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      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 
     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   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     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 
     82 ModulePass *llvm::createStripDeadPrototypesPass() {
     83   return new StripDeadPrototypesLegacyPass();
     84 }
     85