1 //===-- ElimAvailExtern.cpp - DCE unreachable internal functions ----------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This transform is designed to eliminate available external global
11 // definitions from the program, turning them into declarations.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/Transforms/IPO.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Transforms/Utils/CtorUtils.h"
21 #include "llvm/Transforms/Utils/GlobalStatus.h"
22 #include "llvm/Pass.h"
23 using namespace llvm;
24
25 #define DEBUG_TYPE "elim-avail-extern"
26
27 STATISTIC(NumFunctions, "Number of functions removed");
28 STATISTIC(NumVariables, "Number of global variables removed");
29
30 namespace {
31 struct EliminateAvailableExternally : public ModulePass {
32 static char ID; // Pass identification, replacement for typeid
EliminateAvailableExternally__anonefc3233e0111::EliminateAvailableExternally33 EliminateAvailableExternally() : ModulePass(ID) {
34 initializeEliminateAvailableExternallyPass(
35 *PassRegistry::getPassRegistry());
36 }
37
38 // run - Do the EliminateAvailableExternally pass on the specified module,
39 // optionally updating the specified callgraph to reflect the changes.
40 //
41 bool runOnModule(Module &M) override;
42 };
43 }
44
45 char EliminateAvailableExternally::ID = 0;
46 INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
47 "Eliminate Available Externally Globals", false, false)
48
createEliminateAvailableExternallyPass()49 ModulePass *llvm::createEliminateAvailableExternallyPass() {
50 return new EliminateAvailableExternally();
51 }
52
runOnModule(Module & M)53 bool EliminateAvailableExternally::runOnModule(Module &M) {
54 bool Changed = false;
55
56 // Drop initializers of available externally global variables.
57 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
58 I != E; ++I) {
59 if (!I->hasAvailableExternallyLinkage())
60 continue;
61 if (I->hasInitializer()) {
62 Constant *Init = I->getInitializer();
63 I->setInitializer(nullptr);
64 if (isSafeToDestroyConstant(Init))
65 Init->destroyConstant();
66 }
67 I->removeDeadConstantUsers();
68 I->setLinkage(GlobalValue::ExternalLinkage);
69 NumVariables++;
70 }
71
72 // Drop the bodies of available externally functions.
73 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
74 if (!I->hasAvailableExternallyLinkage())
75 continue;
76 if (!I->isDeclaration())
77 // This will set the linkage to external
78 I->deleteBody();
79 I->removeDeadConstantUsers();
80 NumFunctions++;
81 }
82
83 return Changed;
84 }
85