1 //===-- StripDeadPrototypes.cpp - Remove unused function declarations ----===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass loops over all of the functions in the input module, looking for
10 // dead declarations and removes them. Dead declarations are declarations of
11 // functions for which no implementation is available (i.e., declarations for
12 // unused library functions).
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/Transforms/IPO/StripDeadPrototypes.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/IR/Module.h"
19 #include "llvm/InitializePasses.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 
29 static bool stripDeadPrototypes(Module &M) {
30   bool MadeChange = false;
31 
32   // Erase dead function prototypes.
33   for (Function &F : llvm::make_early_inc_range(M)) {
34     // Function must be a prototype and unused.
35     if (F.isDeclaration() && F.use_empty()) {
36       F.eraseFromParent();
37       ++NumDeadPrototypes;
38       MadeChange = true;
39     }
40   }
41 
42   // Erase dead global var prototypes.
43   for (GlobalVariable &GV : llvm::make_early_inc_range(M.globals())) {
44     // Global must be a prototype and unused.
45     if (GV.isDeclaration() && GV.use_empty())
46       GV.eraseFromParent();
47   }
48 
49   // Return an indication of whether we changed anything or not.
50   return MadeChange;
51 }
52 
53 PreservedAnalyses StripDeadPrototypesPass::run(Module &M,
54                                                ModuleAnalysisManager &) {
55   if (stripDeadPrototypes(M))
56     return PreservedAnalyses::none();
57   return PreservedAnalyses::all();
58 }
59 
60 namespace {
61 
62 class StripDeadPrototypesLegacyPass : public ModulePass {
63 public:
64   static char ID; // Pass identification, replacement for typeid
65   StripDeadPrototypesLegacyPass() : ModulePass(ID) {
66     initializeStripDeadPrototypesLegacyPassPass(
67         *PassRegistry::getPassRegistry());
68   }
69   bool runOnModule(Module &M) override {
70     if (skipModule(M))
71       return false;
72 
73     return stripDeadPrototypes(M);
74   }
75 };
76 
77 } // end anonymous namespace
78 
79 char StripDeadPrototypesLegacyPass::ID = 0;
80 INITIALIZE_PASS(StripDeadPrototypesLegacyPass, "strip-dead-prototypes",
81                 "Strip Unused Function Prototypes", false, false)
82 
83 ModulePass *llvm::createStripDeadPrototypesPass() {
84   return new StripDeadPrototypesLegacyPass();
85 }
86