Pretty sure this is wontfix or "win bots shouldn't clobber": we pass a -D flag with the llvm revision, so if that changes all TUs get recompiled. I bet in this case no llvm revision landed in the time between the two builds, so it wasn't necessary to rebuild everything.

Yes, looking at the gclient runhooks step of https://ci.chromium.org/buildbot/chromium.clang/ToTLinux/2479 it seems it had already checked out the latest llvm revision. (However it still built the compiler from scratch, probably due to how we invalidate the cmake cache with a big hammer.)

The ToTWin bot does have a clobber step. I don't think it's supposed to be there..

re c#1: Yeah, let's do that. It makes it so that if LLVM doesn't change, our ToT bots cycle fast and pick up the next available LLVM revision.

Apparently I made the win bots clobber bots in https://codereview.chromium.org/2092553002 due incremental linking getting confused about our in-progress debug info work. We can either undo that now, or undo that once we're on lld.

To fix, remove the 'clobber' entries from //build/scripts/slave/recipe_modules/chromium_tests/chromium_clang.py -- looks like Linux CFI has them too, not clear at all why. probably copy-paste from the crwinasan bots. 'ToTWin' doesn't have a 'clobber' entry; maybe official builders get that automatically from elsewhere (in which case we want to keep it for ToTWin).

The dbg build already doesn't clobber: https://ci.chromium.org/buildbot/chromium.clang/ToTWin%28dbg%29/733 It also doesn't force symbols off as far as I can tell, so the argument for keeping clobber on on the crwinasan bots until we switch to lld doesn't hold any water.

official bots clobber via https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium/config.py?type=cs&q=clobber+file:recipe&sq=package:chromium&g=0&l=442 (
@config_ctx(includes=['static_library', 'clobber'])
def official(c):
)

Sending a CL for the other bots...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build/+/c1a2c5701cf31df341fa170c9518d5036ebe6b0a

commit c1a2c5701cf31df341fa170c9518d5036ebe6b0a
Author: Nico Weber <thakis@chromium.org>
Date: Mon Aug 06 17:07:28 2018

Don't do clobber builds on CrWinAsan* and on Linux CFI.

Bug:  842444 
Change-Id: Ibe00848207bb91ad6058471721f0a54e9f1afc95
Reviewed-on: https://chromium-review.googlesource.com/1163725
Reviewed-by: Reid Kleckner <rnk@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>

[modify] https://crrev.com/c1a2c5701cf31df341fa170c9518d5036ebe6b0a/scripts/slave/recipe_modules/chromium_tests/chromium_clang.py