| //===- DeadArgumentElimination.cpp - Eliminate dead arguments -------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass deletes dead arguments from internal functions. Dead argument |
| // elimination removes arguments which are directly dead, as well as arguments |
| // only passed into function calls as dead arguments of other functions. This |
| // pass also deletes dead return values in a similar way. |
| // |
| // This pass is often useful as a cleanup pass to run after aggressive |
| // interprocedural passes, which add possibly-dead arguments or return values. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/IPO/DeadArgumentElimination.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/IR/Argument.h" |
| #include "llvm/IR/Attributes.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CallSite.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/PassManager.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/Use.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/IPO.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include <cassert> |
| #include <cstdint> |
| #include <utility> |
| #include <vector> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "deadargelim" |
| |
| STATISTIC(NumArgumentsEliminated, "Number of unread args removed"); |
| STATISTIC(NumRetValsEliminated , "Number of unused return values removed"); |
| STATISTIC(NumArgumentsReplacedWithUndef, |
| "Number of unread args replaced with undef"); |
| |
| namespace { |
| |
| /// DAE - The dead argument elimination pass. |
| class DAE : public ModulePass { |
| protected: |
| // DAH uses this to specify a different ID. |
| explicit DAE(char &ID) : ModulePass(ID) {} |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| |
| DAE() : ModulePass(ID) { |
| initializeDAEPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnModule(Module &M) override { |
| if (skipModule(M)) |
| return false; |
| DeadArgumentEliminationPass DAEP(ShouldHackArguments()); |
| ModuleAnalysisManager DummyMAM; |
| PreservedAnalyses PA = DAEP.run(M, DummyMAM); |
| return !PA.areAllPreserved(); |
| } |
| |
| virtual bool ShouldHackArguments() const { return false; } |
| }; |
| |
| } // end anonymous namespace |
| |
| char DAE::ID = 0; |
| |
| INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false) |
| |
| namespace { |
| |
| /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but |
| /// deletes arguments to functions which are external. This is only for use |
| /// by bugpoint. |
| struct DAH : public DAE { |
| static char ID; |
| |
| DAH() : DAE(ID) {} |
| |
| bool ShouldHackArguments() const override { return true; } |
| }; |
| |
| } // end anonymous namespace |
| |
| char DAH::ID = 0; |
| |
| INITIALIZE_PASS(DAH, "deadarghaX0r", |
| "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)", |
| false, false) |
| |
| /// createDeadArgEliminationPass - This pass removes arguments from functions |
| /// which are not used by the body of the function. |
| ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); } |
| |
| ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); } |
| |
| /// DeleteDeadVarargs - If this is an function that takes a ... list, and if |
| /// llvm.vastart is never called, the varargs list is dead for the function. |
| bool DeadArgumentEliminationPass::DeleteDeadVarargs(Function &Fn) { |
| assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!"); |
| if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false; |
| |
| // Ensure that the function is only directly called. |
| if (Fn.hasAddressTaken()) |
| return false; |
| |
| // Don't touch naked functions. The assembly might be using an argument, or |
| // otherwise rely on the frame layout in a way that this analysis will not |
| // see. |
| if (Fn.hasFnAttribute(Attribute::Naked)) { |
| return false; |
| } |
| |
| // Okay, we know we can transform this function if safe. Scan its body |
| // looking for calls marked musttail or calls to llvm.vastart. |
| for (BasicBlock &BB : Fn) { |
| for (Instruction &I : BB) { |
| CallInst *CI = dyn_cast<CallInst>(&I); |
| if (!CI) |
| continue; |
| if (CI->isMustTailCall()) |
| return false; |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) { |
| if (II->getIntrinsicID() == Intrinsic::vastart) |
| return false; |
| } |
| } |
| } |
| |
| // If we get here, there are no calls to llvm.vastart in the function body, |
| // remove the "..." and adjust all the calls. |
| |
| // Start by computing a new prototype for the function, which is the same as |
| // the old function, but doesn't have isVarArg set. |
| FunctionType *FTy = Fn.getFunctionType(); |
| |
| std::vector<Type *> Params(FTy->param_begin(), FTy->param_end()); |
| FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), |
| Params, false); |
| unsigned NumArgs = Params.size(); |
| |
| // Create the new function body and insert it into the module... |
| Function *NF = Function::Create(NFTy, Fn.getLinkage(), Fn.getAddressSpace()); |
| NF->copyAttributesFrom(&Fn); |
| NF->setComdat(Fn.getComdat()); |
| Fn.getParent()->getFunctionList().insert(Fn.getIterator(), NF); |
| NF->takeName(&Fn); |
| |
| // Loop over all of the callers of the function, transforming the call sites |
| // to pass in a smaller number of arguments into the new function. |
| // |
| std::vector<Value *> Args; |
| for (Value::user_iterator I = Fn.user_begin(), E = Fn.user_end(); I != E; ) { |
| CallSite CS(*I++); |
| if (!CS) |
| continue; |
| Instruction *Call = CS.getInstruction(); |
| |
| // Pass all the same arguments. |
| Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs); |
| |
| // Drop any attributes that were on the vararg arguments. |
| AttributeList PAL = CS.getAttributes(); |
| if (!PAL.isEmpty()) { |
| SmallVector<AttributeSet, 8> ArgAttrs; |
| for (unsigned ArgNo = 0; ArgNo < NumArgs; ++ArgNo) |
| ArgAttrs.push_back(PAL.getParamAttributes(ArgNo)); |
| PAL = AttributeList::get(Fn.getContext(), PAL.getFnAttributes(), |
| PAL.getRetAttributes(), ArgAttrs); |
| } |
| |
| SmallVector<OperandBundleDef, 1> OpBundles; |
| CS.getOperandBundlesAsDefs(OpBundles); |
| |
| CallSite NewCS; |
| if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { |
| NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), |
| Args, OpBundles, "", Call); |
| } else { |
| NewCS = CallInst::Create(NF, Args, OpBundles, "", Call); |
| cast<CallInst>(NewCS.getInstruction()) |
| ->setTailCallKind(cast<CallInst>(Call)->getTailCallKind()); |
| } |
| NewCS.setCallingConv(CS.getCallingConv()); |
| NewCS.setAttributes(PAL); |
| NewCS->setDebugLoc(Call->getDebugLoc()); |
| uint64_t W; |
| if (Call->extractProfTotalWeight(W)) |
| NewCS->setProfWeight(W); |
| |
| Args.clear(); |
| |
| if (!Call->use_empty()) |
| Call->replaceAllUsesWith(NewCS.getInstruction()); |
| |
| NewCS->takeName(Call); |
| |
| // Finally, remove the old call from the program, reducing the use-count of |
| // F. |
| Call->eraseFromParent(); |
| } |
| |
| // Since we have now created the new function, splice the body of the old |
| // function right into the new function, leaving the old rotting hulk of the |
| // function empty. |
| NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList()); |
| |
| // Loop over the argument list, transferring uses of the old arguments over to |
| // the new arguments, also transferring over the names as well. While we're at |
| // it, remove the dead arguments from the DeadArguments list. |
| for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(), |
| I2 = NF->arg_begin(); I != E; ++I, ++I2) { |
| // Move the name and users over to the new version. |
| I->replaceAllUsesWith(&*I2); |
| I2->takeName(&*I); |
| } |
| |
| // Clone metadatas from the old function, including debug info descriptor. |
| SmallVector<std::pair<unsigned, MDNode *>, 1> MDs; |
| Fn.getAllMetadata(MDs); |
| for (auto MD : MDs) |
| NF->addMetadata(MD.first, *MD.second); |
| |
| // Fix up any BlockAddresses that refer to the function. |
| Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType())); |
| // Delete the bitcast that we just created, so that NF does not |
| // appear to be address-taken. |
| NF->removeDeadConstantUsers(); |
| // Finally, nuke the old function. |
| Fn.eraseFromParent(); |
| return true; |
| } |
| |
| /// RemoveDeadArgumentsFromCallers - Checks if the given function has any |
| /// arguments that are unused, and changes the caller parameters to be undefined |
| /// instead. |
| bool DeadArgumentEliminationPass::RemoveDeadArgumentsFromCallers(Function &Fn) { |
| // We cannot change the arguments if this TU does not define the function or |
| // if the linker may choose a function body from another TU, even if the |
| // nominal linkage indicates that other copies of the function have the same |
| // semantics. In the below example, the dead load from %p may not have been |
| // eliminated from the linker-chosen copy of f, so replacing %p with undef |
| // in callers may introduce undefined behavior. |
| // |
| // define linkonce_odr void @f(i32* %p) { |
| // %v = load i32 %p |
| // ret void |
| // } |
| if (!Fn.hasExactDefinition()) |
| return false; |
| |
| // Functions with local linkage should already have been handled, except the |
| // fragile (variadic) ones which we can improve here. |
| if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg()) |
| return false; |
| |
| // Don't touch naked functions. The assembly might be using an argument, or |
| // otherwise rely on the frame layout in a way that this analysis will not |
| // see. |
| if (Fn.hasFnAttribute(Attribute::Naked)) |
| return false; |
| |
| if (Fn.use_empty()) |
| return false; |
| |
| SmallVector<unsigned, 8> UnusedArgs; |
| bool Changed = false; |
| |
| for (Argument &Arg : Fn.args()) { |
| if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() && !Arg.hasByValOrInAllocaAttr()) { |
| if (Arg.isUsedByMetadata()) { |
| Arg.replaceAllUsesWith(UndefValue::get(Arg.getType())); |
| Changed = true; |
| } |
| UnusedArgs.push_back(Arg.getArgNo()); |
| } |
| } |
| |
| if (UnusedArgs.empty()) |
| return false; |
| |
| for (Use &U : Fn.uses()) { |
| CallSite CS(U.getUser()); |
| if (!CS || !CS.isCallee(&U)) |
| continue; |
| |
| // Now go through all unused args and replace them with "undef". |
| for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) { |
| unsigned ArgNo = UnusedArgs[I]; |
| |
| Value *Arg = CS.getArgument(ArgNo); |
| CS.setArgument(ArgNo, UndefValue::get(Arg->getType())); |
| ++NumArgumentsReplacedWithUndef; |
| Changed = true; |
| } |
| } |
| |
| return Changed; |
| } |
| |
| /// Convenience function that returns the number of return values. It returns 0 |
| /// for void functions and 1 for functions not returning a struct. It returns |
| /// the number of struct elements for functions returning a struct. |
| static unsigned NumRetVals(const Function *F) { |
| Type *RetTy = F->getReturnType(); |
| if (RetTy->isVoidTy()) |
| return 0; |
| else if (StructType *STy = dyn_cast<StructType>(RetTy)) |
| return STy->getNumElements(); |
| else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy)) |
| return ATy->getNumElements(); |
| else |
| return 1; |
| } |
| |
| /// Returns the sub-type a function will return at a given Idx. Should |
| /// correspond to the result type of an ExtractValue instruction executed with |
| /// just that one Idx (i.e. only top-level structure is considered). |
| static Type *getRetComponentType(const Function *F, unsigned Idx) { |
| Type *RetTy = F->getReturnType(); |
| assert(!RetTy->isVoidTy() && "void type has no subtype"); |
| |
| if (StructType *STy = dyn_cast<StructType>(RetTy)) |
| return STy->getElementType(Idx); |
| else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy)) |
| return ATy->getElementType(); |
| else |
| return RetTy; |
| } |
| |
| /// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not |
| /// live, it adds Use to the MaybeLiveUses argument. Returns the determined |
| /// liveness of Use. |
| DeadArgumentEliminationPass::Liveness |
| DeadArgumentEliminationPass::MarkIfNotLive(RetOrArg Use, |
| UseVector &MaybeLiveUses) { |
| // We're live if our use or its Function is already marked as live. |
| if (LiveFunctions.count(Use.F) || LiveValues.count(Use)) |
| return Live; |
| |
| // We're maybe live otherwise, but remember that we must become live if |
| // Use becomes live. |
| MaybeLiveUses.push_back(Use); |
| return MaybeLive; |
| } |
| |
| /// SurveyUse - This looks at a single use of an argument or return value |
| /// and determines if it should be alive or not. Adds this use to MaybeLiveUses |
| /// if it causes the used value to become MaybeLive. |
| /// |
| /// RetValNum is the return value number to use when this use is used in a |
| /// return instruction. This is used in the recursion, you should always leave |
| /// it at 0. |
| DeadArgumentEliminationPass::Liveness |
| DeadArgumentEliminationPass::SurveyUse(const Use *U, UseVector &MaybeLiveUses, |
| unsigned RetValNum) { |
| const User *V = U->getUser(); |
| if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) { |
| // The value is returned from a function. It's only live when the |
| // function's return value is live. We use RetValNum here, for the case |
| // that U is really a use of an insertvalue instruction that uses the |
| // original Use. |
| const Function *F = RI->getParent()->getParent(); |
| if (RetValNum != -1U) { |
| RetOrArg Use = CreateRet(F, RetValNum); |
| // We might be live, depending on the liveness of Use. |
| return MarkIfNotLive(Use, MaybeLiveUses); |
| } else { |
| DeadArgumentEliminationPass::Liveness Result = MaybeLive; |
| for (unsigned i = 0; i < NumRetVals(F); ++i) { |
| RetOrArg Use = CreateRet(F, i); |
| // We might be live, depending on the liveness of Use. If any |
| // sub-value is live, then the entire value is considered live. This |
| // is a conservative choice, and better tracking is possible. |
| DeadArgumentEliminationPass::Liveness SubResult = |
| MarkIfNotLive(Use, MaybeLiveUses); |
| if (Result != Live) |
| Result = SubResult; |
| } |
| return Result; |
| } |
| } |
| if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) { |
| if (U->getOperandNo() != InsertValueInst::getAggregateOperandIndex() |
| && IV->hasIndices()) |
| // The use we are examining is inserted into an aggregate. Our liveness |
| // depends on all uses of that aggregate, but if it is used as a return |
| // value, only index at which we were inserted counts. |
| RetValNum = *IV->idx_begin(); |
| |
| // Note that if we are used as the aggregate operand to the insertvalue, |
| // we don't change RetValNum, but do survey all our uses. |
| |
| Liveness Result = MaybeLive; |
| for (const Use &UU : IV->uses()) { |
| Result = SurveyUse(&UU, MaybeLiveUses, RetValNum); |
| if (Result == Live) |
| break; |
| } |
| return Result; |
| } |
| |
| if (auto CS = ImmutableCallSite(V)) { |
| const Function *F = CS.getCalledFunction(); |
| if (F) { |
| // Used in a direct call. |
| |
| // The function argument is live if it is used as a bundle operand. |
| if (CS.isBundleOperand(U)) |
| return Live; |
| |
| // Find the argument number. We know for sure that this use is an |
| // argument, since if it was the function argument this would be an |
| // indirect call and the we know can't be looking at a value of the |
| // label type (for the invoke instruction). |
| unsigned ArgNo = CS.getArgumentNo(U); |
| |
| if (ArgNo >= F->getFunctionType()->getNumParams()) |
| // The value is passed in through a vararg! Must be live. |
| return Live; |
| |
| assert(CS.getArgument(ArgNo) |
| == CS->getOperand(U->getOperandNo()) |
| && "Argument is not where we expected it"); |
| |
| // Value passed to a normal call. It's only live when the corresponding |
| // argument to the called function turns out live. |
| RetOrArg Use = CreateArg(F, ArgNo); |
| return MarkIfNotLive(Use, MaybeLiveUses); |
| } |
| } |
| // Used in any other way? Value must be live. |
| return Live; |
| } |
| |
| /// SurveyUses - This looks at all the uses of the given value |
| /// Returns the Liveness deduced from the uses of this value. |
| /// |
| /// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If |
| /// the result is Live, MaybeLiveUses might be modified but its content should |
| /// be ignored (since it might not be complete). |
| DeadArgumentEliminationPass::Liveness |
| DeadArgumentEliminationPass::SurveyUses(const Value *V, |
| UseVector &MaybeLiveUses) { |
| // Assume it's dead (which will only hold if there are no uses at all..). |
| Liveness Result = MaybeLive; |
| // Check each use. |
| for (const Use &U : V->uses()) { |
| Result = SurveyUse(&U, MaybeLiveUses); |
| if (Result == Live) |
| break; |
| } |
| return Result; |
| } |
| |
| // SurveyFunction - This performs the initial survey of the specified function, |
| // checking out whether or not it uses any of its incoming arguments or whether |
| // any callers use the return value. This fills in the LiveValues set and Uses |
| // map. |
| // |
| // We consider arguments of non-internal functions to be intrinsically alive as |
| // well as arguments to functions which have their "address taken". |
| void DeadArgumentEliminationPass::SurveyFunction(const Function &F) { |
| // Functions with inalloca parameters are expecting args in a particular |
| // register and memory layout. |
| if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca)) { |
| MarkLive(F); |
| return; |
| } |
| |
| // Don't touch naked functions. The assembly might be using an argument, or |
| // otherwise rely on the frame layout in a way that this analysis will not |
| // see. |
| if (F.hasFnAttribute(Attribute::Naked)) { |
| MarkLive(F); |
| return; |
| } |
| |
| unsigned RetCount = NumRetVals(&F); |
| |
| // Assume all return values are dead |
| using RetVals = SmallVector<Liveness, 5>; |
| |
| RetVals RetValLiveness(RetCount, MaybeLive); |
| |
| using RetUses = SmallVector<UseVector, 5>; |
| |
| // These vectors map each return value to the uses that make it MaybeLive, so |
| // we can add those to the Uses map if the return value really turns out to be |
| // MaybeLive. Initialized to a list of RetCount empty lists. |
| RetUses MaybeLiveRetUses(RetCount); |
| |
| bool HasMustTailCalls = false; |
| |
| for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { |
| if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { |
| if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType() |
| != F.getFunctionType()->getReturnType()) { |
| // We don't support old style multiple return values. |
| MarkLive(F); |
| return; |
| } |
| } |
| |
| // If we have any returns of `musttail` results - the signature can't |
| // change |
| if (BB->getTerminatingMustTailCall() != nullptr) |
| HasMustTailCalls = true; |
| } |
| |
| if (HasMustTailCalls) { |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName() |
| << " has musttail calls\n"); |
| } |
| |
| if (!F.hasLocalLinkage() && (!ShouldHackArguments || F.isIntrinsic())) { |
| MarkLive(F); |
| return; |
| } |
| |
| LLVM_DEBUG( |
| dbgs() << "DeadArgumentEliminationPass - Inspecting callers for fn: " |
| << F.getName() << "\n"); |
| // Keep track of the number of live retvals, so we can skip checks once all |
| // of them turn out to be live. |
| unsigned NumLiveRetVals = 0; |
| |
| bool HasMustTailCallers = false; |
| |
| // Loop all uses of the function. |
| for (const Use &U : F.uses()) { |
| // If the function is PASSED IN as an argument, its address has been |
| // taken. |
| ImmutableCallSite CS(U.getUser()); |
| if (!CS || !CS.isCallee(&U)) { |
| MarkLive(F); |
| return; |
| } |
| |
| // The number of arguments for `musttail` call must match the number of |
| // arguments of the caller |
| if (CS.isMustTailCall()) |
| HasMustTailCallers = true; |
| |
| // If this use is anything other than a call site, the function is alive. |
| const Instruction *TheCall = CS.getInstruction(); |
| if (!TheCall) { // Not a direct call site? |
| MarkLive(F); |
| return; |
| } |
| |
| // If we end up here, we are looking at a direct call to our function. |
| |
| // Now, check how our return value(s) is/are used in this caller. Don't |
| // bother checking return values if all of them are live already. |
| if (NumLiveRetVals == RetCount) |
| continue; |
| |
| // Check all uses of the return value. |
| for (const Use &U : TheCall->uses()) { |
| if (ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(U.getUser())) { |
| // This use uses a part of our return value, survey the uses of |
| // that part and store the results for this index only. |
| unsigned Idx = *Ext->idx_begin(); |
| if (RetValLiveness[Idx] != Live) { |
| RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]); |
| if (RetValLiveness[Idx] == Live) |
| NumLiveRetVals++; |
| } |
| } else { |
| // Used by something else than extractvalue. Survey, but assume that the |
| // result applies to all sub-values. |
| UseVector MaybeLiveAggregateUses; |
| if (SurveyUse(&U, MaybeLiveAggregateUses) == Live) { |
| NumLiveRetVals = RetCount; |
| RetValLiveness.assign(RetCount, Live); |
| break; |
| } else { |
| for (unsigned i = 0; i != RetCount; ++i) { |
| if (RetValLiveness[i] != Live) |
| MaybeLiveRetUses[i].append(MaybeLiveAggregateUses.begin(), |
| MaybeLiveAggregateUses.end()); |
| } |
| } |
| } |
| } |
| } |
| |
| if (HasMustTailCallers) { |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName() |
| << " has musttail callers\n"); |
| } |
| |
| // Now we've inspected all callers, record the liveness of our return values. |
| for (unsigned i = 0; i != RetCount; ++i) |
| MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]); |
| |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Inspecting args for fn: " |
| << F.getName() << "\n"); |
| |
| // Now, check all of our arguments. |
| unsigned i = 0; |
| UseVector MaybeLiveArgUses; |
| for (Function::const_arg_iterator AI = F.arg_begin(), |
| E = F.arg_end(); AI != E; ++AI, ++i) { |
| Liveness Result; |
| if (F.getFunctionType()->isVarArg() || HasMustTailCallers || |
| HasMustTailCalls) { |
| // Variadic functions will already have a va_arg function expanded inside |
| // them, making them potentially very sensitive to ABI changes resulting |
| // from removing arguments entirely, so don't. For example AArch64 handles |
| // register and stack HFAs very differently, and this is reflected in the |
| // IR which has already been generated. |
| // |
| // `musttail` calls to this function restrict argument removal attempts. |
| // The signature of the caller must match the signature of the function. |
| // |
| // `musttail` calls in this function prevents us from changing its |
| // signature |
| Result = Live; |
| } else { |
| // See what the effect of this use is (recording any uses that cause |
| // MaybeLive in MaybeLiveArgUses). |
| Result = SurveyUses(&*AI, MaybeLiveArgUses); |
| } |
| |
| // Mark the result. |
| MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses); |
| // Clear the vector again for the next iteration. |
| MaybeLiveArgUses.clear(); |
| } |
| } |
| |
| /// MarkValue - This function marks the liveness of RA depending on L. If L is |
| /// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses, |
| /// such that RA will be marked live if any use in MaybeLiveUses gets marked |
| /// live later on. |
| void DeadArgumentEliminationPass::MarkValue(const RetOrArg &RA, Liveness L, |
| const UseVector &MaybeLiveUses) { |
| switch (L) { |
| case Live: |
| MarkLive(RA); |
| break; |
| case MaybeLive: |
| // Note any uses of this value, so this return value can be |
| // marked live whenever one of the uses becomes live. |
| for (const auto &MaybeLiveUse : MaybeLiveUses) |
| Uses.insert(std::make_pair(MaybeLiveUse, RA)); |
| break; |
| } |
| } |
| |
| /// MarkLive - Mark the given Function as alive, meaning that it cannot be |
| /// changed in any way. Additionally, |
| /// mark any values that are used as this function's parameters or by its return |
| /// values (according to Uses) live as well. |
| void DeadArgumentEliminationPass::MarkLive(const Function &F) { |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Intrinsically live fn: " |
| << F.getName() << "\n"); |
| // Mark the function as live. |
| LiveFunctions.insert(&F); |
| // Mark all arguments as live. |
| for (unsigned i = 0, e = F.arg_size(); i != e; ++i) |
| PropagateLiveness(CreateArg(&F, i)); |
| // Mark all return values as live. |
| for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i) |
| PropagateLiveness(CreateRet(&F, i)); |
| } |
| |
| /// MarkLive - Mark the given return value or argument as live. Additionally, |
| /// mark any values that are used by this value (according to Uses) live as |
| /// well. |
| void DeadArgumentEliminationPass::MarkLive(const RetOrArg &RA) { |
| if (LiveFunctions.count(RA.F)) |
| return; // Function was already marked Live. |
| |
| if (!LiveValues.insert(RA).second) |
| return; // We were already marked Live. |
| |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Marking " |
| << RA.getDescription() << " live\n"); |
| PropagateLiveness(RA); |
| } |
| |
| /// PropagateLiveness - Given that RA is a live value, propagate it's liveness |
| /// to any other values it uses (according to Uses). |
| void DeadArgumentEliminationPass::PropagateLiveness(const RetOrArg &RA) { |
| // We don't use upper_bound (or equal_range) here, because our recursive call |
| // to ourselves is likely to cause the upper_bound (which is the first value |
| // not belonging to RA) to become erased and the iterator invalidated. |
| UseMap::iterator Begin = Uses.lower_bound(RA); |
| UseMap::iterator E = Uses.end(); |
| UseMap::iterator I; |
| for (I = Begin; I != E && I->first == RA; ++I) |
| MarkLive(I->second); |
| |
| // Erase RA from the Uses map (from the lower bound to wherever we ended up |
| // after the loop). |
| Uses.erase(Begin, I); |
| } |
| |
| // RemoveDeadStuffFromFunction - Remove any arguments and return values from F |
| // that are not in LiveValues. Transform the function and all of the callees of |
| // the function to not have these arguments and return values. |
| // |
| bool DeadArgumentEliminationPass::RemoveDeadStuffFromFunction(Function *F) { |
| // Don't modify fully live functions |
| if (LiveFunctions.count(F)) |
| return false; |
| |
| // Start by computing a new prototype for the function, which is the same as |
| // the old function, but has fewer arguments and a different return type. |
| FunctionType *FTy = F->getFunctionType(); |
| std::vector<Type*> Params; |
| |
| // Keep track of if we have a live 'returned' argument |
| bool HasLiveReturnedArg = false; |
| |
| // Set up to build a new list of parameter attributes. |
| SmallVector<AttributeSet, 8> ArgAttrVec; |
| const AttributeList &PAL = F->getAttributes(); |
| |
| // Remember which arguments are still alive. |
| SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false); |
| // Construct the new parameter list from non-dead arguments. Also construct |
| // a new set of parameter attributes to correspond. Skip the first parameter |
| // attribute, since that belongs to the return value. |
| unsigned i = 0; |
| for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); |
| I != E; ++I, ++i) { |
| RetOrArg Arg = CreateArg(F, i); |
| if (LiveValues.erase(Arg)) { |
| Params.push_back(I->getType()); |
| ArgAlive[i] = true; |
| ArgAttrVec.push_back(PAL.getParamAttributes(i)); |
| HasLiveReturnedArg |= PAL.hasParamAttribute(i, Attribute::Returned); |
| } else { |
| ++NumArgumentsEliminated; |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Removing argument " |
| << i << " (" << I->getName() << ") from " |
| << F->getName() << "\n"); |
| } |
| } |
| |
| // Find out the new return value. |
| Type *RetTy = FTy->getReturnType(); |
| Type *NRetTy = nullptr; |
| unsigned RetCount = NumRetVals(F); |
| |
| // -1 means unused, other numbers are the new index |
| SmallVector<int, 5> NewRetIdxs(RetCount, -1); |
| std::vector<Type*> RetTypes; |
| |
| // If there is a function with a live 'returned' argument but a dead return |
| // value, then there are two possible actions: |
| // 1) Eliminate the return value and take off the 'returned' attribute on the |
| // argument. |
| // 2) Retain the 'returned' attribute and treat the return value (but not the |
| // entire function) as live so that it is not eliminated. |
| // |
| // It's not clear in the general case which option is more profitable because, |
| // even in the absence of explicit uses of the return value, code generation |
| // is free to use the 'returned' attribute to do things like eliding |
| // save/restores of registers across calls. Whether or not this happens is |
| // target and ABI-specific as well as depending on the amount of register |
| // pressure, so there's no good way for an IR-level pass to figure this out. |
| // |
| // Fortunately, the only places where 'returned' is currently generated by |
| // the FE are places where 'returned' is basically free and almost always a |
| // performance win, so the second option can just be used always for now. |
| // |
| // This should be revisited if 'returned' is ever applied more liberally. |
| if (RetTy->isVoidTy() || HasLiveReturnedArg) { |
| NRetTy = RetTy; |
| } else { |
| // Look at each of the original return values individually. |
| for (unsigned i = 0; i != RetCount; ++i) { |
| RetOrArg Ret = CreateRet(F, i); |
| if (LiveValues.erase(Ret)) { |
| RetTypes.push_back(getRetComponentType(F, i)); |
| NewRetIdxs[i] = RetTypes.size() - 1; |
| } else { |
| ++NumRetValsEliminated; |
| LLVM_DEBUG( |
| dbgs() << "DeadArgumentEliminationPass - Removing return value " |
| << i << " from " << F->getName() << "\n"); |
| } |
| } |
| if (RetTypes.size() > 1) { |
| // More than one return type? Reduce it down to size. |
| if (StructType *STy = dyn_cast<StructType>(RetTy)) { |
| // Make the new struct packed if we used to return a packed struct |
| // already. |
| NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked()); |
| } else { |
| assert(isa<ArrayType>(RetTy) && "unexpected multi-value return"); |
| NRetTy = ArrayType::get(RetTypes[0], RetTypes.size()); |
| } |
| } else if (RetTypes.size() == 1) |
| // One return type? Just a simple value then, but only if we didn't use to |
| // return a struct with that simple value before. |
| NRetTy = RetTypes.front(); |
| else if (RetTypes.empty()) |
| // No return types? Make it void, but only if we didn't use to return {}. |
| NRetTy = Type::getVoidTy(F->getContext()); |
| } |
| |
| assert(NRetTy && "No new return type found?"); |
| |
| // The existing function return attributes. |
| AttrBuilder RAttrs(PAL.getRetAttributes()); |
| |
| // Remove any incompatible attributes, but only if we removed all return |
| // values. Otherwise, ensure that we don't have any conflicting attributes |
| // here. Currently, this should not be possible, but special handling might be |
| // required when new return value attributes are added. |
| if (NRetTy->isVoidTy()) |
| RAttrs.remove(AttributeFuncs::typeIncompatible(NRetTy)); |
| else |
| assert(!RAttrs.overlaps(AttributeFuncs::typeIncompatible(NRetTy)) && |
| "Return attributes no longer compatible?"); |
| |
| AttributeSet RetAttrs = AttributeSet::get(F->getContext(), RAttrs); |
| |
| // Strip allocsize attributes. They might refer to the deleted arguments. |
| AttributeSet FnAttrs = PAL.getFnAttributes().removeAttribute( |
| F->getContext(), Attribute::AllocSize); |
| |
| // Reconstruct the AttributesList based on the vector we constructed. |
| assert(ArgAttrVec.size() == Params.size()); |
| AttributeList NewPAL = |
| AttributeList::get(F->getContext(), FnAttrs, RetAttrs, ArgAttrVec); |
| |
| // Create the new function type based on the recomputed parameters. |
| FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg()); |
| |
| // No change? |
| if (NFTy == FTy) |
| return false; |
| |
| // Create the new function body and insert it into the module... |
| Function *NF = Function::Create(NFTy, F->getLinkage(), F->getAddressSpace()); |
| NF->copyAttributesFrom(F); |
| NF->setComdat(F->getComdat()); |
| NF->setAttributes(NewPAL); |
| // Insert the new function before the old function, so we won't be processing |
| // it again. |
| F->getParent()->getFunctionList().insert(F->getIterator(), NF); |
| NF->takeName(F); |
| |
| // Loop over all of the callers of the function, transforming the call sites |
| // to pass in a smaller number of arguments into the new function. |
| std::vector<Value*> Args; |
| while (!F->use_empty()) { |
| CallSite CS(F->user_back()); |
| Instruction *Call = CS.getInstruction(); |
| |
| ArgAttrVec.clear(); |
| const AttributeList &CallPAL = CS.getAttributes(); |
| |
| // Adjust the call return attributes in case the function was changed to |
| // return void. |
| AttrBuilder RAttrs(CallPAL.getRetAttributes()); |
| RAttrs.remove(AttributeFuncs::typeIncompatible(NRetTy)); |
| AttributeSet RetAttrs = AttributeSet::get(F->getContext(), RAttrs); |
| |
| // Declare these outside of the loops, so we can reuse them for the second |
| // loop, which loops the varargs. |
| CallSite::arg_iterator I = CS.arg_begin(); |
| unsigned i = 0; |
| // Loop over those operands, corresponding to the normal arguments to the |
| // original function, and add those that are still alive. |
| for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i) |
| if (ArgAlive[i]) { |
| Args.push_back(*I); |
| // Get original parameter attributes, but skip return attributes. |
| AttributeSet Attrs = CallPAL.getParamAttributes(i); |
| if (NRetTy != RetTy && Attrs.hasAttribute(Attribute::Returned)) { |
| // If the return type has changed, then get rid of 'returned' on the |
| // call site. The alternative is to make all 'returned' attributes on |
| // call sites keep the return value alive just like 'returned' |
| // attributes on function declaration but it's less clearly a win and |
| // this is not an expected case anyway |
| ArgAttrVec.push_back(AttributeSet::get( |
| F->getContext(), |
| AttrBuilder(Attrs).removeAttribute(Attribute::Returned))); |
| } else { |
| // Otherwise, use the original attributes. |
| ArgAttrVec.push_back(Attrs); |
| } |
| } |
| |
| // Push any varargs arguments on the list. Don't forget their attributes. |
| for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) { |
| Args.push_back(*I); |
| ArgAttrVec.push_back(CallPAL.getParamAttributes(i)); |
| } |
| |
| // Reconstruct the AttributesList based on the vector we constructed. |
| assert(ArgAttrVec.size() == Args.size()); |
| |
| // Again, be sure to remove any allocsize attributes, since their indices |
| // may now be incorrect. |
| AttributeSet FnAttrs = CallPAL.getFnAttributes().removeAttribute( |
| F->getContext(), Attribute::AllocSize); |
| |
| AttributeList NewCallPAL = AttributeList::get( |
| F->getContext(), FnAttrs, RetAttrs, ArgAttrVec); |
| |
| SmallVector<OperandBundleDef, 1> OpBundles; |
| CS.getOperandBundlesAsDefs(OpBundles); |
| |
| CallSite NewCS; |
| if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { |
| NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), |
| Args, OpBundles, "", Call->getParent()); |
| } else { |
| NewCS = CallInst::Create(NFTy, NF, Args, OpBundles, "", Call); |
| cast<CallInst>(NewCS.getInstruction()) |
| ->setTailCallKind(cast<CallInst>(Call)->getTailCallKind()); |
| } |
| NewCS.setCallingConv(CS.getCallingConv()); |
| NewCS.setAttributes(NewCallPAL); |
| NewCS->setDebugLoc(Call->getDebugLoc()); |
| uint64_t W; |
| if (Call->extractProfTotalWeight(W)) |
| NewCS->setProfWeight(W); |
| Args.clear(); |
| ArgAttrVec.clear(); |
| |
| Instruction *New = NewCS.getInstruction(); |
| if (!Call->use_empty() || Call->isUsedByMetadata()) { |
| if (New->getType() == Call->getType()) { |
| // Return type not changed? Just replace users then. |
| Call->replaceAllUsesWith(New); |
| New->takeName(Call); |
| } else if (New->getType()->isVoidTy()) { |
| // If the return value is dead, replace any uses of it with undef |
| // (any non-debug value uses will get removed later on). |
| if (!Call->getType()->isX86_MMXTy()) |
| Call->replaceAllUsesWith(UndefValue::get(Call->getType())); |
| } else { |
| assert((RetTy->isStructTy() || RetTy->isArrayTy()) && |
| "Return type changed, but not into a void. The old return type" |
| " must have been a struct or an array!"); |
| Instruction *InsertPt = Call; |
| if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { |
| BasicBlock *NewEdge = SplitEdge(New->getParent(), II->getNormalDest()); |
| InsertPt = &*NewEdge->getFirstInsertionPt(); |
| } |
| |
| // We used to return a struct or array. Instead of doing smart stuff |
| // with all the uses, we will just rebuild it using extract/insertvalue |
| // chaining and let instcombine clean that up. |
| // |
| // Start out building up our return value from undef |
| Value *RetVal = UndefValue::get(RetTy); |
| for (unsigned i = 0; i != RetCount; ++i) |
| if (NewRetIdxs[i] != -1) { |
| Value *V; |
| if (RetTypes.size() > 1) |
| // We are still returning a struct, so extract the value from our |
| // return value |
| V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret", |
| InsertPt); |
| else |
| // We are now returning a single element, so just insert that |
| V = New; |
| // Insert the value at the old position |
| RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt); |
| } |
| // Now, replace all uses of the old call instruction with the return |
| // struct we built |
| Call->replaceAllUsesWith(RetVal); |
| New->takeName(Call); |
| } |
| } |
| |
| // Finally, remove the old call from the program, reducing the use-count of |
| // F. |
| Call->eraseFromParent(); |
| } |
| |
| // Since we have now created the new function, splice the body of the old |
| // function right into the new function, leaving the old rotting hulk of the |
| // function empty. |
| NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); |
| |
| // Loop over the argument list, transferring uses of the old arguments over to |
| // the new arguments, also transferring over the names as well. |
| i = 0; |
| for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), |
| I2 = NF->arg_begin(); I != E; ++I, ++i) |
| if (ArgAlive[i]) { |
| // If this is a live argument, move the name and users over to the new |
| // version. |
| I->replaceAllUsesWith(&*I2); |
| I2->takeName(&*I); |
| ++I2; |
| } else { |
| // If this argument is dead, replace any uses of it with undef |
| // (any non-debug value uses will get removed later on). |
| if (!I->getType()->isX86_MMXTy()) |
| I->replaceAllUsesWith(UndefValue::get(I->getType())); |
| } |
| |
| // If we change the return value of the function we must rewrite any return |
| // instructions. Check this now. |
| if (F->getReturnType() != NF->getReturnType()) |
| for (BasicBlock &BB : *NF) |
| if (ReturnInst *RI = dyn_cast<ReturnInst>(BB.getTerminator())) { |
| Value *RetVal; |
| |
| if (NFTy->getReturnType()->isVoidTy()) { |
| RetVal = nullptr; |
| } else { |
| assert(RetTy->isStructTy() || RetTy->isArrayTy()); |
| // The original return value was a struct or array, insert |
| // extractvalue/insertvalue chains to extract only the values we need |
| // to return and insert them into our new result. |
| // This does generate messy code, but we'll let it to instcombine to |
| // clean that up. |
| Value *OldRet = RI->getOperand(0); |
| // Start out building up our return value from undef |
| RetVal = UndefValue::get(NRetTy); |
| for (unsigned i = 0; i != RetCount; ++i) |
| if (NewRetIdxs[i] != -1) { |
| ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i, |
| "oldret", RI); |
| if (RetTypes.size() > 1) { |
| // We're still returning a struct, so reinsert the value into |
| // our new return value at the new index |
| |
| RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i], |
| "newret", RI); |
| } else { |
| // We are now only returning a simple value, so just return the |
| // extracted value. |
| RetVal = EV; |
| } |
| } |
| } |
| // Replace the return instruction with one returning the new return |
| // value (possibly 0 if we became void). |
| ReturnInst::Create(F->getContext(), RetVal, RI); |
| BB.getInstList().erase(RI); |
| } |
| |
| // Clone metadatas from the old function, including debug info descriptor. |
| SmallVector<std::pair<unsigned, MDNode *>, 1> MDs; |
| F->getAllMetadata(MDs); |
| for (auto MD : MDs) |
| NF->addMetadata(MD.first, *MD.second); |
| |
| // Now that the old function is dead, delete it. |
| F->eraseFromParent(); |
| |
| return true; |
| } |
| |
| PreservedAnalyses DeadArgumentEliminationPass::run(Module &M, |
| ModuleAnalysisManager &) { |
| bool Changed = false; |
| |
| // First pass: Do a simple check to see if any functions can have their "..." |
| // removed. We can do this if they never call va_start. This loop cannot be |
| // fused with the next loop, because deleting a function invalidates |
| // information computed while surveying other functions. |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Deleting dead varargs\n"); |
| for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { |
| Function &F = *I++; |
| if (F.getFunctionType()->isVarArg()) |
| Changed |= DeleteDeadVarargs(F); |
| } |
| |
| // Second phase:loop through the module, determining which arguments are live. |
| // We assume all arguments are dead unless proven otherwise (allowing us to |
| // determine that dead arguments passed into recursive functions are dead). |
| // |
| LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Determining liveness\n"); |
| for (auto &F : M) |
| SurveyFunction(F); |
| |
| // Now, remove all dead arguments and return values from each function in |
| // turn. |
| for (Module::iterator I = M.begin(), E = M.end(); I != E; ) { |
| // Increment now, because the function will probably get removed (ie. |
| // replaced by a new one). |
| Function *F = &*I++; |
| Changed |= RemoveDeadStuffFromFunction(F); |
| } |
| |
| // Finally, look for any unused parameters in functions with non-local |
| // linkage and replace the passed in parameters with undef. |
| for (auto &F : M) |
| Changed |= RemoveDeadArgumentsFromCallers(F); |
| |
| if (!Changed) |
| return PreservedAnalyses::all(); |
| return PreservedAnalyses::none(); |
| } |