ParallelCG.cpp
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//===-- ParallelCG.cpp ----------------------------------------------------===//
//
// 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 file defines functions that can be used for parallel code generation.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/ParallelCG.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/SplitModule.h"
using namespace llvm;
static void codegen(Module *M, llvm::raw_pwrite_stream &OS,
function_ref<std::unique_ptr<TargetMachine>()> TMFactory,
CodeGenFileType FileType) {
std::unique_ptr<TargetMachine> TM = TMFactory();
legacy::PassManager CodeGenPasses;
if (TM->addPassesToEmitFile(CodeGenPasses, OS, nullptr, FileType))
report_fatal_error("Failed to setup codegen");
CodeGenPasses.run(*M);
}
std::unique_ptr<Module> llvm::splitCodeGen(
std::unique_ptr<Module> M, ArrayRef<llvm::raw_pwrite_stream *> OSs,
ArrayRef<llvm::raw_pwrite_stream *> BCOSs,
const std::function<std::unique_ptr<TargetMachine>()> &TMFactory,
CodeGenFileType FileType, bool PreserveLocals) {
assert(BCOSs.empty() || BCOSs.size() == OSs.size());
if (OSs.size() == 1) {
if (!BCOSs.empty())
WriteBitcodeToFile(*M, *BCOSs[0]);
codegen(M.get(), *OSs[0], TMFactory, FileType);
return M;
}
// Create ThreadPool in nested scope so that threads will be joined
// on destruction.
{
ThreadPool CodegenThreadPool(OSs.size());
int ThreadCount = 0;
SplitModule(
std::move(M), OSs.size(),
[&](std::unique_ptr<Module> MPart) {
// We want to clone the module in a new context to multi-thread the
// codegen. We do it by serializing partition modules to bitcode
// (while still on the main thread, in order to avoid data races) and
// spinning up new threads which deserialize the partitions into
// separate contexts.
// FIXME: Provide a more direct way to do this in LLVM.
SmallString<0> BC;
raw_svector_ostream BCOS(BC);
WriteBitcodeToFile(*MPart, BCOS);
if (!BCOSs.empty()) {
BCOSs[ThreadCount]->write(BC.begin(), BC.size());
BCOSs[ThreadCount]->flush();
}
llvm::raw_pwrite_stream *ThreadOS = OSs[ThreadCount++];
// Enqueue the task
CodegenThreadPool.async(
[TMFactory, FileType, ThreadOS](const SmallString<0> &BC) {
LLVMContext Ctx;
Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
MemoryBufferRef(StringRef(BC.data(), BC.size()),
"<split-module>"),
Ctx);
if (!MOrErr)
report_fatal_error("Failed to read bitcode");
std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
codegen(MPartInCtx.get(), *ThreadOS, TMFactory, FileType);
},
// Pass BC using std::move to ensure that it get moved rather than
// copied into the thread's context.
std::move(BC));
},
PreserveLocals);
}
return {};
}