lib/Transforms/IPO/StripDeadPrototypes.cpp

   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/Pass.h"
  20 #include "llvm/Transforms/IPO.h"
  21
  22 using namespace llvm;
  23
  24 #define DEBUG_TYPE "strip-dead-prototypes"
  25
  26 STATISTIC(NumDeadPrototypes, "Number of dead prototypes removed");
  27
  28 static bool stripDeadPrototypes(Module &M) {
  29   bool MadeChange = false;
  30
  31   // Erase dead function prototypes.
  32   for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
  33     Function *F = &*I++;
  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 (Module::global_iterator I = M.global_begin(), E = M.global_end();
  44        I != E; ) {
  45     GlobalVariable *GV = &*I++;
  46     // Global must be a prototype and unused.
  47     if (GV->isDeclaration() && GV->use_empty())
  48       GV->eraseFromParent();
  49   }
  50
  51   // Return an indication of whether we changed anything or not.
  52   return MadeChange;
  53 }
  54
  55 PreservedAnalyses StripDeadPrototypesPass::run(Module &M,
  56                                                ModuleAnalysisManager &) {
  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
  67   StripDeadPrototypesLegacyPass() : ModulePass(ID) {
  68     initializeStripDeadPrototypesLegacyPassPass(
  69         *PassRegistry::getPassRegistry());
  70   }
  71   bool runOnModule(Module &M) override {
  72     if (skipModule(M))
  73       return false;
  74
  75     return stripDeadPrototypes(M);
  76   }
  77 };
  78
  79 } // end anonymous namespace
  80
  81 char StripDeadPrototypesLegacyPass::ID = 0;
  82 INITIALIZE_PASS(StripDeadPrototypesLegacyPass, "strip-dead-prototypes",
  83                 "Strip Unused Function Prototypes", false, false)
  84
  85 ModulePass *llvm::createStripDeadPrototypesPass() {
  86   return new StripDeadPrototypesLegacyPass();
  87 }