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//===- CtorUtils.cpp - Helpers for working with global_ctors ----*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines functions that are used to process llvm.global_ctors.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/CtorUtils.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "ctor_utils"
namespace llvm {
namespace {
/// Given a specified llvm.global_ctors list, install the
/// specified array.
void installGlobalCtors(GlobalVariable *GCL,
const std::vector<Function *> &Ctors) {
// If we made a change, reassemble the initializer list.
Constant *CSVals[3];
StructType *StructTy =
cast<StructType>(GCL->getType()->getElementType()->getArrayElementType());
// Create the new init list.
std::vector<Constant *> CAList;
for (Function *F : Ctors) {
Type *Int32Ty = Type::getInt32Ty(GCL->getContext());
if (F) {
CSVals[0] = ConstantInt::get(Int32Ty, 65535);
CSVals[1] = F;
} else {
CSVals[0] = ConstantInt::get(Int32Ty, 0x7fffffff);
CSVals[1] = Constant::getNullValue(StructTy->getElementType(1));
}
// FIXME: Only allow the 3-field form in LLVM 4.0.
size_t NumElts = StructTy->getNumElements();
if (NumElts > 2)
CSVals[2] = Constant::getNullValue(StructTy->getElementType(2));
CAList.push_back(
ConstantStruct::get(StructTy, makeArrayRef(CSVals, NumElts)));
}
// Create the array initializer.
Constant *CA =
ConstantArray::get(ArrayType::get(StructTy, CAList.size()), CAList);
// If we didn't change the number of elements, don't create a new GV.
if (CA->getType() == GCL->getInitializer()->getType()) {
GCL->setInitializer(CA);
return;
}
// Create the new global and insert it next to the existing list.
GlobalVariable *NGV =
new GlobalVariable(CA->getType(), GCL->isConstant(), GCL->getLinkage(),
CA, "", GCL->getThreadLocalMode());
GCL->getParent()->getGlobalList().insert(GCL, NGV);
NGV->takeName(GCL);
// Nuke the old list, replacing any uses with the new one.
if (!GCL->use_empty()) {
Constant *V = NGV;
if (V->getType() != GCL->getType())
V = ConstantExpr::getBitCast(V, GCL->getType());
GCL->replaceAllUsesWith(V);
}
GCL->eraseFromParent();
}
/// Given a llvm.global_ctors list that we can understand,
/// return a list of the functions and null terminator as a vector.
std::vector<Function*> parseGlobalCtors(GlobalVariable *GV) {
if (GV->getInitializer()->isNullValue())
return std::vector<Function *>();
ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
std::vector<Function *> Result;
Result.reserve(CA->getNumOperands());
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
ConstantStruct *CS = cast<ConstantStruct>(*i);
Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
}
return Result;
}
/// Find the llvm.global_ctors list, verifying that all initializers have an
/// init priority of 65535.
GlobalVariable *findGlobalCtors(Module &M) {
GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
if (!GV)
return nullptr;
// Verify that the initializer is simple enough for us to handle. We are
// only allowed to optimize the initializer if it is unique.
if (!GV->hasUniqueInitializer())
return nullptr;
if (isa<ConstantAggregateZero>(GV->getInitializer()))
return GV;
ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
if (isa<ConstantAggregateZero>(*i))
continue;
ConstantStruct *CS = cast<ConstantStruct>(*i);
if (isa<ConstantPointerNull>(CS->getOperand(1)))
continue;
// Must have a function or null ptr.
if (!isa<Function>(CS->getOperand(1)))
return nullptr;
// Init priority must be standard.
ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
if (CI->getZExtValue() != 65535)
return nullptr;
}
return GV;
}
} // namespace
/// Call "ShouldRemove" for every entry in M's global_ctor list and remove the
/// entries for which it returns true. Return true if anything changed.
bool optimizeGlobalCtorsList(Module &M,
function_ref<bool(Function *)> ShouldRemove) {
GlobalVariable *GlobalCtors = findGlobalCtors(M);
if (!GlobalCtors)
return false;
std::vector<Function *> Ctors = parseGlobalCtors(GlobalCtors);
if (Ctors.empty())
return false;
bool MadeChange = false;
// Loop over global ctors, optimizing them when we can.
for (unsigned i = 0; i != Ctors.size(); ++i) {
Function *F = Ctors[i];
// Found a null terminator in the middle of the list, prune off the rest of
// the list.
if (!F) {
if (i != Ctors.size() - 1) {
Ctors.resize(i + 1);
MadeChange = true;
}
break;
}
DEBUG(dbgs() << "Optimizing Global Constructor: " << *F << "\n");
// We cannot simplify external ctor functions.
if (F->empty())
continue;
// If we can evaluate the ctor at compile time, do.
if (ShouldRemove(F)) {
Ctors.erase(Ctors.begin() + i);
MadeChange = true;
--i;
continue;
}
}
if (!MadeChange)
return false;
installGlobalCtors(GlobalCtors, Ctors);
return true;
}
} // End llvm namespace
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