1 //===-- ElimAvailExtern.cpp - DCE unreachable internal functions
2 //----------------===//
4 // The LLVM Compiler Infrastructure
6 // This file is distributed under the University of Illinois Open Source
7 // License. See LICENSE.TXT for details.
9 //===----------------------------------------------------------------------===//
11 // This transform is designed to eliminate available external global
12 // definitions from the program, turning them into declarations.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/IPO.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Transforms/Utils/GlobalStatus.h"
21 #include "llvm/Pass.h"
24 #define DEBUG_TYPE "elim-avail-extern"
26 STATISTIC(NumFunctions, "Number of functions removed");
27 STATISTIC(NumVariables, "Number of global variables removed");
30 struct EliminateAvailableExternally : public ModulePass {
31 static char ID; // Pass identification, replacement for typeid
32 EliminateAvailableExternally() : ModulePass(ID) {
33 initializeEliminateAvailableExternallyPass(
34 *PassRegistry::getPassRegistry());
37 // run - Do the EliminateAvailableExternally pass on the specified module,
38 // optionally updating the specified callgraph to reflect the changes.
40 bool runOnModule(Module &M) override;
44 char EliminateAvailableExternally::ID = 0;
45 INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
46 "Eliminate Available Externally Globals", false, false)
48 ModulePass *llvm::createEliminateAvailableExternallyPass() {
49 return new EliminateAvailableExternally();
52 bool EliminateAvailableExternally::runOnModule(Module &M) {
55 // Drop initializers of available externally global variables.
56 for (GlobalVariable &GV : M.globals()) {
57 if (!GV.hasAvailableExternallyLinkage())
59 if (GV.hasInitializer()) {
60 Constant *Init = GV.getInitializer();
61 GV.setInitializer(nullptr);
62 if (isSafeToDestroyConstant(Init))
63 Init->destroyConstant();
65 GV.removeDeadConstantUsers();
66 GV.setLinkage(GlobalValue::ExternalLinkage);
71 // Drop the bodies of available externally functions.
72 for (Function &F : M) {
73 if (!F.hasAvailableExternallyLinkage())
75 if (!F.isDeclaration())
76 // This will set the linkage to external
78 F.removeDeadConstantUsers();