forked from OSchip/llvm-project
122 lines
4.1 KiB
C++
122 lines
4.1 KiB
C++
//===-- ElimAvailExtern.cpp - DCE unreachable internal functions
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//----------------===//
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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/Module.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(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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static void convertAliasToDeclaration(GlobalAlias &GA, Module &M) {
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GlobalValue *GVal = GA.getBaseObject();
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GlobalValue *NewGV;
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if (auto *GVar = dyn_cast<GlobalVariable>(GVal)) {
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GlobalVariable *NewGVar = new GlobalVariable(
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M, GVar->getType()->getElementType(), GVar->isConstant(),
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GVar->getLinkage(), /*init*/ nullptr, GA.getName(), GVar,
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GVar->getThreadLocalMode(), GVar->getType()->getAddressSpace());
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NewGV = NewGVar;
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NewGV->copyAttributesFrom(GVar);
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} else {
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auto *F = dyn_cast<Function>(GVal);
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assert(F);
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Function *NewF = Function::Create(F->getFunctionType(), F->getLinkage(),
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GA.getName(), &M);
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NewGV = NewF;
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NewGV->copyAttributesFrom(F);
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}
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GA.replaceAllUsesWith(ConstantExpr::getBitCast(NewGV, GA.getType()));
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GA.eraseFromParent();
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}
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bool EliminateAvailableExternally::runOnModule(Module &M) {
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bool Changed = false;
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// Convert any aliases that alias with an available externally
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// value (which will be turned into declarations later on in this routine)
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// into declarations themselves. All aliases must be definitions, and
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// must alias with a definition. So this involves creating a declaration
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// equivalent to the alias's base object.
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for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;) {
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// Increment the iterator first since we may delete the current alias.
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GlobalAlias &GA = *(I++);
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GlobalValue *GVal = GA.getBaseObject();
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if (!GVal->hasAvailableExternallyLinkage())
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continue;
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convertAliasToDeclaration(GA, M);
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Changed = true;
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}
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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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