[all-commits] [llvm/llvm-project] 75184f: [DebugInfo] Fix handling '# line "file"' for DWARFv5

[Igor Kudrin via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 75184f14aecd8147a02189a843789a4eb5e5b571
      https://github.com/llvm/llvm-project/commit/75184f14aecd8147a02189a843789a4eb5e5b571
  Author: Igor Kudrin <ikudrin at accesssoftek.com>
  Date:   2022-01-21 (Fri, 21 Jan 2022)

  Changed paths:
    M llvm/lib/MC/MCDwarf.cpp
    M llvm/test/MC/ELF/debug-hash-file.s

  Log Message:
  -----------
  [DebugInfo] Fix handling '# line "file"' for DWARFv5

`CppHashInfo.Filename` is a `StringRef` that references a part of the
source file and it is not null-terminated at the end of the file name.
`AsmParser::parseAndMatchAndEmitTargetInstruction()` passes it to
`getStreamer().emitDwarfFileDirective()`, and it eventually comes to
`isRootFile()`. The comparison fails because `FileName.data()` is not
properly terminated.

In addition, the old code might cause a significant speed degradation
for long source files. The `operator!=()` for `std::string` and
`const char *` can be implemented in a way that it finds the length of
the second argument first, which slows the comparison for long data.
`parseAndMatchAndEmitTargetInstruction()` calls
`emitDwarfFileDirective()` every time if `CppHashInfo.Filename` is not
empty. As a result, the longer the source file is, the slower the
compilation wend, and for a very long file, it might take hours instead
of a couple of seconds normally.

Differential Revision: https://reviews.llvm.org/D117785


  Commit: 86b08ed6bb16a96e921445299858f3cabd6f9e45
      https://github.com/llvm/llvm-project/commit/86b08ed6bb16a96e921445299858f3cabd6f9e45
  Author: Igor Kudrin <ikudrin at accesssoftek.com>
  Date:   2022-01-21 (Fri, 21 Jan 2022)

  Changed paths:
    M llvm/lib/MC/MCDwarf.cpp

  Log Message:
  -----------
  [DebugInfo][NFC] Do not call 'isRootFile' for DWARF Version < 5

A quicker comparison should be done first.

Differential Revision: https://reviews.llvm.org/D117786


Compare: https://github.com/llvm/llvm-project/compare/8def89b5dc82...86b08ed6bb16