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
25using namespace llvm;
26
27static 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
37std::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