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;
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(const RetOrArg &RA);
136 void MarkLive(const Function &F);
137 void PropagateLiveness(const RetOrArg &RA);
138 bool RemoveDeadStuffFromFunction(Function *F);
139 bool DeleteDeadVarargs(Function &Fn);
145 static RegisterPass<DAE>
146 X("deadargelim", "Dead Argument Elimination");
149 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
150 /// deletes arguments to functions which are external. This is only for use
152 struct DAH : public DAE {
154 virtual bool ShouldHackArguments() const { return true; }
159 static RegisterPass<DAH>
160 Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
162 /// createDeadArgEliminationPass - This pass removes arguments from functions
163 /// which are not used by the body of the function.
165 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
166 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
168 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
169 /// llvm.vastart is never called, the varargs list is dead for the function.
170 bool DAE::DeleteDeadVarargs(Function &Fn) {
171 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
172 if (Fn.isDeclaration() || !Fn.hasInternalLinkage()) return false;
174 // Ensure that the function is only directly called.
175 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ++I) {
176 // If this use is anything other than a call site, give up.
177 CallSite CS = CallSite::get(*I);
178 Instruction *TheCall = CS.getInstruction();
179 if (!TheCall) return false; // Not a direct call site?
181 // The addr of this function is passed to the call.
182 if (I.getOperandNo() != 0) return false;
185 // Okay, we know we can transform this function if safe. Scan its body
186 // looking for calls to llvm.vastart.
187 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
188 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
189 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
190 if (II->getIntrinsicID() == Intrinsic::vastart)
196 // If we get here, there are no calls to llvm.vastart in the function body,
197 // remove the "..." and adjust all the calls.
199 // Start by computing a new prototype for the function, which is the same as
200 // the old function, but doesn't have isVarArg set.
201 const FunctionType *FTy = Fn.getFunctionType();
202 std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
203 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params, false);
204 unsigned NumArgs = Params.size();
206 // Create the new function body and insert it into the module...
207 Function *NF = Function::Create(NFTy, Fn.getLinkage());
208 NF->copyAttributesFrom(&Fn);
209 Fn.getParent()->getFunctionList().insert(&Fn, NF);
212 // Loop over all of the callers of the function, transforming the call sites
213 // to pass in a smaller number of arguments into the new function.
215 std::vector<Value*> Args;
216 while (!Fn.use_empty()) {
217 CallSite CS = CallSite::get(Fn.use_back());
218 Instruction *Call = CS.getInstruction();
220 // Pass all the same arguments.
221 Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
223 // Drop any attributes that were on the vararg arguments.
224 PAListPtr PAL = CS.getParamAttrs();
225 if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
226 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
227 for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
228 ParamAttrsVec.push_back(PAL.getSlot(i));
229 PAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
233 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
234 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
235 Args.begin(), Args.end(), "", Call);
236 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
237 cast<InvokeInst>(New)->setParamAttrs(PAL);
239 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
240 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
241 cast<CallInst>(New)->setParamAttrs(PAL);
242 if (cast<CallInst>(Call)->isTailCall())
243 cast<CallInst>(New)->setTailCall();
247 if (!Call->use_empty())
248 Call->replaceAllUsesWith(New);
252 // Finally, remove the old call from the program, reducing the use-count of
254 Call->eraseFromParent();
257 // Since we have now created the new function, splice the body of the old
258 // function right into the new function, leaving the old rotting hulk of the
260 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
262 // Loop over the argument list, transfering uses of the old arguments over to
263 // the new arguments, also transfering over the names as well. While we're at
264 // it, remove the dead arguments from the DeadArguments list.
266 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
267 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
268 // Move the name and users over to the new version.
269 I->replaceAllUsesWith(I2);
273 // Finally, nuke the old function.
274 Fn.eraseFromParent();
278 /// Convenience function that returns the number of return values. It returns 0
279 /// for void functions and 1 for functions not returning a struct. It returns
280 /// the number of struct elements for functions returning a struct.
281 static unsigned NumRetVals(const Function *F) {
282 if (F->getReturnType() == Type::VoidTy)
284 else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
285 return STy->getNumElements();
290 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
291 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
293 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
294 // We're live if our use is already marked as live.
295 if (LiveValues.count(Use))
298 // We're maybe live otherwise, but remember that we must become live if
300 MaybeLiveUses.push_back(Use);
305 /// SurveyUse - This looks at a single use of an argument or return value
306 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
307 /// if it causes the used value to become MaybeAlive.
309 /// RetValNum is the return value number to use when this use is used in a
310 /// return instruction. This is used in the recursion, you should always leave
312 DAE::Liveness DAE::SurveyUse(Value::use_iterator U, UseVector &MaybeLiveUses,
313 unsigned RetValNum) {
315 if (ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
316 // The value is returned from a function. It's only live when the
317 // function's return value is live. We use RetValNum here, for the case
318 // that U is really a use of an insertvalue instruction that uses the
320 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
321 // We might be live, depending on the liveness of Use.
322 return MarkIfNotLive(Use, MaybeLiveUses);
324 if (InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
325 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
327 // The use we are examining is inserted into an aggregate. Our liveness
328 // depends on all uses of that aggregate, but if it is used as a return
329 // value, only index at which we were inserted counts.
330 RetValNum = *IV->idx_begin();
332 // Note that if we are used as the aggregate operand to the insertvalue,
333 // we don't change RetValNum, but do survey all our uses.
335 Liveness Result = MaybeLive;
336 for (Value::use_iterator I = IV->use_begin(),
337 E = V->use_end(); I != E; ++I) {
338 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
344 CallSite CS = CallSite::get(V);
345 if (CS.getInstruction()) {
346 Function *F = CS.getCalledFunction();
348 // Used in a direct call.
350 // Find the argument number. We know for sure that this use is an
351 // argument, since if it was the function argument this would be an
352 // indirect call and the we know can't be looking at a value of the
353 // label type (for the invoke instruction).
354 unsigned ArgNo = CS.getArgumentNo(U.getOperandNo());
356 if (ArgNo >= F->getFunctionType()->getNumParams())
357 // The value is passed in through a vararg! Must be live.
360 assert(CS.getArgument(ArgNo)
361 == CS.getInstruction()->getOperand(U.getOperandNo())
362 && "Argument is not where we expected it");
364 // Value passed to a normal call. It's only live when the corresponding
365 // argument to the called function turns out live.
366 RetOrArg Use = CreateArg(F, ArgNo);
367 return MarkIfNotLive(Use, MaybeLiveUses);
370 // Used in any other way? Value must be live.
374 /// SurveyUses - This looks at all the uses of the given value
375 /// Returns the Liveness deduced from the uses of this value.
377 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
378 /// the result is Live, MaybeLiveUses might be modified but its content should
379 /// be ignored (since it might not be complete).
380 DAE::Liveness DAE::SurveyUses(Value *V, UseVector &MaybeLiveUses) {
381 // Assume it's dead (which will only hold if there are no uses at all..).
382 Liveness Result = MaybeLive;
384 for (Value::use_iterator I = V->use_begin(),
385 E = V->use_end(); I != E; ++I) {
386 Result = SurveyUse(I, MaybeLiveUses);
393 // SurveyFunction - This performs the initial survey of the specified function,
394 // checking out whether or not it uses any of its incoming arguments or whether
395 // any callers use the return value. This fills in the LiveValues set and Uses
398 // We consider arguments of non-internal functions to be intrinsically alive as
399 // well as arguments to functions which have their "address taken".
401 void DAE::SurveyFunction(Function &F) {
402 unsigned RetCount = NumRetVals(&F);
403 // Assume all return values are dead
404 typedef SmallVector<Liveness, 5> RetVals;
405 RetVals RetValLiveness(RetCount, MaybeLive);
407 typedef SmallVector<UseVector, 5> RetUses;
408 // These vectors map each return value to the uses that make it MaybeLive, so
409 // we can add those to the Uses map if the return value really turns out to be
410 // MaybeLive. Initialized to a list of RetCount empty lists.
411 RetUses MaybeLiveRetUses(RetCount);
413 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
414 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
415 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
416 != F.getFunctionType()->getReturnType()) {
417 // We don't support old style multiple return values.
422 if (!F.hasInternalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
427 DOUT << "DAE - Inspecting callers for fn: " << F.getName() << "\n";
428 // Keep track of the number of live retvals, so we can skip checks once all
429 // of them turn out to be live.
430 unsigned NumLiveRetVals = 0;
431 const Type *STy = dyn_cast<StructType>(F.getReturnType());
432 // Loop all uses of the function.
433 for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
434 // If the function is PASSED IN as an argument, its address has been
436 if (I.getOperandNo() != 0) {
441 // If this use is anything other than a call site, the function is alive.
442 CallSite CS = CallSite::get(*I);
443 Instruction *TheCall = CS.getInstruction();
444 if (!TheCall) { // Not a direct call site?
449 // If we end up here, we are looking at a direct call to our function.
451 // Now, check how our return value(s) is/are used in this caller. Don't
452 // bother checking return values if all of them are live already.
453 if (NumLiveRetVals != RetCount) {
455 // Check all uses of the return value.
456 for (Value::use_iterator I = TheCall->use_begin(),
457 E = TheCall->use_end(); I != E; ++I) {
458 ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
459 if (Ext && Ext->hasIndices()) {
460 // This use uses a part of our return value, survey the uses of
461 // that part and store the results for this index only.
462 unsigned Idx = *Ext->idx_begin();
463 if (RetValLiveness[Idx] != Live) {
464 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
465 if (RetValLiveness[Idx] == Live)
469 // Used by something else than extractvalue. Mark all return
471 for (unsigned i = 0; i != RetCount; ++i )
472 RetValLiveness[i] = Live;
473 NumLiveRetVals = RetCount;
478 // Single return value
479 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
480 if (RetValLiveness[0] == Live)
481 NumLiveRetVals = RetCount;
486 // Now we've inspected all callers, record the liveness of our return values.
487 for (unsigned i = 0; i != RetCount; ++i)
488 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
490 DOUT << "DAE - Inspecting args for fn: " << F.getName() << "\n";
492 // Now, check all of our arguments.
494 UseVector MaybeLiveArgUses;
495 for (Function::arg_iterator AI = F.arg_begin(),
496 E = F.arg_end(); AI != E; ++AI, ++i) {
497 // See what the effect of this use is (recording any uses that cause
498 // MaybeLive in MaybeLiveArgUses).
499 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
501 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
502 // Clear the vector again for the next iteration.
503 MaybeLiveArgUses.clear();
507 /// MarkValue - This function marks the liveness of RA depending on L. If L is
508 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
509 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
511 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
512 const UseVector &MaybeLiveUses) {
514 case Live: MarkLive(RA); break;
517 // Note any uses of this value, so this return value can be
518 // marked live whenever one of the uses becomes live.
519 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
520 UE = MaybeLiveUses.end(); UI != UE; ++UI)
521 Uses.insert(std::make_pair(*UI, RA));
527 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
528 /// changed in any way. Additionally,
529 /// mark any values that are used as this function's parameters or by its return
530 /// values (according to Uses) live as well.
531 void DAE::MarkLive(const Function &F) {
532 DOUT << "DAE - Intrinsically live fn: " << F.getName() << "\n";
533 // Mark all arguments as live.
534 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
535 MarkLive(CreateArg(&F, i));
536 // Mark all return values as live.
537 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
538 MarkLive(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 (!LiveValues.insert(RA).second)
546 return; // We were already marked Live.
548 DOUT << "DAE - Marking " << RA.getDescription() << " live\n";
549 PropagateLiveness(RA);
552 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
553 /// to any other values it uses (according to Uses).
554 void DAE::PropagateLiveness(const RetOrArg &RA) {
555 // We don't use upper_bound (or equal_range) here, because our recursive call
556 // to ourselves is likely to cause the upper_bound (which is the first value
557 // not belonging to RA) to become erased and the iterator invalidated.
558 UseMap::iterator Begin = Uses.lower_bound(RA);
559 UseMap::iterator E = Uses.end();
561 for (I = Begin; I != E && I->first == RA; ++I)
564 // Erase RA from the Uses map (from the lower bound to wherever we ended up
566 Uses.erase(Begin, I);
569 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
570 // that are not in LiveValues. Transform the function and all of the callees of
571 // the function to not have these arguments and return values.
573 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
574 // Quick exit path for external functions
575 if (!F->hasInternalLinkage() && (!ShouldHackArguments() || F->isIntrinsic()))
578 // Start by computing a new prototype for the function, which is the same as
579 // the old function, but has fewer arguments and a different return type.
580 const FunctionType *FTy = F->getFunctionType();
581 std::vector<const Type*> Params;
583 // Set up to build a new list of parameter attributes.
584 SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
585 const PAListPtr &PAL = F->getParamAttrs();
587 // The existing function return attributes.
588 ParameterAttributes RAttrs = PAL.getParamAttrs(0);
591 // Find out the new return value.
593 const Type *RetTy = FTy->getReturnType();
594 const Type *NRetTy = NULL;
595 unsigned RetCount = NumRetVals(F);
596 // Explicitly track if anything changed, for debugging.
597 bool Changed = false;
598 // -1 means unused, other numbers are the new index
599 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
600 std::vector<const Type*> RetTypes;
601 if (RetTy == Type::VoidTy) {
602 NRetTy = Type::VoidTy;
604 const StructType *STy = dyn_cast<StructType>(RetTy);
606 // Look at each of the original return values individually.
607 for (unsigned i = 0; i != RetCount; ++i) {
608 RetOrArg Ret = CreateRet(F, i);
609 if (LiveValues.erase(Ret)) {
610 RetTypes.push_back(STy->getElementType(i));
611 NewRetIdxs[i] = RetTypes.size() - 1;
613 ++NumRetValsEliminated;
614 DOUT << "DAE - Removing return value " << i << " from "
615 << 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;
630 if (RetTypes.size() > 1 || (STy && STy->getNumElements()==RetTypes.size()))
631 // More than one return type? Return a struct with them. Also, if we used
632 // to return a struct and didn't change the number of return values,
633 // return a struct again. This prevents changing {something} into
634 // something and {} into void.
635 // Make the new struct packed if we used to return a packed struct
637 NRetTy = StructType::get(RetTypes, STy->isPacked());
638 else if (RetTypes.size() == 1)
639 // One return type? Just a simple value then, but only if we didn't use to
640 // return a struct with that simple value before.
641 NRetTy = RetTypes.front();
642 else if (RetTypes.size() == 0)
643 // No return types? Make it void, but only if we didn't use to return {}.
644 NRetTy = Type::VoidTy;
647 assert(NRetTy && "No new return type found?");
649 // Remove any incompatible attributes, but only if we removed all return
650 // values. Otherwise, ensure that we don't have any conflicting attributes
651 // here. Currently, this should not be possible, but special handling might be
652 // required when new return value attributes are added.
653 if (NRetTy == Type::VoidTy)
654 RAttrs &= ~ParamAttr::typeIncompatible(NRetTy);
656 assert((RAttrs & ParamAttr::typeIncompatible(NRetTy)) == 0
657 && "Return attributes no longer compatible?");
660 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
662 // Remember which arguments are still alive.
663 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
664 // Construct the new parameter list from non-dead arguments. Also construct
665 // a new set of parameter attributes to correspond. Skip the first parameter
666 // attribute, since that belongs to the return value.
668 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
670 RetOrArg Arg = CreateArg(F, i);
671 if (LiveValues.erase(Arg)) {
672 Params.push_back(I->getType());
675 // Get the original parameter attributes (skipping the first one, that is
676 // for the return value.
677 if (ParameterAttributes Attrs = PAL.getParamAttrs(i + 1))
678 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), Attrs));
680 ++NumArgumentsEliminated;
681 DOUT << "DAE - Removing argument " << i << " (" << I->getNameStart()
682 << ") from " << F->getNameStart() << "\n";
687 // Reconstruct the ParamAttrsList based on the vector we constructed.
688 PAListPtr NewPAL = PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end());
690 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
691 // have zero fixed arguments.
693 // Note that we apply this hack for a vararg fuction that does not have any
694 // arguments anymore, but did have them before (so don't bother fixing
695 // functions that were already broken wrt CWriter).
696 bool ExtraArgHack = false;
697 if (Params.empty() && FTy->isVarArg() && FTy->getNumParams() != 0) {
699 Params.push_back(Type::Int32Ty);
702 // Create the new function type based on the recomputed parameters.
703 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
709 // The function type is only allowed to be different if we actually left out
710 // an argument or return value.
711 assert(Changed && "Function type changed while no arguments or return values"
714 // Create the new function body and insert it into the module...
715 Function *NF = Function::Create(NFTy, F->getLinkage());
716 NF->copyAttributesFrom(F);
717 NF->setParamAttrs(NewPAL);
718 // Insert the new function before the old function, so we won't be processing
720 F->getParent()->getFunctionList().insert(F, NF);
723 // Loop over all of the callers of the function, transforming the call sites
724 // to pass in a smaller number of arguments into the new function.
726 std::vector<Value*> Args;
727 while (!F->use_empty()) {
728 CallSite CS = CallSite::get(F->use_back());
729 Instruction *Call = CS.getInstruction();
731 ParamAttrsVec.clear();
732 const PAListPtr &CallPAL = CS.getParamAttrs();
734 // The call return attributes.
735 ParameterAttributes RAttrs = CallPAL.getParamAttrs(0);
736 // Adjust in case the function was changed to return void.
737 RAttrs &= ~ParamAttr::typeIncompatible(NF->getReturnType());
739 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, RAttrs));
741 // Declare these outside of the loops, so we can reuse them for the second
742 // loop, which loops the varargs.
743 CallSite::arg_iterator I = CS.arg_begin();
745 // Loop over those operands, corresponding to the normal arguments to the
746 // original function, and add those that are still alive.
747 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
750 // Get original parameter attributes, but skip return attributes.
751 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1))
752 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
756 Args.push_back(UndefValue::get(Type::Int32Ty));
758 // Push any varargs arguments on the list. Don't forget their attributes.
759 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
761 if (ParameterAttributes Attrs = CallPAL.getParamAttrs(i + 1))
762 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Args.size(), Attrs));
765 // Reconstruct the ParamAttrsList based on the vector we constructed.
766 PAListPtr NewCallPAL = PAListPtr::get(ParamAttrsVec.begin(),
767 ParamAttrsVec.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)->setParamAttrs(NewCallPAL);
776 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
777 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
778 cast<CallInst>(New)->setParamAttrs(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) && "Return type changed, but not into a"
795 "void. The old return type must have"
797 // The original return value was a struct, update all uses (which are
798 // all extractvalue instructions).
799 for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
801 assert(isa<ExtractValueInst>(*I) && "Return value not only used by"
803 ExtractValueInst *EV = cast<ExtractValueInst>(*I);
804 // Increment now, since we're about to throw away this use.
806 assert(EV->hasIndices() && "Return value used by extractvalue without"
808 unsigned Idx = *EV->idx_begin();
809 if (NewRetIdxs[Idx] != -1) {
810 if (RetTypes.size() > 1) {
811 // We're still returning a struct, create a new extractvalue
812 // instruction with the first index updated
813 std::vector<unsigned> NewIdxs(EV->idx_begin(), EV->idx_end());
814 NewIdxs[0] = NewRetIdxs[Idx];
815 Value *NEV = ExtractValueInst::Create(New, NewIdxs.begin(),
816 NewIdxs.end(), "retval",
818 EV->replaceAllUsesWith(NEV);
819 EV->eraseFromParent();
821 // We are now only returning a simple value, remove the
823 EV->replaceAllUsesWith(New);
824 EV->eraseFromParent();
827 // Value unused, replace uses by null for now, they will get removed
829 EV->replaceAllUsesWith(Constant::getNullValue(EV->getType()));
830 EV->eraseFromParent();
837 // Finally, remove the old call from the program, reducing the use-count of
839 Call->eraseFromParent();
842 // Since we have now created the new function, splice the body of the old
843 // function right into the new function, leaving the old rotting hulk of the
845 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
847 // Loop over the argument list, transfering uses of the old arguments over to
848 // the new arguments, also transfering over the names as well.
850 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
851 I2 = NF->arg_begin(); I != E; ++I, ++i)
853 // If this is a live argument, move the name and users over to the new
855 I->replaceAllUsesWith(I2);
859 // If this argument is dead, replace any uses of it with null constants
860 // (these are guaranteed to become unused later on).
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() == Type::VoidTy) {
874 assert (isa<StructType>(RetTy));
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 = llvm::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(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 DOUT << "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 DOUT << "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);