[all-commits] [llvm/llvm-project] 850592: [lld-macho] Implement -why_live (without perf over...

[Jez Ng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 850592ec14d0a5f2431aa780cb130d6ec20eb969
      https://github.com/llvm/llvm-project/commit/850592ec14d0a5f2431aa780cb130d6ec20eb969
  Author: Jez Ng <jezng at fb.com>
  Date:   2022-02-24 (Thu, 24 Feb 2022)

  Changed paths:
    M lld/MachO/Config.h
    M lld/MachO/Driver.cpp
    M lld/MachO/MarkLive.cpp
    M lld/MachO/Options.td
    M lld/MachO/Symbols.h
    A lld/test/MachO/why-live.s

  Log Message:
  -----------
  [lld-macho] Implement -why_live (without perf overhead)

This was based off @thakis' draft in {D103517}. I employed templates to ensure
the support for `-why_live` wouldn't slow down the regular non-why-live code
path.

No stat sig perf difference on my 3.2 GHz 16-Core Intel Xeon W:

             base           diff           difference (95% CI)
  sys_time   1.195 ± 0.015  1.199 ± 0.022  [  -0.4% ..   +1.0%]
  user_time  3.716 ± 0.022  3.701 ± 0.025  [  -0.7% ..   -0.1%]
  wall_time  4.606 ± 0.034  4.597 ± 0.046  [  -0.6% ..   +0.2%]
  samples    44             37

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D120377