ParallelCG.cpp revision 292941 
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/ReaderWriter.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/TargetRegistry.h"
22#include "llvm/Support/thread.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                    const Target *TheTarget, StringRef CPU, StringRef Features,
30                    const TargetOptions &Options, Reloc::Model RM,
31                    CodeModel::Model CM, CodeGenOpt::Level OL,
32                    TargetMachine::CodeGenFileType FileType) {
33  std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
34      M->getTargetTriple(), CPU, Features, Options, RM, CM, OL));
35
36  legacy::PassManager CodeGenPasses;
37  if (TM->addPassesToEmitFile(CodeGenPasses, OS, FileType))
38    report_fatal_error("Failed to setup codegen");
39  CodeGenPasses.run(*M);
40}
41
42std::unique_ptr<Module>
43llvm::splitCodeGen(std::unique_ptr<Module> M,
44                   ArrayRef<llvm::raw_pwrite_stream *> OSs, StringRef CPU,
45                   StringRef Features, const TargetOptions &Options,
46                   Reloc::Model RM, CodeModel::Model CM, CodeGenOpt::Level OL,
47                   TargetMachine::CodeGenFileType FileType) {
48  StringRef TripleStr = M->getTargetTriple();
49  std::string ErrMsg;
50  const Target *TheTarget = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
51  if (!TheTarget)
52    report_fatal_error(Twine("Target not found: ") + ErrMsg);
53
54  if (OSs.size() == 1) {
55    codegen(M.get(), *OSs[0], TheTarget, CPU, Features, Options, RM, CM,
56            OL, FileType);
57    return M;
58  }
59
60  std::vector<thread> Threads;
61  SplitModule(std::move(M), OSs.size(), [&](std::unique_ptr<Module> MPart) {
62    // We want to clone the module in a new context to multi-thread the codegen.
63    // We do it by serializing partition modules to bitcode (while still on the
64    // main thread, in order to avoid data races) and spinning up new threads
65    // which deserialize the partitions into separate contexts.
66    // FIXME: Provide a more direct way to do this in LLVM.
67    SmallVector<char, 0> BC;
68    raw_svector_ostream BCOS(BC);
69    WriteBitcodeToFile(MPart.get(), BCOS);
70
71    llvm::raw_pwrite_stream *ThreadOS = OSs[Threads.size()];
72    Threads.emplace_back(
73        [TheTarget, CPU, Features, Options, RM, CM, OL, FileType,
74         ThreadOS](const SmallVector<char, 0> &BC) {
75          LLVMContext Ctx;
76          ErrorOr<std::unique_ptr<Module>> MOrErr =
77              parseBitcodeFile(MemoryBufferRef(StringRef(BC.data(), BC.size()),
78                                               "<split-module>"),
79                               Ctx);
80          if (!MOrErr)
81            report_fatal_error("Failed to read bitcode");
82          std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
83
84          codegen(MPartInCtx.get(), *ThreadOS, TheTarget, CPU, Features,
85                  Options, RM, CM, OL, FileType);
86        },
87        // Pass BC using std::move to ensure that it get moved rather than
88        // copied into the thread's context.
89        std::move(BC));
90  });
91
92  for (thread &T : Threads)
93    T.join();
94
95  return {};
96}
97