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      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 (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 
     56 PreservedAnalyses StripDeadPrototypesPass::run(Module &M,
     57                                                ModuleAnalysisManager &) {
     58   if (stripDeadPrototypes(M))
     59     return PreservedAnalyses::none();
     60   return PreservedAnalyses::all();
     61 }
     62 
     63 namespace {
     64 
     65 class StripDeadPrototypesLegacyPass : public ModulePass {
     66 public:
     67   static char ID; // Pass identification, replacement for typeid
     68   StripDeadPrototypesLegacyPass() : ModulePass(ID) {
     69     initializeStripDeadPrototypesLegacyPassPass(
     70         *PassRegistry::getPassRegistry());
     71   }
     72   bool runOnModule(Module &M) override {
     73     if (skipModule(M))
     74       return false;
     75 
     76     return stripDeadPrototypes(M);
     77   }
     78 };
     79 
     80 } // end anonymous namespace
     81 
     82 char StripDeadPrototypesLegacyPass::ID = 0;
     83 INITIALIZE_PASS(StripDeadPrototypesLegacyPass, "strip-dead-prototypes",
     84                 "Strip Unused Function Prototypes", false, false)
     85 
     86 ModulePass *llvm::createStripDeadPrototypesPass() {
     87   return new StripDeadPrototypesLegacyPass();
     88 }
     89