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/Module.h"
  16 #include "llvm/Pass.h"
  17 #include "llvm/Constants.h"
  18 #include "llvm/Transforms/IPO.h"
  19 #include "llvm/Support/Compiler.h"
  20 #include <algorithm>
  21 using namespace llvm;
  22
  23 namespace {
  24   /// @brief A pass to extract specific functions and their dependencies.
  25   class VISIBILITY_HIDDEN GVExtractorPass : public ModulePass {
  26     std::vector<GlobalValue*> Named;
  27     bool deleteStuff;
  28     bool reLink;
  29   public:
  30     static char ID; // Pass identification, replacement for typeid
  31
  32     /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
  33     /// specified function. Otherwise, it deletes as much of the module as
  34     /// possible, except for the function specified.
  35     ///
  36     explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true,
  37                              bool relinkCallees = false)
  38       : ModulePass(&ID), Named(GVs), deleteStuff(deleteS),
  39         reLink(relinkCallees) {}
  40
  41     bool runOnModule(Module &M) {
  42       if (Named.size() == 0) {
  43         return false;  // Nothing to extract
  44       }
  45
  46       if (deleteStuff)
  47         return deleteGV();
  48       M.setModuleInlineAsm("");
  49       return isolateGV(M);
  50     }
  51
  52     bool deleteGV() {
  53       for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
  54              GE = Named.end(); GI != GE; ++GI) {
  55         if (Function* NamedFunc = dyn_cast<Function>(*GI)) {
  56          // If we're in relinking mode, set linkage of all internal callees to
  57          // external. This will allow us extract function, and then - link
  58          // everything together
  59          if (reLink) {
  60            for (Function::iterator B = NamedFunc->begin(), BE = NamedFunc->end();
  61                 B != BE; ++B) {
  62              for (BasicBlock::iterator I = B->begin(), E = B->end();
  63                   I != E; ++I) {
  64                if (CallInst* callInst = dyn_cast<CallInst>(&*I)) {
  65                  Function* Callee = callInst->getCalledFunction();
  66                  if (Callee && Callee->hasLocalLinkage())
  67                    Callee->setLinkage(GlobalValue::ExternalLinkage);
  68                }
  69              }
  70            }
  71          }
  72
  73          NamedFunc->setLinkage(GlobalValue::ExternalLinkage);
  74          NamedFunc->deleteBody();
  75          assert(NamedFunc->isDeclaration() && "This didn't make the function external!");
  76        } else {
  77           if (!(*GI)->isDeclaration()) {
  78             cast<GlobalVariable>(*GI)->setInitializer(0);  //clear the initializer
  79             (*GI)->setLinkage(GlobalValue::ExternalLinkage);
  80           }
  81         }
  82       }
  83       return true;
  84     }
  85
  86     bool isolateGV(Module &M) {
  87       // Mark all globals internal
  88       // FIXME: what should we do with private linkage?
  89       for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I)
  90         if (!I->isDeclaration()) {
  91           I->setLinkage(GlobalValue::InternalLinkage);
  92         }
  93       for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
  94         if (!I->isDeclaration()) {
  95           I->setLinkage(GlobalValue::InternalLinkage);
  96         }
  97
  98       // Make sure our result is globally accessible...
  99       // by putting them in the used array
 100       {
 101         std::vector<Constant *> AUGs;
 102         const Type *SBP= PointerType::getUnqual(Type::Int8Ty);
 103         for (std::vector<GlobalValue*>::iterator GI = Named.begin(),
 104                GE = Named.end(); GI != GE; ++GI) {
 105           (*GI)->setLinkage(GlobalValue::ExternalLinkage);
 106           AUGs.push_back(ConstantExpr::getBitCast(*GI, SBP));
 107         }
 108         ArrayType *AT = ArrayType::get(SBP, AUGs.size());
 109         Constant *Init = ConstantArray::get(AT, AUGs);
 110         GlobalValue *gv = new GlobalVariable(AT, false,
 111                                              GlobalValue::AppendingLinkage,
 112                                              Init, "llvm.used", &M);
 113         gv->setSection("llvm.metadata");
 114       }
 115
 116       // All of the functions may be used by global variables or the named
 117       // globals.  Loop through them and create a new, external functions that
 118       // can be "used", instead of ones with bodies.
 119       std::vector<Function*> NewFunctions;
 120
 121       Function *Last = --M.end();  // Figure out where the last real fn is.
 122
 123       for (Module::iterator I = M.begin(); ; ++I) {
 124         if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
 125           Function *New = Function::Create(I->getFunctionType(),
 126                                            GlobalValue::ExternalLinkage);
 127           New->copyAttributesFrom(I);
 128
 129           // If it's not the named function, delete the body of the function
 130           I->dropAllReferences();
 131
 132           M.getFunctionList().push_back(New);
 133           NewFunctions.push_back(New);
 134           New->takeName(I);
 135         }
 136
 137         if (&*I == Last) break;  // Stop after processing the last function
 138       }
 139
 140       // Now that we have replacements all set up, loop through the module,
 141       // deleting the old functions, replacing them with the newly created
 142       // functions.
 143       if (!NewFunctions.empty()) {
 144         unsigned FuncNum = 0;
 145         Module::iterator I = M.begin();
 146         do {
 147           if (std::find(Named.begin(), Named.end(), &*I) == Named.end()) {
 148             // Make everything that uses the old function use the new dummy fn
 149             I->replaceAllUsesWith(NewFunctions[FuncNum++]);
 150
 151             Function *Old = I;
 152             ++I;  // Move the iterator to the new function
 153
 154             // Delete the old function!
 155             M.getFunctionList().erase(Old);
 156
 157           } else {
 158             ++I;  // Skip the function we are extracting
 159           }
 160         } while (&*I != NewFunctions[0]);
 161       }
 162
 163       return true;
 164     }
 165   };
 166
 167   char GVExtractorPass::ID = 0;
 168 }
 169
 170 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
 171                                          bool deleteFn, bool relinkCallees) {
 172   return new GVExtractorPass(GVs, deleteFn, relinkCallees);
 173 }