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 #include "llvm/Transforms/IPO/StripDeadPrototypes.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Pass.h"
21 #include "llvm/Transforms/IPO.h"
22 
23 using namespace llvm;
24 
25 #define DEBUG_TYPE "strip-dead-prototypes"
26 
27 STATISTIC(NumDeadPrototypes, "Number of dead prototypes removed");
28 
stripDeadPrototypes(Module & M)29 static bool stripDeadPrototypes(Module &M) {
30   bool MadeChange = false;
31 
32   // Erase dead function prototypes.
33   for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
34     Function *F = &*I++;
35     // Function must be a prototype and unused.
36     if (F->isDeclaration() && F->use_empty()) {
37       F->eraseFromParent();
38       ++NumDeadPrototypes;
39       MadeChange = true;
40     }
41   }
42 
43   // Erase dead global var prototypes.
44   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
45        I != E; ) {
46     GlobalVariable *GV = &*I++;
47     // Global must be a prototype and unused.
48     if (GV->isDeclaration() && GV->use_empty())
49       GV->eraseFromParent();
50   }
51 
52   // Return an indication of whether we changed anything or not.
53   return MadeChange;
54 }
55 
run(Module & M)56 PreservedAnalyses StripDeadPrototypesPass::run(Module &M) {
57   if (stripDeadPrototypes(M))
58     return PreservedAnalyses::none();
59   return PreservedAnalyses::all();
60 }
61 
62 namespace {
63 
64 class StripDeadPrototypesLegacyPass : public ModulePass {
65 public:
66   static char ID; // Pass identification, replacement for typeid
StripDeadPrototypesLegacyPass()67   StripDeadPrototypesLegacyPass() : ModulePass(ID) {
68     initializeStripDeadPrototypesLegacyPassPass(
69         *PassRegistry::getPassRegistry());
70   }
runOnModule(Module & M)71   bool runOnModule(Module &M) override {
72     return stripDeadPrototypes(M);
73   }
74 };
75 
76 } // end anonymous namespace
77 
78 char StripDeadPrototypesLegacyPass::ID = 0;
79 INITIALIZE_PASS(StripDeadPrototypesLegacyPass, "strip-dead-prototypes",
80                 "Strip Unused Function Prototypes", false, false)
81 
createStripDeadPrototypesPass()82 ModulePass *llvm::createStripDeadPrototypesPass() {
83   return new StripDeadPrototypesLegacyPass();
84 }
85