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//===-- ExtractGV.cpp - Global Value extraction pass ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass extracts global values
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SetVector.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/IPO.h"
#include <algorithm>
using namespace llvm;
/// Make sure GV is visible from both modules. Delete is true if it is
/// being deleted from this module.
/// This also makes sure GV cannot be dropped so that references from
/// the split module remain valid.
static void makeVisible(GlobalValue &GV, bool Delete) {
bool Local = GV.hasLocalLinkage();
if (Local || Delete) {
GV.setLinkage(GlobalValue::ExternalLinkage);
if (Local)
GV.setVisibility(GlobalValue::HiddenVisibility);
return;
}
if (!GV.hasLinkOnceLinkage()) {
assert(!GV.isDiscardableIfUnused());
return;
}
// Map linkonce* to weak* so that llvm doesn't drop this GV.
switch(GV.getLinkage()) {
default:
llvm_unreachable("Unexpected linkage");
case GlobalValue::LinkOnceAnyLinkage:
GV.setLinkage(GlobalValue::WeakAnyLinkage);
return;
case GlobalValue::LinkOnceODRLinkage:
GV.setLinkage(GlobalValue::WeakODRLinkage);
return;
}
}
namespace {
/// A pass to extract specific global values and their dependencies.
class GVExtractorPass : public ModulePass {
SetVector<GlobalValue *> Named;
bool deleteStuff;
bool keepConstInit;
public:
static char ID; // Pass identification, replacement for typeid
/// If deleteS is true, this pass deletes the specified global values.
/// Otherwise, it deletes as much of the module as possible, except for the
/// global values specified.
explicit GVExtractorPass(std::vector<GlobalValue*> &GVs,
bool deleteS = true, bool keepConstInit = false)
: ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS),
keepConstInit(keepConstInit) {}
bool runOnModule(Module &M) override {
if (skipModule(M))
return false;
// Visit the global inline asm.
if (!deleteStuff)
M.setModuleInlineAsm("");
// For simplicity, just give all GlobalValues ExternalLinkage. A trickier
// implementation could figure out which GlobalValues are actually
// referenced by the Named set, and which GlobalValues in the rest of
// the module are referenced by the NamedSet, and get away with leaving
// more internal and private things internal and private. But for now,
// be conservative and simple.
// Visit the GlobalVariables.
for (GlobalVariable &GV : M.globals()) {
bool Delete = deleteStuff == (bool)Named.count(&GV) &&
!GV.isDeclaration() &&
(!GV.isConstant() || !keepConstInit);
if (!Delete) {
if (GV.hasAvailableExternallyLinkage())
continue;
if (GV.getName() == "llvm.global_ctors")
continue;
}
makeVisible(GV, Delete);
if (Delete) {
// Make this a declaration and drop it's comdat.
GV.setInitializer(nullptr);
GV.setComdat(nullptr);
}
}
// Visit the Functions.
for (Function &F : M) {
bool Delete =
deleteStuff == (bool)Named.count(&F) && !F.isDeclaration();
if (!Delete) {
if (F.hasAvailableExternallyLinkage())
continue;
}
makeVisible(F, Delete);
if (Delete) {
// Make this a declaration and drop it's comdat.
F.deleteBody();
F.setComdat(nullptr);
}
}
// Visit the Aliases.
for (GlobalAlias &GA : llvm::make_early_inc_range(M.aliases())) {
bool Delete = deleteStuff == (bool)Named.count(&GA);
makeVisible(GA, Delete);
if (Delete) {
Type *Ty = GA.getValueType();
GA.removeFromParent();
llvm::Value *Declaration;
if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
Declaration =
Function::Create(FTy, GlobalValue::ExternalLinkage,
GA.getAddressSpace(), GA.getName(), &M);
} else {
Declaration =
new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
nullptr, GA.getName());
}
GA.replaceAllUsesWith(Declaration);
delete &GA;
}
}
return true;
}
};
char GVExtractorPass::ID = 0;
}
ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
bool deleteFn, bool keepConstInit) {
return new GVExtractorPass(GVs, deleteFn, keepConstInit);
}
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