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1 //===-Caching.cpp - LLVM Link Time Optimizer Cache Handling ---------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file implements the Caching for ThinLTO.
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10 //
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11 //===----------------------------------------------------------------------===//
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12
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13 #include "llvm/LTO/Caching.h"
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14 #include "llvm/ADT/StringExtras.h"
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15 #include "llvm/Support/Errc.h"
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16 #include "llvm/Support/MemoryBuffer.h"
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17 #include "llvm/Support/Path.h"
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18 #include "llvm/Support/Process.h"
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19 #include "llvm/Support/raw_ostream.h"
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20
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21 #if !defined(_MSC_VER) && !defined(__MINGW32__)
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22 #include <unistd.h>
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23 #else
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24 #include <io.h>
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25 #endif
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26
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27 using namespace llvm;
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28 using namespace llvm::lto;
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29
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30 Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
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31 AddBufferFn AddBuffer) {
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32 if (std::error_code EC = sys::fs::create_directories(CacheDirectoryPath))
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33 return errorCodeToError(EC);
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34
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35 return [=](unsigned Task, StringRef Key) -> AddStreamFn {
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36 // This choice of file name allows the cache to be pruned (see pruneCache()
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37 // in include/llvm/Support/CachePruning.h).
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38 SmallString<64> EntryPath;
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39 sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
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40 // First, see if we have a cache hit.
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41 SmallString<64> ResultPath;
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42 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
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43 Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
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44 std::error_code EC;
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45 if (FDOrErr) {
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46 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
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47 MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
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48 /*FileSize=*/-1,
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49 /*RequiresNullTerminator=*/false);
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50 sys::fs::closeFile(*FDOrErr);
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51 if (MBOrErr) {
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52 AddBuffer(Task, std::move(*MBOrErr));
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53 return AddStreamFn();
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54 }
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55 EC = MBOrErr.getError();
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56 } else {
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57 EC = errorToErrorCode(FDOrErr.takeError());
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58 }
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59
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60 // On Windows we can fail to open a cache file with a permission denied
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61 // error. This generally means that another process has requested to delete
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62 // the file while it is still open, but it could also mean that another
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63 // process has opened the file without the sharing permissions we need.
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64 // Since the file is probably being deleted we handle it in the same way as
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65 // if the file did not exist at all.
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66 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
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67 report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
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68 ": " + EC.message() + "\n");
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69
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70 // This native object stream is responsible for commiting the resulting
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71 // file to the cache and calling AddBuffer to add it to the link.
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72 struct CacheStream : NativeObjectStream {
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73 AddBufferFn AddBuffer;
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74 sys::fs::TempFile TempFile;
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75 std::string EntryPath;
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76 unsigned Task;
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77
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78 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
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79 sys::fs::TempFile TempFile, std::string EntryPath,
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80 unsigned Task)
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81 : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
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82 TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
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83 Task(Task) {}
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84
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85 ~CacheStream() {
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86 // Make sure the stream is closed before committing it.
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87 OS.reset();
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88
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89 // Open the file first to avoid racing with a cache pruner.
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90 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
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91 MemoryBuffer::getOpenFile(
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92 sys::fs::convertFDToNativeFile(TempFile.FD), TempFile.TmpName,
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93 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
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94 if (!MBOrErr)
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95 report_fatal_error(Twine("Failed to open new cache file ") +
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96 TempFile.TmpName + ": " +
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97 MBOrErr.getError().message() + "\n");
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98
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99 // On POSIX systems, this will atomically replace the destination if
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100 // it already exists. We try to emulate this on Windows, but this may
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101 // fail with a permission denied error (for example, if the destination
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102 // is currently opened by another process that does not give us the
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103 // sharing permissions we need). Since the existing file should be
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104 // semantically equivalent to the one we are trying to write, we give
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105 // AddBuffer a copy of the bytes we wrote in that case. We do this
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106 // instead of just using the existing file, because the pruner might
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107 // delete the file before we get a chance to use it.
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108 Error E = TempFile.keep(EntryPath);
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109 E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
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110 std::error_code EC = E.convertToErrorCode();
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111 if (EC != errc::permission_denied)
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112 return errorCodeToError(EC);
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113
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114 auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
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115 EntryPath);
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116 MBOrErr = std::move(MBCopy);
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117
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118 // FIXME: should we consume the discard error?
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119 consumeError(TempFile.discard());
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120
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121 return Error::success();
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122 });
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123
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124 if (E)
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125 report_fatal_error(Twine("Failed to rename temporary file ") +
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126 TempFile.TmpName + " to " + EntryPath + ": " +
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127 toString(std::move(E)) + "\n");
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128
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129 AddBuffer(Task, std::move(*MBOrErr));
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130 }
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131 };
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132
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133 return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
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134 // Write to a temporary to avoid race condition
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135 SmallString<64> TempFilenameModel;
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136 sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
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137 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
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138 TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
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139 if (!Temp) {
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140 errs() << "Error: " << toString(Temp.takeError()) << "\n";
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141 report_fatal_error("ThinLTO: Can't get a temporary file");
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142 }
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143
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144 // This CacheStream will move the temporary file into the cache when done.
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145 return std::make_unique<CacheStream>(
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146 std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
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147 AddBuffer, std::move(*Temp), std::string(EntryPath.str()), Task);
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148 };
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149 };
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150 }
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