTailCall();
245 if (!Call->use_empty())
246 Call->replaceAllUsesWith(New);
250 // Finally, remove the old call from the program, reducing the use-count of
252 Call->eraseFromParent();
255 // Since we have now created the new function, splice the body of the old
256 // function right into the new function, leaving the old rotting hulk of the
258 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
260 // Loop over the argument list, transfering uses of the old arguments over to
261 // the new arguments, also transfering over the names as well. While we're at
262 // it, remove the dead arguments from the DeadArguments list.
264 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
265 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
266 // Move the name and users over to the new version.
267 I->replaceAllUsesWith(I2);
271 // Finally, nuke the old function.
272 Fn.eraseFromParent();
276 /// Convenience function that returns the number of return values. It returns 0
277 /// for void functions and 1 for functions not returning a struct. It returns
278 /// the number of struct elements for functions returning a struct.
279 static unsigned NumRetVals(const Function *F) {
280 if (F->getReturnType() == Type::VoidTy)
282 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
283 return STy->getNumElements();
288 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
289 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
291 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
292 // We're live if our use or its Function is already marked as live.
293 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
296 // We're maybe live otherwise, but remember that we must become live if
298 MaybeLiveUses.push_back(Use);
303 /// SurveyUse - This looks at a single use of an argument or return value
304 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
305 /// if it causes the used value to become MaybeAlive.
307 /// RetValNum is the return value number to use when this use is used in a
308 /// return instruction. This is used in the recursion, you should always leave
310 DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
311 unsigned RetValNum) {
313 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
314 // The value is returned from a function. It's only live when the
315 // function's return value is live. We use RetValNum here, for the case
316 // that U is really a use of an insertvalue instruction that uses the
318 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
319 // We might be live, depending on the liveness of Use.
320 return MarkIfNotLive(Use, MaybeLiveUses);
322 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
323 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
325 // The use we are examining is inserted into an aggregate. Our liveness
326 // depends on all uses of that aggregate, but if it is used as a return
327 // value, only index at which we were inserted counts.
328 RetValNum = *IV->idx_begin();
330 // Note that if we are used as the aggregate operand to the insertvalue,
331 // we don't change RetValNum, but do survey all our uses.
333 Liveness Result = MaybeLive;
334 for (Value::use_iterator I = IV->use_begin(),
335 E = V->use_end(); I != E; ++I) {
336 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
342 CallSite CS = CallSite::get(V);
343 if (CS.getInstruction()) {
344 Function *F = CS.getCalledFunction();
346 // Used in a direct call.
348 // Find the argument number. We know for sure that this use is an
349 // argument, since if it was the function argument this would be an
350 // indirect call and the we know can't be looking at a value of the
351 // label type (for the invoke instruction).
352 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo());
354 if (ArgNo >= F->getFunctionType()->getNumParams())
355 // The value is passed in through a vararg! Must be live.
358 assert(CS.getArgument(ArgNo)
359 == CS.getInstruction()->getOperand(U.getOperandNo())
360 && "Argument is not where we expected it");
362 // Value passed to a normal call. It's only live when the corresponding
363 // argument to the called function turns out live.
364 RetOrArg Use = CreateArg(F, ArgNo);
365 return MarkIfNotLive(Use, MaybeLiveUses);
368 // Used in any other way? Value must be live.
372 /// SurveyUses - This looks at all the uses of the given value
373 /// Returns the Liveness deduced from the uses of this value.
375 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
376 /// the result is Live, MaybeLiveUses might be modified but its content should
377 /// be ignored (since it might not be complete).
378 DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) {
379 // Assume it's dead (which will only hold if there are no uses at all..).
380 Liveness Result = MaybeLive;
382 for (Value::use_iterator I = V->use_begin(),
383 E = V->use_end(); I != E; ++I) {
384 Result = SurveyUse(I, MaybeLiveUses);
391 // SurveyFunction - This performs the initial survey of the specified function,
392 // checking out whether or not it uses any of its incoming arguments or whether
393 // any callers use the return value. This fills in the LiveValues set and Uses
396 // We consider arguments of non-internal functions to be intrinsically alive as
397 // well as arguments to functions which have their "address taken".
399 void DAE::SurveyFunction(Function &F) {
400 unsigned RetCount = NumRetVals(&F);
401 // Assume all return values are dead
402 typedef SmallVector<Liveness, 5> RetVals;
403 RetVals RetValLiveness(RetCount, MaybeLive);
405 typedef SmallVector<UseVector, 5> RetUses;
406 // These vectors map each return value to the uses that make it MaybeLive, so
407 // we can add those to the Uses map if the return value really turns out to be
408 // MaybeLive. Initialized to a list of RetCount empty lists.
409 RetUses MaybeLiveRetUses(RetCount);
411 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
412 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
413 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
414 != F.getFunctionType()->getReturnType()) {
415 // We don't support old style multiple return values.
420 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
425 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n";
426 // Keep track of the number of live retvals, so we can skip checks once all
427 // of them turn out to be live.
428 unsigned NumLiveRetVals = 0;
429 const Type *STy = dyn_cast<StructType>(F.getReturnType());
430 // Loop all uses of the function.
431 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
432 // If the function is PASSED IN as an argument, its address has been
434 CallSite CS = CallSite::get(*I);
435 if (!CS.getInstruction() || !CS.isCallee(I)) {
440 // If this use is anything other than a call site, the function is alive.
441 Instruction *TheCall = CS.getInstruction();
442 if (!TheCall) { // Not a direct call site?
447 // If we end up here, we are looking at a direct call to our function.
449 // Now, check how our return value(s) is/are used in this caller. Don't
450 // bother checking return values if all of them are live already.
451 if (NumLiveRetVals != RetCount) {
453 // Check all uses of the return value.
454 for (Value::use_iterator I = TheCall->use_begin(),
455 E = TheCall->use_end(); I != E; ++I) {
456 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
457 if (Ext && Ext->hasIndices()) {
458 // This use uses a part of our return value, survey the uses of
459 // that part and store the results for this index only.
460 unsigned Idx = *Ext->idx_begin();
461 if (RetValLiveness[Idx] != Live) {
462 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
463 if (RetValLiveness[Idx] == Live)
467 // Used by something else than extractvalue. Mark all return
469 for (unsigned i = 0; i != RetCount; ++i )
470 RetValLiveness[i] = Live;
471 NumLiveRetVals = RetCount;
476 // Single return value
477 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
478 if (RetValLiveness[0] == Live)
479 NumLiveRetVals = RetCount;
484 // Now we've inspected all callers, record the liveness of our return values.
485 for (unsigned i = 0; i != RetCount; ++i)
486 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
488 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n";
490 // Now, check all of our arguments.
492 UseVector MaybeLiveArgUses;
493 for (Function::arg_iterator AI = F.arg_begin(),
494 E = F.arg_end(); AI != E; ++AI, ++i) {
495 // See what the effect of this use is (recording any uses that cause
496 // MaybeLive in MaybeLiveArgUses).
497 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
499 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
500 // Clear the vector again for the next iteration.
501 MaybeLiveArgUses.clear();
505 /// MarkValue - This function marks the liveness of RA depending on L. If L is
506 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
507 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
509 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
510 const UseVector &MaybeLiveUses) {
512 case Live: MarkLive(RA); break;
515 // Note any uses of this value, so this return value can be
516 // marked live whenever one of the uses becomes live.
517 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
518 UE = MaybeLiveUses.end(); UI != UE; ++UI)
519 Uses.insert(std::make_pair(*UI, RA));
525 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
526 /// changed in any way. Additionally,
527 /// mark any values that are used as this function's parameters or by its return
528 /// values (according to Uses) live as well.
529 void DAE::MarkLive(const Function &F) {
530 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n";
531 // Mark the function as live.
532 LiveFunctions.insert(&F);
533 // Mark all arguments as live.
534 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
535 PropagateLiveness(CreateArg(&F, i));
536 // Mark all return values as live.
537 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
538 PropagateLiveness(CreateRet(&F, i));
541 /// MarkLive - Mark the given return value or argument as live. Additionally,
542 /// mark any values that are used by this value (according to Uses) live as
544 void DAE::MarkLive(const RetOrArg &RA) {
545 if (LiveFunctions.count(RA.F))
546 return; // Function was already marked Live.
548 if (!LiveValues.insert(RA).second)
549 return; // We were already marked Live.
551 DOUT << "DAE - Marking " << RA.getDescription() << " live\n";
552 PropagateLiveness(RA);
555 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
556 /// to any other values it uses (according to Uses).
557 void DAE::PropagateLiveness(const RetOrArg &RA) {
558 // We don't use upper_bound (or equal_range) here, because our recursive call
559 // to ourselves is likely to cause the upper_bound (which is the first value
560 // not belonging to RA) to become erased and the iterator invalidated.
561 UseMap::iterator Begin = Uses.lower_bound(RA);
562 UseMap::iterator E = Uses.end();
564 for (I = Begin; I != E && I->first == RA; ++I)
567 // Erase RA from the Uses map (from the lower bound to wherever we ended up
569 Uses.erase(Begin, I);
572 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
573 // that are not in LiveValues. Transform the function and all of the callees of
574 // the function to not have these arguments and return values.
576 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
577 // Don't modify fully live functions
578 if (LiveFunctions.count(F))
581 // Start by computing a new prototype for the function, which is the same as
582 // the old function, but has fewer arguments and a different return type.
583 const FunctionType *FTy = F->getFunctionType();
584 std::vector<const Type*> Params;
586 // Set up to build a new list of parameter attributes.
587 SmallVector<AttributeWithIndex, 8> AttributesVec;
588 const AttrListPtr &PAL = F->getAttributes();
590 // The existing function return attributes.
591 Attributes RAttrs = PAL.getRetAttributes();
592 Attributes FnAttrs = PAL.getFnAttributes();
594 // Find out the new return value.
596 const Type *RetTy = FTy->getReturnType();
597 const Type *NRetTy = NULL;
598 unsigned RetCount = NumRetVals(F);
599 // -1 means unused, other numbers are the new index
600 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
601 std::vector<const Type*> RetTypes;
602 if (RetTy == Type::VoidTy) {
603 NRetTy = Type::VoidTy;
605 const StructType *STy = dyn_cast<StructType>(RetTy);
607 // Look at each of the original return values individually.
608 for (unsigned i = 0; i != RetCount; ++i) {
609 RetOrArg Ret = CreateRet(F, i);
610 if (LiveValues.erase(Ret)) {
611 RetTypes.push_back(STy->getElementType(i));
612 NewRetIdxs[i] = RetTypes.size() - 1;
614 ++NumRetValsEliminated;
615 DOUT << "DAE - Removing return value " << i << " from "
616 << F->getNameStart() << "\n";
620 // We used to return a single value.
621 if (LiveValues.erase(CreateRet(F, 0))) {
622 RetTypes.push_back(RetTy);
625 DOUT << "DAE - Removing return value from " << F->getNameStart()
627 ++NumRetValsEliminated;
629 if (RetTypes.size() > 1)
630 // More than one return type? Return a struct with them. Also, if we used
631 // to return a struct and didn't change the number of return values,
632 // return a struct again. This prevents changing {something} into
633 // something and {} into void.
634 // Make the new struct packed if we used to return a packed struct
636 NRetTy = StructType::get(RetTypes, STy->isPacked());
637 else if (RetTypes.size() == 1)
638 // One return type? Just a simple value then, but only if we didn't use to
639 // return a struct with that simple value before.
640 NRetTy = RetTypes.front();
641 else if (RetTypes.size() == 0)
642 // No return types? Make it void, but only if we didn't use to return {}.
643 NRetTy = Type::VoidTy;
646 assert(NRetTy && "No new return type found?");
648 // Remove any incompatible attributes, but only if we removed all return
649 // values. Otherwise, ensure that we don't have any conflicting attributes
650 // here. Currently, this should not be possible, but special handling might be
651 // required when new return value attributes are added.
652 if (NRetTy == Type::VoidTy)
653 RAttrs &= ~Attribute::typeIncompatible(NRetTy);
655 assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
656 && "Return attributes no longer compatible?");
659 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
661 // Remember which arguments are still alive.
662 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
663 // Construct the new parameter list from non-dead arguments. Also construct
664 // a new set of parameter attributes to correspond. Skip the first parameter
665 // attribute, since that belongs to the return value.
667 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
669 RetOrArg Arg = CreateArg(F, i);
670 if (LiveValues.erase(Arg)) {
671 Params.push_back(I->getType());
674 // Get the original parameter attributes (skipping the first one, that is
675 // for the return value.
676 if (Attributes Attrs = PAL.getParamAttributes(i + 1))
677 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
679 ++NumArgumentsEliminated;
680 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart()
681 << ") from " << F->getNameStart() << "\n";
685 if (FnAttrs != Attribute::None)
686 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
688 // Reconstruct the AttributesList based on the vector we constructed.
689 AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
691 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
692 // have zero fixed arguments.
694 // Note that we apply this hack for a vararg fuction that does not have any
695 // arguments anymore, but did have them before (so don't bother fixing
696 // functions that were already broken wrt CWriter).
697 bool ExtraArgHack = false;
698 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) {
700 Params.push_back(Type::Int32Ty);
703 // Create the new function type based on the recomputed parameters.
704 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
710 // Create the new function body and insert it into the module...
711 Function *NF = Function::Create(NFTy, F->getLinkage());
712 NF->copyAttributesFrom(F);
713 NF->setAttributes(NewPAL);
714 // Insert the new function before the old function, so we won't be processing
716 F->getParent()->getFunctionList().insert(F, NF);
719 // Loop over all of the callers of the function, transforming the call sites
720 // to pass in a smaller number of arguments into the new function.
722 std::vector<Value*> Args;
723 while (!F->use_empty()) {
724 CallSite CS = CallSite::get(F->use_back());
725 Instruction *Call = CS.getInstruction();
727 AttributesVec.clear();
728 const AttrListPtr &CallPAL = CS.getAttributes();
730 // The call return attributes.
731 Attributes RAttrs = CallPAL.getRetAttributes();
732 Attributes FnAttrs = CallPAL.getFnAttributes();
733 // Adjust in case the function was changed to return void.
734 RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
736 AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
738 // Declare these outside of the loops, so we can reuse them for the second
739 // loop, which loops the varargs.
740 CallSite::arg_iterator I = CS.arg_begin();
742 // Loop over those operands, corresponding to the normal arguments to the
743 // original function, and add those that are still alive.
744 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
747 // Get original parameter attributes, but skip return attributes.
748 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
749 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
753 Args.push_back(UndefValue::get(Type::Int32Ty));
755 // Push any varargs arguments on the list. Don't forget their attributes.
756 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
758 if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
759 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
762 if (FnAttrs != Attribute::None)
763 AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
765 // Reconstruct the AttributesList based on the vector we constructed.
766 AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
767 AttributesVec.end());
770 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
771 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
772 Args.begin(), Args.end(), "", Call);
773 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
774 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
776 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
777 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
778 cast<CallInst>(New)->setAttributes(NewCallPAL);
779 if (cast<CallInst>(Call)->isTailCall())
780 cast<CallInst>(New)->setTailCall();
784 if (!Call->use_empty()) {
785 if (New->getType() == Call->getType()) {
786 // Return type not changed? Just replace users then.
787 Call->replaceAllUsesWith(New);
789 } else if (New->getType() == Type::VoidTy) {
790 // Our return value has uses, but they will get removed later on.
791 // Replace by null for now.
792 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
794 assert(isa<StructType>(RetTy) &&
795 "Return type changed, but not into a void. The old return type"
796 " must have been a struct!");
797 Instruction *InsertPt = Call;
798 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
799 BasicBlock::iterator IP = II->getNormalDest()->begin();
800 while (isa<PHINode>(IP)) ++IP;
804 // We used to return a struct. Instead of doing smart stuff with all the
805 // uses of this struct, we will just rebuild it using
806 // extract/insertvalue chaining and let instcombine clean that up.
808 // Start out building up our return value from undef
809 Value *RetVal = llvm::UndefValue::get(RetTy);
810 for (unsigned i = 0; i != RetCount; ++i)
811 if (NewRetIdxs[i] != -1) {
813 if (RetTypes.size() > 1)
814 // We are still returning a struct, so extract the value from our
816 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
819 // We are now returning a single element, so just insert that
821 // Insert the value at the old position
822 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
824 // Now, replace all uses of the old call instruction with the return
826 Call->replaceAllUsesWith(RetVal);
831 // Finally, remove the old call from the program, reducing the use-count of
833 Call->eraseFromParent();
836 // Since we have now created the new function, splice the body of the old
837 // function right into the new function, leaving the old rotting hulk of the
839 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
841 // Loop over the argument list, transfering uses of the old arguments over to
842 // the new arguments, also transfering over the names as well.
844 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
845 I2 = NF->arg_begin(); I != E; ++I, ++i)
847 // If this is a live argument, move the name and users over to the new
849 I->replaceAllUsesWith(I2);
853 // If this argument is dead, replace any uses of it with null constants
854 // (these are guaranteed to become unused later on).
855 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
858 // If we change the return value of the function we must rewrite any return
859 // instructions. Check this now.
860 if (F->getReturnType() != NF->getReturnType())
861 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
862 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
865 if (NFTy->getReturnType() == Type::VoidTy) {
868 assert (isa<StructType>(RetTy));
869 // The original return value was a struct, insert
870 // extractvalue/insertvalue chains to extract only the values we need
871 // to return and insert them into our new result.
872 // This does generate messy code, but we'll let it to instcombine to
874 Value *OldRet = RI->getOperand(0);
875 // Start out building up our return value from undef
876 RetVal = llvm::UndefValue::get(NRetTy);
877 for (unsigned i = 0; i != RetCount; ++i)
878 if (NewRetIdxs[i] != -1) {
879 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
881 if (RetTypes.size() > 1) {
882 // We're still returning a struct, so reinsert the value into
883 // our new return value at the new index
885 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
888 // We are now only returning a simple value, so just return the
894 // Replace the return instruction with one returning the new return
895 // value (possibly 0 if we became void).
896 ReturnInst::Create(RetVal, RI);
897 BB->getInstList().erase(RI);
900 // Now that the old function is dead, delete it.
901 F->eraseFromParent();
906 bool DAE::runOnModule(Module &M) {
907 bool Changed = false;
909 // First pass: Do a simple check to see if any functions can have their "..."
910 // removed. We can do this if they never call va_start. This loop cannot be
911 // fused with the next loop, because deleting a function invalidates
912 // information computed while surveying other functions.
913 DOUT << "DAE - Deleting dead varargs\n";
914 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
916 if (F.getFunctionType()->isVarArg())
917 Changed |= DeleteDeadVarargs(F);
920 // Second phase:loop through the module, determining which arguments are live.
921 // We assume all arguments are dead unless proven otherwise (allowing us to
922 // determine that dead arguments passed into recursive functions are dead).
924 DOUT << "DAE - Determining liveness\n";
925 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
928 // Now, remove all dead arguments and return values from each function in
930 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
931 // Increment now, because the function will probably get removed (ie
932 // replaced by a new one).
934 Changed |= RemoveDeadStuffFromFunction(F);