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1125 lines
43 KiB
1125 lines
43 KiB
//===- DeadArgumentElimination.cpp - Eliminate dead arguments -------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass deletes dead arguments from internal functions. Dead argument
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// elimination removes arguments which are directly dead, as well as arguments
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// only passed into function calls as dead arguments of other functions. This
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// pass also deletes dead return values in a similar way.
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//
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// This pass is often useful as a cleanup pass to run after aggressive
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// interprocedural passes, which add possibly-dead arguments or return values.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO/DeadArgumentElimination.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/NoFolder.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/Use.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/Value.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include <cassert>
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#include <cstdint>
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#include <utility>
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "deadargelim"
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STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
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STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
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STATISTIC(NumArgumentsReplacedWithUndef,
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"Number of unread args replaced with undef");
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namespace {
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/// DAE - The dead argument elimination pass.
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class DAE : public ModulePass {
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protected:
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// DAH uses this to specify a different ID.
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explicit DAE(char &ID) : ModulePass(ID) {}
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public:
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static char ID; // Pass identification, replacement for typeid
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DAE() : ModulePass(ID) {
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initializeDAEPass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override {
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if (skipModule(M))
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return false;
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DeadArgumentEliminationPass DAEP(ShouldHackArguments());
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ModuleAnalysisManager DummyMAM;
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PreservedAnalyses PA = DAEP.run(M, DummyMAM);
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return !PA.areAllPreserved();
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}
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virtual bool ShouldHackArguments() const { return false; }
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};
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} // end anonymous namespace
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char DAE::ID = 0;
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INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
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namespace {
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/// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
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/// deletes arguments to functions which are external. This is only for use
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/// by bugpoint.
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struct DAH : public DAE {
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static char ID;
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DAH() : DAE(ID) {}
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bool ShouldHackArguments() const override { return true; }
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};
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} // end anonymous namespace
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char DAH::ID = 0;
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INITIALIZE_PASS(DAH, "deadarghaX0r",
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"Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
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false, false)
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/// createDeadArgEliminationPass - This pass removes arguments from functions
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/// which are not used by the body of the function.
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ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
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ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
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/// DeleteDeadVarargs - If this is an function that takes a ... list, and if
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/// llvm.vastart is never called, the varargs list is dead for the function.
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bool DeadArgumentEliminationPass::DeleteDeadVarargs(Function &Fn) {
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assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
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if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
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// Ensure that the function is only directly called.
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if (Fn.hasAddressTaken())
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return false;
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// Don't touch naked functions. The assembly might be using an argument, or
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// otherwise rely on the frame layout in a way that this analysis will not
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// see.
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if (Fn.hasFnAttribute(Attribute::Naked)) {
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return false;
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}
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// Okay, we know we can transform this function if safe. Scan its body
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// looking for calls marked musttail or calls to llvm.vastart.
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for (BasicBlock &BB : Fn) {
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for (Instruction &I : BB) {
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CallInst *CI = dyn_cast<CallInst>(&I);
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if (!CI)
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continue;
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if (CI->isMustTailCall())
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return false;
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) {
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if (II->getIntrinsicID() == Intrinsic::vastart)
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return false;
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}
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}
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}
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// If we get here, there are no calls to llvm.vastart in the function body,
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// remove the "..." and adjust all the calls.
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// Start by computing a new prototype for the function, which is the same as
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// the old function, but doesn't have isVarArg set.
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FunctionType *FTy = Fn.getFunctionType();
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std::vector<Type *> Params(FTy->param_begin(), FTy->param_end());
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FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
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Params, false);
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unsigned NumArgs = Params.size();
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// Create the new function body and insert it into the module...
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Function *NF = Function::Create(NFTy, Fn.getLinkage(), Fn.getAddressSpace());
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NF->copyAttributesFrom(&Fn);
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NF->setComdat(Fn.getComdat());
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Fn.getParent()->getFunctionList().insert(Fn.getIterator(), NF);
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NF->takeName(&Fn);
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// Loop over all of the callers of the function, transforming the call sites
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// to pass in a smaller number of arguments into the new function.
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//
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std::vector<Value *> Args;
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for (Value::user_iterator I = Fn.user_begin(), E = Fn.user_end(); I != E; ) {
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CallBase *CB = dyn_cast<CallBase>(*I++);
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if (!CB)
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continue;
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// Pass all the same arguments.
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Args.assign(CB->arg_begin(), CB->arg_begin() + NumArgs);
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// Drop any attributes that were on the vararg arguments.
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AttributeList PAL = CB->getAttributes();
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if (!PAL.isEmpty()) {
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SmallVector<AttributeSet, 8> ArgAttrs;
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for (unsigned ArgNo = 0; ArgNo < NumArgs; ++ArgNo)
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ArgAttrs.push_back(PAL.getParamAttributes(ArgNo));
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PAL = AttributeList::get(Fn.getContext(), PAL.getFnAttributes(),
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PAL.getRetAttributes(), ArgAttrs);
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}
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SmallVector<OperandBundleDef, 1> OpBundles;
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CB->getOperandBundlesAsDefs(OpBundles);
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CallBase *NewCB = nullptr;
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if (InvokeInst *II = dyn_cast<InvokeInst>(CB)) {
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NewCB = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
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Args, OpBundles, "", CB);
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} else {
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NewCB = CallInst::Create(NF, Args, OpBundles, "", CB);
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cast<CallInst>(NewCB)->setTailCallKind(
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cast<CallInst>(CB)->getTailCallKind());
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}
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NewCB->setCallingConv(CB->getCallingConv());
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NewCB->setAttributes(PAL);
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NewCB->copyMetadata(*CB, {LLVMContext::MD_prof, LLVMContext::MD_dbg});
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Args.clear();
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if (!CB->use_empty())
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CB->replaceAllUsesWith(NewCB);
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NewCB->takeName(CB);
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// Finally, remove the old call from the program, reducing the use-count of
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// F.
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CB->eraseFromParent();
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}
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// Since we have now created the new function, splice the body of the old
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// function right into the new function, leaving the old rotting hulk of the
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// function empty.
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NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
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// Loop over the argument list, transferring uses of the old arguments over to
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// the new arguments, also transferring over the names as well. While we're at
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// it, remove the dead arguments from the DeadArguments list.
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for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
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I2 = NF->arg_begin(); I != E; ++I, ++I2) {
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// Move the name and users over to the new version.
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I->replaceAllUsesWith(&*I2);
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I2->takeName(&*I);
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}
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// Clone metadatas from the old function, including debug info descriptor.
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SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
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Fn.getAllMetadata(MDs);
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for (auto MD : MDs)
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NF->addMetadata(MD.first, *MD.second);
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// Fix up any BlockAddresses that refer to the function.
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Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType()));
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// Delete the bitcast that we just created, so that NF does not
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// appear to be address-taken.
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NF->removeDeadConstantUsers();
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// Finally, nuke the old function.
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Fn.eraseFromParent();
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return true;
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}
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/// RemoveDeadArgumentsFromCallers - Checks if the given function has any
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/// arguments that are unused, and changes the caller parameters to be undefined
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/// instead.
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bool DeadArgumentEliminationPass::RemoveDeadArgumentsFromCallers(Function &Fn) {
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// We cannot change the arguments if this TU does not define the function or
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// if the linker may choose a function body from another TU, even if the
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// nominal linkage indicates that other copies of the function have the same
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// semantics. In the below example, the dead load from %p may not have been
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// eliminated from the linker-chosen copy of f, so replacing %p with undef
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// in callers may introduce undefined behavior.
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//
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// define linkonce_odr void @f(i32* %p) {
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// %v = load i32 %p
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// ret void
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// }
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if (!Fn.hasExactDefinition())
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return false;
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// Functions with local linkage should already have been handled, except the
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// fragile (variadic) ones which we can improve here.
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if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
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return false;
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// Don't touch naked functions. The assembly might be using an argument, or
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// otherwise rely on the frame layout in a way that this analysis will not
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// see.
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if (Fn.hasFnAttribute(Attribute::Naked))
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return false;
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if (Fn.use_empty())
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return false;
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SmallVector<unsigned, 8> UnusedArgs;
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bool Changed = false;
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for (Argument &Arg : Fn.args()) {
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if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() &&
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!Arg.hasPassPointeeByValueCopyAttr()) {
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if (Arg.isUsedByMetadata()) {
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Arg.replaceAllUsesWith(UndefValue::get(Arg.getType()));
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Changed = true;
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}
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UnusedArgs.push_back(Arg.getArgNo());
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}
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}
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if (UnusedArgs.empty())
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return false;
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for (Use &U : Fn.uses()) {
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CallBase *CB = dyn_cast<CallBase>(U.getUser());
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if (!CB || !CB->isCallee(&U))
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continue;
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// Now go through all unused args and replace them with "undef".
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for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
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unsigned ArgNo = UnusedArgs[I];
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Value *Arg = CB->getArgOperand(ArgNo);
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CB->setArgOperand(ArgNo, UndefValue::get(Arg->getType()));
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++NumArgumentsReplacedWithUndef;
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Changed = true;
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}
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}
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return Changed;
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}
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/// Convenience function that returns the number of return values. It returns 0
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/// for void functions and 1 for functions not returning a struct. It returns
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/// the number of struct elements for functions returning a struct.
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static unsigned NumRetVals(const Function *F) {
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Type *RetTy = F->getReturnType();
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if (RetTy->isVoidTy())
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return 0;
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else if (StructType *STy = dyn_cast<StructType>(RetTy))
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return STy->getNumElements();
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else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy))
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return ATy->getNumElements();
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else
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return 1;
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}
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/// Returns the sub-type a function will return at a given Idx. Should
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/// correspond to the result type of an ExtractValue instruction executed with
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/// just that one Idx (i.e. only top-level structure is considered).
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static Type *getRetComponentType(const Function *F, unsigned Idx) {
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Type *RetTy = F->getReturnType();
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assert(!RetTy->isVoidTy() && "void type has no subtype");
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if (StructType *STy = dyn_cast<StructType>(RetTy))
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return STy->getElementType(Idx);
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else if (ArrayType *ATy = dyn_cast<ArrayType>(RetTy))
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return ATy->getElementType();
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else
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return RetTy;
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}
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/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
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/// live, it adds Use to the MaybeLiveUses argument. Returns the determined
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/// liveness of Use.
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DeadArgumentEliminationPass::Liveness
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DeadArgumentEliminationPass::MarkIfNotLive(RetOrArg Use,
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UseVector &MaybeLiveUses) {
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// We're live if our use or its Function is already marked as live.
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if (IsLive(Use))
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return Live;
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// We're maybe live otherwise, but remember that we must become live if
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// Use becomes live.
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MaybeLiveUses.push_back(Use);
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return MaybeLive;
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}
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/// SurveyUse - This looks at a single use of an argument or return value
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/// and determines if it should be alive or not. Adds this use to MaybeLiveUses
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/// if it causes the used value to become MaybeLive.
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///
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/// RetValNum is the return value number to use when this use is used in a
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/// return instruction. This is used in the recursion, you should always leave
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/// it at 0.
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DeadArgumentEliminationPass::Liveness
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DeadArgumentEliminationPass::SurveyUse(const Use *U, UseVector &MaybeLiveUses,
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unsigned RetValNum) {
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const User *V = U->getUser();
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if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
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// The value is returned from a function. It's only live when the
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// function's return value is live. We use RetValNum here, for the case
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// that U is really a use of an insertvalue instruction that uses the
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// original Use.
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const Function *F = RI->getParent()->getParent();
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if (RetValNum != -1U) {
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RetOrArg Use = CreateRet(F, RetValNum);
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// We might be live, depending on the liveness of Use.
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return MarkIfNotLive(Use, MaybeLiveUses);
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} else {
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DeadArgumentEliminationPass::Liveness Result = MaybeLive;
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for (unsigned Ri = 0; Ri < NumRetVals(F); ++Ri) {
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RetOrArg Use = CreateRet(F, Ri);
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// We might be live, depending on the liveness of Use. If any
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// sub-value is live, then the entire value is considered live. This
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// is a conservative choice, and better tracking is possible.
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DeadArgumentEliminationPass::Liveness SubResult =
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MarkIfNotLive(Use, MaybeLiveUses);
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if (Result != Live)
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Result = SubResult;
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}
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return Result;
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}
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}
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if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
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if (U->getOperandNo() != InsertValueInst::getAggregateOperandIndex()
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&& IV->hasIndices())
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// The use we are examining is inserted into an aggregate. Our liveness
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// depends on all uses of that aggregate, but if it is used as a return
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// value, only index at which we were inserted counts.
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RetValNum = *IV->idx_begin();
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// Note that if we are used as the aggregate operand to the insertvalue,
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// we don't change RetValNum, but do survey all our uses.
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Liveness Result = MaybeLive;
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for (const Use &UU : IV->uses()) {
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Result = SurveyUse(&UU, MaybeLiveUses, RetValNum);
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if (Result == Live)
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break;
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}
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return Result;
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}
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if (const auto *CB = dyn_cast<CallBase>(V)) {
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const Function *F = CB->getCalledFunction();
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if (F) {
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// Used in a direct call.
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// The function argument is live if it is used as a bundle operand.
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if (CB->isBundleOperand(U))
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return Live;
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// Find the argument number. We know for sure that this use is an
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// argument, since if it was the function argument this would be an
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// indirect call and the we know can't be looking at a value of the
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// label type (for the invoke instruction).
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unsigned ArgNo = CB->getArgOperandNo(U);
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if (ArgNo >= F->getFunctionType()->getNumParams())
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// The value is passed in through a vararg! Must be live.
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return Live;
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assert(CB->getArgOperand(ArgNo) == CB->getOperand(U->getOperandNo()) &&
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"Argument is not where we expected it");
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// Value passed to a normal call. It's only live when the corresponding
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// argument to the called function turns out live.
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RetOrArg Use = CreateArg(F, ArgNo);
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return MarkIfNotLive(Use, MaybeLiveUses);
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}
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}
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// Used in any other way? Value must be live.
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return Live;
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}
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/// SurveyUses - This looks at all the uses of the given value
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/// Returns the Liveness deduced from the uses of this value.
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///
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/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
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/// the result is Live, MaybeLiveUses might be modified but its content should
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/// be ignored (since it might not be complete).
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DeadArgumentEliminationPass::Liveness
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DeadArgumentEliminationPass::SurveyUses(const Value *V,
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UseVector &MaybeLiveUses) {
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// Assume it's dead (which will only hold if there are no uses at all..).
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Liveness Result = MaybeLive;
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// Check each use.
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for (const Use &U : V->uses()) {
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Result = SurveyUse(&U, MaybeLiveUses);
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if (Result == Live)
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break;
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}
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return Result;
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}
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// SurveyFunction - This performs the initial survey of the specified function,
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// 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/preallocated parameters are expecting args in a
|
|
// particular register and memory layout.
|
|
if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca) ||
|
|
F.getAttributes().hasAttrSomewhere(Attribute::Preallocated)) {
|
|
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.
|
|
const auto *CB = dyn_cast<CallBase>(U.getUser());
|
|
if (!CB || !CB->isCallee(&U)) {
|
|
MarkLive(F);
|
|
return;
|
|
}
|
|
|
|
// The number of arguments for `musttail` call must match the number of
|
|
// arguments of the caller
|
|
if (CB->isMustTailCall())
|
|
HasMustTailCallers = true;
|
|
|
|
// 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 : CB->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 Ri = 0; Ri != RetCount; ++Ri) {
|
|
if (RetValLiveness[Ri] != Live)
|
|
MaybeLiveRetUses[Ri].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 Ri = 0; Ri != RetCount; ++Ri)
|
|
MarkValue(CreateRet(&F, Ri), RetValLiveness[Ri], MaybeLiveRetUses[Ri]);
|
|
|
|
LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Inspecting args for fn: "
|
|
<< F.getName() << "\n");
|
|
|
|
// Now, check all of our arguments.
|
|
unsigned ArgI = 0;
|
|
UseVector MaybeLiveArgUses;
|
|
for (Function::const_arg_iterator AI = F.arg_begin(), E = F.arg_end();
|
|
AI != E; ++AI, ++ArgI) {
|
|
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, ArgI), 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:
|
|
assert(!IsLive(RA) && "Use is already live!");
|
|
for (const auto &MaybeLiveUse : MaybeLiveUses) {
|
|
if (IsLive(MaybeLiveUse)) {
|
|
// A use is live, so this value is live.
|
|
MarkLive(RA);
|
|
break;
|
|
} else {
|
|
// Note any uses of this value, so this value can be
|
|
// marked live whenever one of the uses becomes live.
|
|
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 ArgI = 0, E = F.arg_size(); ArgI != E; ++ArgI)
|
|
PropagateLiveness(CreateArg(&F, ArgI));
|
|
// Mark all return values as live.
|
|
for (unsigned Ri = 0, E = NumRetVals(&F); Ri != E; ++Ri)
|
|
PropagateLiveness(CreateRet(&F, Ri));
|
|
}
|
|
|
|
/// 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 (IsLive(RA))
|
|
return; // Already marked Live.
|
|
|
|
LiveValues.insert(RA);
|
|
|
|
LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Marking "
|
|
<< RA.getDescription() << " live\n");
|
|
PropagateLiveness(RA);
|
|
}
|
|
|
|
bool DeadArgumentEliminationPass::IsLive(const RetOrArg &RA) {
|
|
return LiveFunctions.count(RA.F) || LiveValues.count(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 ArgI = 0;
|
|
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
|
|
++I, ++ArgI) {
|
|
RetOrArg Arg = CreateArg(F, ArgI);
|
|
if (LiveValues.erase(Arg)) {
|
|
Params.push_back(I->getType());
|
|
ArgAlive[ArgI] = true;
|
|
ArgAttrVec.push_back(PAL.getParamAttributes(ArgI));
|
|
HasLiveReturnedArg |= PAL.hasParamAttribute(ArgI, Attribute::Returned);
|
|
} else {
|
|
++NumArgumentsEliminated;
|
|
LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Removing argument "
|
|
<< ArgI << " (" << 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 Ri = 0; Ri != RetCount; ++Ri) {
|
|
RetOrArg Ret = CreateRet(F, Ri);
|
|
if (LiveValues.erase(Ret)) {
|
|
RetTypes.push_back(getRetComponentType(F, Ri));
|
|
NewRetIdxs[Ri] = RetTypes.size() - 1;
|
|
} else {
|
|
++NumRetValsEliminated;
|
|
LLVM_DEBUG(
|
|
dbgs() << "DeadArgumentEliminationPass - Removing return value "
|
|
<< Ri << " 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()) {
|
|
CallBase &CB = cast<CallBase>(*F->user_back());
|
|
|
|
ArgAttrVec.clear();
|
|
const AttributeList &CallPAL = CB.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.
|
|
auto I = CB.arg_begin();
|
|
unsigned Pi = 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(); Pi != E; ++I, ++Pi)
|
|
if (ArgAlive[Pi]) {
|
|
Args.push_back(*I);
|
|
// Get original parameter attributes, but skip return attributes.
|
|
AttributeSet Attrs = CallPAL.getParamAttributes(Pi);
|
|
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 (auto E = CB.arg_end(); I != E; ++I, ++Pi) {
|
|
Args.push_back(*I);
|
|
ArgAttrVec.push_back(CallPAL.getParamAttributes(Pi));
|
|
}
|
|
|
|
// 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;
|
|
CB.getOperandBundlesAsDefs(OpBundles);
|
|
|
|
CallBase *NewCB = nullptr;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(&CB)) {
|
|
NewCB = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
|
|
Args, OpBundles, "", CB.getParent());
|
|
} else {
|
|
NewCB = CallInst::Create(NFTy, NF, Args, OpBundles, "", &CB);
|
|
cast<CallInst>(NewCB)->setTailCallKind(
|
|
cast<CallInst>(&CB)->getTailCallKind());
|
|
}
|
|
NewCB->setCallingConv(CB.getCallingConv());
|
|
NewCB->setAttributes(NewCallPAL);
|
|
NewCB->copyMetadata(CB, {LLVMContext::MD_prof, LLVMContext::MD_dbg});
|
|
Args.clear();
|
|
ArgAttrVec.clear();
|
|
|
|
if (!CB.use_empty() || CB.isUsedByMetadata()) {
|
|
if (NewCB->getType() == CB.getType()) {
|
|
// Return type not changed? Just replace users then.
|
|
CB.replaceAllUsesWith(NewCB);
|
|
NewCB->takeName(&CB);
|
|
} else if (NewCB->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 (!CB.getType()->isX86_MMXTy())
|
|
CB.replaceAllUsesWith(UndefValue::get(CB.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 = &CB;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(&CB)) {
|
|
BasicBlock *NewEdge =
|
|
SplitEdge(NewCB->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 Ri = 0; Ri != RetCount; ++Ri)
|
|
if (NewRetIdxs[Ri] != -1) {
|
|
Value *V;
|
|
IRBuilder<NoFolder> IRB(InsertPt);
|
|
if (RetTypes.size() > 1)
|
|
// We are still returning a struct, so extract the value from our
|
|
// return value
|
|
V = IRB.CreateExtractValue(NewCB, NewRetIdxs[Ri], "newret");
|
|
else
|
|
// We are now returning a single element, so just insert that
|
|
V = NewCB;
|
|
// Insert the value at the old position
|
|
RetVal = IRB.CreateInsertValue(RetVal, V, Ri, "oldret");
|
|
}
|
|
// Now, replace all uses of the old call instruction with the return
|
|
// struct we built
|
|
CB.replaceAllUsesWith(RetVal);
|
|
NewCB->takeName(&CB);
|
|
}
|
|
}
|
|
|
|
// Finally, remove the old call from the program, reducing the use-count of
|
|
// F.
|
|
CB.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.
|
|
ArgI = 0;
|
|
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
|
|
I2 = NF->arg_begin();
|
|
I != E; ++I, ++ArgI)
|
|
if (ArgAlive[ArgI]) {
|
|
// 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())) {
|
|
IRBuilder<NoFolder> IRB(RI);
|
|
Value *RetVal = nullptr;
|
|
|
|
if (!NFTy->getReturnType()->isVoidTy()) {
|
|
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 RetI = 0; RetI != RetCount; ++RetI)
|
|
if (NewRetIdxs[RetI] != -1) {
|
|
Value *EV = IRB.CreateExtractValue(OldRet, RetI, "oldret");
|
|
|
|
if (RetTypes.size() > 1) {
|
|
// We're still returning a struct, so reinsert the value into
|
|
// our new return value at the new index
|
|
|
|
RetVal = IRB.CreateInsertValue(RetVal, EV, NewRetIdxs[RetI],
|
|
"newret");
|
|
} 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).
|
|
auto *NewRet = ReturnInst::Create(F->getContext(), RetVal, RI);
|
|
NewRet->setDebugLoc(RI->getDebugLoc());
|
|
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();
|
|
}
|