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(AttributeSet::get(Fn.getContext(),
281 PAL.getFnAttributes()));
282 PAL = AttributeSet::get(Fn.getContext(), AttributesVec);
286 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
287 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
289 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
290 cast<InvokeInst>(New)->setAttributes(PAL);
292 New = CallInst::Create(NF, Args, "", Call);
293 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
294 cast<CallInst>(New)->setAttributes(PAL);
295 if (cast<CallInst>(Call)->isTailCall())
296 cast<CallInst>(New)->setTailCall();
298 New->setDebugLoc(Call->getDebugLoc());
302 if (!Call->use_empty())
303 Call->replaceAllUsesWith(New);
307 // Finally, remove the old call from the program, reducing the use-count of
309 Call->eraseFromParent();
312 // Since we have now created the new function, splice the body of the old
313 // function right into the new function, leaving the old rotting hulk of the
315 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
317 // Loop over the argument list, transferring uses of the old arguments over to
318 // the new arguments, also transferring over the names as well. While we're at
319 // it, remove the dead arguments from the DeadArguments list.
321 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
322 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
323 // Move the name and users over to the new version.
324 I->replaceAllUsesWith(I2);
328 // Patch the pointer to LLVM function in debug info descriptor.
329 FunctionDIMap::iterator DI = FunctionDIs.find(&Fn);
330 if (DI != FunctionDIs.end())
331 DI->second.replaceFunction(NF);
333 // Finally, nuke the old function.
334 Fn.eraseFromParent();
338 /// RemoveDeadArgumentsFromCallers - Checks if the given function has any
339 /// arguments that are unused, and changes the caller parameters to be undefined
341 bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
343 if (Fn.isDeclaration() || Fn.mayBeOverridden())
346 // Functions with local linkage should already have been handled.
347 if (Fn.hasLocalLinkage())
353 SmallVector<unsigned, 8> UnusedArgs;
354 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
358 if (Arg->use_empty() && !Arg->hasByValAttr())
359 UnusedArgs.push_back(Arg->getArgNo());
362 if (UnusedArgs.empty())
365 bool Changed = false;
367 for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end();
370 if (!CS || !CS.isCallee(I))
373 // Now go through all unused args and replace them with "undef".
374 for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
375 unsigned ArgNo = UnusedArgs[I];
377 Value *Arg = CS.getArgument(ArgNo);
378 CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
379 ++NumArgumentsReplacedWithUndef;
387 /// Convenience function that returns the number of return values. It returns 0
388 /// for void functions and 1 for functions not returning a struct. It returns
389 /// the number of struct elements for functions returning a struct.
390 static unsigned NumRetVals(const Function *F) {
391 if (F->getReturnType()->isVoidTy())
393 else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
394 return STy->getNumElements();
399 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
400 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
402 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
403 // We're live if our use or its Function is already marked as live.
404 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
407 // We're maybe live otherwise, but remember that we must become live if
409 MaybeLiveUses.push_back(Use);
414 /// SurveyUse - This looks at a single use of an argument or return value
415 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
416 /// if it causes the used value to become MaybeLive.
418 /// RetValNum is the return value number to use when this use is used in a
419 /// return instruction. This is used in the recursion, you should always leave
421 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
422 UseVector &MaybeLiveUses, unsigned RetValNum) {
424 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
425 // The value is returned from a function. It's only live when the
426 // function's return value is live. We use RetValNum here, for the case
427 // that U is really a use of an insertvalue instruction that uses the
429 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
430 // We might be live, depending on the liveness of Use.
431 return MarkIfNotLive(Use, MaybeLiveUses);
433 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
434 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
436 // The use we are examining is inserted into an aggregate. Our liveness
437 // depends on all uses of that aggregate, but if it is used as a return
438 // value, only index at which we were inserted counts.
439 RetValNum = *IV->idx_begin();
441 // Note that if we are used as the aggregate operand to the insertvalue,
442 // we don't change RetValNum, but do survey all our uses.
444 Liveness Result = MaybeLive;
445 for (Value::const_use_iterator I = IV->use_begin(),
446 E = V->use_end(); I != E; ++I) {
447 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
454 if (ImmutableCallSite CS = V) {
455 const Function *F = CS.getCalledFunction();
457 // Used in a direct call.
459 // Find the argument number. We know for sure that this use is an
460 // argument, since if it was the function argument this would be an
461 // indirect call and the we know can't be looking at a value of the
462 // label type (for the invoke instruction).
463 unsigned ArgNo = CS.getArgumentNo(U);
465 if (ArgNo >= F->getFunctionType()->getNumParams())
466 // The value is passed in through a vararg! Must be live.
469 assert(CS.getArgument(ArgNo)
470 == CS->getOperand(U.getOperandNo())
471 && "Argument is not where we expected it");
473 // Value passed to a normal call. It's only live when the corresponding
474 // argument to the called function turns out live.
475 RetOrArg Use = CreateArg(F, ArgNo);
476 return MarkIfNotLive(Use, MaybeLiveUses);
479 // Used in any other way? Value must be live.
483 /// SurveyUses - This looks at all the uses of the given value
484 /// Returns the Liveness deduced from the uses of this value.
486 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
487 /// the result is Live, MaybeLiveUses might be modified but its content should
488 /// be ignored (since it might not be complete).
489 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
490 // Assume it's dead (which will only hold if there are no uses at all..).
491 Liveness Result = MaybeLive;
493 for (Value::const_use_iterator I = V->use_begin(),
494 E = V->use_end(); I != E; ++I) {
495 Result = SurveyUse(I, MaybeLiveUses);
502 // SurveyFunction - This performs the initial survey of the specified function,
503 // checking out whether or not it uses any of its incoming arguments or whether
504 // any callers use the return value. This fills in the LiveValues set and Uses
507 // We consider arguments of non-internal functions to be intrinsically alive as
508 // well as arguments to functions which have their "address taken".
510 void DAE::SurveyFunction(const Function &F) {
511 unsigned RetCount = NumRetVals(&F);
512 // Assume all return values are dead
513 typedef SmallVector<Liveness, 5> RetVals;
514 RetVals RetValLiveness(RetCount, MaybeLive);
516 typedef SmallVector<UseVector, 5> RetUses;
517 // These vectors map each return value to the uses that make it MaybeLive, so
518 // we can add those to the Uses map if the return value really turns out to be
519 // MaybeLive. Initialized to a list of RetCount empty lists.
520 RetUses MaybeLiveRetUses(RetCount);
522 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
523 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
524 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
525 != F.getFunctionType()->getReturnType()) {
526 // We don't support old style multiple return values.
531 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
536 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
537 // Keep track of the number of live retvals, so we can skip checks once all
538 // of them turn out to be live.
539 unsigned NumLiveRetVals = 0;
540 Type *STy = dyn_cast<StructType>(F.getReturnType());
541 // Loop all uses of the function.
542 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
544 // If the function is PASSED IN as an argument, its address has been
546 ImmutableCallSite CS(*I);
547 if (!CS || !CS.isCallee(I)) {
552 // If this use is anything other than a call site, the function is alive.
553 const Instruction *TheCall = CS.getInstruction();
554 if (!TheCall) { // Not a direct call site?
559 // If we end up here, we are looking at a direct call to our function.
561 // Now, check how our return value(s) is/are used in this caller. Don't
562 // bother checking return values if all of them are live already.
563 if (NumLiveRetVals != RetCount) {
565 // Check all uses of the return value.
566 for (Value::const_use_iterator I = TheCall->use_begin(),
567 E = TheCall->use_end(); I != E; ++I) {
568 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
569 if (Ext && Ext->hasIndices()) {
570 // This use uses a part of our return value, survey the uses of
571 // that part and store the results for this index only.
572 unsigned Idx = *Ext->idx_begin();
573 if (RetValLiveness[Idx] != Live) {
574 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
575 if (RetValLiveness[Idx] == Live)
579 // Used by something else than extractvalue. Mark all return
581 for (unsigned i = 0; i != RetCount; ++i )
582 RetValLiveness[i] = Live;
583 NumLiveRetVals = RetCount;
588 // Single return value
589 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
590 if (RetValLiveness[0] == Live)
591 NumLiveRetVals = RetCount;
596 // Now we've inspected all callers, record the liveness of our return values.
597 for (unsigned i = 0; i != RetCount; ++i)
598 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
600 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
602 // Now, check all of our arguments.
604 UseVector MaybeLiveArgUses;
605 for (Function::const_arg_iterator AI = F.arg_begin(),
606 E = F.arg_end(); AI != E; ++AI, ++i) {
607 // See what the effect of this use is (recording any uses that cause
608 // MaybeLive in MaybeLiveArgUses).
609 Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
611 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
612 // Clear the vector again for the next iteration.
613 MaybeLiveArgUses.clear();
617 /// MarkValue - This function marks the liveness of RA depending on L. If L is
618 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
619 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
621 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
622 const UseVector &MaybeLiveUses) {
624 case Live: MarkLive(RA); break;
627 // Note any uses of this value, so this return value can be
628 // marked live whenever one of the uses becomes live.
629 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
630 UE = MaybeLiveUses.end(); UI != UE; ++UI)
631 Uses.insert(std::make_pair(*UI, RA));
637 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
638 /// changed in any way. Additionally,
639 /// mark any values that are used as this function's parameters or by its return
640 /// values (according to Uses) live as well.
641 void DAE::MarkLive(const Function &F) {
642 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
643 // Mark the function as live.
644 LiveFunctions.insert(&F);
645 // Mark all arguments as live.
646 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
647 PropagateLiveness(CreateArg(&F, i));
648 // Mark all return values as live.
649 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
650 PropagateLiveness(CreateRet(&F, i));
653 /// MarkLive - Mark the given return value or argument as live. Additionally,
654 /// mark any values that are used by this value (according to Uses) live as
656 void DAE::MarkLive(const RetOrArg &RA) {
657 if (LiveFunctions.count(RA.F))
658 return; // Function was already marked Live.
660 if (!LiveValues.insert(RA).second)
661 return; // We were already marked Live.
663 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
664 PropagateLiveness(RA);
667 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
668 /// to any other values it uses (according to Uses).
669 void DAE::PropagateLiveness(const RetOrArg &RA) {
670 // We don't use upper_bound (or equal_range) here, because our recursive call
671 // to ourselves is likely to cause the upper_bound (which is the first value
672 // not belonging to RA) to become erased and the iterator invalidated.
673 UseMap::iterator Begin = Uses.lower_bound(RA);
674 UseMap::iterator E = Uses.end();
676 for (I = Begin; I != E && I->first == RA; ++I)
679 // Erase RA from the Uses map (from the lower bound to wherever we ended up
681 Uses.erase(Begin, I);
684 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
685 // that are not in LiveValues. Transform the function and all of the callees of
686 // the function to not have these arguments and return values.
688 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
689 // Don't modify fully live functions
690 if (LiveFunctions.count(F))
693 // Start by computing a new prototype for the function, which is the same as
694 // the old function, but has fewer arguments and a different return type.
695 FunctionType *FTy = F->getFunctionType();
696 std::vector<Type*> Params;
698 // Set up to build a new list of parameter attributes.
699 SmallVector<AttributeSet, 8> AttributesVec;
700 const AttributeSet &PAL = F->getAttributes();
702 // Find out the new return value.
703 Type *RetTy = FTy->getReturnType();
705 unsigned RetCount = NumRetVals(F);
707 // -1 means unused, other numbers are the new index
708 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
709 std::vector<Type*> RetTypes;
710 if (RetTy->isVoidTy()) {
713 StructType *STy = dyn_cast<StructType>(RetTy);
715 // Look at each of the original return values individually.
716 for (unsigned i = 0; i != RetCount; ++i) {
717 RetOrArg Ret = CreateRet(F, i);
718 if (LiveValues.erase(Ret)) {
719 RetTypes.push_back(STy->getElementType(i));
720 NewRetIdxs[i] = RetTypes.size() - 1;
722 ++NumRetValsEliminated;
723 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
724 << F->getName() << "\n");
728 // We used to return a single value.
729 if (LiveValues.erase(CreateRet(F, 0))) {
730 RetTypes.push_back(RetTy);
733 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
735 ++NumRetValsEliminated;
737 if (RetTypes.size() > 1)
738 // More than one return type? Return a struct with them. Also, if we used
739 // to return a struct and didn't change the number of return values,
740 // return a struct again. This prevents changing {something} into
741 // something and {} into void.
742 // Make the new struct packed if we used to return a packed struct
744 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
745 else if (RetTypes.size() == 1)
746 // One return type? Just a simple value then, but only if we didn't use to
747 // return a struct with that simple value before.
748 NRetTy = RetTypes.front();
749 else if (RetTypes.size() == 0)
750 // No return types? Make it void, but only if we didn't use to return {}.
751 NRetTy = Type::getVoidTy(F->getContext());
754 assert(NRetTy && "No new return type found?");
756 // The existing function return attributes.
757 AttributeSet RAttrs = PAL.getRetAttributes();
759 // Remove any incompatible attributes, but only if we removed all return
760 // values. Otherwise, ensure that we don't have any conflicting attributes
761 // here. Currently, this should not be possible, but special handling might be
762 // required when new return value attributes are added.
763 if (NRetTy->isVoidTy())
765 AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex,
766 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
767 removeAttributes(AttributeFuncs::
768 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
769 AttributeSet::ReturnIndex));
771 assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
772 hasAttributes(AttributeFuncs::
773 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
774 AttributeSet::ReturnIndex) &&
775 "Return attributes no longer compatible?");
777 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
778 AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs));
780 // Remember which arguments are still alive.
781 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
782 // Construct the new parameter list from non-dead arguments. Also construct
783 // a new set of parameter attributes to correspond. Skip the first parameter
784 // attribute, since that belongs to the return value.
786 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
788 RetOrArg Arg = CreateArg(F, i);
789 if (LiveValues.erase(Arg)) {
790 Params.push_back(I->getType());
793 // Get the original parameter attributes (skipping the first one, that is
794 // for the return value.
795 if (PAL.hasAttributes(i + 1)) {
796 AttrBuilder B(PAL, i + 1);
798 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
801 ++NumArgumentsEliminated;
802 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
803 << ") from " << F->getName() << "\n");
807 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
808 AttributesVec.push_back(AttributeSet::get(F->getContext(),
809 PAL.getFnAttributes()));
811 // Reconstruct the AttributesList based on the vector we constructed.
812 AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec);
814 // Create the new function type based on the recomputed parameters.
815 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
821 // Create the new function body and insert it into the module...
822 Function *NF = Function::Create(NFTy, F->getLinkage());
823 NF->copyAttributesFrom(F);
824 NF->setAttributes(NewPAL);
825 // Insert the new function before the old function, so we won't be processing
827 F->getParent()->getFunctionList().insert(F, NF);
830 // Loop over all of the callers of the function, transforming the call sites
831 // to pass in a smaller number of arguments into the new function.
833 std::vector<Value*> Args;
834 while (!F->use_empty()) {
835 CallSite CS(F->use_back());
836 Instruction *Call = CS.getInstruction();
838 AttributesVec.clear();
839 const AttributeSet &CallPAL = CS.getAttributes();
841 // The call return attributes.
842 AttributeSet RAttrs = CallPAL.getRetAttributes();
844 // Adjust in case the function was changed to return void.
846 AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex,
847 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
848 removeAttributes(AttributeFuncs::
849 typeIncompatible(NF->getReturnType(),
850 AttributeSet::ReturnIndex),
851 AttributeSet::ReturnIndex));
852 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
853 AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs));
855 // Declare these outside of the loops, so we can reuse them for the second
856 // loop, which loops the varargs.
857 CallSite::arg_iterator I = CS.arg_begin();
859 // Loop over those operands, corresponding to the normal arguments to the
860 // original function, and add those that are still alive.
861 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
864 // Get original parameter attributes, but skip return attributes.
865 if (CallPAL.hasAttributes(i + 1)) {
866 AttrBuilder B(CallPAL, i + 1);
868 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
872 // Push any varargs arguments on the list. Don't forget their attributes.
873 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
875 if (CallPAL.hasAttributes(i + 1)) {
876 AttrBuilder B(CallPAL, i + 1);
878 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
882 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
883 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
884 CallPAL.getFnAttributes()));
886 // Reconstruct the AttributesList based on the vector we constructed.
887 AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec);
890 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
891 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
893 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
894 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
896 New = CallInst::Create(NF, Args, "", Call);
897 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
898 cast<CallInst>(New)->setAttributes(NewCallPAL);
899 if (cast<CallInst>(Call)->isTailCall())
900 cast<CallInst>(New)->setTailCall();
902 New->setDebugLoc(Call->getDebugLoc());
906 if (!Call->use_empty()) {
907 if (New->getType() == Call->getType()) {
908 // Return type not changed? Just replace users then.
909 Call->replaceAllUsesWith(New);
911 } else if (New->getType()->isVoidTy()) {
912 // Our return value has uses, but they will get removed later on.
913 // Replace by null for now.
914 if (!Call->getType()->isX86_MMXTy())
915 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
917 assert(RetTy->isStructTy() &&
918 "Return type changed, but not into a void. The old return type"
919 " must have been a struct!");
920 Instruction *InsertPt = Call;
921 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
922 BasicBlock::iterator IP = II->getNormalDest()->begin();
923 while (isa<PHINode>(IP)) ++IP;
927 // We used to return a struct. Instead of doing smart stuff with all the
928 // uses of this struct, we will just rebuild it using
929 // extract/insertvalue chaining and let instcombine clean that up.
931 // Start out building up our return value from undef
932 Value *RetVal = UndefValue::get(RetTy);
933 for (unsigned i = 0; i != RetCount; ++i)
934 if (NewRetIdxs[i] != -1) {
936 if (RetTypes.size() > 1)
937 // We are still returning a struct, so extract the value from our
939 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
942 // We are now returning a single element, so just insert that
944 // Insert the value at the old position
945 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
947 // Now, replace all uses of the old call instruction with the return
949 Call->replaceAllUsesWith(RetVal);
954 // Finally, remove the old call from the program, reducing the use-count of
956 Call->eraseFromParent();
959 // Since we have now created the new function, splice the body of the old
960 // function right into the new function, leaving the old rotting hulk of the
962 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
964 // Loop over the argument list, transferring uses of the old arguments over to
965 // the new arguments, also transferring over the names as well.
967 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
968 I2 = NF->arg_begin(); I != E; ++I, ++i)
970 // If this is a live argument, move the name and users over to the new
972 I->replaceAllUsesWith(I2);
976 // If this argument is dead, replace any uses of it with null constants
977 // (these are guaranteed to become unused later on).
978 if (!I->getType()->isX86_MMXTy())
979 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
982 // If we change the return value of the function we must rewrite any return
983 // instructions. Check this now.
984 if (F->getReturnType() != NF->getReturnType())
985 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
986 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
989 if (NFTy->getReturnType()->isVoidTy()) {
992 assert (RetTy->isStructTy());
993 // The original return value was a struct, insert
994 // extractvalue/insertvalue chains to extract only the values we need
995 // to return and insert them into our new result.
996 // This does generate messy code, but we'll let it to instcombine to
998 Value *OldRet = RI->getOperand(0);
999 // Start out building up our return value from undef
1000 RetVal = UndefValue::get(NRetTy);
1001 for (unsigned i = 0; i != RetCount; ++i)
1002 if (NewRetIdxs[i] != -1) {
1003 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
1005 if (RetTypes.size() > 1) {
1006 // We're still returning a struct, so reinsert the value into
1007 // our new return value at the new index
1009 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
1012 // We are now only returning a simple value, so just return the
1018 // Replace the return instruction with one returning the new return
1019 // value (possibly 0 if we became void).
1020 ReturnInst::Create(F->getContext(), RetVal, RI);
1021 BB->getInstList().erase(RI);
1024 // Patch the pointer to LLVM function in debug info descriptor.
1025 FunctionDIMap::iterator DI = FunctionDIs.find(F);
1026 if (DI != FunctionDIs.end())
1027 DI->second.replaceFunction(NF);
1029 // Now that the old function is dead, delete it.
1030 F->eraseFromParent();
1035 bool DAE::runOnModule(Module &M) {
1036 bool Changed = false;
1038 // Collect debug info descriptors for functions.
1039 CollectFunctionDIs(M);
1041 // First pass: Do a simple check to see if any functions can have their "..."
1042 // removed. We can do this if they never call va_start. This loop cannot be
1043 // fused with the next loop, because deleting a function invalidates
1044 // information computed while surveying other functions.
1045 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
1046 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1048 if (F.getFunctionType()->isVarArg())
1049 Changed |= DeleteDeadVarargs(F);
1052 // Second phase:loop through the module, determining which arguments are live.
1053 // We assume all arguments are dead unless proven otherwise (allowing us to
1054 // determine that dead arguments passed into recursive functions are dead).
1056 DEBUG(dbgs() << "DAE - Determining liveness\n");
1057 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
1060 // Now, remove all dead arguments and return values from each function in
1062 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1063 // Increment now, because the function will probably get removed (ie.
1064 // replaced by a new one).
1066 Changed |= RemoveDeadStuffFromFunction(F);
1069 // Finally, look for any unused parameters in functions with non-local
1070 // linkage and replace the passed in parameters with undef.
1071 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
1074 Changed |= RemoveDeadArgumentsFromCallers(F);