[all-commits] [llvm/llvm-project] 14e3be: Reland "[lld] Preliminary fat-lto-object support"

[Paul Kirth via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 14e3bec8fc3e1f10c3dc57277ae3dbf9a4087b1c
      https://github.com/llvm/llvm-project/commit/14e3bec8fc3e1f10c3dc57277ae3dbf9a4087b1c
  Author: Paul Kirth <paulkirth at google.com>
  Date:   2023-08-18 (Fri, 18 Aug 2023)

  Changed paths:
    M lld/ELF/Config.h
    M lld/ELF/Driver.cpp
    M lld/ELF/Options.td
    M lld/docs/ReleaseNotes.rst
    M lld/docs/ld.lld.1
    A lld/test/ELF/fatlto/fatlto.invalid.s
    A lld/test/ELF/fatlto/fatlto.test

  Log Message:
  -----------
  Reland "[lld] Preliminary fat-lto-object support"

This patch adds support to lld for --fat-lto-objects. We add a new
--fat-lto-objects option to LLD, and slightly change how it chooses input
files in the driver when the option is set.

Fat LTO objects contain both LTO compatible IR, as well as generated object
code. This allows users to defer the choice of whether to use LTO or not to
link-time. This is a feature available in GCC for some time, and makes the
existing -ffat-lto-objects option functional in the same way as GCC's.

If the --fat-lto-objects option is passed to LLD and the input files are fat
object files, then the linker will chose the LTO compatible bitcode sections
embedded within the fat object and link them together using LTO. Otherwise,
standard object file linking is done using the assembly section in the object
files.

The previous version of this patch had a missing `REQUIRES: x86` line in
`fatlto.invalid.s`. Additionally, it was reported that this patch caused
a test failure in `export-dynamic-symbols.s`, however,
29112a994694baee070a2021e00f772f1913d214 disabled the
`export-dynamic-symbols.s` test on Windows due to a quotation difference
between platforms, unrelated to this patch.

Original RFC: https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D146778