[all-commits] [llvm/llvm-project] d9b6f7: [lld-macho] Teach ICF to dedup functions with iden...

[Jez Ng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d9b6f7e312c11ff69779939bb2be0bd53936a333
      https://github.com/llvm/llvm-project/commit/d9b6f7e312c11ff69779939bb2be0bd53936a333
  Author: Jez Ng <jezng at fb.com>
  Date:   2021-11-12 (Fri, 12 Nov 2021)

  Changed paths:
    M lld/MachO/ICF.cpp
    M lld/MachO/InputFiles.cpp
    M lld/MachO/UnwindInfoSection.cpp
    M lld/test/MachO/icf.s

  Log Message:
  -----------
  [lld-macho] Teach ICF to dedup functions with identical unwind info

Dedup'ing unwind info is tricky because each CUE contains a different
function address, if ICF operated naively and compared the entire
contents of each CUE, entries with identical unwind info but belonging
to different functions would never be considered identical. To work
around this problem, we slice away the function address before
performing ICF. We rely on `relocateCompactUnwind()` to correctly handle
these truncated input sections.

Here are the numbers before and after D109944, D109945, and this diff
were applied, as tested on my 3.2 GHz 16-Core Intel Xeon W:

Without any optimizations:

             base           diff           difference (95% CI)
  sys_time   0.849 ± 0.015  0.896 ± 0.012  [  +4.8% ..   +6.2%]
  user_time  3.357 ± 0.030  3.512 ± 0.023  [  +4.3% ..   +5.0%]
  wall_time  3.944 ± 0.039  4.032 ± 0.031  [  +1.8% ..   +2.6%]
  samples    40             38

With `-dead_strip`:

             base           diff           difference (95% CI)
  sys_time   0.847 ± 0.010  0.896 ± 0.012  [  +5.2% ..   +6.5%]
  user_time  3.377 ± 0.014  3.532 ± 0.015  [  +4.4% ..   +4.8%]
  wall_time  3.962 ± 0.024  4.060 ± 0.030  [  +2.1% ..   +2.8%]
  samples    47             30

With `-dead_strip` and `--icf=all`:

             base           diff           difference (95% CI)
  sys_time   0.935 ± 0.013  0.957 ± 0.018  [  +1.5% ..   +3.2%]
  user_time  3.472 ± 0.022  6.531 ± 0.046  [ +87.6% ..  +88.7%]
  wall_time  4.080 ± 0.040  5.329 ± 0.060  [ +30.0% ..  +31.2%]
  samples    37             30

Unsurprisingly, ICF is now a lot slower, likely due to the much larger
number of input sections it needs to process. But the rest of the
linker only suffers a mild slowdown.

Note that the compact-unwind-bad-reloc.s test was expanded because we
now handle the relocation for CUE's function address in a separate code
path from the rest of the CUE relocations. The extended test covers both
code paths.

Reviewed By: #lld-macho, oontvoo

Differential Revision: https://reviews.llvm.org/D109946


  Commit: 9d0b237c516f935482cfff5c3df9cb44ee766664
      https://github.com/llvm/llvm-project/commit/9d0b237c516f935482cfff5c3df9cb44ee766664
  Author: Jez Ng <jezng at fb.com>
  Date:   2021-11-12 (Fri, 12 Nov 2021)

  Changed paths:
    M lld/MachO/UnwindInfoSection.cpp
    M lld/test/MachO/compact-unwind-sym-relocs.s

  Log Message:
  -----------
  [lld-macho] Fix symbol relocs handling for LSDAs

Similar to D113702, but for the LSDAs. Clang seems to emit all LSDA
relocs as section relocs, but ld -r can turn those relocs into symbol
ones.

Reviewed By: #lld-macho, oontvoo

Differential Revision: https://reviews.llvm.org/D113721


Compare: https://github.com/llvm/llvm-project/compare/6c32dd4dfafe...9d0b237c516f