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Rather than slurping in and splatting out the whole ctor list, preserve the existing array entries without trying to understand them. Only remove the entries that we know we can optimize away. This way we don't need to wire through priority and comdats or anything else we might add. Fixes a linker issue where the .init_array or .ctors entry would point to discarded initialization code if the comdat group from the TU with the faulty global_ctors entry was dropped. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218337 91177308-0d34-0410-b5e6-96231b3b80d8
165 lines
5.2 KiB
C++
165 lines
5.2 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/ADT/BitVector.h"
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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, remove the listed elements.
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void removeGlobalCtors(GlobalVariable *GCL, const BitVector &CtorsToRemove) {
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// Filter out the initializer elements to remove.
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ConstantArray *OldCA = cast<ConstantArray>(GCL->getInitializer());
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SmallVector<Constant *, 10> CAList;
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for (unsigned I = 0, E = OldCA->getNumOperands(); I < E; ++I)
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if (!CtorsToRemove.test(I))
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CAList.push_back(OldCA->getOperand(I));
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// Create the new array initializer.
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ArrayType *ATy =
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ArrayType::get(OldCA->getType()->getElementType(), CAList.size());
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Constant *CA = ConstantArray::get(ATy, 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() == OldCA->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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unsigned NumCtors = Ctors.size();
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BitVector CtorsToRemove(NumCtors);
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for (unsigned i = 0; i != Ctors.size() && NumCtors > 0; ++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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continue;
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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[i] = nullptr;
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CtorsToRemove.set(i);
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NumCtors--;
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MadeChange = true;
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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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removeGlobalCtors(GlobalCtors, CtorsToRemove);
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return true;
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}
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} // End llvm namespace
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