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b78ea510c1
O2 compiles just before GlobalDCE, unless we are preparing for LTO. This pass eliminates available externally globals (turning them into declarations), regardless of whether they are dead/unreferenced, since we are guaranteed to have a copy available elsewhere at link time. This enables additional opportunities for GlobalDCE. If we are preparing for LTO (e.g. a -flto -c compile), the pass is not included as we want to preserve available externally functions for possible link time inlining. The FE indicates whether we are doing an -flto compile via the new PrepareForLTO flag on the PassManagerBuilder. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239480 91177308-0d34-0410-b5e6-96231b3b80d8
97 lines
3.1 KiB
C++
97 lines
3.1 KiB
C++
//===-- ElimAvailExtern.cpp - DCE unreachable internal functions ----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Transforms/Utils/CtorUtils.h"
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#include "llvm/Transforms/Utils/GlobalStatus.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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#define DEBUG_TYPE "elim-avail-extern"
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STATISTIC(NumAliases , "Number of global aliases removed");
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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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namespace {
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struct EliminateAvailableExternally : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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EliminateAvailableExternally() : ModulePass(ID) {
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initializeEliminateAvailableExternallyPass(
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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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//
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bool runOnModule(Module &M) override;
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};
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}
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char EliminateAvailableExternally::ID = 0;
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INITIALIZE_PASS(EliminateAvailableExternally, "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 EliminateAvailableExternally();
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}
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bool EliminateAvailableExternally::runOnModule(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 (Module::global_iterator I = M.global_begin(), E = M.global_end();
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I != E; ++I) {
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if (!I->hasAvailableExternallyLinkage())
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continue;
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if (I->hasInitializer()) {
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Constant *Init = I->getInitializer();
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I->setInitializer(nullptr);
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if (isSafeToDestroyConstant(Init))
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Init->destroyConstant();
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}
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I->removeDeadConstantUsers();
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I->setLinkage(GlobalValue::ExternalLinkage);
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NumVariables++;
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}
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// Drop the bodies of available externally functions.
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
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if (!I->hasAvailableExternallyLinkage())
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continue;
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if (!I->isDeclaration())
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// This will set the linkage to external
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I->deleteBody();
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I->removeDeadConstantUsers();
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NumFunctions++;
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}
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// Drop targets of available externally aliases.
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for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;
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++I) {
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if (!I->hasAvailableExternallyLinkage())
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continue;
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I->setAliasee(nullptr);
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I->removeDeadConstantUsers();
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I->setLinkage(GlobalValue::ExternalLinkage);
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NumAliases++;
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}
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return Changed;
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}
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