lib/Remarks/BitstreamRemarkParser.cpp

   1 //===- BitstreamRemarkParser.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 provides utility methods used by clients that want to use the
  10 // parser for remark diagnostics in LLVM.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Remarks/BitstreamRemarkParser.h"
  15 #include "BitstreamRemarkParser.h"
  16 #include "llvm/Remarks/BitstreamRemarkContainer.h"
  17 #include "llvm/Support/MemoryBuffer.h"
  18
  19 using namespace llvm;
  20 using namespace llvm::remarks;
  21
  22 static Error unknownRecord(const char *BlockName, unsigned RecordID) {
  23   return createStringError(
  24       std::make_error_code(std::errc::illegal_byte_sequence),
  25       "Error while parsing %s: unknown record entry (%lu).", BlockName,
  26       RecordID);
  27 }
  28
  29 static Error malformedRecord(const char *BlockName, const char *RecordName) {
  30   return createStringError(
  31       std::make_error_code(std::errc::illegal_byte_sequence),
  32       "Error while parsing %s: malformed record entry (%s).", BlockName,
  33       RecordName);
  34 }
  35
  36 BitstreamMetaParserHelper::BitstreamMetaParserHelper(
  37     BitstreamCursor &Stream, BitstreamBlockInfo &BlockInfo)
  38     : Stream(Stream), BlockInfo(BlockInfo) {}
  39
  40 /// Parse a record and fill in the fields in the parser.
  41 static Error parseRecord(BitstreamMetaParserHelper &Parser, unsigned Code) {
  42   BitstreamCursor &Stream = Parser.Stream;
  43   // Note: 2 is used here because it's the max number of fields we have per
  44   // record.
  45   SmallVector<uint64_t, 2> Record;
  46   StringRef Blob;
  47   Expected<unsigned> RecordID = Stream.readRecord(Code, Record, &Blob);
  48   if (!RecordID)
  49     return RecordID.takeError();
  50
  51   switch (*RecordID) {
  52   case RECORD_META_CONTAINER_INFO: {
  53     if (Record.size() != 2)
  54       return malformedRecord("BLOCK_META", "RECORD_META_CONTAINER_INFO");
  55     Parser.ContainerVersion = Record[0];
  56     Parser.ContainerType = Record[1];
  57     break;
  58   }
  59   case RECORD_META_REMARK_VERSION: {
  60     if (Record.size() != 1)
  61       return malformedRecord("BLOCK_META", "RECORD_META_REMARK_VERSION");
  62     Parser.RemarkVersion = Record[0];
  63     break;
  64   }
  65   case RECORD_META_STRTAB: {
  66     if (Record.size() != 0)
  67       return malformedRecord("BLOCK_META", "RECORD_META_STRTAB");
  68     Parser.StrTabBuf = Blob;
  69     break;
  70   }
  71   case RECORD_META_EXTERNAL_FILE: {
  72     if (Record.size() != 0)
  73       return malformedRecord("BLOCK_META", "RECORD_META_EXTERNAL_FILE");
  74     Parser.ExternalFilePath = Blob;
  75     break;
  76   }
  77   default:
  78     return unknownRecord("BLOCK_META", *RecordID);
  79   }
  80   return Error::success();
  81 }
  82
  83 BitstreamRemarkParserHelper::BitstreamRemarkParserHelper(
  84     BitstreamCursor &Stream)
  85     : Stream(Stream) {}
  86
  87 /// Parse a record and fill in the fields in the parser.
  88 static Error parseRecord(BitstreamRemarkParserHelper &Parser, unsigned Code) {
  89   BitstreamCursor &Stream = Parser.Stream;
  90   // Note: 5 is used here because it's the max number of fields we have per
  91   // record.
  92   SmallVector<uint64_t, 5> Record;
  93   StringRef Blob;
  94   Expected<unsigned> RecordID = Stream.readRecord(Code, Record, &Blob);
  95   if (!RecordID)
  96     return RecordID.takeError();
  97
  98   switch (*RecordID) {
  99   case RECORD_REMARK_HEADER: {
 100     if (Record.size() != 4)
 101       return malformedRecord("BLOCK_REMARK", "RECORD_REMARK_HEADER");
 102     Parser.Type = Record[0];
 103     Parser.RemarkNameIdx = Record[1];
 104     Parser.PassNameIdx = Record[2];
 105     Parser.FunctionNameIdx = Record[3];
 106     break;
 107   }
 108   case RECORD_REMARK_DEBUG_LOC: {
 109     if (Record.size() != 3)
 110       return malformedRecord("BLOCK_REMARK", "RECORD_REMARK_DEBUG_LOC");
 111     Parser.SourceFileNameIdx = Record[0];
 112     Parser.SourceLine = Record[1];
 113     Parser.SourceColumn = Record[2];
 114     break;
 115   }
 116   case RECORD_REMARK_HOTNESS: {
 117     if (Record.size() != 1)
 118       return malformedRecord("BLOCK_REMARK", "RECORD_REMARK_HOTNESS");
 119     Parser.Hotness = Record[0];
 120     break;
 121   }
 122   case RECORD_REMARK_ARG_WITH_DEBUGLOC: {
 123     if (Record.size() != 5)
 124       return malformedRecord("BLOCK_REMARK", "RECORD_REMARK_ARG_WITH_DEBUGLOC");
 125     // Create a temporary argument. Use that as a valid memory location for this
 126     // argument entry.
 127     Parser.TmpArgs.emplace_back();
 128     Parser.TmpArgs.back().KeyIdx = Record[0];
 129     Parser.TmpArgs.back().ValueIdx = Record[1];
 130     Parser.TmpArgs.back().SourceFileNameIdx = Record[2];
 131     Parser.TmpArgs.back().SourceLine = Record[3];
 132     Parser.TmpArgs.back().SourceColumn = Record[4];
 133     Parser.Args =
 134         ArrayRef<BitstreamRemarkParserHelper::Argument>(Parser.TmpArgs);
 135     break;
 136   }
 137   case RECORD_REMARK_ARG_WITHOUT_DEBUGLOC: {
 138     if (Record.size() != 2)
 139       return malformedRecord("BLOCK_REMARK",
 140                              "RECORD_REMARK_ARG_WITHOUT_DEBUGLOC");
 141     // Create a temporary argument. Use that as a valid memory location for this
 142     // argument entry.
 143     Parser.TmpArgs.emplace_back();
 144     Parser.TmpArgs.back().KeyIdx = Record[0];
 145     Parser.TmpArgs.back().ValueIdx = Record[1];
 146     Parser.Args =
 147         ArrayRef<BitstreamRemarkParserHelper::Argument>(Parser.TmpArgs);
 148     break;
 149   }
 150   default:
 151     return unknownRecord("BLOCK_REMARK", *RecordID);
 152   }
 153   return Error::success();
 154 }
 155
 156 template <typename T>
 157 static Error parseBlock(T &ParserHelper, unsigned BlockID,
 158                         const char *BlockName) {
 159   BitstreamCursor &Stream = ParserHelper.Stream;
 160   Expected<BitstreamEntry> Next = Stream.advance();
 161   if (!Next)
 162     return Next.takeError();
 163   if (Next->Kind != BitstreamEntry::SubBlock || Next->ID != BlockID)
 164     return createStringError(
 165         std::make_error_code(std::errc::illegal_byte_sequence),
 166         "Error while parsing %s: expecting [ENTER_SUBBLOCK, %s, ...].",
 167         BlockName, BlockName);
 168   if (Stream.EnterSubBlock(BlockID))
 169     return createStringError(
 170         std::make_error_code(std::errc::illegal_byte_sequence),
 171         "Error while entering %s.", BlockName);
 172
 173   // Stop when there is nothing to read anymore or when we encounter an
 174   // END_BLOCK.
 175   while (!Stream.AtEndOfStream()) {
 176     Expected<BitstreamEntry> Next = Stream.advance();
 177     if (!Next)
 178       return Next.takeError();
 179     switch (Next->Kind) {
 180     case BitstreamEntry::EndBlock:
 181       return Error::success();
 182     case BitstreamEntry::Error:
 183     case BitstreamEntry::SubBlock:
 184       return createStringError(
 185           std::make_error_code(std::errc::illegal_byte_sequence),
 186           "Error while parsing %s: expecting records.", BlockName);
 187     case BitstreamEntry::Record:
 188       if (Error E = parseRecord(ParserHelper, Next->ID))
 189         return E;
 190       continue;
 191     }
 192   }
 193   // If we're here, it means we didn't get an END_BLOCK yet, but we're at the
 194   // end of the stream. In this case, error.
 195   return createStringError(
 196       std::make_error_code(std::errc::illegal_byte_sequence),
 197       "Error while parsing %s: unterminated block.", BlockName);
 198 }
 199
 200 Error BitstreamMetaParserHelper::parse() {
 201   return parseBlock(*this, META_BLOCK_ID, "META_BLOCK");
 202 }
 203
 204 Error BitstreamRemarkParserHelper::parse() {
 205   return parseBlock(*this, REMARK_BLOCK_ID, "REMARK_BLOCK");
 206 }
 207
 208 BitstreamParserHelper::BitstreamParserHelper(StringRef Buffer)
 209     : Stream(Buffer) {}
 210
 211 Expected<std::array<char, 4>> BitstreamParserHelper::parseMagic() {
 212   std::array<char, 4> Result;
 213   for (unsigned i = 0; i < 4; ++i)
 214     if (Expected<unsigned> R = Stream.Read(8))
 215       Result[i] = *R;
 216     else
 217       return R.takeError();
 218   return Result;
 219 }
 220
 221 Error BitstreamParserHelper::parseBlockInfoBlock() {
 222   Expected<BitstreamEntry> Next = Stream.advance();
 223   if (!Next)
 224     return Next.takeError();
 225   if (Next->Kind != BitstreamEntry::SubBlock ||
 226       Next->ID != llvm::bitc::BLOCKINFO_BLOCK_ID)
 227     return createStringError(
 228         std::make_error_code(std::errc::illegal_byte_sequence),
 229         "Error while parsing BLOCKINFO_BLOCK: expecting [ENTER_SUBBLOCK, "
 230         "BLOCKINFO_BLOCK, ...].");
 231
 232   Expected<Optional<BitstreamBlockInfo>> MaybeBlockInfo =
 233       Stream.ReadBlockInfoBlock();
 234   if (!MaybeBlockInfo)
 235     return MaybeBlockInfo.takeError();
 236
 237   if (!*MaybeBlockInfo)
 238     return createStringError(
 239         std::make_error_code(std::errc::illegal_byte_sequence),
 240         "Error while parsing BLOCKINFO_BLOCK.");
 241
 242   BlockInfo = **MaybeBlockInfo;
 243
 244   Stream.setBlockInfo(&BlockInfo);
 245   return Error::success();
 246 }
 247
 248 static Expected<bool> isBlock(BitstreamCursor &Stream, unsigned BlockID) {
 249   bool Result = false;
 250   uint64_t PreviousBitNo = Stream.GetCurrentBitNo();
 251   Expected<BitstreamEntry> Next = Stream.advance();
 252   if (!Next)
 253     return Next.takeError();
 254   switch (Next->Kind) {
 255   case BitstreamEntry::SubBlock:
 256     // Check for the block id.
 257     Result = Next->ID == BlockID;
 258     break;
 259   case BitstreamEntry::Error:
 260     return createStringError(
 261         std::make_error_code(std::errc::illegal_byte_sequence),
 262         "Unexpected error while parsing bitstream.");
 263   default:
 264     Result = false;
 265     break;
 266   }
 267   if (Error E = Stream.JumpToBit(PreviousBitNo))
 268     return std::move(E);
 269   return Result;
 270 }
 271
 272 Expected<bool> BitstreamParserHelper::isMetaBlock() {
 273   return isBlock(Stream, META_BLOCK_ID);
 274 }
 275
 276 Expected<bool> BitstreamParserHelper::isRemarkBlock() {
 277   return isBlock(Stream, META_BLOCK_ID);
 278 }
 279
 280 static Error validateMagicNumber(StringRef Magic) {
 281   if (Magic != remarks::ContainerMagic)
 282     return createStringError(std::make_error_code(std::errc::invalid_argument),
 283                              "Unknown magic number: expecting %s, got %.4s.",
 284                              remarks::ContainerMagic.data(), Magic.data());
 285   return Error::success();
 286 }
 287
 288 static Error advanceToMetaBlock(BitstreamParserHelper &Helper) {
 289   Expected<std::array<char, 4>> Magic = Helper.parseMagic();
 290   if (!Magic)
 291     return Magic.takeError();
 292   if (Error E = validateMagicNumber(StringRef(Magic->data(), Magic->size())))
 293     return E;
 294   if (Error E = Helper.parseBlockInfoBlock())
 295     return E;
 296   Expected<bool> isMetaBlock = Helper.isMetaBlock();
 297   if (!isMetaBlock)
 298     return isMetaBlock.takeError();
 299   if (!*isMetaBlock)
 300     return createStringError(
 301         std::make_error_code(std::errc::illegal_byte_sequence),
 302         "Expecting META_BLOCK after the BLOCKINFO_BLOCK.");
 303   return Error::success();
 304 }
 305
 306 Expected<std::unique_ptr<BitstreamRemarkParser>>
 307 remarks::createBitstreamParserFromMeta(StringRef Buf,
 308                                        Optional<ParsedStringTable> StrTab) {
 309   BitstreamParserHelper Helper(Buf);
 310   Expected<std::array<char, 4>> Magic = Helper.parseMagic();
 311   if (!Magic)
 312     return Magic.takeError();
 313
 314   if (Error E = validateMagicNumber(StringRef(Magic->data(), Magic->size())))
 315     return std::move(E);
 316
 317   return StrTab
 318              ? std::make_unique<BitstreamRemarkParser>(Buf, std::move(*StrTab))
 319              : std::make_unique<BitstreamRemarkParser>(Buf);
 320 }
 321
 322 Expected<std::unique_ptr<Remark>> BitstreamRemarkParser::next() {
 323   if (ParserHelper.atEndOfStream())
 324     return make_error<EndOfFileError>();
 325
 326   if (!ReadyToParseRemarks) {
 327     if (Error E = parseMeta())
 328       return std::move(E);
 329     ReadyToParseRemarks = true;
 330   }
 331
 332   return parseRemark();
 333 }
 334
 335 Error BitstreamRemarkParser::parseMeta() {
 336   // Advance and to the meta block.
 337   if (Error E = advanceToMetaBlock(ParserHelper))
 338     return E;
 339
 340   BitstreamMetaParserHelper MetaHelper(ParserHelper.Stream,
 341                                        ParserHelper.BlockInfo);
 342   if (Error E = MetaHelper.parse())
 343     return E;
 344
 345   if (Error E = processCommonMeta(MetaHelper))
 346     return E;
 347
 348   switch (ContainerType) {
 349   case BitstreamRemarkContainerType::Standalone:
 350     return processStandaloneMeta(MetaHelper);
 351   case BitstreamRemarkContainerType::SeparateRemarksFile:
 352     return processSeparateRemarksFileMeta(MetaHelper);
 353   case BitstreamRemarkContainerType::SeparateRemarksMeta:
 354     return processSeparateRemarksMetaMeta(MetaHelper);
 355   }
 356   llvm_unreachable("Unknown BitstreamRemarkContainerType enum");
 357 }
 358
 359 Error BitstreamRemarkParser::processCommonMeta(
 360     BitstreamMetaParserHelper &MetaHelper) {
 361   if (Optional<uint64_t> Version = MetaHelper.ContainerVersion)
 362     ContainerVersion = *Version;
 363   else
 364     return createStringError(
 365         std::make_error_code(std::errc::illegal_byte_sequence),
 366         "Error while parsing BLOCK_META: missing container version.");
 367
 368   if (Optional<uint8_t> Type = MetaHelper.ContainerType) {
 369     // Always >= BitstreamRemarkContainerType::First since it's unsigned.
 370     if (*Type > static_cast<uint8_t>(BitstreamRemarkContainerType::Last))
 371       return createStringError(
 372           std::make_error_code(std::errc::illegal_byte_sequence),
 373           "Error while parsing BLOCK_META: invalid container type.");
 374
 375     ContainerType = static_cast<BitstreamRemarkContainerType>(*Type);
 376   } else
 377     return createStringError(
 378         std::make_error_code(std::errc::illegal_byte_sequence),
 379         "Error while parsing BLOCK_META: missing container type.");
 380
 381   return Error::success();
 382 }
 383
 384 static Error processStrTab(BitstreamRemarkParser &P,
 385                            Optional<StringRef> StrTabBuf) {
 386   if (!StrTabBuf)
 387     return createStringError(
 388         std::make_error_code(std::errc::illegal_byte_sequence),
 389         "Error while parsing BLOCK_META: missing string table.");
 390   // Parse and assign the string table.
 391   P.StrTab.emplace(*StrTabBuf);
 392   return Error::success();
 393 }
 394
 395 static Error processRemarkVersion(BitstreamRemarkParser &P,
 396                                   Optional<uint64_t> RemarkVersion) {
 397   if (!RemarkVersion)
 398     return createStringError(
 399         std::make_error_code(std::errc::illegal_byte_sequence),
 400         "Error while parsing BLOCK_META: missing remark version.");
 401   P.RemarkVersion = *RemarkVersion;
 402   return Error::success();
 403 }
 404
 405 Error BitstreamRemarkParser::processExternalFilePath(
 406     Optional<StringRef> ExternalFilePath) {
 407   if (!ExternalFilePath)
 408     return createStringError(
 409         std::make_error_code(std::errc::illegal_byte_sequence),
 410         "Error while parsing BLOCK_META: missing external file path.");
 411
 412   // External file: open the external file, parse it, check if its metadata
 413   // matches the one from the separate metadata, then replace the current parser
 414   // with the one parsing the remarks.
 415   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
 416       MemoryBuffer::getFile(*ExternalFilePath);
 417   if (std::error_code EC = BufferOrErr.getError())
 418     return errorCodeToError(EC);
 419   TmpRemarkBuffer = std::move(*BufferOrErr);
 420
 421   // Create a separate parser used for parsing the separate file.
 422   ParserHelper = BitstreamParserHelper(TmpRemarkBuffer->getBuffer());
 423   // Advance and check until we can parse the meta block.
 424   if (Error E = advanceToMetaBlock(ParserHelper))
 425     return E;
 426   // Parse the meta from the separate file.
 427   // Note: here we overwrite the BlockInfo with the one from the file. This will
 428   // be used to parse the rest of the file.
 429   BitstreamMetaParserHelper SeparateMetaHelper(ParserHelper.Stream,
 430                                                ParserHelper.BlockInfo);
 431   if (Error E = SeparateMetaHelper.parse())
 432     return E;
 433
 434   uint64_t PreviousContainerVersion = ContainerVersion;
 435   if (Error E = processCommonMeta(SeparateMetaHelper))
 436     return E;
 437
 438   if (ContainerType != BitstreamRemarkContainerType::SeparateRemarksFile)
 439     return createStringError(
 440         std::make_error_code(std::errc::illegal_byte_sequence),
 441         "Error while parsing external file's BLOCK_META: wrong container "
 442         "type.");
 443
 444   if (PreviousContainerVersion != ContainerVersion)
 445     return createStringError(
 446         std::make_error_code(std::errc::illegal_byte_sequence),
 447         "Error while parsing external file's BLOCK_META: mismatching versions: "
 448         "original meta: %lu, external file meta: %lu.",
 449         PreviousContainerVersion, ContainerVersion);
 450
 451   // Process the meta from the separate file.
 452   return processSeparateRemarksFileMeta(SeparateMetaHelper);
 453 }
 454
 455 Error BitstreamRemarkParser::processStandaloneMeta(
 456     BitstreamMetaParserHelper &Helper) {
 457   if (Error E = processStrTab(*this, Helper.StrTabBuf))
 458     return E;
 459   return processRemarkVersion(*this, Helper.RemarkVersion);
 460 }
 461
 462 Error BitstreamRemarkParser::processSeparateRemarksFileMeta(
 463     BitstreamMetaParserHelper &Helper) {
 464   return processRemarkVersion(*this, Helper.RemarkVersion);
 465 }
 466
 467 Error BitstreamRemarkParser::processSeparateRemarksMetaMeta(
 468     BitstreamMetaParserHelper &Helper) {
 469   if (Error E = processStrTab(*this, Helper.StrTabBuf))
 470     return E;
 471   return processExternalFilePath(Helper.ExternalFilePath);
 472 }
 473
 474 Expected<std::unique_ptr<Remark>> BitstreamRemarkParser::parseRemark() {
 475   BitstreamRemarkParserHelper RemarkHelper(ParserHelper.Stream);
 476   if (Error E = RemarkHelper.parse())
 477     return std::move(E);
 478
 479   return processRemark(RemarkHelper);
 480 }
 481
 482 Expected<std::unique_ptr<Remark>>
 483 BitstreamRemarkParser::processRemark(BitstreamRemarkParserHelper &Helper) {
 484   std::unique_ptr<Remark> Result = std::make_unique<Remark>();
 485   Remark &R = *Result;
 486
 487   if (StrTab == None)
 488     return createStringError(
 489         std::make_error_code(std::errc::invalid_argument),
 490         "Error while parsing BLOCK_REMARK: missing string table.");
 491
 492   if (!Helper.Type)
 493     return createStringError(
 494         std::make_error_code(std::errc::illegal_byte_sequence),
 495         "Error while parsing BLOCK_REMARK: missing remark type.");
 496
 497   // Always >= Type::First since it's unsigned.
 498   if (*Helper.Type > static_cast<uint8_t>(Type::Last))
 499     return createStringError(
 500         std::make_error_code(std::errc::illegal_byte_sequence),
 501         "Error while parsing BLOCK_REMARK: unknown remark type.");
 502
 503   R.RemarkType = static_cast<Type>(*Helper.Type);
 504
 505   if (!Helper.RemarkNameIdx)
 506     return createStringError(
 507         std::make_error_code(std::errc::illegal_byte_sequence),
 508         "Error while parsing BLOCK_REMARK: missing remark name.");
 509
 510   if (Expected<StringRef> RemarkName = (*StrTab)[*Helper.RemarkNameIdx])
 511     R.RemarkName = *RemarkName;
 512   else
 513     return RemarkName.takeError();
 514
 515   if (!Helper.PassNameIdx)
 516     return createStringError(
 517         std::make_error_code(std::errc::illegal_byte_sequence),
 518         "Error while parsing BLOCK_REMARK: missing remark pass.");
 519
 520   if (Expected<StringRef> PassName = (*StrTab)[*Helper.PassNameIdx])
 521     R.PassName = *PassName;
 522   else
 523     return PassName.takeError();
 524
 525   if (!Helper.FunctionNameIdx)
 526     return createStringError(
 527         std::make_error_code(std::errc::illegal_byte_sequence),
 528         "Error while parsing BLOCK_REMARK: missing remark function name.");
 529   if (Expected<StringRef> FunctionName = (*StrTab)[*Helper.FunctionNameIdx])
 530     R.FunctionName = *FunctionName;
 531   else
 532     return FunctionName.takeError();
 533
 534   if (Helper.SourceFileNameIdx && Helper.SourceLine && Helper.SourceColumn) {
 535     Expected<StringRef> SourceFileName = (*StrTab)[*Helper.SourceFileNameIdx];
 536     if (!SourceFileName)
 537       return SourceFileName.takeError();
 538     R.Loc.emplace();
 539     R.Loc->SourceFilePath = *SourceFileName;
 540     R.Loc->SourceLine = *Helper.SourceLine;
 541     R.Loc->SourceColumn = *Helper.SourceColumn;
 542   }
 543
 544   if (Helper.Hotness)
 545     R.Hotness = *Helper.Hotness;
 546
 547   if (!Helper.Args)
 548     return std::move(Result);
 549
 550   for (const BitstreamRemarkParserHelper::Argument &Arg : *Helper.Args) {
 551     if (!Arg.KeyIdx)
 552       return createStringError(
 553           std::make_error_code(std::errc::illegal_byte_sequence),
 554           "Error while parsing BLOCK_REMARK: missing key in remark argument.");
 555     if (!Arg.ValueIdx)
 556       return createStringError(
 557           std::make_error_code(std::errc::illegal_byte_sequence),
 558           "Error while parsing BLOCK_REMARK: missing value in remark "
 559           "argument.");
 560
 561     // We have at least a key and a value, create an entry.
 562     R.Args.emplace_back();
 563
 564     if (Expected<StringRef> Key = (*StrTab)[*Arg.KeyIdx])
 565       R.Args.back().Key = *Key;
 566     else
 567       return Key.takeError();
 568
 569     if (Expected<StringRef> Value = (*StrTab)[*Arg.ValueIdx])
 570       R.Args.back().Val = *Value;
 571     else
 572       return Value.takeError();
 573
 574     if (Arg.SourceFileNameIdx && Arg.SourceLine && Arg.SourceColumn) {
 575       if (Expected<StringRef> SourceFileName =
 576               (*StrTab)[*Arg.SourceFileNameIdx]) {
 577         R.Args.back().Loc.emplace();
 578         R.Args.back().Loc->SourceFilePath = *SourceFileName;
 579         R.Args.back().Loc->SourceLine = *Arg.SourceLine;
 580         R.Args.back().Loc->SourceColumn = *Arg.SourceColumn;
 581       } else
 582         return SourceFileName.takeError();
 583     }
 584   }
 585
 586   return std::move(Result);
 587 }