+//===-- ElimAvailExtern.cpp - DCE unreachable internal functions ----------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This transform is designed to eliminate available external global
+// definitions from the program, turning them into declarations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/CtorUtils.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
+#include "llvm/Pass.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "elim-avail-extern"
+
+STATISTIC(NumAliases , "Number of global aliases removed");
+STATISTIC(NumFunctions, "Number of functions removed");
+STATISTIC(NumVariables, "Number of global variables removed");
+
+namespace {
+ struct EliminateAvailableExternally : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ EliminateAvailableExternally() : ModulePass(ID) {
+ initializeEliminateAvailableExternallyPass(
+ *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;
+ };
+}
+
+char EliminateAvailableExternally::ID = 0;
+INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
+ "Eliminate Available Externally Globals", false, false)
+
+ModulePass *llvm::createEliminateAvailableExternallyPass() {
+ return new EliminateAvailableExternally();
+}
+
+bool EliminateAvailableExternally::runOnModule(Module &M) {
+ bool Changed = false;
+
+ // Drop initializers of available externally global variables.
+ for (Module::global_iterator I = M.global_begin(), E = M.global_end();
+ I != E; ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ if (I->hasInitializer()) {
+ Constant *Init = I->getInitializer();
+ I->setInitializer(nullptr);
+ if (isSafeToDestroyConstant(Init))
+ Init->destroyConstant();
+ }
+ I->removeDeadConstantUsers();
+ I->setLinkage(GlobalValue::ExternalLinkage);
+ NumVariables++;
+ }
+
+ // Drop the bodies of available externally functions.
+ for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ if (!I->isDeclaration())
+ // This will set the linkage to external
+ I->deleteBody();
+ I->removeDeadConstantUsers();
+ NumFunctions++;
+ }
+
+ // Drop targets of available externally aliases.
+ for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;
+ ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ I->setAliasee(nullptr);
+ I->removeDeadConstantUsers();
+ I->setLinkage(GlobalValue::ExternalLinkage);
+ NumAliases++;
+ }
+
+ return Changed;
+}