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/ThreadPool.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Transforms/Utils/SplitModule.h"
25 
26 using namespace llvm;
27 
codegen(Module * M,llvm::raw_pwrite_stream & OS,function_ref<std::unique_ptr<TargetMachine> ()> TMFactory,TargetMachine::CodeGenFileType FileType)28 static 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 
splitCodeGen(std::unique_ptr<Module> M,ArrayRef<llvm::raw_pwrite_stream * > OSs,ArrayRef<llvm::raw_pwrite_stream * > BCOSs,const std::function<std::unique_ptr<TargetMachine> ()> & TMFactory,TargetMachine::CodeGenFileType FileType,bool PreserveLocals)38 std::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                 ErrorOr<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