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/ADT/DenseMap.h"
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/ADT/StringExtras.h"
26 #include "llvm/DIBuilder.h"
27 #include "llvm/DebugInfo.h"
28 #include "llvm/IR/CallingConv.h"
29 #include "llvm/IR/Constant.h"
30 #include "llvm/IR/DerivedTypes.h"
31 #include "llvm/IR/Instructions.h"
32 #include "llvm/IR/IntrinsicInst.h"
33 #include "llvm/IR/LLVMContext.h"
34 #include "llvm/IR/Module.h"
35 #include "llvm/Pass.h"
36 #include "llvm/Support/CallSite.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/raw_ostream.h"
43 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
44 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
45 STATISTIC(NumArgumentsReplacedWithUndef,
46 "Number of unread args replaced with undef");
48 /// DAE - The dead argument elimination pass.
50 class DAE : public ModulePass {
53 /// Struct that represents (part of) either a return value or a function
54 /// argument. Used so that arguments and return values can be used
57 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
63 /// Make RetOrArg comparable, so we can put it into a map.
64 bool operator<(const RetOrArg &O) const {
67 else if (Idx != O.Idx)
70 return IsArg < O.IsArg;
73 /// Make RetOrArg comparable, so we can easily iterate the multimap.
74 bool operator==(const RetOrArg &O) const {
75 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
78 std::string getDescription() const {
79 return std::string((IsArg ? "Argument #" : "Return value #"))
80 + utostr(Idx) + " of function " + F->getName().str();
84 /// Liveness enum - During our initial pass over the program, we determine
85 /// that things are either alive or maybe alive. We don't mark anything
86 /// explicitly dead (even if we know they are), since anything not alive
87 /// with no registered uses (in Uses) will never be marked alive and will
88 /// thus become dead in the end.
89 enum Liveness { Live, MaybeLive };
91 /// Convenience wrapper
92 RetOrArg CreateRet(const Function *F, unsigned Idx) {
93 return RetOrArg(F, Idx, false);
95 /// Convenience wrapper
96 RetOrArg CreateArg(const Function *F, unsigned Idx) {
97 return RetOrArg(F, Idx, true);
100 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
101 /// This maps a return value or argument to any MaybeLive return values or
102 /// arguments it uses. This allows the MaybeLive values to be marked live
103 /// when any of its users is marked live.
104 /// For example (indices are left out for clarity):
105 /// - Uses[ret F] = ret G
106 /// This means that F calls G, and F returns the value returned by G.
107 /// - Uses[arg F] = ret G
108 /// This means that some function calls G and passes its result as an
110 /// - Uses[ret F] = arg F
111 /// This means that F returns one of its own arguments.
112 /// - Uses[arg F] = arg G
113 /// This means that G calls F and passes one of its own (G's) arguments
117 typedef std::set<RetOrArg> LiveSet;
118 typedef std::set<const Function*> LiveFuncSet;
120 /// This set contains all values that have been determined to be live.
122 /// This set contains all values that are cannot be changed in any way.
123 LiveFuncSet LiveFunctions;
125 typedef SmallVector<RetOrArg, 5> UseVector;
127 // Map each LLVM function to corresponding metadata with debug info. If
128 // the function is replaced with another one, we should patch the pointer
129 // to LLVM function in metadata.
130 // As the code generation for module is finished (and DIBuilder is
131 // finalized) we assume that subprogram descriptors won't be changed, and
132 // they are stored in map for short duration anyway.
133 typedef DenseMap<Function*, DISubprogram> FunctionDIMap;
134 FunctionDIMap FunctionDIs;
137 // DAH uses this to specify a different ID.
138 explicit DAE(char &ID) : ModulePass(ID) {}
141 static char ID; // Pass identification, replacement for typeid
142 DAE() : ModulePass(ID) {
143 initializeDAEPass(*PassRegistry::getPassRegistry());
146 bool runOnModule(Module &M);
148 virtual bool ShouldHackArguments() const { return false; }
151 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
152 Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
153 unsigned RetValNum = 0);
154 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
156 void CollectFunctionDIs(Module &M);
157 void SurveyFunction(const Function &F);
158 void MarkValue(const RetOrArg &RA, Liveness L,
159 const UseVector &MaybeLiveUses);
160 void MarkLive(const RetOrArg &RA);
161 void MarkLive(const Function &F);
162 void PropagateLiveness(const RetOrArg &RA);
163 bool RemoveDeadStuffFromFunction(Function *F);
164 bool DeleteDeadVarargs(Function &Fn);
165 bool RemoveDeadArgumentsFromCallers(Function &Fn);
171 INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
174 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
175 /// deletes arguments to functions which are external. This is only for use
177 struct DAH : public DAE {
181 virtual bool ShouldHackArguments() const { return true; }
186 INITIALIZE_PASS(DAH, "deadarghaX0r",
187 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
190 /// createDeadArgEliminationPass - This pass removes arguments from functions
191 /// which are not used by the body of the function.
193 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
194 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
196 /// CollectFunctionDIs - Map each function in the module to its debug info
198 void DAE::CollectFunctionDIs(Module &M) {
201 for (Module::named_metadata_iterator I = M.named_metadata_begin(),
202 E = M.named_metadata_end(); I != E; ++I) {
203 NamedMDNode &NMD = *I;
204 for (unsigned MDIndex = 0, MDNum = NMD.getNumOperands();
205 MDIndex < MDNum; ++MDIndex) {
206 MDNode *Node = NMD.getOperand(MDIndex);
207 if (!DIDescriptor(Node).isCompileUnit())
209 DICompileUnit CU(Node);
210 const DIArray &SPs = CU.getSubprograms();
211 for (unsigned SPIndex = 0, SPNum = SPs.getNumElements();
212 SPIndex < SPNum; ++SPIndex) {
213 DISubprogram SP(SPs.getElement(SPIndex));
216 if (Function *F = SP.getFunction())
223 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
224 /// llvm.vastart is never called, the varargs list is dead for the function.
225 bool DAE::DeleteDeadVarargs(Function &Fn) {
226 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
227 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
229 // Ensure that the function is only directly called.
230 if (Fn.hasAddressTaken())
233 // Okay, we know we can transform this function if safe. Scan its body
234 // looking for calls to llvm.vastart.
235 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
236 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
237 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
238 if (II->getIntrinsicID() == Intrinsic::vastart)
244 // If we get here, there are no calls to llvm.vastart in the function body,
245 // remove the "..." and adjust all the calls.
247 // Start by computing a new prototype for the function, which is the same as
248 // the old function, but doesn't have isVarArg set.
249 FunctionType *FTy = Fn.getFunctionType();
251 std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
252 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
254 unsigned NumArgs = Params.size();
256 // Create the new function body and insert it into the module...
257 Function *NF = Function::Create(NFTy, Fn.getLinkage());
258 NF->copyAttributesFrom(&Fn);
259 Fn.getParent()->getFunctionList().insert(&Fn, NF);
262 // Loop over all of the callers of the function, transforming the call sites
263 // to pass in a smaller number of arguments into the new function.
265 std::vector<Value*> Args;
266 while (!Fn.use_empty()) {
267 CallSite CS(Fn.use_back());
268 Instruction *Call = CS.getInstruction();
270 // Pass all the same arguments.
271 Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
273 // Drop any attributes that were on the vararg arguments.
274 AttributeSet PAL = CS.getAttributes();
275 if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) {
276 SmallVector<AttributeSet, 8> AttributesVec;
277 for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i)
278 AttributesVec.push_back(PAL.getSlotAttributes(i));
279 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
280 AttributesVec.push_back(
281 AttributeSet::get(Fn.getContext(),
282 AttributeWithIndex::get(Fn.getContext(),
283 AttributeSet::FunctionIndex,
284 PAL.getFnAttributes())));
285 PAL = AttributeSet::get(Fn.getContext(), AttributesVec);
289 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
290 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
292 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
293 cast<InvokeInst>(New)->setAttributes(PAL);
295 New = CallInst::Create(NF, Args, "", Call);
296 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
297 cast<CallInst>(New)->setAttributes(PAL);
298 if (cast<CallInst>(Call)->isTailCall())
299 cast<CallInst>(New)->setTailCall();
301 New->setDebugLoc(Call->getDebugLoc());
305 if (!Call->use_empty())
306 Call->replaceAllUsesWith(New);
310 // Finally, remove the old call from the program, reducing the use-count of
312 Call->eraseFromParent();
315 // Since we have now created the new function, splice the body of the old
316 // function right into the new function, leaving the old rotting hulk of the
318 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
320 // Loop over the argument list, transferring uses of the old arguments over to
321 // the new arguments, also transferring over the names as well. While we're at
322 // it, remove the dead arguments from the DeadArguments list.
324 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
325 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
326 // Move the name and users over to the new version.
327 I->replaceAllUsesWith(I2);
331 // Patch the pointer to LLVM function in debug info descriptor.
332 FunctionDIMap::iterator DI = FunctionDIs.find(&Fn);
333 if (DI != FunctionDIs.end())
334 DI->second.replaceFunction(NF);
336 // Finally, nuke the old function.
337 Fn.eraseFromParent();
341 /// RemoveDeadArgumentsFromCallers - Checks if the given function has any
342 /// arguments that are unused, and changes the caller parameters to be undefined
344 bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
346 if (Fn.isDeclaration() || Fn.mayBeOverridden())
349 // Functions with local linkage should already have been handled.
350 if (Fn.hasLocalLinkage())
356 SmallVector<unsigned, 8> UnusedArgs;
357 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
361 if (Arg->use_empty() && !Arg->hasByValAttr())
362 UnusedArgs.push_back(Arg->getArgNo());
365 if (UnusedArgs.empty())
368 bool Changed = false;
370 for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end();
373 if (!CS || !CS.isCallee(I))
376 // Now go through all unused args and replace them with "undef".
377 for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
378 unsigned ArgNo = UnusedArgs[I];
380 Value *Arg = CS.getArgument(ArgNo);
381 CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
382 ++NumArgumentsReplacedWithUndef;
390 /// Convenience function that returns the number of return values. It returns 0
391 /// for void functions and 1 for functions not returning a struct. It returns
392 /// the number of struct elements for functions returning a struct.
393 static unsigned NumRetVals(const Function *F) {
394 if (F->getReturnType()->isVoidTy())
396 else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
397 return STy->getNumElements();
402 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
403 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
405 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
406 // We're live if our use or its Function is already marked as live.
407 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
410 // We're maybe live otherwise, but remember that we must become live if
412 MaybeLiveUses.push_back(Use);
417 /// SurveyUse - This looks at a single use of an argument or return value
418 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
419 /// if it causes the used value to become MaybeLive.
421 /// RetValNum is the return value number to use when this use is used in a
422 /// return instruction. This is used in the recursion, you should always leave
424 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
425 UseVector &MaybeLiveUses, unsigned RetValNum) {
427 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
428 // The value is returned from a function. It's only live when the
429 // function's return value is live. We use RetValNum here, for the case
430 // that U is really a use of an insertvalue instruction that uses the
432 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
433 // We might be live, depending on the liveness of Use.
434 return MarkIfNotLive(Use, MaybeLiveUses);
436 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
437 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
439 // The use we are examining is inserted into an aggregate. Our liveness
440 // depends on all uses of that aggregate, but if it is used as a return
441 // value, only index at which we were inserted counts.
442 RetValNum = *IV->idx_begin();
444 // Note that if we are used as the aggregate operand to the insertvalue,
445 // we don't change RetValNum, but do survey all our uses.
447 Liveness Result = MaybeLive;
448 for (Value::const_use_iterator I = IV->use_begin(),
449 E = V->use_end(); I != E; ++I) {
450 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
457 if (ImmutableCallSite CS = V) {
458 const Function *F = CS.getCalledFunction();
460 // Used in a direct call.
462 // Find the argument number. We know for sure that this use is an
463 // argument, since if it was the function argument this would be an
464 // indirect call and the we know can't be looking at a value of the
465 // label type (for the invoke instruction).
466 unsigned ArgNo = CS.getArgumentNo(U);
468 if (ArgNo >= F->getFunctionType()->getNumParams())
469 // The value is passed in through a vararg! Must be live.
472 assert(CS.getArgument(ArgNo)
473 == CS->getOperand(U.getOperandNo())
474 && "Argument is not where we expected it");
476 // Value passed to a normal call. It's only live when the corresponding
477 // argument to the called function turns out live.
478 RetOrArg Use = CreateArg(F, ArgNo);
479 return MarkIfNotLive(Use, MaybeLiveUses);
482 // Used in any other way? Value must be live.
486 /// SurveyUses - This looks at all the uses of the given value
487 /// Returns the Liveness deduced from the uses of this value.
489 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
490 /// the result is Live, MaybeLiveUses might be modified but its content should
491 /// be ignored (since it might not be complete).
492 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
493 // Assume it's dead (which will only hold if there are no uses at all..).
494 Liveness Result = MaybeLive;
496 for (Value::const_use_iterator I = V->use_begin(),
497 E = V->use_end(); I != E; ++I) {
498 Result = SurveyUse(I, MaybeLiveUses);
505 // SurveyFunction - This performs the initial survey of the specified function,
506 // checking out whether or not it uses any of its incoming arguments or whether
507 // any callers use the return value. This fills in the LiveValues set and Uses
510 // We consider arguments of non-internal functions to be intrinsically alive as
511 // well as arguments to functions which have their "address taken".
513 void DAE::SurveyFunction(const Function &F) {
514 unsigned RetCount = NumRetVals(&F);
515 // Assume all return values are dead
516 typedef SmallVector<Liveness, 5> RetVals;
517 RetVals RetValLiveness(RetCount, MaybeLive);
519 typedef SmallVector<UseVector, 5> RetUses;
520 // These vectors map each return value to the uses that make it MaybeLive, so
521 // we can add those to the Uses map if the return value really turns out to be
522 // MaybeLive. Initialized to a list of RetCount empty lists.
523 RetUses MaybeLiveRetUses(RetCount);
525 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
526 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
527 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
528 != F.getFunctionType()->getReturnType()) {
529 // We don't support old style multiple return values.
534 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
539 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
540 // Keep track of the number of live retvals, so we can skip checks once all
541 // of them turn out to be live.
542 unsigned NumLiveRetVals = 0;
543 Type *STy = dyn_cast<StructType>(F.getReturnType());
544 // Loop all uses of the function.
545 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
547 // If the function is PASSED IN as an argument, its address has been
549 ImmutableCallSite CS(*I);
550 if (!CS || !CS.isCallee(I)) {
555 // If this use is anything other than a call site, the function is alive.
556 const Instruction *TheCall = CS.getInstruction();
557 if (!TheCall) { // Not a direct call site?
562 // If we end up here, we are looking at a direct call to our function.
564 // Now, check how our return value(s) is/are used in this caller. Don't
565 // bother checking return values if all of them are live already.
566 if (NumLiveRetVals != RetCount) {
568 // Check all uses of the return value.
569 for (Value::const_use_iterator I = TheCall->use_begin(),
570 E = TheCall->use_end(); I != E; ++I) {
571 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
572 if (Ext && Ext->hasIndices()) {
573 // This use uses a part of our return value, survey the uses of
574 // that part and store the results for this index only.
575 unsigned Idx = *Ext->idx_begin();
576 if (RetValLiveness[Idx] != Live) {
577 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
578 if (RetValLiveness[Idx] == Live)
582 // Used by something else than extractvalue. Mark all return
584 for (unsigned i = 0; i != RetCount; ++i )
585 RetValLiveness[i] = Live;
586 NumLiveRetVals = RetCount;
591 // Single return value
592 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
593 if (RetValLiveness[0] == Live)
594 NumLiveRetVals = RetCount;
599 // Now we've inspected all callers, record the liveness of our return values.
600 for (unsigned i = 0; i != RetCount; ++i)
601 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
603 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
605 // Now, check all of our arguments.
607 UseVector MaybeLiveArgUses;
608 for (Function::const_arg_iterator AI = F.arg_begin(),
609 E = F.arg_end(); AI != E; ++AI, ++i) {
610 // See what the effect of this use is (recording any uses that cause
611 // MaybeLive in MaybeLiveArgUses).
612 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
614 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
615 // Clear the vector again for the next iteration.
616 MaybeLiveArgUses.clear();
620 /// MarkValue - This function marks the liveness of RA depending on L. If L is
621 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
622 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
624 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
625 const UseVector &MaybeLiveUses) {
627 case Live: MarkLive(RA); break;
630 // Note any uses of this value, so this return value can be
631 // marked live whenever one of the uses becomes live.
632 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
633 UE = MaybeLiveUses.end(); UI != UE; ++UI)
634 Uses.insert(std::make_pair(*UI, RA));
640 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
641 /// changed in any way. Additionally,
642 /// mark any values that are used as this function's parameters or by its return
643 /// values (according to Uses) live as well.
644 void DAE::MarkLive(const Function &F) {
645 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
646 // Mark the function as live.
647 LiveFunctions.insert(&F);
648 // Mark all arguments as live.
649 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
650 PropagateLiveness(CreateArg(&F, i));
651 // Mark all return values as live.
652 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
653 PropagateLiveness(CreateRet(&F, i));
656 /// MarkLive - Mark the given return value or argument as live. Additionally,
657 /// mark any values that are used by this value (according to Uses) live as
659 void DAE::MarkLive(const RetOrArg &RA) {
660 if (LiveFunctions.count(RA.F))
661 return; // Function was already marked Live.
663 if (!LiveValues.insert(RA).second)
664 return; // We were already marked Live.
666 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
667 PropagateLiveness(RA);
670 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
671 /// to any other values it uses (according to Uses).
672 void DAE::PropagateLiveness(const RetOrArg &RA) {
673 // We don't use upper_bound (or equal_range) here, because our recursive call
674 // to ourselves is likely to cause the upper_bound (which is the first value
675 // not belonging to RA) to become erased and the iterator invalidated.
676 UseMap::iterator Begin = Uses.lower_bound(RA);
677 UseMap::iterator E = Uses.end();
679 for (I = Begin; I != E && I->first == RA; ++I)
682 // Erase RA from the Uses map (from the lower bound to wherever we ended up
684 Uses.erase(Begin, I);
687 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
688 // that are not in LiveValues. Transform the function and all of the callees of
689 // the function to not have these arguments and return values.
691 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
692 // Don't modify fully live functions
693 if (LiveFunctions.count(F))
696 // Start by computing a new prototype for the function, which is the same as
697 // the old function, but has fewer arguments and a different return type.
698 FunctionType *FTy = F->getFunctionType();
699 std::vector<Type*> Params;
701 // Set up to build a new list of parameter attributes.
702 SmallVector<AttributeWithIndex, 8> AttributesVec;
703 const AttributeSet &PAL = F->getAttributes();
705 // Find out the new return value.
706 Type *RetTy = FTy->getReturnType();
708 unsigned RetCount = NumRetVals(F);
710 // -1 means unused, other numbers are the new index
711 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
712 std::vector<Type*> RetTypes;
713 if (RetTy->isVoidTy()) {
716 StructType *STy = dyn_cast<StructType>(RetTy);
718 // Look at each of the original return values individually.
719 for (unsigned i = 0; i != RetCount; ++i) {
720 RetOrArg Ret = CreateRet(F, i);
721 if (LiveValues.erase(Ret)) {
722 RetTypes.push_back(STy->getElementType(i));
723 NewRetIdxs[i] = RetTypes.size() - 1;
725 ++NumRetValsEliminated;
726 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
727 << F->getName() << "\n");
731 // We used to return a single value.
732 if (LiveValues.erase(CreateRet(F, 0))) {
733 RetTypes.push_back(RetTy);
736 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
738 ++NumRetValsEliminated;
740 if (RetTypes.size() > 1)
741 // More than one return type? Return a struct with them. Also, if we used
742 // to return a struct and didn't change the number of return values,
743 // return a struct again. This prevents changing {something} into
744 // something and {} into void.
745 // Make the new struct packed if we used to return a packed struct
747 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
748 else if (RetTypes.size() == 1)
749 // One return type? Just a simple value then, but only if we didn't use to
750 // return a struct with that simple value before.
751 NRetTy = RetTypes.front();
752 else if (RetTypes.size() == 0)
753 // No return types? Make it void, but only if we didn't use to return {}.
754 NRetTy = Type::getVoidTy(F->getContext());
757 assert(NRetTy && "No new return type found?");
759 // The existing function return attributes.
760 AttributeSet RAttrs = PAL.getRetAttributes();
762 // Remove any incompatible attributes, but only if we removed all return
763 // values. Otherwise, ensure that we don't have any conflicting attributes
764 // here. Currently, this should not be possible, but special handling might be
765 // required when new return value attributes are added.
766 if (NRetTy->isVoidTy())
768 AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex,
769 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
770 removeAttributes(AttributeFuncs::typeIncompatible(NRetTy)));
772 assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
773 hasAttributes(AttributeFuncs::typeIncompatible(NRetTy)) &&
774 "Return attributes no longer compatible?");
776 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
777 AttributesVec.push_back(AttributeWithIndex::get(NRetTy->getContext(),
778 AttributeSet::ReturnIndex,
781 // Remember which arguments are still alive.
782 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
783 // Construct the new parameter list from non-dead arguments. Also construct
784 // a new set of parameter attributes to correspond. Skip the first parameter
785 // attribute, since that belongs to the return value.
787 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
789 RetOrArg Arg = CreateArg(F, i);
790 if (LiveValues.erase(Arg)) {
791 Params.push_back(I->getType());
794 // Get the original parameter attributes (skipping the first one, that is
795 // for the return value.
796 if (PAL.hasAttributes(i + 1)) {
798 push_back(AttributeWithIndex::get(F->getContext(), i + 1,
799 PAL.getParamAttributes(i + 1)));
800 AttributesVec.back().Index = Params.size();
803 ++NumArgumentsEliminated;
804 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
805 << ") from " << F->getName() << "\n");
809 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
810 AttributesVec.push_back(AttributeWithIndex::get(F->getContext(),
811 AttributeSet::FunctionIndex,
812 PAL.getFnAttributes()));
814 // Reconstruct the AttributesList based on the vector we constructed.
815 AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec);
817 // Create the new function type based on the recomputed parameters.
818 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
824 // Create the new function body and insert it into the module...
825 Function *NF = Function::Create(NFTy, F->getLinkage());
826 NF->copyAttributesFrom(F);
827 NF->setAttributes(NewPAL);
828 // Insert the new function before the old function, so we won't be processing
830 F->getParent()->getFunctionList().insert(F, NF);
833 // Loop over all of the callers of the function, transforming the call sites
834 // to pass in a smaller number of arguments into the new function.
836 std::vector<Value*> Args;
837 while (!F->use_empty()) {
838 CallSite CS(F->use_back());
839 Instruction *Call = CS.getInstruction();
841 AttributesVec.clear();
842 const AttributeSet &CallPAL = CS.getAttributes();
844 // The call return attributes.
845 AttributeSet RAttrs = CallPAL.getRetAttributes();
847 // Adjust in case the function was changed to return void.
849 AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex,
850 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
851 removeAttributes(AttributeFuncs::typeIncompatible(NF->getReturnType())));
852 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
853 AttributesVec.push_back(AttributeWithIndex::get(NF->getContext(),
854 AttributeSet::ReturnIndex,
857 // Declare these outside of the loops, so we can reuse them for the second
858 // loop, which loops the varargs.
859 CallSite::arg_iterator I = CS.arg_begin();
861 // Loop over those operands, corresponding to the normal arguments to the
862 // original function, and add those that are still alive.
863 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
866 // Get original parameter attributes, but skip return attributes.
867 if (CallPAL.hasAttributes(i + 1)) {
869 push_back(AttributeWithIndex::get(F->getContext(), i + 1,
870 CallPAL.getParamAttributes(i + 1)));
871 AttributesVec.back().Index = Args.size();
875 // Push any varargs arguments on the list. Don't forget their attributes.
876 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
878 if (CallPAL.hasAttributes(i + 1)) {
880 push_back(AttributeWithIndex::get(F->getContext(), i + 1,
881 CallPAL.getParamAttributes(i + 1)));
882 AttributesVec.back().Index = Args.size();
886 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
887 AttributesVec.push_back(AttributeWithIndex::get(Call->getContext(),
888 AttributeSet::FunctionIndex,
889 CallPAL.getFnAttributes()));
891 // Reconstruct the AttributesList based on the vector we constructed.
892 AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec);
895 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
896 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
898 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
899 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
901 New = CallInst::Create(NF, Args, "", Call);
902 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
903 cast<CallInst>(New)->setAttributes(NewCallPAL);
904 if (cast<CallInst>(Call)->isTailCall())
905 cast<CallInst>(New)->setTailCall();
907 New->setDebugLoc(Call->getDebugLoc());
911 if (!Call->use_empty()) {
912 if (New->getType() == Call->getType()) {
913 // Return type not changed? Just replace users then.
914 Call->replaceAllUsesWith(New);
916 } else if (New->getType()->isVoidTy()) {
917 // Our return value has uses, but they will get removed later on.
918 // Replace by null for now.
919 if (!Call->getType()->isX86_MMXTy())
920 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
922 assert(RetTy->isStructTy() &&
923 "Return type changed, but not into a void. The old return type"
924 " must have been a struct!");
925 Instruction *InsertPt = Call;
926 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
927 BasicBlock::iterator IP = II->getNormalDest()->begin();
928 while (isa<PHINode>(IP)) ++IP;
932 // We used to return a struct. Instead of doing smart stuff with all the
933 // uses of this struct, we will just rebuild it using
934 // extract/insertvalue chaining and let instcombine clean that up.
936 // Start out building up our return value from undef
937 Value *RetVal = UndefValue::get(RetTy);
938 for (unsigned i = 0; i != RetCount; ++i)
939 if (NewRetIdxs[i] != -1) {
941 if (RetTypes.size() > 1)
942 // We are still returning a struct, so extract the value from our
944 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
947 // We are now returning a single element, so just insert that
949 // Insert the value at the old position
950 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
952 // Now, replace all uses of the old call instruction with the return
954 Call->replaceAllUsesWith(RetVal);
959 // Finally, remove the old call from the program, reducing the use-count of
961 Call->eraseFromParent();
964 // Since we have now created the new function, splice the body of the old
965 // function right into the new function, leaving the old rotting hulk of the
967 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
969 // Loop over the argument list, transferring uses of the old arguments over to
970 // the new arguments, also transferring over the names as well.
972 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
973 I2 = NF->arg_begin(); I != E; ++I, ++i)
975 // If this is a live argument, move the name and users over to the new
977 I->replaceAllUsesWith(I2);
981 // If this argument is dead, replace any uses of it with null constants
982 // (these are guaranteed to become unused later on).
983 if (!I->getType()->isX86_MMXTy())
984 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
987 // If we change the return value of the function we must rewrite any return
988 // instructions. Check this now.
989 if (F->getReturnType() != NF->getReturnType())
990 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
991 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
994 if (NFTy->getReturnType()->isVoidTy()) {
997 assert (RetTy->isStructTy());
998 // The original return value was a struct, insert
999 // extractvalue/insertvalue chains to extract only the values we need
1000 // to return and insert them into our new result.
1001 // This does generate messy code, but we'll let it to instcombine to
1003 Value *OldRet = RI->getOperand(0);
1004 // Start out building up our return value from undef
1005 RetVal = UndefValue::get(NRetTy);
1006 for (unsigned i = 0; i != RetCount; ++i)
1007 if (NewRetIdxs[i] != -1) {
1008 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
1010 if (RetTypes.size() > 1) {
1011 // We're still returning a struct, so reinsert the value into
1012 // our new return value at the new index
1014 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
1017 // We are now only returning a simple value, so just return the
1023 // Replace the return instruction with one returning the new return
1024 // value (possibly 0 if we became void).
1025 ReturnInst::Create(F->getContext(), RetVal, RI);
1026 BB->getInstList().erase(RI);
1029 // Patch the pointer to LLVM function in debug info descriptor.
1030 FunctionDIMap::iterator DI = FunctionDIs.find(F);
1031 if (DI != FunctionDIs.end())
1032 DI->second.replaceFunction(NF);
1034 // Now that the old function is dead, delete it.
1035 F->eraseFromParent();
1040 bool DAE::runOnModule(Module &M) {
1041 bool Changed = false;
1043 // Collect debug info descriptors for functions.
1044 CollectFunctionDIs(M);
1046 // First pass: Do a simple check to see if any functions can have their "..."
1047 // removed. We can do this if they never call va_start. This loop cannot be
1048 // fused with the next loop, because deleting a function invalidates
1049 // information computed while surveying other functions.
1050 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
1051 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1053 if (F.getFunctionType()->isVarArg())
1054 Changed |= DeleteDeadVarargs(F);
1057 // Second phase:loop through the module, determining which arguments are live.
1058 // We assume all arguments are dead unless proven otherwise (allowing us to
1059 // determine that dead arguments passed into recursive functions are dead).
1061 DEBUG(dbgs() << "DAE - Determining liveness\n");
1062 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
1065 // Now, remove all dead arguments and return values from each function in
1067 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1068 // Increment now, because the function will probably get removed (ie.
1069 // replaced by a new one).
1071 Changed |= RemoveDeadStuffFromFunction(F);
1074 // Finally, look for any unused parameters in functions with non-local
1075 // linkage and replace the passed in parameters with undef.
1076 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
1079 Changed |= RemoveDeadArgumentsFromCallers(F);