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