User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:34.0) Gecko/20100101 Firefox/34.0 Build ID: 20141208120101 Steps to reproduce: https://tbpl.mozilla.org/php/getParsedLog.php?id=54110988&tree=Mozilla-Inbound&full=1 xul is built twice for both profile-generate and profile-use

From the nightly build logs: cd /pub/mozilla.org/firefox/nightly/ zgrep -c -- "-o libxul.so" 2014/07/*-mozilla-central/mozilla-central-linux64-nightly*.gz .... 2014/07/2014-07-24-03-02-01-mozilla-central/mozilla-central-linux64-nightly-bm77-build1-build8.txt.gz:3 2014/07/2014-07-25-03-02-02-mozilla-central/mozilla-central-linux64-nightly-bm71-build1-build13.txt.gz:3 2014/07/2014-07-26-03-02-04-mozilla-central/mozilla-central-linux64-nightly-bm91-build1-build18.txt.gz:5 2014/07/2014-07-27-03-02-04-mozilla-central/mozilla-central-linux64-nightly-bm91-build1-build19.txt.gz:5 Regression range is http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=613e79262240&tochange=e07264876182 For a finer regression window you can look at http://inbound-archive.pub.build.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-central-linux64-pgo/, but only for another month or so before they expire.

That regression range suggests bug 1043344, I think?

I see 5 links here: http://inbound-archive.pub.build.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-central-linux64-pgo/1406331007/mozilla-central-linux64-pgo-bm70-build1-build30.txt.gz and 3 here: http://inbound-archive.pub.build.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-central-linux64-pgo/1406309404/mozilla-central-linux64-pgo-bm91-build1-build33.txt.gz http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=8da875b402fe&tochange=e07264876182

On mozilla-inbound: 3 here: http://inbound-archive.pub.build.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-inbound-linux64-pgo//1406233807/mozilla-inbound-linux64-pgo-bm94-build1-build142.txt.gz 5 here: http://inbound-archive.pub.build.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-inbound-linux64-pgo//1406244609/mozilla-inbound-linux64-pgo-bm77-build1-build79.txt.gz http://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=51ff7710ccbc&tochange=0300f04572b6

Thanks to REBUILD_CHECK, I figured what's going on. We're hitting this: https://hg.mozilla.org/integration/mozilla-inbound/file/119ce28762a9/config/rules.mk#l623 which combined with: https://hg.mozilla.org/integration/mozilla-inbound/file/119ce28762a9/toolkit/library/Makefile.in#l17 and https://hg.mozilla.org/integration/mozilla-inbound/file/119ce28762a9/toolkit/library/Makefile.in#l20 makes libxul built both during target and libs.

I see a nice, but brief, drop in PGO build times after this was landed: http://people.mozilla.org/~catlee/sattap/aaabfe3b.png