1//===-- ParallelCG.cpp ----------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines functions that can be used for parallel code generation.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/CodeGen/ParallelCG.h"
14#include "llvm/Bitcode/BitcodeReader.h"
15#include "llvm/Bitcode/BitcodeWriter.h"
16#include "llvm/IR/LLVMContext.h"
17#include "llvm/IR/LegacyPassManager.h"
18#include "llvm/IR/Module.h"
19#include "llvm/Support/MemoryBufferRef.h"
20#include "llvm/Support/ThreadPool.h"
21#include "llvm/Target/TargetMachine.h"
22#include "llvm/Transforms/Utils/SplitModule.h"
23
24using namespace llvm;
25
26static void codegen(Module *M, llvm::raw_pwrite_stream &OS,
27 function_ref<std::unique_ptr<TargetMachine>()> TMFactory,
28 CodeGenFileType FileType) {
29 std::unique_ptr<TargetMachine> TM = TMFactory();
30 assert(TM && "Failed to create target machine!");
31
32 legacy::PassManager CodeGenPasses;
33 if (TM->addPassesToEmitFile(CodeGenPasses, OS, nullptr, FileType))
34 report_fatal_error("Failed to setup codegen");
35 CodeGenPasses.run(*M);
36}
37
38void llvm::splitCodeGen(
39 Module &M, ArrayRef<llvm::raw_pwrite_stream *> OSs,
40 ArrayRef<llvm::raw_pwrite_stream *> BCOSs,
41 const std::function<std::unique_ptr<TargetMachine>()> &TMFactory,
42 CodeGenFileType FileType, bool PreserveLocals) {
43 assert(BCOSs.empty() || BCOSs.size() == OSs.size());
44
45 if (OSs.size() == 1) {
46 if (!BCOSs.empty())
47 WriteBitcodeToFile(M, *BCOSs[0]);
48 codegen(&M, *OSs[0], TMFactory, FileType);
49 return;
50 }
51
52 // Create ThreadPool in nested scope so that threads will be joined
53 // on destruction.
54 {
55 ThreadPool CodegenThreadPool(hardware_concurrency(OSs.size()));
56 int ThreadCount = 0;
57
58 SplitModule(
59 M, OSs.size(),
60 [&](std::unique_ptr<Module> MPart) {
61 // We want to clone the module in a new context to multi-thread the
62 // codegen. We do it by serializing partition modules to bitcode
63 // (while still on the main thread, in order to avoid data races) and
64 // spinning up new threads which deserialize the partitions into
65 // separate contexts.
66 // FIXME: Provide a more direct way to do this in LLVM.
67 SmallString<0> BC;
68 raw_svector_ostream BCOS(BC);
69 WriteBitcodeToFile(*MPart, BCOS);
70
71 if (!BCOSs.empty()) {
72 BCOSs[ThreadCount]->write(BC.begin(), BC.size());
73 BCOSs[ThreadCount]->flush();
74 }
75
76 llvm::raw_pwrite_stream *ThreadOS = OSs[ThreadCount++];
77 // Enqueue the task
78 CodegenThreadPool.async(
79 [TMFactory, FileType, ThreadOS](const SmallString<0> &BC) {
80 LLVMContext Ctx;
81 Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
82 MemoryBufferRef(StringRef(BC.data(), BC.size()),
83 "<split-module>"),
84 Ctx);
85 if (!MOrErr)
86 report_fatal_error("Failed to read bitcode");
87 std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
88
89 codegen(MPartInCtx.get(), *ThreadOS, TMFactory, FileType);
90 },
91 // Pass BC using std::move to ensure that it get moved rather than
92 // copied into the thread's context.
93 std::move(BC));
94 },
95 PreserveLocals);
96 }
97}
98

source code of llvm/lib/CodeGen/ParallelCG.cpp