[PATCH] D54487: Implement llvm.commandline named metadata

[Scott Linder via Phabricator via llvm-commits]

scott.linder created this revision.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.

Implement a new special named metadata, `llvm.commandline`, to support frontends embedding their command-line options in IR/ASM/code-objects. Specifically this supports adding the `-frecord-gcc-switches` option to Clang.

This differs from the GCC implementation in a few ways, and I am looking for feedback on whether these differences are reasonable/correct.

In GCC there is only one command-line possible per compilation-unit, in LLVM it mirrors `llvm.ident` and multiple are allowed. In GCC it is emitted to an ELF section named `.GCC.command.line`, for LLVM it is emitted to an ELF section named `.LLVM.command.line`. In GCC there is no special syntax in ASM (.section/.ascii/.zero are used), in LLVM there is a special `.commandline` directive.

For the ELF section, in the case of GCC the options are null-terminated (e.g. '-foo\0-bar\0-baz\0'); in LLVM, in order to differentiate multiple merged command-lines, the null byte instead separates entire command-lines (e.g. '\0compiler1 -foo -bar -baz\0compiler2 -qux\0'). This is the biggest departure in terms of implementation, but in the face of section merging I don't understand how the GCC approach works in any meaningful way. The advantage I see to the GCC approach is unambiguously separating individual arguments without relying on shell-style parsing.


Repository:
  rL LLVM

https://reviews.llvm.org/D54487

Files:
  include/llvm/CodeGen/AsmPrinter.h
  include/llvm/MC/MCAsmInfo.h
  include/llvm/MC/MCELFStreamer.h
  include/llvm/MC/MCStreamer.h
  lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  lib/IR/Verifier.cpp
  lib/MC/MCAsmInfoELF.cpp
  lib/MC/MCAsmStreamer.cpp
  lib/MC/MCELFStreamer.cpp
  lib/MC/MCParser/ELFAsmParser.cpp
  test/CodeGen/X86/commandline-metadata.ll
  test/Linker/Inputs/commandline.a.ll
  test/Linker/Inputs/commandline.b.ll
  test/Linker/commandline.ll
  test/MC/ELF/commandline.s
  test/Verifier/commandline-meta1.ll
  test/Verifier/commandline-meta2.ll
  test/Verifier/commandline-meta3.ll
  test/Verifier/commandline-meta4.ll

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