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));
214 assert((!SP || SP.isSubprogram()) &&
215 "A MDNode in subprograms of a CU should be null or a DISubprogram.");
218 if (Function *F = SP.getFunction())
225 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
226 /// llvm.vastart is never called, the varargs list is dead for the function.
227 bool DAE::DeleteDeadVarargs(Function &Fn) {
228 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
229 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
231 // Ensure that the function is only directly called.
232 if (Fn.hasAddressTaken())
235 // Okay, we know we can transform this function if safe. Scan its body
236 // looking for calls to llvm.vastart.
237 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
238 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
239 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
240 if (II->getIntrinsicID() == Intrinsic::vastart)
246 // If we get here, there are no calls to llvm.vastart in the function body,
247 // remove the "..." and adjust all the calls.
249 // Start by computing a new prototype for the function, which is the same as
250 // the old function, but doesn't have isVarArg set.
251 FunctionType *FTy = Fn.getFunctionType();
253 std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
254 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
256 unsigned NumArgs = Params.size();
258 // Create the new function body and insert it into the module...
259 Function *NF = Function::Create(NFTy, Fn.getLinkage());
260 NF->copyAttributesFrom(&Fn);
261 Fn.getParent()->getFunctionList().insert(&Fn, NF);
264 // Loop over all of the callers of the function, transforming the call sites
265 // to pass in a smaller number of arguments into the new function.
267 std::vector<Value*> Args;
268 for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ) {
272 Instruction *Call = CS.getInstruction();
274 // Pass all the same arguments.
275 Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
277 // Drop any attributes that were on the vararg arguments.
278 AttributeSet PAL = CS.getAttributes();
279 if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) {
280 SmallVector<AttributeSet, 8> AttributesVec;
281 for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i)
282 AttributesVec.push_back(PAL.getSlotAttributes(i));
283 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
284 AttributesVec.push_back(AttributeSet::get(Fn.getContext(),
285 PAL.getFnAttributes()));
286 PAL = AttributeSet::get(Fn.getContext(), AttributesVec);
290 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
291 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
293 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
294 cast<InvokeInst>(New)->setAttributes(PAL);
296 New = CallInst::Create(NF, Args, "", Call);
297 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
298 cast<CallInst>(New)->setAttributes(PAL);
299 if (cast<CallInst>(Call)->isTailCall())
300 cast<CallInst>(New)->setTailCall();
302 New->setDebugLoc(Call->getDebugLoc());
306 if (!Call->use_empty())
307 Call->replaceAllUsesWith(New);
311 // Finally, remove the old call from the program, reducing the use-count of
313 Call->eraseFromParent();
316 // Since we have now created the new function, splice the body of the old
317 // function right into the new function, leaving the old rotting hulk of the
319 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
321 // Loop over the argument list, transferring uses of the old arguments over to
322 // the new arguments, also transferring over the names as well. While we're at
323 // it, remove the dead arguments from the DeadArguments list.
325 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
326 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
327 // Move the name and users over to the new version.
328 I->replaceAllUsesWith(I2);
332 // Patch the pointer to LLVM function in debug info descriptor.
333 FunctionDIMap::iterator DI = FunctionDIs.find(&Fn);
334 if (DI != FunctionDIs.end())
335 DI->second.replaceFunction(NF);
337 // Fix up any BlockAddresses that refer to the function.
338 Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType()));
339 // Delete the bitcast that we just created, so that NF does not
340 // appear to be address-taken.
341 NF->removeDeadConstantUsers();
342 // Finally, nuke the old function.
343 Fn.eraseFromParent();
347 /// RemoveDeadArgumentsFromCallers - Checks if the given function has any
348 /// arguments that are unused, and changes the caller parameters to be undefined
350 bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
352 if (Fn.isDeclaration() || Fn.mayBeOverridden())
355 // Functions with local linkage should already have been handled, except the
356 // fragile (variadic) ones which we can improve here.
357 if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
363 SmallVector<unsigned, 8> UnusedArgs;
364 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
368 if (Arg->use_empty() && !Arg->hasByValAttr())
369 UnusedArgs.push_back(Arg->getArgNo());
372 if (UnusedArgs.empty())
375 bool Changed = false;
377 for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end();
380 if (!CS || !CS.isCallee(I))
383 // Now go through all unused args and replace them with "undef".
384 for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
385 unsigned ArgNo = UnusedArgs[I];
387 Value *Arg = CS.getArgument(ArgNo);
388 CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
389 ++NumArgumentsReplacedWithUndef;
397 /// Convenience function that returns the number of return values. It returns 0
398 /// for void functions and 1 for functions not returning a struct. It returns
399 /// the number of struct elements for functions returning a struct.
400 static unsigned NumRetVals(const Function *F) {
401 if (F->getReturnType()->isVoidTy())
403 else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
404 return STy->getNumElements();
409 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
410 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
412 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
413 // We're live if our use or its Function is already marked as live.
414 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
417 // We're maybe live otherwise, but remember that we must become live if
419 MaybeLiveUses.push_back(Use);
424 /// SurveyUse - This looks at a single use of an argument or return value
425 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
426 /// if it causes the used value to become MaybeLive.
428 /// RetValNum is the return value number to use when this use is used in a
429 /// return instruction. This is used in the recursion, you should always leave
431 DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
432 UseVector &MaybeLiveUses, unsigned RetValNum) {
434 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
435 // The value is returned from a function. It's only live when the
436 // function's return value is live. We use RetValNum here, for the case
437 // that U is really a use of an insertvalue instruction that uses the
439 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
440 // We might be live, depending on the liveness of Use.
441 return MarkIfNotLive(Use, MaybeLiveUses);
443 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
444 if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
446 // The use we are examining is inserted into an aggregate. Our liveness
447 // depends on all uses of that aggregate, but if it is used as a return
448 // value, only index at which we were inserted counts.
449 RetValNum = *IV->idx_begin();
451 // Note that if we are used as the aggregate operand to the insertvalue,
452 // we don't change RetValNum, but do survey all our uses.
454 Liveness Result = MaybeLive;
455 for (Value::const_use_iterator I = IV->use_begin(),
456 E = V->use_end(); I != E; ++I) {
457 Result = SurveyUse(I, MaybeLiveUses, RetValNum);
464 if (ImmutableCallSite CS = V) {
465 const Function *F = CS.getCalledFunction();
467 // Used in a direct call.
469 // Find the argument number. We know for sure that this use is an
470 // argument, since if it was the function argument this would be an
471 // indirect call and the we know can't be looking at a value of the
472 // label type (for the invoke instruction).
473 unsigned ArgNo = CS.getArgumentNo(U);
475 if (ArgNo >= F->getFunctionType()->getNumParams())
476 // The value is passed in through a vararg! Must be live.
479 assert(CS.getArgument(ArgNo)
480 == CS->getOperand(U.getOperandNo())
481 && "Argument is not where we expected it");
483 // Value passed to a normal call. It's only live when the corresponding
484 // argument to the called function turns out live.
485 RetOrArg Use = CreateArg(F, ArgNo);
486 return MarkIfNotLive(Use, MaybeLiveUses);
489 // Used in any other way? Value must be live.
493 /// SurveyUses - This looks at all the uses of the given value
494 /// Returns the Liveness deduced from the uses of this value.
496 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
497 /// the result is Live, MaybeLiveUses might be modified but its content should
498 /// be ignored (since it might not be complete).
499 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
500 // Assume it's dead (which will only hold if there are no uses at all..).
501 Liveness Result = MaybeLive;
503 for (Value::const_use_iterator I = V->use_begin(),
504 E = V->use_end(); I != E; ++I) {
505 Result = SurveyUse(I, MaybeLiveUses);
512 // SurveyFunction - This performs the initial survey of the specified function,
513 // checking out whether or not it uses any of its incoming arguments or whether
514 // any callers use the return value. This fills in the LiveValues set and Uses
517 // We consider arguments of non-internal functions to be intrinsically alive as
518 // well as arguments to functions which have their "address taken".
520 void DAE::SurveyFunction(const Function &F) {
521 unsigned RetCount = NumRetVals(&F);
522 // Assume all return values are dead
523 typedef SmallVector<Liveness, 5> RetVals;
524 RetVals RetValLiveness(RetCount, MaybeLive);
526 typedef SmallVector<UseVector, 5> RetUses;
527 // These vectors map each return value to the uses that make it MaybeLive, so
528 // we can add those to the Uses map if the return value really turns out to be
529 // MaybeLive. Initialized to a list of RetCount empty lists.
530 RetUses MaybeLiveRetUses(RetCount);
532 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
533 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
534 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
535 != F.getFunctionType()->getReturnType()) {
536 // We don't support old style multiple return values.
541 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
546 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
547 // Keep track of the number of live retvals, so we can skip checks once all
548 // of them turn out to be live.
549 unsigned NumLiveRetVals = 0;
550 Type *STy = dyn_cast<StructType>(F.getReturnType());
551 // Loop all uses of the function.
552 for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
554 // If the function is PASSED IN as an argument, its address has been
556 ImmutableCallSite CS(*I);
557 if (!CS || !CS.isCallee(I)) {
562 // If this use is anything other than a call site, the function is alive.
563 const Instruction *TheCall = CS.getInstruction();
564 if (!TheCall) { // Not a direct call site?
569 // If we end up here, we are looking at a direct call to our function.
571 // Now, check how our return value(s) is/are used in this caller. Don't
572 // bother checking return values if all of them are live already.
573 if (NumLiveRetVals != RetCount) {
575 // Check all uses of the return value.
576 for (Value::const_use_iterator I = TheCall->use_begin(),
577 E = TheCall->use_end(); I != E; ++I) {
578 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
579 if (Ext && Ext->hasIndices()) {
580 // This use uses a part of our return value, survey the uses of
581 // that part and store the results for this index only.
582 unsigned Idx = *Ext->idx_begin();
583 if (RetValLiveness[Idx] != Live) {
584 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
585 if (RetValLiveness[Idx] == Live)
589 // Used by something else than extractvalue. Mark all return
591 for (unsigned i = 0; i != RetCount; ++i )
592 RetValLiveness[i] = Live;
593 NumLiveRetVals = RetCount;
598 // Single return value
599 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
600 if (RetValLiveness[0] == Live)
601 NumLiveRetVals = RetCount;
606 // Now we've inspected all callers, record the liveness of our return values.
607 for (unsigned i = 0; i != RetCount; ++i)
608 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
610 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
612 // Now, check all of our arguments.
614 UseVector MaybeLiveArgUses;
615 for (Function::const_arg_iterator AI = F.arg_begin(),
616 E = F.arg_end(); AI != E; ++AI, ++i) {
618 if (F.getFunctionType()->isVarArg()) {
619 // Variadic functions will already have a va_arg function expanded inside
620 // them, making them potentially very sensitive to ABI changes resulting
621 // from removing arguments entirely, so don't. For example AArch64 handles
622 // register and stack HFAs very differently, and this is reflected in the
623 // IR which has already been generated.
626 // See what the effect of this use is (recording any uses that cause
627 // MaybeLive in MaybeLiveArgUses).
628 Result = SurveyUses(AI, MaybeLiveArgUses);
632 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
633 // Clear the vector again for the next iteration.
634 MaybeLiveArgUses.clear();
638 /// MarkValue - This function marks the liveness of RA depending on L. If L is
639 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
640 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
642 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
643 const UseVector &MaybeLiveUses) {
645 case Live: MarkLive(RA); break;
648 // Note any uses of this value, so this return value can be
649 // marked live whenever one of the uses becomes live.
650 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
651 UE = MaybeLiveUses.end(); UI != UE; ++UI)
652 Uses.insert(std::make_pair(*UI, RA));
658 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
659 /// changed in any way. Additionally,
660 /// mark any values that are used as this function's parameters or by its return
661 /// values (according to Uses) live as well.
662 void DAE::MarkLive(const Function &F) {
663 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
664 // Mark the function as live.
665 LiveFunctions.insert(&F);
666 // Mark all arguments as live.
667 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
668 PropagateLiveness(CreateArg(&F, i));
669 // Mark all return values as live.
670 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
671 PropagateLiveness(CreateRet(&F, i));
674 /// MarkLive - Mark the given return value or argument as live. Additionally,
675 /// mark any values that are used by this value (according to Uses) live as
677 void DAE::MarkLive(const RetOrArg &RA) {
678 if (LiveFunctions.count(RA.F))
679 return; // Function was already marked Live.
681 if (!LiveValues.insert(RA).second)
682 return; // We were already marked Live.
684 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
685 PropagateLiveness(RA);
688 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
689 /// to any other values it uses (according to Uses).
690 void DAE::PropagateLiveness(const RetOrArg &RA) {
691 // We don't use upper_bound (or equal_range) here, because our recursive call
692 // to ourselves is likely to cause the upper_bound (which is the first value
693 // not belonging to RA) to become erased and the iterator invalidated.
694 UseMap::iterator Begin = Uses.lower_bound(RA);
695 UseMap::iterator E = Uses.end();
697 for (I = Begin; I != E && I->first == RA; ++I)
700 // Erase RA from the Uses map (from the lower bound to wherever we ended up
702 Uses.erase(Begin, I);
705 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
706 // that are not in LiveValues. Transform the function and all of the callees of
707 // the function to not have these arguments and return values.
709 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
710 // Don't modify fully live functions
711 if (LiveFunctions.count(F))
714 // Start by computing a new prototype for the function, which is the same as
715 // the old function, but has fewer arguments and a different return type.
716 FunctionType *FTy = F->getFunctionType();
717 std::vector<Type*> Params;
719 // Set up to build a new list of parameter attributes.
720 SmallVector<AttributeSet, 8> AttributesVec;
721 const AttributeSet &PAL = F->getAttributes();
723 // Find out the new return value.
724 Type *RetTy = FTy->getReturnType();
726 unsigned RetCount = NumRetVals(F);
728 // -1 means unused, other numbers are the new index
729 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
730 std::vector<Type*> RetTypes;
731 if (RetTy->isVoidTy()) {
734 StructType *STy = dyn_cast<StructType>(RetTy);
736 // Look at each of the original return values individually.
737 for (unsigned i = 0; i != RetCount; ++i) {
738 RetOrArg Ret = CreateRet(F, i);
739 if (LiveValues.erase(Ret)) {
740 RetTypes.push_back(STy->getElementType(i));
741 NewRetIdxs[i] = RetTypes.size() - 1;
743 ++NumRetValsEliminated;
744 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
745 << F->getName() << "\n");
749 // We used to return a single value.
750 if (LiveValues.erase(CreateRet(F, 0))) {
751 RetTypes.push_back(RetTy);
754 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
756 ++NumRetValsEliminated;
758 if (RetTypes.size() > 1)
759 // More than one return type? Return a struct with them. Also, if we used
760 // to return a struct and didn't change the number of return values,
761 // return a struct again. This prevents changing {something} into
762 // something and {} into void.
763 // Make the new struct packed if we used to return a packed struct
765 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
766 else if (RetTypes.size() == 1)
767 // One return type? Just a simple value then, but only if we didn't use to
768 // return a struct with that simple value before.
769 NRetTy = RetTypes.front();
770 else if (RetTypes.size() == 0)
771 // No return types? Make it void, but only if we didn't use to return {}.
772 NRetTy = Type::getVoidTy(F->getContext());
775 assert(NRetTy && "No new return type found?");
777 // The existing function return attributes.
778 AttributeSet RAttrs = PAL.getRetAttributes();
780 // Remove any incompatible attributes, but only if we removed all return
781 // values. Otherwise, ensure that we don't have any conflicting attributes
782 // here. Currently, this should not be possible, but special handling might be
783 // required when new return value attributes are added.
784 if (NRetTy->isVoidTy())
786 AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex,
787 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
788 removeAttributes(AttributeFuncs::
789 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
790 AttributeSet::ReturnIndex));
792 assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
793 hasAttributes(AttributeFuncs::
794 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
795 AttributeSet::ReturnIndex) &&
796 "Return attributes no longer compatible?");
798 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
799 AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs));
801 // Remember which arguments are still alive.
802 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
803 // Construct the new parameter list from non-dead arguments. Also construct
804 // a new set of parameter attributes to correspond. Skip the first parameter
805 // attribute, since that belongs to the return value.
807 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
809 RetOrArg Arg = CreateArg(F, i);
810 if (LiveValues.erase(Arg)) {
811 Params.push_back(I->getType());
814 // Get the original parameter attributes (skipping the first one, that is
815 // for the return value.
816 if (PAL.hasAttributes(i + 1)) {
817 AttrBuilder B(PAL, i + 1);
819 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
822 ++NumArgumentsEliminated;
823 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
824 << ") from " << F->getName() << "\n");
828 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
829 AttributesVec.push_back(AttributeSet::get(F->getContext(),
830 PAL.getFnAttributes()));
832 // Reconstruct the AttributesList based on the vector we constructed.
833 AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec);
835 // Create the new function type based on the recomputed parameters.
836 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
842 // Create the new function body and insert it into the module...
843 Function *NF = Function::Create(NFTy, F->getLinkage());
844 NF->copyAttributesFrom(F);
845 NF->setAttributes(NewPAL);
846 // Insert the new function before the old function, so we won't be processing
848 F->getParent()->getFunctionList().insert(F, NF);
851 // Loop over all of the callers of the function, transforming the call sites
852 // to pass in a smaller number of arguments into the new function.
854 std::vector<Value*> Args;
855 while (!F->use_empty()) {
856 CallSite CS(F->use_back());
857 Instruction *Call = CS.getInstruction();
859 AttributesVec.clear();
860 const AttributeSet &CallPAL = CS.getAttributes();
862 // The call return attributes.
863 AttributeSet RAttrs = CallPAL.getRetAttributes();
865 // Adjust in case the function was changed to return void.
867 AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex,
868 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
869 removeAttributes(AttributeFuncs::
870 typeIncompatible(NF->getReturnType(),
871 AttributeSet::ReturnIndex),
872 AttributeSet::ReturnIndex));
873 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
874 AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs));
876 // Declare these outside of the loops, so we can reuse them for the second
877 // loop, which loops the varargs.
878 CallSite::arg_iterator I = CS.arg_begin();
880 // Loop over those operands, corresponding to the normal arguments to the
881 // original function, and add those that are still alive.
882 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
885 // Get original parameter attributes, but skip return attributes.
886 if (CallPAL.hasAttributes(i + 1)) {
887 AttrBuilder B(CallPAL, i + 1);
889 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
893 // Push any varargs arguments on the list. Don't forget their attributes.
894 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
896 if (CallPAL.hasAttributes(i + 1)) {
897 AttrBuilder B(CallPAL, i + 1);
899 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
903 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
904 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
905 CallPAL.getFnAttributes()));
907 // Reconstruct the AttributesList based on the vector we constructed.
908 AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec);
911 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
912 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
914 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
915 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
917 New = CallInst::Create(NF, Args, "", Call);
918 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
919 cast<CallInst>(New)->setAttributes(NewCallPAL);
920 if (cast<CallInst>(Call)->isTailCall())
921 cast<CallInst>(New)->setTailCall();
923 New->setDebugLoc(Call->getDebugLoc());
927 if (!Call->use_empty()) {
928 if (New->getType() == Call->getType()) {
929 // Return type not changed? Just replace users then.
930 Call->replaceAllUsesWith(New);
932 } else if (New->getType()->isVoidTy()) {
933 // Our return value has uses, but they will get removed later on.
934 // Replace by null for now.
935 if (!Call->getType()->isX86_MMXTy())
936 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
938 assert(RetTy->isStructTy() &&
939 "Return type changed, but not into a void. The old return type"
940 " must have been a struct!");
941 Instruction *InsertPt = Call;
942 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
943 BasicBlock::iterator IP = II->getNormalDest()->begin();
944 while (isa<PHINode>(IP)) ++IP;
948 // We used to return a struct. Instead of doing smart stuff with all the
949 // uses of this struct, we will just rebuild it using
950 // extract/insertvalue chaining and let instcombine clean that up.
952 // Start out building up our return value from undef
953 Value *RetVal = UndefValue::get(RetTy);
954 for (unsigned i = 0; i != RetCount; ++i)
955 if (NewRetIdxs[i] != -1) {
957 if (RetTypes.size() > 1)
958 // We are still returning a struct, so extract the value from our
960 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
963 // We are now returning a single element, so just insert that
965 // Insert the value at the old position
966 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
968 // Now, replace all uses of the old call instruction with the return
970 Call->replaceAllUsesWith(RetVal);
975 // Finally, remove the old call from the program, reducing the use-count of
977 Call->eraseFromParent();
980 // Since we have now created the new function, splice the body of the old
981 // function right into the new function, leaving the old rotting hulk of the
983 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
985 // Loop over the argument list, transferring uses of the old arguments over to
986 // the new arguments, also transferring over the names as well.
988 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
989 I2 = NF->arg_begin(); I != E; ++I, ++i)
991 // If this is a live argument, move the name and users over to the new
993 I->replaceAllUsesWith(I2);
997 // If this argument is dead, replace any uses of it with null constants
998 // (these are guaranteed to become unused later on).
999 if (!I->getType()->isX86_MMXTy())
1000 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
1003 // If we change the return value of the function we must rewrite any return
1004 // instructions. Check this now.
1005 if (F->getReturnType() != NF->getReturnType())
1006 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
1007 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1010 if (NFTy->getReturnType()->isVoidTy()) {
1013 assert (RetTy->isStructTy());
1014 // The original return value was a struct, insert
1015 // extractvalue/insertvalue chains to extract only the values we need
1016 // to return and insert them into our new result.
1017 // This does generate messy code, but we'll let it to instcombine to
1019 Value *OldRet = RI->getOperand(0);
1020 // Start out building up our return value from undef
1021 RetVal = UndefValue::get(NRetTy);
1022 for (unsigned i = 0; i != RetCount; ++i)
1023 if (NewRetIdxs[i] != -1) {
1024 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
1026 if (RetTypes.size() > 1) {
1027 // We're still returning a struct, so reinsert the value into
1028 // our new return value at the new index
1030 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
1033 // We are now only returning a simple value, so just return the
1039 // Replace the return instruction with one returning the new return
1040 // value (possibly 0 if we became void).
1041 ReturnInst::Create(F->getContext(), RetVal, RI);
1042 BB->getInstList().erase(RI);
1045 // Patch the pointer to LLVM function in debug info descriptor.
1046 FunctionDIMap::iterator DI = FunctionDIs.find(F);
1047 if (DI != FunctionDIs.end())
1048 DI->second.replaceFunction(NF);
1050 // Now that the old function is dead, delete it.
1051 F->eraseFromParent();
1056 bool DAE::runOnModule(Module &M) {
1057 bool Changed = false;
1059 // Collect debug info descriptors for functions.
1060 CollectFunctionDIs(M);
1062 // First pass: Do a simple check to see if any functions can have their "..."
1063 // removed. We can do this if they never call va_start. This loop cannot be
1064 // fused with the next loop, because deleting a function invalidates
1065 // information computed while surveying other functions.
1066 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
1067 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1069 if (F.getFunctionType()->isVarArg())
1070 Changed |= DeleteDeadVarargs(F);
1073 // Second phase:loop through the module, determining which arguments are live.
1074 // We assume all arguments are dead unless proven otherwise (allowing us to
1075 // determine that dead arguments passed into recursive functions are dead).
1077 DEBUG(dbgs() << "DAE - Determining liveness\n");
1078 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
1081 // Now, remove all dead arguments and return values from each function in
1083 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1084 // Increment now, because the function will probably get removed (ie.
1085 // replaced by a new one).
1087 Changed |= RemoveDeadStuffFromFunction(F);
1090 // Finally, look for any unused parameters in functions with non-local
1091 // linkage and replace the passed in parameters with undef.
1092 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
1095 Changed |= RemoveDeadArgumentsFromCallers(F);