StripDeadPrototypes.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
1//===-- StripDeadPrototypes.cpp - Remove unused function declarations ----===//
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 pass loops over all of the functions in the input module, looking for
11// dead declarations and removes them. Dead declarations are declarations of
12// functions for which no implementation is available (i.e., declarations for
13// unused library functions).
14//
15//===----------------------------------------------------------------------===//
16
17#define DEBUG_TYPE "strip-dead-prototypes"
18#include "llvm/Transforms/IPO.h"
19#include "llvm/ADT/Statistic.h"
20#include "llvm/IR/Module.h"
21#include "llvm/Pass.h"
22using namespace llvm;
23
24STATISTIC(NumDeadPrototypes, "Number of dead prototypes removed");
25
26namespace {
27
28/// @brief Pass to remove unused function declarations.
29class StripDeadPrototypesPass : public ModulePass {
30public:
31  static char ID; // Pass identification, replacement for typeid
32  StripDeadPrototypesPass() : ModulePass(ID) {
33    initializeStripDeadPrototypesPassPass(*PassRegistry::getPassRegistry());
34  }
35  bool runOnModule(Module &M) override;
36};
37
38} // end anonymous namespace
39
40char StripDeadPrototypesPass::ID = 0;
41INITIALIZE_PASS(StripDeadPrototypesPass, "strip-dead-prototypes",
42                "Strip Unused Function Prototypes", false, false)
43
44bool StripDeadPrototypesPass::runOnModule(Module &M) {
45  bool MadeChange = false;
46
47  // Erase dead function prototypes.
48  for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
49    Function *F = I++;
50    // Function must be a prototype and unused.
51    if (F->isDeclaration() && F->use_empty()) {
52      F->eraseFromParent();
53      ++NumDeadPrototypes;
54      MadeChange = true;
55    }
56  }
57
58  // Erase dead global var prototypes.
59  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
60       I != E; ) {
61    GlobalVariable *GV = I++;
62    // Global must be a prototype and unused.
63    if (GV->isDeclaration() && GV->use_empty())
64      GV->eraseFromParent();
65  }
66
67  // Return an indication of whether we changed anything or not.
68  return MadeChange;
69}
70
71ModulePass *llvm::createStripDeadPrototypesPass() {
72  return new StripDeadPrototypesPass();
73}
74