ParallelCG.cpp revision 327952 
1//===-- ParallelCG.cpp ----------------------------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines functions that can be used for parallel code generation.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/ParallelCG.h"
15#include "llvm/Bitcode/BitcodeReader.h"
16#include "llvm/Bitcode/BitcodeWriter.h"
17#include "llvm/IR/LLVMContext.h"
18#include "llvm/IR/LegacyPassManager.h"
19#include "llvm/IR/Module.h"
20#include "llvm/Support/ErrorOr.h"
21#include "llvm/Support/MemoryBuffer.h"
22#include "llvm/Support/ThreadPool.h"
23#include "llvm/Target/TargetMachine.h"
24#include "llvm/Transforms/Utils/SplitModule.h"
25
26using namespace llvm;
27
28static void codegen(Module *M, llvm::raw_pwrite_stream &OS,
29                    function_ref<std::unique_ptr<TargetMachine>()> TMFactory,
30                    TargetMachine::CodeGenFileType FileType) {
31  std::unique_ptr<TargetMachine> TM = TMFactory();
32  legacy::PassManager CodeGenPasses;
33  if (TM->addPassesToEmitFile(CodeGenPasses, OS, FileType))
34    report_fatal_error("Failed to setup codegen");
35  CodeGenPasses.run(*M);
36}
37
38std::unique_ptr<Module> llvm::splitCodeGen(
39    std::unique_ptr<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    TargetMachine::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.get(), *BCOSs[0]);
48    codegen(M.get(), *OSs[0], TMFactory, FileType);
49    return M;
50  }
51
52  // Create ThreadPool in nested scope so that threads will be joined
53  // on destruction.
54  {
55    ThreadPool CodegenThreadPool(OSs.size());
56    int ThreadCount = 0;
57
58    SplitModule(
59        std::move(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.get(), 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  return {};
99}
100