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This allows us to put dynamic initializers for weak data into the same comdat group as the data being initialized. This is necessary for MSVC ABI compatibility. Once we have comdats for guard variables, we can use the combination to help GlobalOpt fire more often for weak data with guarded initialization on other platforms. Reviewers: nlewycky Differential Revision: http://reviews.llvm.org/D3499 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209015 91177308-0d34-0410-b5e6-96231b3b80d8
184 lines
5.7 KiB
C++
184 lines
5.7 KiB
C++
//===- CtorUtils.cpp - Helpers for working with global_ctors ----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines functions that are used to process llvm.global_ctors.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/CtorUtils.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/Debug.h"
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#define DEBUG_TYPE "ctor_utils"
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namespace llvm {
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namespace {
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/// Given a specified llvm.global_ctors list, install the
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/// specified array.
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void installGlobalCtors(GlobalVariable *GCL,
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const std::vector<Function *> &Ctors) {
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// If we made a change, reassemble the initializer list.
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Constant *CSVals[3];
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StructType *StructTy =
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cast<StructType>(GCL->getType()->getElementType()->getArrayElementType());
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// Create the new init list.
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std::vector<Constant *> CAList;
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for (Function *F : Ctors) {
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Type *Int32Ty = Type::getInt32Ty(GCL->getContext());
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if (F) {
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CSVals[0] = ConstantInt::get(Int32Ty, 65535);
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CSVals[1] = F;
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} else {
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CSVals[0] = ConstantInt::get(Int32Ty, 0x7fffffff);
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CSVals[1] = Constant::getNullValue(StructTy->getElementType(1));
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}
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// FIXME: Only allow the 3-field form in LLVM 4.0.
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size_t NumElts = StructTy->getNumElements();
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if (NumElts > 2)
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CSVals[2] = Constant::getNullValue(StructTy->getElementType(2));
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CAList.push_back(
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ConstantStruct::get(StructTy, makeArrayRef(CSVals, NumElts)));
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}
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// Create the array initializer.
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Constant *CA =
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ConstantArray::get(ArrayType::get(StructTy, CAList.size()), CAList);
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// If we didn't change the number of elements, don't create a new GV.
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if (CA->getType() == GCL->getInitializer()->getType()) {
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GCL->setInitializer(CA);
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return;
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}
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// Create the new global and insert it next to the existing list.
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GlobalVariable *NGV =
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new GlobalVariable(CA->getType(), GCL->isConstant(), GCL->getLinkage(),
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CA, "", GCL->getThreadLocalMode());
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GCL->getParent()->getGlobalList().insert(GCL, NGV);
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NGV->takeName(GCL);
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// Nuke the old list, replacing any uses with the new one.
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if (!GCL->use_empty()) {
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Constant *V = NGV;
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if (V->getType() != GCL->getType())
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V = ConstantExpr::getBitCast(V, GCL->getType());
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GCL->replaceAllUsesWith(V);
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}
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GCL->eraseFromParent();
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}
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/// Given a llvm.global_ctors list that we can understand,
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/// return a list of the functions and null terminator as a vector.
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std::vector<Function*> parseGlobalCtors(GlobalVariable *GV) {
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if (GV->getInitializer()->isNullValue())
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return std::vector<Function *>();
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ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
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std::vector<Function *> Result;
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Result.reserve(CA->getNumOperands());
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for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
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ConstantStruct *CS = cast<ConstantStruct>(*i);
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Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
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}
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return Result;
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}
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/// Find the llvm.global_ctors list, verifying that all initializers have an
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/// init priority of 65535.
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GlobalVariable *findGlobalCtors(Module &M) {
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GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
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if (!GV)
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return nullptr;
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// Verify that the initializer is simple enough for us to handle. We are
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// only allowed to optimize the initializer if it is unique.
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if (!GV->hasUniqueInitializer())
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return nullptr;
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if (isa<ConstantAggregateZero>(GV->getInitializer()))
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return GV;
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ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
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for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
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if (isa<ConstantAggregateZero>(*i))
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continue;
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ConstantStruct *CS = cast<ConstantStruct>(*i);
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if (isa<ConstantPointerNull>(CS->getOperand(1)))
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continue;
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// Must have a function or null ptr.
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if (!isa<Function>(CS->getOperand(1)))
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return nullptr;
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// Init priority must be standard.
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ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
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if (CI->getZExtValue() != 65535)
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return nullptr;
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}
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return GV;
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}
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} // namespace
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/// Call "ShouldRemove" for every entry in M's global_ctor list and remove the
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/// entries for which it returns true. Return true if anything changed.
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bool optimizeGlobalCtorsList(Module &M,
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function_ref<bool(Function *)> ShouldRemove) {
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GlobalVariable *GlobalCtors = findGlobalCtors(M);
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if (!GlobalCtors)
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return false;
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std::vector<Function *> Ctors = parseGlobalCtors(GlobalCtors);
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if (Ctors.empty())
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return false;
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bool MadeChange = false;
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// Loop over global ctors, optimizing them when we can.
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for (unsigned i = 0; i != Ctors.size(); ++i) {
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Function *F = Ctors[i];
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// Found a null terminator in the middle of the list, prune off the rest of
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// the list.
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if (!F) {
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if (i != Ctors.size() - 1) {
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Ctors.resize(i + 1);
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MadeChange = true;
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}
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break;
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}
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DEBUG(dbgs() << "Optimizing Global Constructor: " << *F << "\n");
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// We cannot simplify external ctor functions.
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if (F->empty())
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continue;
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// If we can evaluate the ctor at compile time, do.
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if (ShouldRemove(F)) {
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Ctors.erase(Ctors.begin() + i);
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MadeChange = true;
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--i;
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continue;
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}
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}
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if (!MadeChange)
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return false;
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installGlobalCtors(GlobalCtors, Ctors);
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return true;
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}
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} // End llvm namespace
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