103 lines
3.1 KiB
C++
103 lines
3.1 KiB
C++
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//===- ElimAvailExtern.cpp - DCE unreachable internal functions -----------===//
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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 transform is designed to eliminate available external global
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// definitions from the program, turning them into declarations.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO/ElimAvailExtern.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/Module.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Transforms/Utils/GlobalStatus.h"
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using namespace llvm;
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#define DEBUG_TYPE "elim-avail-extern"
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STATISTIC(NumFunctions, "Number of functions removed");
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STATISTIC(NumVariables, "Number of global variables removed");
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static bool eliminateAvailableExternally(Module &M) {
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bool Changed = false;
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// Drop initializers of available externally global variables.
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for (GlobalVariable &GV : M.globals()) {
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if (!GV.hasAvailableExternallyLinkage())
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continue;
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if (GV.hasInitializer()) {
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Constant *Init = GV.getInitializer();
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GV.setInitializer(nullptr);
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if (isSafeToDestroyConstant(Init))
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Init->destroyConstant();
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}
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GV.removeDeadConstantUsers();
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GV.setLinkage(GlobalValue::ExternalLinkage);
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NumVariables++;
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Changed = true;
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}
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// Drop the bodies of available externally functions.
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for (Function &F : M) {
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if (!F.hasAvailableExternallyLinkage())
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continue;
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if (!F.isDeclaration())
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// This will set the linkage to external
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F.deleteBody();
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F.removeDeadConstantUsers();
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NumFunctions++;
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Changed = true;
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}
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return Changed;
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}
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PreservedAnalyses
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EliminateAvailableExternallyPass::run(Module &M, ModuleAnalysisManager &) {
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if (!eliminateAvailableExternally(M))
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return PreservedAnalyses::all();
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return PreservedAnalyses::none();
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}
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namespace {
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struct EliminateAvailableExternallyLegacyPass : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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EliminateAvailableExternallyLegacyPass() : ModulePass(ID) {
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initializeEliminateAvailableExternallyLegacyPassPass(
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*PassRegistry::getPassRegistry());
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}
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// run - Do the EliminateAvailableExternally pass on the specified module,
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// optionally updating the specified callgraph to reflect the changes.
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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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return eliminateAvailableExternally(M);
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}
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};
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} // end anonymous namespace
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char EliminateAvailableExternallyLegacyPass::ID = 0;
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INITIALIZE_PASS(EliminateAvailableExternallyLegacyPass, "elim-avail-extern",
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"Eliminate Available Externally Globals", false, false)
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ModulePass *llvm::createEliminateAvailableExternallyPass() {
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return new EliminateAvailableExternallyLegacyPass();
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}
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