659311 - Avoid clobber between profile generate and use passes of PGO builds

Status: RESOLVED WONTFIX

(Firefox Build System :: General, defect)

Comment 1

[Mike Hommey [:glandium]]

Attachment: Avoid clobber between profile generate and use passes of PGO builds

Comment 2

[(not currently active) Ted Mielczarek]

Comment on attachment 534760 [details] [diff] [review]
Avoid clobber between profile generate and use passes of PGO builds

Review of attachment 534760 [details] [diff] [review]:
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This all looks sane, I just have one large reservation here. Any way to test this? (Clearly the try server isn't going to help.)

::: config/rules.mk
@@ +903,5 @@
>  endif # SHARED_LIBRARY || PROGRAM
> +else  # ! WINNT_
> +# Force rebuilding all objects on the second pass
> +$(OBJS): pgo.rebuild
> +.PHONY: pgo.rebuild

Is this going to do weird things to the profiling phase? Presumably you can wind up with object files that aren't compiled with instrumentation because they had no changes, so you wouldn't profile them and then they wouldn't get optimized properly. Is there going to be weird perf impact on a dep build after this?

Comment 3

[Mike Hommey [:glandium]]

Another possibility would be to try to keep the -fprofile-generate objects around.

Comment 4

[Mike Hommey [:glandium]]

(In reply to comment #2)
> Is this going to do weird things to the profiling phase? Presumably you can
> wind up with object files that aren't compiled with instrumentation because
> they had no changes, so you wouldn't profile them and then they wouldn't get
> optimized properly. Is there going to be weird perf impact on a dep build
> after this?

In practice, this is what happens since bug 659942 :(
See bug 676252.

Comment 5

[Mike Hommey [:glandium]]

Attachment: Avoid clobber between profile generate and use passes of PGO builds.

As landed

Comment 6

[Mike Hommey [:glandium]]

http://hg.mozilla.org/projects/build-system/rev/b0fa6b9a3e47

Comment 7

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

http://hg.mozilla.org/mozilla-central/rev/b0fa6b9a3e47

Comment 8

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

http://hg.mozilla.org/mozilla-central/rev/1d19ff806783

Comment 9

[Mike Hommey [:glandium]]

http://hg.mozilla.org/projects/build-system/rev/3e4db1a10caa

Comment 10

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

Backed out in:

http://hg.mozilla.org/projects/build-system/rev/9e4aea4d7030

Comment 11

[Mike Hommey [:glandium]]

Now that we don't do PGO in one go, it doesn't matter anymore.