lib/Transforms/IPO/ExtractGV.cpp

   1 //===-- ExtractGV.cpp - Global Value extraction pass ----------------------===//
   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 extracts global values
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Instructions.h"
  15 #include "llvm/LLVMContext.h"
  16 #include "llvm/Module.h"
  17 #include "llvm/Pass.h"
  18 #include "llvm/Constants.h"
  19 #include "llvm/Transforms/IPO.h"
  20 #include "llvm/Support/Compiler.h"
  21 #include <algorithm>
  22 using namespace llvm;
  23
  24 namespace {
  25   /// @brief A pass to extract specific functions and their dependencies.
  26   class VISIBILITY_HIDDEN GVExtractorPass : public ModulePass {
  27     std::vector<GlobalValue*> Named;
  28     bool deleteStuff;
  29     bool reLink;
  30   public:
  31     static char ID; // Pass identification, replacement for typeid
  32
  33     /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
  34     /// specified function. Otherwise, it deletes as much of the module as
  35     /// possible, except for the function specified.
  36     ///
  37     explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true,
  38                              bool relinkCallees = false)
  39       : ModulePass(&ID), Named(GVs), deleteStuff(deleteS),
  40         reLink(relinkCallees) {}
  41
  42     bool runOnModule(Module &M) {
  43       if (Named.size() == 0) {
  44         return false;  // Nothing to extract
  45       }
  46
  47
  48       if (deleteStuff)
  49         return deleteGV();
  50       M.setModuleInlineAsm("");
  51       return isolateGV(M);
  52     }
  53
  54     bool deleteGV() {
  55       for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
  56              GE = Named.end(); GI != GE; ++GI) {
  57         if (Function* NamedFunc = dyn_cast<Function>(*GI)) {
  58          // If we're in relinking mode, set linkage of all internal callees to
  59          // external. This will allow us extract function, and then - link
  60          // everything together
  61          if (reLink) {
  62            for (Function::iterator B = NamedFunc->begin(), BE = NamedFunc->end();
  63                 B != BE; ++B) {
  64              for (BasicBlock::iterator I = B->begin(), E = B->end();
  65                   I != E; ++I) {
  66                if (CallInst* callInst = dyn_cast<CallInst>(&*I)) {
  67                  Function* Callee = callInst->getCalledFunction();
  68                  if (Callee && Callee->hasLocalLinkage())
  69                    Callee->setLinkage(GlobalValue::ExternalLinkage);
  70                }
  71              }
  72            }
  73          }
  74
  75          NamedFunc->setLinkage(GlobalValue::ExternalLinkage);
  76          NamedFunc->deleteBody();
  77          assert(NamedFunc->isDeclaration() && "This didn't make the function external!");
  78        } else {
  79           if (!(*GI)->isDeclaration()) {
  80             cast<GlobalVariable>(*GI)->setInitializer(0);  //clear the initializer
  81             (*GI)->setLinkage(GlobalValue::ExternalLinkage);
  82           }
  83         }
  84       }
  85       return true;
  86     }
  87
  88     bool isolateGV(Module &M) {
  89       // Mark all globals internal
  90       // FIXME: what should we do with private linkage?
  91       for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
  92         if (!I->isDeclaration()) {
  93           I->setLinkage(GlobalValue::InternalLinkage);
  94         }
  95       for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
  96         if (!I->isDeclaration()) {
  97           I->setLinkage(GlobalValue::InternalLinkage);
  98         }
  99
 100       // Make sure our result is globally accessible...
 101       // by putting them in the used array
 102       {
 103         std::vector<Constant *> AUGs;
 104         const Type *SBP=
 105               PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
 106         for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
 107                GE = Named.end(); GI != GE; ++GI) {
 108           (*GI)->setLinkage(GlobalValue::ExternalLinkage);
 109           AUGs.push_back(ConstantExpr::getBitCast(*GI, SBP));
 110         }
 111         ArrayType *AT = ArrayType::get(SBP, AUGs.size());
 112         Constant *Init = ConstantArray::get(AT, AUGs);
 113         GlobalValue *gv = new GlobalVariable(M, AT, false,
 114                                              GlobalValue::AppendingLinkage,
 115                                              Init, "llvm.used");
 116         gv->setSection("llvm.metadata");
 117       }
 118
 119       // All of the functions may be used by global variables or the named
 120       // globals.  Loop through them and create a new, external functions that
 121       // can be "used", instead of ones with bodies.
 122       std::vector<Function*> NewFunctions;
 123
 124       Function *Last = --M.end();  // Figure out where the last real fn is.
 125
 126       for (Module::iterator I = M.begin(); ; ++I) {
 127         if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
 128           Function *New = Function::Create(I->getFunctionType(),
 129                                            GlobalValue::ExternalLinkage);
 130           New->copyAttributesFrom(I);
 131
 132           // If it's not the named function, delete the body of the function
 133           I->dropAllReferences();
 134
 135           M.getFunctionList().push_back(New);
 136           NewFunctions.push_back(New);
 137           New->takeName(I);
 138         }
 139
 140         if (&*I == Last) break;  // Stop after processing the last function
 141       }
 142
 143       // Now that we have replacements all set up, loop through the module,
 144       // deleting the old functions, replacing them with the newly created
 145       // functions.
 146       if (!NewFunctions.empty()) {
 147         unsigned FuncNum = 0;
 148         Module::iterator I = M.begin();
 149         do {
 150           if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
 151             // Make everything that uses the old function use the new dummy fn
 152             I->replaceAllUsesWith(NewFunctions[FuncNum++]);
 153
 154             Function *Old = I;
 155             ++I;  // Move the iterator to the new function
 156
 157             // Delete the old function!
 158             M.getFunctionList().erase(Old);
 159
 160           } else {
 161             ++I;  // Skip the function we are extracting
 162           }
 163         } while (&*I != NewFunctions[0]);
 164       }
 165
 166       return true;
 167     }
 168   };
 169
 170   char GVExtractorPass::ID = 0;
 171 }
 172
 173 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
 174                                          bool deleteFn, bool relinkCallees) {
 175   return new GVExtractorPass(GVs, deleteFn, relinkCallees);
 176 }