1475660 - Make PGO imply LTO in clang-cl builds

Status: RESOLVED FIXED

(Firefox Build System :: General, enhancement)

Description

[(Away)]

The design of MSVC's PGO implementation is such that you have to use it in conjunction with LTO.

For at least the short term, I propose that we make clang-cl builds behave the same way. This way we can keep producing win{32,64}-pgo as our shipping build platform without extra changes, and we can throw just one switch to go back and forth between MSVC+PGO+LTO and clang-cl+faux-PGO+ThinLTO if needed.

Comment 1

[(Away)]

Attachment: Make PGO imply ThinLTO in clang-cl builds

This builds on the changes in bug 1448980 so this patch may need updates depending on review of the other bug.

It's worth pointing out that, while the patch looks pretty inconsequential at first glance, this will actually "flip the switch" on ThinLTO in official builds.

Comment 2

[Mike Hommey [:glandium]]

Comment on attachment 8992316 [details] [diff] [review]
Make PGO imply ThinLTO in clang-cl builds

and value.origin == 'default'. You don't want an explicit --disable-lto to still enable it magically.

Comment 3

[(Away)]

Attachment: Make PGO imply ThinLTO in clang-cl builds

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/e09ba0bb848a
Make clang-cl PGO enable LTO (enables ThinLTO in official builds) r=froydnj,glandium

Comment 5

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/e09ba0bb848a

Comment 6

[Ionuț Goldan [:igoldan]]

Perf wins on Windows:

== Change summary for alert #14377 (as of Mon, 16 Jul 2018 19:10:37 GMT) ==

Improvements:

  9%  a11yr windows7-32 pgo e10s stylo     177.75 -> 161.75
  8%  perf_reftest_singletons windows7-32 pgo e10s stylo49.02 -> 45.09
  8%  a11yr windows10-64 pgo e10s stylo    182.30 -> 167.80
  7%  perf_reftest_singletons windows10-64 pgo e10s stylo49.64 -> 46.03
  4%  tp6_amazon windows7-32 pgo e10s stylo223.88 -> 215.29
  3%  speedometer windows7-32 pgo e10s stylo71.45 -> 73.52
  2%  tp6_google windows7-32 pgo e10s stylo401.23 -> 391.25
  2%  speedometer windows10-64 pgo e10s stylo66.52 -> 68.17

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=14377