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 #include "llvm/Transforms/IPO.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/ADT/StringExtras.h"
25 #include "llvm/IR/CallSite.h"
26 #include "llvm/IR/CallingConv.h"
27 #include "llvm/IR/Constant.h"
28 #include "llvm/IR/DIBuilder.h"
29 #include "llvm/IR/DebugInfo.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/Debug.h"
37 #include "llvm/Support/raw_ostream.h"
43 #define DEBUG_TYPE "deadargelim"
45 STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
46 STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
47 STATISTIC(NumArgumentsReplacedWithUndef,
48 "Number of unread args replaced with undef");
50 /// DAE - The dead argument elimination pass.
52 class DAE : public ModulePass {
55 /// Struct that represents (part of) either a return value or a function
56 /// argument. Used so that arguments and return values can be used
59 RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
65 /// Make RetOrArg comparable, so we can put it into a map.
66 bool operator<(const RetOrArg &O) const {
67 return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg);
70 /// Make RetOrArg comparable, so we can easily iterate the multimap.
71 bool operator==(const RetOrArg &O) const {
72 return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
75 std::string getDescription() const {
76 return std::string((IsArg ? "Argument #" : "Return value #"))
77 + utostr(Idx) + " of function " + F->getName().str();
81 /// Liveness enum - During our initial pass over the program, we determine
82 /// that things are either alive or maybe alive. We don't mark anything
83 /// explicitly dead (even if we know they are), since anything not alive
84 /// with no registered uses (in Uses) will never be marked alive and will
85 /// thus become dead in the end.
86 enum Liveness { Live, MaybeLive };
88 /// Convenience wrapper
89 RetOrArg CreateRet(const Function *F, unsigned Idx) {
90 return RetOrArg(F, Idx, false);
92 /// Convenience wrapper
93 RetOrArg CreateArg(const Function *F, unsigned Idx) {
94 return RetOrArg(F, Idx, true);
97 typedef std::multimap<RetOrArg, RetOrArg> UseMap;
98 /// This maps a return value or argument to any MaybeLive return values or
99 /// arguments it uses. This allows the MaybeLive values to be marked live
100 /// when any of its users is marked live.
101 /// For example (indices are left out for clarity):
102 /// - Uses[ret F] = ret G
103 /// This means that F calls G, and F returns the value returned by G.
104 /// - Uses[arg F] = ret G
105 /// This means that some function calls G and passes its result as an
107 /// - Uses[ret F] = arg F
108 /// This means that F returns one of its own arguments.
109 /// - Uses[arg F] = arg G
110 /// This means that G calls F and passes one of its own (G's) arguments
114 typedef std::set<RetOrArg> LiveSet;
115 typedef std::set<const Function*> LiveFuncSet;
117 /// This set contains all values that have been determined to be live.
119 /// This set contains all values that are cannot be changed in any way.
120 LiveFuncSet LiveFunctions;
122 typedef SmallVector<RetOrArg, 5> UseVector;
124 // Map each LLVM function to corresponding metadata with debug info. If
125 // the function is replaced with another one, we should patch the pointer
126 // to LLVM function in metadata.
127 // As the code generation for module is finished (and DIBuilder is
128 // finalized) we assume that subprogram descriptors won't be changed, and
129 // they are stored in map for short duration anyway.
130 DenseMap<const Function *, DISubprogram> FunctionDIs;
133 // DAH uses this to specify a different ID.
134 explicit DAE(char &ID) : ModulePass(ID) {}
137 static char ID; // Pass identification, replacement for typeid
138 DAE() : ModulePass(ID) {
139 initializeDAEPass(*PassRegistry::getPassRegistry());
142 bool runOnModule(Module &M) override;
144 virtual bool ShouldHackArguments() const { return false; }
147 Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
148 Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses,
149 unsigned RetValNum = 0);
150 Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
152 void SurveyFunction(const Function &F);
153 void MarkValue(const RetOrArg &RA, Liveness L,
154 const UseVector &MaybeLiveUses);
155 void MarkLive(const RetOrArg &RA);
156 void MarkLive(const Function &F);
157 void PropagateLiveness(const RetOrArg &RA);
158 bool RemoveDeadStuffFromFunction(Function *F);
159 bool DeleteDeadVarargs(Function &Fn);
160 bool RemoveDeadArgumentsFromCallers(Function &Fn);
166 INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
169 /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
170 /// deletes arguments to functions which are external. This is only for use
172 struct DAH : public DAE {
176 bool ShouldHackArguments() const override { return true; }
181 INITIALIZE_PASS(DAH, "deadarghaX0r",
182 "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
185 /// createDeadArgEliminationPass - This pass removes arguments from functions
186 /// which are not used by the body of the function.
188 ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
189 ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
191 /// DeleteDeadVarargs - If this is an function that takes a ... list, and if
192 /// llvm.vastart is never called, the varargs list is dead for the function.
193 bool DAE::DeleteDeadVarargs(Function &Fn) {
194 assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
195 if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
197 // Ensure that the function is only directly called.
198 if (Fn.hasAddressTaken())
201 // Okay, we know we can transform this function if safe. Scan its body
202 // looking for calls marked musttail or calls to llvm.vastart.
203 for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
204 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
205 CallInst *CI = dyn_cast<CallInst>(I);
208 if (CI->isMustTailCall())
210 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) {
211 if (II->getIntrinsicID() == Intrinsic::vastart)
217 // If we get here, there are no calls to llvm.vastart in the function body,
218 // remove the "..." and adjust all the calls.
220 // Start by computing a new prototype for the function, which is the same as
221 // the old function, but doesn't have isVarArg set.
222 FunctionType *FTy = Fn.getFunctionType();
224 std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
225 FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
227 unsigned NumArgs = Params.size();
229 // Create the new function body and insert it into the module...
230 Function *NF = Function::Create(NFTy, Fn.getLinkage());
231 NF->copyAttributesFrom(&Fn);
232 Fn.getParent()->getFunctionList().insert(&Fn, NF);
235 // Loop over all of the callers of the function, transforming the call sites
236 // to pass in a smaller number of arguments into the new function.
238 std::vector<Value*> Args;
239 for (Value::user_iterator I = Fn.user_begin(), E = Fn.user_end(); I != E; ) {
243 Instruction *Call = CS.getInstruction();
245 // Pass all the same arguments.
246 Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
248 // Drop any attributes that were on the vararg arguments.
249 AttributeSet PAL = CS.getAttributes();
250 if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) {
251 SmallVector<AttributeSet, 8> AttributesVec;
252 for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i)
253 AttributesVec.push_back(PAL.getSlotAttributes(i));
254 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
255 AttributesVec.push_back(AttributeSet::get(Fn.getContext(),
256 PAL.getFnAttributes()));
257 PAL = AttributeSet::get(Fn.getContext(), AttributesVec);
261 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
262 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
264 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
265 cast<InvokeInst>(New)->setAttributes(PAL);
267 New = CallInst::Create(NF, Args, "", Call);
268 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
269 cast<CallInst>(New)->setAttributes(PAL);
270 if (cast<CallInst>(Call)->isTailCall())
271 cast<CallInst>(New)->setTailCall();
273 New->setDebugLoc(Call->getDebugLoc());
277 if (!Call->use_empty())
278 Call->replaceAllUsesWith(New);
282 // Finally, remove the old call from the program, reducing the use-count of
284 Call->eraseFromParent();
287 // Since we have now created the new function, splice the body of the old
288 // function right into the new function, leaving the old rotting hulk of the
290 NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
292 // Loop over the argument list, transferring uses of the old arguments over to
293 // the new arguments, also transferring over the names as well. While we're at
294 // it, remove the dead arguments from the DeadArguments list.
296 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
297 I2 = NF->arg_begin(); I != E; ++I, ++I2) {
298 // Move the name and users over to the new version.
299 I->replaceAllUsesWith(I2);
303 // Patch the pointer to LLVM function in debug info descriptor.
304 auto DI = FunctionDIs.find(&Fn);
305 if (DI != FunctionDIs.end())
306 DI->second.replaceFunction(NF);
308 // Fix up any BlockAddresses that refer to the function.
309 Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType()));
310 // Delete the bitcast that we just created, so that NF does not
311 // appear to be address-taken.
312 NF->removeDeadConstantUsers();
313 // Finally, nuke the old function.
314 Fn.eraseFromParent();
318 /// RemoveDeadArgumentsFromCallers - Checks if the given function has any
319 /// arguments that are unused, and changes the caller parameters to be undefined
321 bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
323 if (Fn.isDeclaration() || Fn.mayBeOverridden())
326 // Functions with local linkage should already have been handled, except the
327 // fragile (variadic) ones which we can improve here.
328 if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
331 // If a function seen at compile time is not necessarily the one linked to
332 // the binary being built, it is illegal to change the actual arguments
333 // passed to it. These functions can be captured by isWeakForLinker().
334 // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
335 // doesn't include linkage types like AvailableExternallyLinkage and
336 // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
337 // *EQUIVALENT* globals that can be merged at link-time. However, the
338 // semantic of *EQUIVALENT*-functions includes parameters. Changing
339 // parameters breaks this assumption.
341 if (Fn.isWeakForLinker())
347 SmallVector<unsigned, 8> UnusedArgs;
348 for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
352 if (Arg->use_empty() && !Arg->hasByValOrInAllocaAttr())
353 UnusedArgs.push_back(Arg->getArgNo());
356 if (UnusedArgs.empty())
359 bool Changed = false;
361 for (Use &U : Fn.uses()) {
362 CallSite CS(U.getUser());
363 if (!CS || !CS.isCallee(&U))
366 // Now go through all unused args and replace them with "undef".
367 for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
368 unsigned ArgNo = UnusedArgs[I];
370 Value *Arg = CS.getArgument(ArgNo);
371 CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
372 ++NumArgumentsReplacedWithUndef;
380 /// Convenience function that returns the number of return values. It returns 0
381 /// for void functions and 1 for functions not returning a struct. It returns
382 /// the number of struct elements for functions returning a struct.
383 static unsigned NumRetVals(const Function *F) {
384 if (F->getReturnType()->isVoidTy())
386 else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
387 return STy->getNumElements();
392 /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
393 /// live, it adds Use to the MaybeLiveUses argument. Returns the determined
395 DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
396 // We're live if our use or its Function is already marked as live.
397 if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
400 // We're maybe live otherwise, but remember that we must become live if
402 MaybeLiveUses.push_back(Use);
407 /// SurveyUse - This looks at a single use of an argument or return value
408 /// and determines if it should be alive or not. Adds this use to MaybeLiveUses
409 /// if it causes the used value to become MaybeLive.
411 /// RetValNum is the return value number to use when this use is used in a
412 /// return instruction. This is used in the recursion, you should always leave
414 DAE::Liveness DAE::SurveyUse(const Use *U,
415 UseVector &MaybeLiveUses, unsigned RetValNum) {
416 const User *V = U->getUser();
417 if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
418 // The value is returned from a function. It's only live when the
419 // function's return value is live. We use RetValNum here, for the case
420 // that U is really a use of an insertvalue instruction that uses the
422 RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
423 // We might be live, depending on the liveness of Use.
424 return MarkIfNotLive(Use, MaybeLiveUses);
426 if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
427 if (U->getOperandNo() != InsertValueInst::getAggregateOperandIndex()
429 // The use we are examining is inserted into an aggregate. Our liveness
430 // depends on all uses of that aggregate, but if it is used as a return
431 // value, only index at which we were inserted counts.
432 RetValNum = *IV->idx_begin();
434 // Note that if we are used as the aggregate operand to the insertvalue,
435 // we don't change RetValNum, but do survey all our uses.
437 Liveness Result = MaybeLive;
438 for (const Use &UU : IV->uses()) {
439 Result = SurveyUse(&UU, MaybeLiveUses, RetValNum);
446 if (ImmutableCallSite CS = V) {
447 const Function *F = CS.getCalledFunction();
449 // Used in a direct call.
451 // Find the argument number. We know for sure that this use is an
452 // argument, since if it was the function argument this would be an
453 // indirect call and the we know can't be looking at a value of the
454 // label type (for the invoke instruction).
455 unsigned ArgNo = CS.getArgumentNo(U);
457 if (ArgNo >= F->getFunctionType()->getNumParams())
458 // The value is passed in through a vararg! Must be live.
461 assert(CS.getArgument(ArgNo)
462 == CS->getOperand(U->getOperandNo())
463 && "Argument is not where we expected it");
465 // Value passed to a normal call. It's only live when the corresponding
466 // argument to the called function turns out live.
467 RetOrArg Use = CreateArg(F, ArgNo);
468 return MarkIfNotLive(Use, MaybeLiveUses);
471 // Used in any other way? Value must be live.
475 /// SurveyUses - This looks at all the uses of the given value
476 /// Returns the Liveness deduced from the uses of this value.
478 /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
479 /// the result is Live, MaybeLiveUses might be modified but its content should
480 /// be ignored (since it might not be complete).
481 DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
482 // Assume it's dead (which will only hold if there are no uses at all..).
483 Liveness Result = MaybeLive;
485 for (const Use &U : V->uses()) {
486 Result = SurveyUse(&U, MaybeLiveUses);
493 // SurveyFunction - This performs the initial survey of the specified function,
494 // checking out whether or not it uses any of its incoming arguments or whether
495 // any callers use the return value. This fills in the LiveValues set and Uses
498 // We consider arguments of non-internal functions to be intrinsically alive as
499 // well as arguments to functions which have their "address taken".
501 void DAE::SurveyFunction(const Function &F) {
502 // Functions with inalloca parameters are expecting args in a particular
503 // register and memory layout.
504 if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca)) {
509 unsigned RetCount = NumRetVals(&F);
510 // Assume all return values are dead
511 typedef SmallVector<Liveness, 5> RetVals;
512 RetVals RetValLiveness(RetCount, MaybeLive);
514 typedef SmallVector<UseVector, 5> RetUses;
515 // These vectors map each return value to the uses that make it MaybeLive, so
516 // we can add those to the Uses map if the return value really turns out to be
517 // MaybeLive. Initialized to a list of RetCount empty lists.
518 RetUses MaybeLiveRetUses(RetCount);
520 for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
521 if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
522 if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
523 != F.getFunctionType()->getReturnType()) {
524 // We don't support old style multiple return values.
529 if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
534 DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
535 // Keep track of the number of live retvals, so we can skip checks once all
536 // of them turn out to be live.
537 unsigned NumLiveRetVals = 0;
538 Type *STy = dyn_cast<StructType>(F.getReturnType());
539 // Loop all uses of the function.
540 for (const Use &U : F.uses()) {
541 // If the function is PASSED IN as an argument, its address has been
543 ImmutableCallSite CS(U.getUser());
544 if (!CS || !CS.isCallee(&U)) {
549 // If this use is anything other than a call site, the function is alive.
550 const Instruction *TheCall = CS.getInstruction();
551 if (!TheCall) { // Not a direct call site?
556 // If we end up here, we are looking at a direct call to our function.
558 // Now, check how our return value(s) is/are used in this caller. Don't
559 // bother checking return values if all of them are live already.
560 if (NumLiveRetVals != RetCount) {
562 // Check all uses of the return value.
563 for (const User *U : TheCall->users()) {
564 const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(U);
565 if (Ext && Ext->hasIndices()) {
566 // This use uses a part of our return value, survey the uses of
567 // that part and store the results for this index only.
568 unsigned Idx = *Ext->idx_begin();
569 if (RetValLiveness[Idx] != Live) {
570 RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
571 if (RetValLiveness[Idx] == Live)
575 // Used by something else than extractvalue. Mark all return
577 for (unsigned i = 0; i != RetCount; ++i )
578 RetValLiveness[i] = Live;
579 NumLiveRetVals = RetCount;
584 // Single return value
585 RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
586 if (RetValLiveness[0] == Live)
587 NumLiveRetVals = RetCount;
592 // Now we've inspected all callers, record the liveness of our return values.
593 for (unsigned i = 0; i != RetCount; ++i)
594 MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
596 DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
598 // Now, check all of our arguments.
600 UseVector MaybeLiveArgUses;
601 for (Function::const_arg_iterator AI = F.arg_begin(),
602 E = F.arg_end(); AI != E; ++AI, ++i) {
604 if (F.getFunctionType()->isVarArg()) {
605 // Variadic functions will already have a va_arg function expanded inside
606 // them, making them potentially very sensitive to ABI changes resulting
607 // from removing arguments entirely, so don't. For example AArch64 handles
608 // register and stack HFAs very differently, and this is reflected in the
609 // IR which has already been generated.
612 // See what the effect of this use is (recording any uses that cause
613 // MaybeLive in MaybeLiveArgUses).
614 Result = SurveyUses(AI, MaybeLiveArgUses);
618 MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
619 // Clear the vector again for the next iteration.
620 MaybeLiveArgUses.clear();
624 /// MarkValue - This function marks the liveness of RA depending on L. If L is
625 /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
626 /// such that RA will be marked live if any use in MaybeLiveUses gets marked
628 void DAE::MarkValue(const RetOrArg &RA, Liveness L,
629 const UseVector &MaybeLiveUses) {
631 case Live: MarkLive(RA); break;
634 // Note any uses of this value, so this return value can be
635 // marked live whenever one of the uses becomes live.
636 for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
637 UE = MaybeLiveUses.end(); UI != UE; ++UI)
638 Uses.insert(std::make_pair(*UI, RA));
644 /// MarkLive - Mark the given Function as alive, meaning that it cannot be
645 /// changed in any way. Additionally,
646 /// mark any values that are used as this function's parameters or by its return
647 /// values (according to Uses) live as well.
648 void DAE::MarkLive(const Function &F) {
649 DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
650 // Mark the function as live.
651 LiveFunctions.insert(&F);
652 // Mark all arguments as live.
653 for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
654 PropagateLiveness(CreateArg(&F, i));
655 // Mark all return values as live.
656 for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
657 PropagateLiveness(CreateRet(&F, i));
660 /// MarkLive - Mark the given return value or argument as live. Additionally,
661 /// mark any values that are used by this value (according to Uses) live as
663 void DAE::MarkLive(const RetOrArg &RA) {
664 if (LiveFunctions.count(RA.F))
665 return; // Function was already marked Live.
667 if (!LiveValues.insert(RA).second)
668 return; // We were already marked Live.
670 DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
671 PropagateLiveness(RA);
674 /// PropagateLiveness - Given that RA is a live value, propagate it's liveness
675 /// to any other values it uses (according to Uses).
676 void DAE::PropagateLiveness(const RetOrArg &RA) {
677 // We don't use upper_bound (or equal_range) here, because our recursive call
678 // to ourselves is likely to cause the upper_bound (which is the first value
679 // not belonging to RA) to become erased and the iterator invalidated.
680 UseMap::iterator Begin = Uses.lower_bound(RA);
681 UseMap::iterator E = Uses.end();
683 for (I = Begin; I != E && I->first == RA; ++I)
686 // Erase RA from the Uses map (from the lower bound to wherever we ended up
688 Uses.erase(Begin, I);
691 // RemoveDeadStuffFromFunction - Remove any arguments and return values from F
692 // that are not in LiveValues. Transform the function and all of the callees of
693 // the function to not have these arguments and return values.
695 bool DAE::RemoveDeadStuffFromFunction(Function *F) {
696 // Don't modify fully live functions
697 if (LiveFunctions.count(F))
700 // Start by computing a new prototype for the function, which is the same as
701 // the old function, but has fewer arguments and a different return type.
702 FunctionType *FTy = F->getFunctionType();
703 std::vector<Type*> Params;
705 // Keep track of if we have a live 'returned' argument
706 bool HasLiveReturnedArg = false;
708 // Set up to build a new list of parameter attributes.
709 SmallVector<AttributeSet, 8> AttributesVec;
710 const AttributeSet &PAL = F->getAttributes();
712 // Remember which arguments are still alive.
713 SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
714 // Construct the new parameter list from non-dead arguments. Also construct
715 // a new set of parameter attributes to correspond. Skip the first parameter
716 // attribute, since that belongs to the return value.
718 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
720 RetOrArg Arg = CreateArg(F, i);
721 if (LiveValues.erase(Arg)) {
722 Params.push_back(I->getType());
725 // Get the original parameter attributes (skipping the first one, that is
726 // for the return value.
727 if (PAL.hasAttributes(i + 1)) {
728 AttrBuilder B(PAL, i + 1);
729 if (B.contains(Attribute::Returned))
730 HasLiveReturnedArg = true;
732 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
735 ++NumArgumentsEliminated;
736 DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
737 << ") from " << F->getName() << "\n");
741 // Find out the new return value.
742 Type *RetTy = FTy->getReturnType();
743 Type *NRetTy = nullptr;
744 unsigned RetCount = NumRetVals(F);
746 // -1 means unused, other numbers are the new index
747 SmallVector<int, 5> NewRetIdxs(RetCount, -1);
748 std::vector<Type*> RetTypes;
750 // If there is a function with a live 'returned' argument but a dead return
751 // value, then there are two possible actions:
752 // 1) Eliminate the return value and take off the 'returned' attribute on the
754 // 2) Retain the 'returned' attribute and treat the return value (but not the
755 // entire function) as live so that it is not eliminated.
757 // It's not clear in the general case which option is more profitable because,
758 // even in the absence of explicit uses of the return value, code generation
759 // is free to use the 'returned' attribute to do things like eliding
760 // save/restores of registers across calls. Whether or not this happens is
761 // target and ABI-specific as well as depending on the amount of register
762 // pressure, so there's no good way for an IR-level pass to figure this out.
764 // Fortunately, the only places where 'returned' is currently generated by
765 // the FE are places where 'returned' is basically free and almost always a
766 // performance win, so the second option can just be used always for now.
768 // This should be revisited if 'returned' is ever applied more liberally.
769 if (RetTy->isVoidTy() || HasLiveReturnedArg) {
772 StructType *STy = dyn_cast<StructType>(RetTy);
774 // Look at each of the original return values individually.
775 for (unsigned i = 0; i != RetCount; ++i) {
776 RetOrArg Ret = CreateRet(F, i);
777 if (LiveValues.erase(Ret)) {
778 RetTypes.push_back(STy->getElementType(i));
779 NewRetIdxs[i] = RetTypes.size() - 1;
781 ++NumRetValsEliminated;
782 DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
783 << F->getName() << "\n");
787 // We used to return a single value.
788 if (LiveValues.erase(CreateRet(F, 0))) {
789 RetTypes.push_back(RetTy);
792 DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
794 ++NumRetValsEliminated;
796 if (RetTypes.size() > 1)
797 // More than one return type? Return a struct with them. Also, if we used
798 // to return a struct and didn't change the number of return values,
799 // return a struct again. This prevents changing {something} into
800 // something and {} into void.
801 // Make the new struct packed if we used to return a packed struct
803 NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
804 else if (RetTypes.size() == 1)
805 // One return type? Just a simple value then, but only if we didn't use to
806 // return a struct with that simple value before.
807 NRetTy = RetTypes.front();
808 else if (RetTypes.size() == 0)
809 // No return types? Make it void, but only if we didn't use to return {}.
810 NRetTy = Type::getVoidTy(F->getContext());
813 assert(NRetTy && "No new return type found?");
815 // The existing function return attributes.
816 AttributeSet RAttrs = PAL.getRetAttributes();
818 // Remove any incompatible attributes, but only if we removed all return
819 // values. Otherwise, ensure that we don't have any conflicting attributes
820 // here. Currently, this should not be possible, but special handling might be
821 // required when new return value attributes are added.
822 if (NRetTy->isVoidTy())
824 AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex,
825 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
826 removeAttributes(AttributeFuncs::
827 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
828 AttributeSet::ReturnIndex));
830 assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
831 hasAttributes(AttributeFuncs::
832 typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
833 AttributeSet::ReturnIndex) &&
834 "Return attributes no longer compatible?");
836 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
837 AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs));
839 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
840 AttributesVec.push_back(AttributeSet::get(F->getContext(),
841 PAL.getFnAttributes()));
843 // Reconstruct the AttributesList based on the vector we constructed.
844 AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec);
846 // Create the new function type based on the recomputed parameters.
847 FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
853 // Create the new function body and insert it into the module...
854 Function *NF = Function::Create(NFTy, F->getLinkage());
855 NF->copyAttributesFrom(F);
856 NF->setAttributes(NewPAL);
857 // Insert the new function before the old function, so we won't be processing
859 F->getParent()->getFunctionList().insert(F, NF);
862 // Loop over all of the callers of the function, transforming the call sites
863 // to pass in a smaller number of arguments into the new function.
865 std::vector<Value*> Args;
866 while (!F->use_empty()) {
867 CallSite CS(F->user_back());
868 Instruction *Call = CS.getInstruction();
870 AttributesVec.clear();
871 const AttributeSet &CallPAL = CS.getAttributes();
873 // The call return attributes.
874 AttributeSet RAttrs = CallPAL.getRetAttributes();
876 // Adjust in case the function was changed to return void.
878 AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex,
879 AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
880 removeAttributes(AttributeFuncs::
881 typeIncompatible(NF->getReturnType(),
882 AttributeSet::ReturnIndex),
883 AttributeSet::ReturnIndex));
884 if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
885 AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs));
887 // Declare these outside of the loops, so we can reuse them for the second
888 // loop, which loops the varargs.
889 CallSite::arg_iterator I = CS.arg_begin();
891 // Loop over those operands, corresponding to the normal arguments to the
892 // original function, and add those that are still alive.
893 for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
896 // Get original parameter attributes, but skip return attributes.
897 if (CallPAL.hasAttributes(i + 1)) {
898 AttrBuilder B(CallPAL, i + 1);
899 // If the return type has changed, then get rid of 'returned' on the
900 // call site. The alternative is to make all 'returned' attributes on
901 // call sites keep the return value alive just like 'returned'
902 // attributes on function declaration but it's less clearly a win
903 // and this is not an expected case anyway
904 if (NRetTy != RetTy && B.contains(Attribute::Returned))
905 B.removeAttribute(Attribute::Returned);
907 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
911 // Push any varargs arguments on the list. Don't forget their attributes.
912 for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
914 if (CallPAL.hasAttributes(i + 1)) {
915 AttrBuilder B(CallPAL, i + 1);
917 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
921 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
922 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
923 CallPAL.getFnAttributes()));
925 // Reconstruct the AttributesList based on the vector we constructed.
926 AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec);
929 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
930 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
932 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
933 cast<InvokeInst>(New)->setAttributes(NewCallPAL);
935 New = CallInst::Create(NF, Args, "", Call);
936 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
937 cast<CallInst>(New)->setAttributes(NewCallPAL);
938 if (cast<CallInst>(Call)->isTailCall())
939 cast<CallInst>(New)->setTailCall();
941 New->setDebugLoc(Call->getDebugLoc());
945 if (!Call->use_empty()) {
946 if (New->getType() == Call->getType()) {
947 // Return type not changed? Just replace users then.
948 Call->replaceAllUsesWith(New);
950 } else if (New->getType()->isVoidTy()) {
951 // Our return value has uses, but they will get removed later on.
952 // Replace by null for now.
953 if (!Call->getType()->isX86_MMXTy())
954 Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
956 assert(RetTy->isStructTy() &&
957 "Return type changed, but not into a void. The old return type"
958 " must have been a struct!");
959 Instruction *InsertPt = Call;
960 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
961 BasicBlock::iterator IP = II->getNormalDest()->begin();
962 while (isa<PHINode>(IP)) ++IP;
966 // We used to return a struct. Instead of doing smart stuff with all the
967 // uses of this struct, we will just rebuild it using
968 // extract/insertvalue chaining and let instcombine clean that up.
970 // Start out building up our return value from undef
971 Value *RetVal = UndefValue::get(RetTy);
972 for (unsigned i = 0; i != RetCount; ++i)
973 if (NewRetIdxs[i] != -1) {
975 if (RetTypes.size() > 1)
976 // We are still returning a struct, so extract the value from our
978 V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
981 // We are now returning a single element, so just insert that
983 // Insert the value at the old position
984 RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
986 // Now, replace all uses of the old call instruction with the return
988 Call->replaceAllUsesWith(RetVal);
993 // Finally, remove the old call from the program, reducing the use-count of
995 Call->eraseFromParent();
998 // Since we have now created the new function, splice the body of the old
999 // function right into the new function, leaving the old rotting hulk of the
1001 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
1003 // Loop over the argument list, transferring uses of the old arguments over to
1004 // the new arguments, also transferring over the names as well.
1006 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
1007 I2 = NF->arg_begin(); I != E; ++I, ++i)
1009 // If this is a live argument, move the name and users over to the new
1011 I->replaceAllUsesWith(I2);
1015 // If this argument is dead, replace any uses of it with null constants
1016 // (these are guaranteed to become unused later on).
1017 if (!I->getType()->isX86_MMXTy())
1018 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
1021 // If we change the return value of the function we must rewrite any return
1022 // instructions. Check this now.
1023 if (F->getReturnType() != NF->getReturnType())
1024 for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
1025 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1028 if (NFTy->getReturnType()->isVoidTy()) {
1031 assert (RetTy->isStructTy());
1032 // The original return value was a struct, insert
1033 // extractvalue/insertvalue chains to extract only the values we need
1034 // to return and insert them into our new result.
1035 // This does generate messy code, but we'll let it to instcombine to
1037 Value *OldRet = RI->getOperand(0);
1038 // Start out building up our return value from undef
1039 RetVal = UndefValue::get(NRetTy);
1040 for (unsigned i = 0; i != RetCount; ++i)
1041 if (NewRetIdxs[i] != -1) {
1042 ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
1044 if (RetTypes.size() > 1) {
1045 // We're still returning a struct, so reinsert the value into
1046 // our new return value at the new index
1048 RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
1051 // We are now only returning a simple value, so just return the
1057 // Replace the return instruction with one returning the new return
1058 // value (possibly 0 if we became void).
1059 ReturnInst::Create(F->getContext(), RetVal, RI);
1060 BB->getInstList().erase(RI);
1063 // Patch the pointer to LLVM function in debug info descriptor.
1064 auto DI = FunctionDIs.find(F);
1065 if (DI != FunctionDIs.end())
1066 DI->second.replaceFunction(NF);
1068 // Now that the old function is dead, delete it.
1069 F->eraseFromParent();
1074 bool DAE::runOnModule(Module &M) {
1075 bool Changed = false;
1077 // Collect debug info descriptors for functions.
1078 FunctionDIs = makeSubprogramMap(M);
1080 // First pass: Do a simple check to see if any functions can have their "..."
1081 // removed. We can do this if they never call va_start. This loop cannot be
1082 // fused with the next loop, because deleting a function invalidates
1083 // information computed while surveying other functions.
1084 DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
1085 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1087 if (F.getFunctionType()->isVarArg())
1088 Changed |= DeleteDeadVarargs(F);
1091 // Second phase:loop through the module, determining which arguments are live.
1092 // We assume all arguments are dead unless proven otherwise (allowing us to
1093 // determine that dead arguments passed into recursive functions are dead).
1095 DEBUG(dbgs() << "DAE - Determining liveness\n");
1096 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
1099 // Now, remove all dead arguments and return values from each function in
1101 for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
1102 // Increment now, because the function will probably get removed (ie.
1103 // replaced by a new one).
1105 Changed |= RemoveDeadStuffFromFunction(F);
1108 // Finally, look for any unused parameters in functions with non-local
1109 // linkage and replace the passed in parameters with undef.
1110 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
1113 Changed |= RemoveDeadArgumentsFromCallers(F);