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      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/Transforms/IPO.h"
     15 #include "llvm/ADT/SetVector.h"
     16 #include "llvm/IR/Constants.h"
     17 #include "llvm/IR/Instructions.h"
     18 #include "llvm/IR/LLVMContext.h"
     19 #include "llvm/IR/Module.h"
     20 #include "llvm/Pass.h"
     21 #include <algorithm>
     22 using namespace llvm;
     23 
     24 /// Make sure GV is visible from both modules. Delete is true if it is
     25 /// being deleted from this module.
     26 /// This also makes sure GV cannot be dropped so that references from
     27 /// the split module remain valid.
     28 static void makeVisible(GlobalValue &GV, bool Delete) {
     29   bool Local = GV.hasLocalLinkage();
     30   if (Local || Delete) {
     31     GV.setLinkage(GlobalValue::ExternalLinkage);
     32     if (Local)
     33       GV.setVisibility(GlobalValue::HiddenVisibility);
     34     return;
     35   }
     36 
     37   if (!GV.hasLinkOnceLinkage()) {
     38     assert(!GV.isDiscardableIfUnused());
     39     return;
     40   }
     41 
     42   // Map linkonce* to weak* so that llvm doesn't drop this GV.
     43   switch(GV.getLinkage()) {
     44   default:
     45     llvm_unreachable("Unexpected linkage");
     46   case GlobalValue::LinkOnceAnyLinkage:
     47     GV.setLinkage(GlobalValue::WeakAnyLinkage);
     48     return;
     49   case GlobalValue::LinkOnceODRLinkage:
     50     GV.setLinkage(GlobalValue::WeakODRLinkage);
     51     return;
     52   }
     53 }
     54 
     55 namespace {
     56   /// @brief A pass to extract specific functions and their dependencies.
     57   class GVExtractorPass : public ModulePass {
     58     SetVector<GlobalValue *> Named;
     59     bool deleteStuff;
     60   public:
     61     static char ID; // Pass identification, replacement for typeid
     62 
     63     /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
     64     /// specified function. Otherwise, it deletes as much of the module as
     65     /// possible, except for the function specified.
     66     ///
     67     explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true)
     68       : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS) {}
     69 
     70     bool runOnModule(Module &M) override {
     71       // Visit the global inline asm.
     72       if (!deleteStuff)
     73         M.setModuleInlineAsm("");
     74 
     75       // For simplicity, just give all GlobalValues ExternalLinkage. A trickier
     76       // implementation could figure out which GlobalValues are actually
     77       // referenced by the Named set, and which GlobalValues in the rest of
     78       // the module are referenced by the NamedSet, and get away with leaving
     79       // more internal and private things internal and private. But for now,
     80       // be conservative and simple.
     81 
     82       // Visit the GlobalVariables.
     83       for (Module::global_iterator I = M.global_begin(), E = M.global_end();
     84            I != E; ++I) {
     85         bool Delete =
     86           deleteStuff == (bool)Named.count(I) && !I->isDeclaration();
     87         if (!Delete) {
     88           if (I->hasAvailableExternallyLinkage())
     89             continue;
     90           if (I->getName() == "llvm.global_ctors")
     91             continue;
     92         }
     93 
     94 	makeVisible(*I, Delete);
     95 
     96         if (Delete)
     97           I->setInitializer(nullptr);
     98       }
     99 
    100       // Visit the Functions.
    101       for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
    102         bool Delete =
    103           deleteStuff == (bool)Named.count(I) && !I->isDeclaration();
    104         if (!Delete) {
    105           if (I->hasAvailableExternallyLinkage())
    106             continue;
    107         }
    108 
    109 	makeVisible(*I, Delete);
    110 
    111         if (Delete)
    112           I->deleteBody();
    113       }
    114 
    115       // Visit the Aliases.
    116       for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
    117            I != E;) {
    118         Module::alias_iterator CurI = I;
    119         ++I;
    120 
    121 	bool Delete = deleteStuff == (bool)Named.count(CurI);
    122 	makeVisible(*CurI, Delete);
    123 
    124         if (Delete) {
    125           Type *Ty =  CurI->getType()->getElementType();
    126 
    127           CurI->removeFromParent();
    128           llvm::Value *Declaration;
    129           if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
    130             Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
    131                                            CurI->getName(), &M);
    132 
    133           } else {
    134             Declaration =
    135               new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
    136                                  nullptr, CurI->getName());
    137 
    138           }
    139           CurI->replaceAllUsesWith(Declaration);
    140           delete CurI;
    141         }
    142       }
    143 
    144       return true;
    145     }
    146   };
    147 
    148   char GVExtractorPass::ID = 0;
    149 }
    150 
    151 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue*>& GVs,
    152                                          bool deleteFn) {
    153   return new GVExtractorPass(GVs, deleteFn);
    154 }
    155