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 }
98