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() {
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;
114 /// This set contains all values that have been determined to be live.
117 typedef SmallVector<RetOrArg, 5> UseVector;
120 static char ID; // Pass identification, replacement for typeid
121 DAE() : ModulePass((intptr_t)&ID) {}
122 bool runOnModule(Module &M);
124 virtual bool ShouldHackArguments() const { return false; }
127 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
128 Liveness SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
129 unsigned RetValNum = 0);
130 Liveness SurveyUses(Value *V, UseVector &MaybeLiveUses);
132 void SurveyFunction(Function &F);
133 void MarkValue(const RetOrArg &RA, Liveness L,
134 const UseVector &MaybeLiveUses);
135 void MarkLive(RetOrArg RA);
136 void MarkLive(const Function &F);
137 bool RemoveDeadStuffFromFunction(Function *F);
138 bool DeleteDeadVarargs(Function &Fn);
144 static RegisterPass<DAE>
145 X("deadargelim", "Dead Argument Elimination");
148 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
149 /// deletes arguments to functions which are external. This is only for use
151 struct DAH : public DAE {
153 virtual bool ShouldHackArguments() const { return true; }
158 static RegisterPass<DAH>
159 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
161 /// createDeadArgEliminationPass - This pass removes arguments from functions
162 /// which are not used by the body of the function.
164 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
165 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
167 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
168 /// llvm.vastart is never called, the varargs list is dead for the function.
169 bool DAE::DeleteDeadVarargs(Function &Fn) {
170 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
171 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false;
173 // Ensure that the function is only directly called.
174 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) {
175 // If this use is anything other than a call site, give up.
176 CallSite CS = CallSite::get(*I);
177 Instruction *TheCall = CS.getInstruction();
178 if (!TheCall) return false; // Not a direct call site?
180 // The addr of this function is passed to the call.
181 if (I.getOperandNo() != 0) return false;
184 // Okay, we know we can transform this function if safe. Scan its body
185 // looking for calls to llvm.vastart.
186 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
187 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
188 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
189 if (II->getIntrinsicID() == Intrinsic::vastart)
195 // If we get here, there are no calls to llvm.vastart in the function body,
196 // remove the "..." and adjust all the calls.
198 // Start by computing a new prototype for the function, which is the same as
199 // the old function, but doesn't have isVarArg set.
200 const FunctionType *FTy = Fn.getFunctionType();
201 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
202 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
203 unsigned NumArgs = Params.size();
205 // Create the new function body and insert it into the module...
206 Function *NF = Function::Create(NFTy, Fn.getLinkage());
207 NF->copyAttributesFrom(&Fn);
208 Fn.getParent()->getFunctionList().insert(&Fn, NF);
211 // Loop over all of the callers of the function, transforming the call sites
212 // to pass in a smaller number of arguments into the new function.
214 std::vector<Value*> Args;
215 while (!Fn.use_empty()) {
216 CallSite CS = CallSite::get(Fn.use_back());
217 Instruction *Call = CS.getInstruction();
219 // Pass all the same arguments.
220 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
222 // Drop any attributes that were on the vararg arguments.
223 PAListPtr PAL = CS.getParamAttrs();
224 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
225 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
226 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
227 ParamAttrsVec.push_back(PAL.getSlot(i));
228 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
232 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
233 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
234 Args.begin(), Args.end(), "", Call);
235 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
236 cast<InvokeInst>(New)->setParamAttrs(PAL);
238 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
239 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
240 cast<CallInst>(New)->setParamAttrs(PAL);
241 if (cast<CallInst>(Call)->isTailCall())
242 cast<CallInst>(New)->setTailCall();
246 if (!Call->use_empty())
247 Call->replaceAllUsesWith(New);
251 // Finally, remove the old call from the program, reducing the use-count of
253 Call->eraseFromParent();
256 // Since we have now created the new function, splice the body of the old
257 // function right into the new function, leaving the old rotting hulk of the
259 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
261 // Loop over the argument list, transfering uses of the old arguments over to
262 // the new arguments, also transfering over the names as well. While we're at
263 // it, remove the dead arguments from the DeadArguments list.
265 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
266 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
267 // Move the name and users over to the new version.
268 I->replaceAllUsesWith(I2);
272 // Finally, nuke the old function.
273 Fn.eraseFromParent();
277 /// Convenience function that returns the number of return values. It returns 0
278 /// for void functions and 1 for functions not returning a struct. It returns
279 /// the number of struct elements for functions returning a struct.
280 static unsigned NumRetVals(const Function *F) {
281 if (F->getReturnType() == Type::VoidTy)
283 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
284 return STy->getNumElements();
289 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
290 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
292 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
293 // We're live if our use is already marked as live.
294 if (LiveValues.count(Use))
297 // We're maybe live otherwise, but remember that we must become live if
299 MaybeLiveUses.push_back(Use);
304 /// SurveyUse - This looks at a single use of an argument or return value
305 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
306 /// if it causes the used value to become MaybeAlive.
308 /// RetValNum is the return value number to use when this use is used in a
309 /// return instruction. This is used in the recursion, you should always leave
311 DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
312 unsigned RetValNum) {
314 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
315 // The value is returned from a function. It's only live when the
316 // function's return value is live. We use RetValNum here, for the case
317 // that U is really a use of an insertvalue instruction that uses the
319 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
320 // We might be live, depending on the liveness of Use.
321 return MarkIfNotLive(Use, MaybeLiveUses);
323 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
324 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
326 // The use we are examining is inserted into an aggregate. Our liveness
327 // depends on all uses of that aggregate, but if it is used as a return
328 // value, only index at which we were inserted counts.
329 RetValNum = *IV->idx_begin();
331 // Note that if we are used as the aggregate operand to the insertvalue,
332 // we don't change RetValNum, but do survey all our uses.
334 Liveness Result = MaybeLive;
335 for (Value::use_iterator I = IV->use_begin(),
336 E = V->use_end(); I != E; ++I) {
337 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
343 CallSite CS = CallSite::get(V);
344 if (CS.getInstruction()) {
345 Function *F = CS.getCalledFunction();
347 // Used in a direct call.
349 // Find the argument number. We know for sure that this use is an
350 // argument, since if it was the function argument this would be an
351 // indirect call and the we know can't be looking at a value of the
352 // label type (for the invoke instruction).
353 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo());
355 if (ArgNo >= F->getFunctionType()->getNumParams())
356 // The value is passed in through a vararg! Must be live.
359 assert(CS.getArgument(ArgNo)
360 == CS.getInstruction()->getOperand(U.getOperandNo())
361 && "Argument is not where we expected it");
363 // Value passed to a normal call. It's only live when the corresponding
364 // argument to the called function turns out live.
365 RetOrArg Use = CreateArg(F, ArgNo);
366 return MarkIfNotLive(Use, MaybeLiveUses);
369 // Used in any other way? Value must be live.
373 /// SurveyUses - This looks at all the uses of the given value
374 /// Returns the Liveness deduced from the uses of this value.
376 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
377 /// the result is Live, MaybeLiveUses might be modified but its content should
378 /// be ignored (since it might not be complete).
379 DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) {
380 // Assume it's dead (which will only hold if there are no uses at all..).
381 Liveness Result = MaybeLive;
383 for (Value::use_iterator I = V->use_begin(),
384 E = V->use_end(); I != E; ++I) {
385 Result = SurveyUse(I, MaybeLiveUses);
392 // SurveyFunction - This performs the initial survey of the specified function,
393 // checking out whether or not it uses any of its incoming arguments or whether
394 // any callers use the return value. This fills in the LiveValues set and Uses
397 // We consider arguments of non-internal functions to be intrinsically alive as
398 // well as arguments to functions which have their "address taken".
400 void DAE::SurveyFunction(Function &F) {
401 unsigned RetCount = NumRetVals(&F);
402 // Assume all return values are dead
403 typedef SmallVector<Liveness, 5> RetVals;
404 RetVals RetValLiveness(RetCount, MaybeLive);
406 typedef SmallVector<UseVector, 5> RetUses;
407 // These vectors map each return value to the uses that make it MaybeLive, so
408 // we can add those to the Uses map if the return value really turns out to be
409 // MaybeLive. Initialized to a list of RetCount empty lists.
410 RetUses MaybeLiveRetUses(RetCount);
412 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
413 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
414 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
415 != F.getFunctionType()->getReturnType()) {
416 // We don't support old style multiple return values.
421 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
426 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n";
427 // Keep track of the number of live retvals, so we can skip checks once all
428 // of them turn out to be live.
429 unsigned NumLiveRetVals = 0;
430 const Type *STy = dyn_cast<StructType>(F.getReturnType());
431 // Loop all uses of the function.
432 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
433 // If the function is PASSED IN as an argument, its address has been
435 if (I.getOperandNo() != 0) {
440 // If this use is anything other than a call site, the function is alive.
441 CallSite CS = CallSite::get(*I);
442 Instruction *TheCall = CS.getInstruction();
443 if (!TheCall) { // Not a direct call site?
448 // If we end up here, we are looking at a direct call to our function.
450 // Now, check how our return value(s) is/are used in this caller. Don't
451 // bother checking return values if all of them are live already.
452 if (NumLiveRetVals != RetCount) {
454 // Check all uses of the return value.
455 for (Value::use_iterator I = TheCall->use_begin(),
456 E = TheCall->use_end(); I != E; ++I) {
457 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
458 if (Ext && Ext->hasIndices()) {
459 // This use uses a part of our return value, survey the uses of
460 // that part and store the results for this index only.
461 unsigned Idx = *Ext->idx_begin();
462 if (RetValLiveness[Idx] != Live) {
463 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
464 if (RetValLiveness[Idx] == Live)
468 // Used by something else than extractvalue. Mark all return
470 for (unsigned i = 0; i != RetCount; ++i )
471 RetValLiveness[i] = Live;
472 NumLiveRetVals = RetCount;
477 // Single return value
478 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
479 if (RetValLiveness[0] == Live)
480 NumLiveRetVals = RetCount;
485 // Now we've inspected all callers, record the liveness of our return values.
486 for (unsigned i = 0; i != RetCount; ++i)
487 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
489 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n";
491 // Now, check all of our arguments.
493 UseVector MaybeLiveArgUses;
494 for (Function::arg_iterator AI = F.arg_begin(),
495 E = F.arg_end(); AI != E; ++AI, ++i) {
496 // See what the effect of this use is (recording any uses that cause
497 // MaybeLive in MaybeLiveArgUses).
498 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
500 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
501 // Clear the vector again for the next iteration.
502 MaybeLiveArgUses.clear();
506 /// MarkValue - This function marks the liveness of RA depending on L. If L is
507 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
508 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
510 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
511 const UseVector &MaybeLiveUses) {
513 case Live: MarkLive(RA); break;
516 // Note any uses of this value, so this return value can be
517 // marked live whenever one of the uses becomes live.
518 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
519 UE = MaybeLiveUses.end(); UI != UE; ++UI)
520 Uses.insert(std::make_pair(*UI, RA));
526 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
527 /// changed in any way. Additionally,
528 /// mark any values that are used as this function's parameters or by its return
529 /// values (according to Uses) live as well.
530 void DAE::MarkLive(const Function &F) {
531 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n";
532 // Mark all arguments as live.
533 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
534 MarkLive(CreateArg(&F, i));
535 // Mark all return values as live.
536 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
537 MarkLive(CreateRet(&F, i));
540 /// MarkLive - Mark the given return value or argument as live. Additionally,
541 /// mark any values that are used by this value (according to Uses) live as
543 void DAE::MarkLive(RetOrArg RA) {
544 if (!LiveValues.insert(RA).second)
545 return; // We were already marked Live.
548 DOUT << "DAE - Marking argument " << RA.Idx << " to function "
549 << RA.F->getNameStart() << " live\n";
551 DOUT << "DAE - Marking return value " << RA.Idx << " of function "
552 << RA.F->getNameStart() << " live\n";
554 // We don't use upper_bound (or equal_range) here, because our recursive call
555 // to ourselves is likely to cause the upper_bound (which is the first value
556 // not belonging to RA) to become erased and the iterator invalidated.
557 UseMap::iterator Begin = Uses.lower_bound(RA);
558 UseMap::iterator E = Uses.end();
560 for (I = Begin; I != E && I->first == RA; ++I)
563 // Erase RA from the Uses map (from the lower bound to wherever we ended up
565 Uses.erase(Begin, I);
568 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
569 // that are not in LiveValues. Transform the function and all of the callees of
570 // the function to not have these arguments and return values.
572 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
573 // Quick exit path for external functions
574 if (!F->hasInternalLinkage() && (!ShouldHackArguments() || F->isIntrinsic()))
577 // Start by computing a new prototype for the function, which is the same as
578 // the old function, but has fewer arguments and a different return type.
579 const FunctionType *FTy = F->getFunctionType();
580 std::vector<const Type*> Params;
582 // Set up to build a new list of parameter attributes.
583 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
584 const PAListPtr &PAL = F->getParamAttrs();
586 // The existing function return attributes.
587 ParameterAttributes RAttrs = PAL.getParamAttrs(0);
590 // Find out the new return value.
592 const Type *RetTy = FTy->getReturnType();
593 const Type *NRetTy = NULL;
594 unsigned RetCount = NumRetVals(F);
595 // Explicitly track if anything changed, for debugging.
596 bool Changed = false;
597 // -1 means unused, other numbers are the new index
598 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
599 std::vector<const Type*> RetTypes;
600 if (RetTy == Type::VoidTy) {
601 NRetTy = Type::VoidTy;
603 const StructType *STy = dyn_cast<StructType>(RetTy);
605 // Look at each of the original return values individually.
606 for (unsigned i = 0; i != RetCount; ++i) {
607 RetOrArg Ret = CreateRet(F, i);
608 if (LiveValues.erase(Ret)) {
609 RetTypes.push_back(STy->getElementType(i));
610 NewRetIdxs[i] = RetTypes.size() - 1;
612 ++NumRetValsEliminated;
613 DOUT << "DAE - Removing return value " << i << " from "
614 << F->getNameStart() << "\n";
619 // We used to return a single value.
620 if (LiveValues.erase(CreateRet(F, 0))) {
621 RetTypes.push_back(RetTy);
624 DOUT << "DAE - Removing return value from " << F->getNameStart()
626 ++NumRetValsEliminated;
629 if (RetTypes.size() > 1 || (STy && STy->getNumElements()==RetTypes.size()))
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 &= ~ParamAttr::typeIncompatible(NRetTy);
655 assert((RAttrs & ParamAttr::typeIncompatible(NRetTy)) == 0
656 && "Return attributes no longer compatible?");
659 ParamAttrsVec.push_back(ParamAttrsWithIndex::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 (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1))
677 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
679 ++NumArgumentsEliminated;
680 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart()
681 << ") from " << F->getNameStart() << "\n";
686 // Reconstruct the ParamAttrsList based on the vector we constructed.
687 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
689 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
690 // have zero fixed arguments.
692 // Note that we apply this hack for a vararg fuction that does not have any
693 // arguments anymore, but did have them before (so don't bother fixing
694 // functions that were already broken wrt CWriter).
695 bool ExtraArgHack = false;
696 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) {
698 Params.push_back(Type::Int32Ty);
701 // Create the new function type based on the recomputed parameters.
702 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
708 // The function type is only allowed to be different if we actually left out
709 // an argument or return value.
710 assert(Changed && "Function type changed while no arguments or return values"
713 // Create the new function body and insert it into the module...
714 Function *NF = Function::Create(NFTy, F->getLinkage());
715 NF->copyAttributesFrom(F);
716 NF->setParamAttrs(NewPAL);
717 // Insert the new function before the old function, so we won't be processing
719 F->getParent()->getFunctionList().insert(F, NF);
722 // Loop over all of the callers of the function, transforming the call sites
723 // to pass in a smaller number of arguments into the new function.
725 std::vector<Value*> Args;
726 while (!F->use_empty()) {
727 CallSite CS = CallSite::get(F->use_back());
728 Instruction *Call = CS.getInstruction();
730 ParamAttrsVec.clear();
731 const PAListPtr &CallPAL = CS.getParamAttrs();
733 // The call return attributes.
734 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0);
735 // Adjust in case the function was changed to return void.
736 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType());
738 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
740 // Declare these outside of the loops, so we can reuse them for the second
741 // loop, which loops the varargs.
742 CallSite::arg_iterator I = CS.arg_begin();
744 // Loop over those operands, corresponding to the normal arguments to the
745 // original function, and add those that are still alive.
746 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
749 // Get original parameter attributes, but skip return attributes.
750 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1))
751 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
755 Args.push_back(UndefValue::get(Type::Int32Ty));
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 (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1))
761 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
764 // Reconstruct the ParamAttrsList based on the vector we constructed.
765 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(),
766 ParamAttrsVec.end());
769 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
770 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
771 Args.begin(), Args.end(), "", Call);
772 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
773 cast<InvokeInst>(New)->setParamAttrs(NewCallPAL);
775 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
776 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
777 cast<CallInst>(New)->setParamAttrs(NewCallPAL);
778 if (cast<CallInst>(Call)->isTailCall())
779 cast<CallInst>(New)->setTailCall();
783 if (!Call->use_empty()) {
784 if (New->getType() == Call->getType()) {
785 // Return type not changed? Just replace users then.
786 Call->replaceAllUsesWith(New);
788 } else if (New->getType() == Type::VoidTy) {
789 // Our return value has uses, but they will get removed later on.
790 // Replace by null for now.
791 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
793 assert(isa<StructType>(RetTy) && "Return type changed, but not into a"
794 "void. The old return type must have"
796 // The original return value was a struct, update all uses (which are
797 // all extractvalue instructions).
798 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
800 assert(isa<ExtractValueInst>(*I) && "Return value not only used by"
802 ExtractValueInst *EV = cast<ExtractValueInst>(*I);
803 // Increment now, since we're about to throw away this use.
805 assert(EV->hasIndices() && "Return value used by extractvalue without"
807 unsigned Idx = *EV->idx_begin();
808 if (NewRetIdxs[Idx] != -1) {
809 if (RetTypes.size() > 1) {
810 // We're still returning a struct, create a new extractvalue
811 // instruction with the first index updated
812 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end());
813 NewIdxs[0] = NewRetIdxs[Idx];
814 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(),
815 NewIdxs.end(), "retval",
817 EV->replaceAllUsesWith(NEV);
818 EV->eraseFromParent();
820 // We are now only returning a simple value, remove the
822 EV->replaceAllUsesWith(New);
823 EV->eraseFromParent();
826 // Value unused, replace uses by null for now, they will get removed
828 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType()));
829 EV->eraseFromParent();
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 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
863 // If we change the return value of the function we must rewrite any return
864 // instructions. Check this now.
865 if (F->getReturnType() != NF->getReturnType())
866 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
867 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
870 if (NFTy->getReturnType() == Type::VoidTy) {
873 assert (isa<StructType>(RetTy));
874 // The original return value was a struct, insert
875 // extractvalue/insertvalue chains to extract only the values we need
876 // to return and insert them into our new result.
877 // This does generate messy code, but we'll let it to instcombine to
879 Value *OldRet = RI->getOperand(0);
880 // Start out building up our return value from undef
881 RetVal = llvm::UndefValue::get(NRetTy);
882 for (unsigned i = 0; i != RetCount; ++i)
883 if (NewRetIdxs[i] != -1) {
884 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
886 if (RetTypes.size() > 1) {
887 // We're still returning a struct, so reinsert the value into
888 // our new return value at the new index
890 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
893 // We are now only returning a simple value, so just return the
899 // Replace the return instruction with one returning the new return
900 // value (possibly 0 if we became void).
901 ReturnInst::Create(RetVal, RI);
902 BB->getInstList().erase(RI);
905 // Now that the old function is dead, delete it.
906 F->eraseFromParent();
911 bool DAE::runOnModule(Module &M) {
912 bool Changed = false;
914 // First pass: Do a simple check to see if any functions can have their "..."
915 // removed. We can do this if they never call va_start. This loop cannot be
916 // fused with the next loop, because deleting a function invalidates
917 // information computed while surveying other functions.
918 DOUT << "DAE - Deleting dead varargs\n";
919 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
921 if (F.getFunctionType()->isVarArg())
922 Changed |= DeleteDeadVarargs(F);
925 // Second phase:loop through the module, determining which arguments are live.
926 // We assume all arguments are dead unless proven otherwise (allowing us to
927 // determine that dead arguments passed into recursive functions are dead).
929 DOUT << "DAE - Determining liveness\n";
930 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
933 // Now, remove all dead arguments and return values from each function in
935 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
936 // Increment now, because the function will probably get removed (ie
937 // replaced by a new one).
939 Changed |= RemoveDeadStuffFromFunction(F);