llvm/lib/CodeGen/ParallelCG.cpp

   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
  24 using namespace llvm;
  25
  26 static 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
  38 void 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 }