1 //===-- ElimAvailExtern.cpp - DCE unreachable internal functions
2 //----------------===//
3 //
4 // The LLVM Compiler Infrastructure
5 //
6 // This file is distributed under the University of Illinois Open Source
7 // License. See LICENSE.TXT for details.
8 //
9 //===----------------------------------------------------------------------===//
10 //
11 // This transform is designed to eliminate available external global
12 // definitions from the program, turning them into declarations.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/Transforms/IPO/ElimAvailExtern.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Transforms/IPO.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
eliminateAvailableExternally(Module & M)30 static bool eliminateAvailableExternally(Module &M) {
31 bool Changed = false;
32
33 // Drop initializers of available externally global variables.
34 for (GlobalVariable &GV : M.globals()) {
35 if (!GV.hasAvailableExternallyLinkage())
36 continue;
37 if (GV.hasInitializer()) {
38 Constant *Init = GV.getInitializer();
39 GV.setInitializer(nullptr);
40 if (isSafeToDestroyConstant(Init))
41 Init->destroyConstant();
42 }
43 GV.removeDeadConstantUsers();
44 GV.setLinkage(GlobalValue::ExternalLinkage);
45 NumVariables++;
46 Changed = true;
47 }
48
49 // Drop the bodies of available externally functions.
50 for (Function &F : M) {
51 if (!F.hasAvailableExternallyLinkage())
52 continue;
53 if (!F.isDeclaration())
54 // This will set the linkage to external
55 F.deleteBody();
56 F.removeDeadConstantUsers();
57 NumFunctions++;
58 Changed = true;
59 }
60
61 return Changed;
62 }
63
64 PreservedAnalyses
run(Module & M,ModuleAnalysisManager &)65 EliminateAvailableExternallyPass::run(Module &M, ModuleAnalysisManager &) {
66 if (!eliminateAvailableExternally(M))
67 return PreservedAnalyses::all();
68 return PreservedAnalyses::none();
69 }
70
71 namespace {
72 struct EliminateAvailableExternallyLegacyPass : public ModulePass {
73 static char ID; // Pass identification, replacement for typeid
EliminateAvailableExternallyLegacyPass__anond93dac900111::EliminateAvailableExternallyLegacyPass74 EliminateAvailableExternallyLegacyPass() : ModulePass(ID) {
75 initializeEliminateAvailableExternallyLegacyPassPass(
76 *PassRegistry::getPassRegistry());
77 }
78
79 // run - Do the EliminateAvailableExternally pass on the specified module,
80 // optionally updating the specified callgraph to reflect the changes.
81 //
runOnModule__anond93dac900111::EliminateAvailableExternallyLegacyPass82 bool runOnModule(Module &M) {
83 if (skipModule(M))
84 return false;
85 return eliminateAvailableExternally(M);
86 }
87 };
88 }
89
90 char EliminateAvailableExternallyLegacyPass::ID = 0;
91 INITIALIZE_PASS(EliminateAvailableExternallyLegacyPass, "elim-avail-extern",
92 "Eliminate Available Externally Globals", false, false)
93
createEliminateAvailableExternallyPass()94 ModulePass *llvm::createEliminateAvailableExternallyPass() {
95 return new EliminateAvailableExternallyLegacyPass();
96 }
97