diff options
Diffstat (limited to 'lib/Transforms/Utils/CtorUtils.cpp')
| -rw-r--r-- | lib/Transforms/Utils/CtorUtils.cpp | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/CtorUtils.cpp b/lib/Transforms/Utils/CtorUtils.cpp new file mode 100644 index 0000000..a359424 --- /dev/null +++ b/lib/Transforms/Utils/CtorUtils.cpp @@ -0,0 +1,183 @@ +//===- 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 |