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/ErrorOr.h"
20 #include "llvm/Support/MemoryBuffer.h"
21 #include "llvm/Support/ThreadPool.h"
22 #include "llvm/Target/TargetMachine.h"
23 #include "llvm/Transforms/Utils/SplitModule.h"
24
25 using namespace llvm;
26
codegen(Module * M,llvm::raw_pwrite_stream & OS,function_ref<std::unique_ptr<TargetMachine> ()> TMFactory,CodeGenFileType FileType)27 static void codegen(Module *M, llvm::raw_pwrite_stream &OS,
28 function_ref<std::unique_ptr<TargetMachine>()> TMFactory,
29 CodeGenFileType FileType) {
30 std::unique_ptr<TargetMachine> TM = TMFactory();
31 legacy::PassManager CodeGenPasses;
32 if (TM->addPassesToEmitFile(CodeGenPasses, OS, nullptr, FileType))
33 report_fatal_error("Failed to setup codegen");
34 CodeGenPasses.run(*M);
35 }
36
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)37 std::unique_ptr<Module> llvm::splitCodeGen(
38 std::unique_ptr<Module> M, ArrayRef<llvm::raw_pwrite_stream *> OSs,
39 ArrayRef<llvm::raw_pwrite_stream *> BCOSs,
40 const std::function<std::unique_ptr<TargetMachine>()> &TMFactory,
41 CodeGenFileType FileType, bool PreserveLocals) {
42 assert(BCOSs.empty() || BCOSs.size() == OSs.size());
43
44 if (OSs.size() == 1) {
45 if (!BCOSs.empty())
46 WriteBitcodeToFile(*M, *BCOSs[0]);
47 codegen(M.get(), *OSs[0], TMFactory, FileType);
48 return M;
49 }
50
51 // Create ThreadPool in nested scope so that threads will be joined
52 // on destruction.
53 {
54 ThreadPool CodegenThreadPool(OSs.size());
55 int ThreadCount = 0;
56
57 SplitModule(
58 std::move(M), OSs.size(),
59 [&](std::unique_ptr<Module> MPart) {
60 // We want to clone the module in a new context to multi-thread the
61 // codegen. We do it by serializing partition modules to bitcode
62 // (while still on the main thread, in order to avoid data races) and
63 // spinning up new threads which deserialize the partitions into
64 // separate contexts.
65 // FIXME: Provide a more direct way to do this in LLVM.
66 SmallString<0> BC;
67 raw_svector_ostream BCOS(BC);
68 WriteBitcodeToFile(*MPart, BCOS);
69
70 if (!BCOSs.empty()) {
71 BCOSs[ThreadCount]->write(BC.begin(), BC.size());
72 BCOSs[ThreadCount]->flush();
73 }
74
75 llvm::raw_pwrite_stream *ThreadOS = OSs[ThreadCount++];
76 // Enqueue the task
77 CodegenThreadPool.async(
78 [TMFactory, FileType, ThreadOS](const SmallString<0> &BC) {
79 LLVMContext Ctx;
80 Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
81 MemoryBufferRef(StringRef(BC.data(), BC.size()),
82 "<split-module>"),
83 Ctx);
84 if (!MOrErr)
85 report_fatal_error("Failed to read bitcode");
86 std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
87
88 codegen(MPartInCtx.get(), *ThreadOS, TMFactory, FileType);
89 },
90 // Pass BC using std::move to ensure that it get moved rather than
91 // copied into the thread's context.
92 std::move(BC));
93 },
94 PreserveLocals);
95 }
96
97 return {};
98 }
99