Introduced in
https://swiftshader-review.googlesource.com/#/c/SwiftShader/+/11328/

https://build.chromium.org/p/chromium.win/builders/WinClang64%20(dbg) is happy, where are you seeing this?

It's probably a MSVC 2017 thing

Nope, I get this in MSVC 2015 too. 

There must be another config difference somewhere.

The reason why this works for Win Clang (dbg) is because of this setting in its GN args:
is_debug = false

Turns out our debug bots aren't using a debug config. Oops!

That's intentional; it's more important to keep the release config buildable since the release builders use that config.

But yes, the breakage is visible on https://build.chromium.org/p/chromium.fyi/console?category=win%20clang (which are also all msvc bots) Looks like other stuff is broken too:

FAILED: obj/sandbox/win/sbox_integration_tests/lpc_policy_test.obj 
ninja -t msvc -e environment.x86 -- C:\b\c\goma_client/gomacc.exe "c:\b\c\win_toolchain\vs_files\f53e4598951162bad6330f7a167486c7ae5db1e5\vc\bin\amd64_x86/cl.exe" /nologo /showIncludes  @obj/sandbox/win/sbox_integration_tests/lpc_policy_test.obj.rsp /c ../../sandbox/win/src/lpc_policy_test.cc /Foobj/sandbox/win/sbox_integration_tests/lpc_policy_test.obj /Fd"obj/sandbox/win/sbox_integration_tests_cc.pdb"
c:\b\c\builder\crwinclang_shared_\src\sandbox\win\src\lpc_policy_test.cc(35) : error C2220: warning treated as error - no 'object' file generated
c:\b\c\builder\crwinclang_shared_\src\sandbox\win\src\lpc_policy_test.cc(35) : warning C4702: unreachable code


Consider not using msvc? :-)

(to be clear, i'll try to get these bots green, but they'll be broken again until I then fix them again, etc)

> Consider not using msvc? :-)
If the debug info is on par, sure. Until then, this is what we've got.

I've already got a fix on the way for swiftshader btw.

> If the debug info is on par

Are there bug filed for whatever shortcomings you see?

The following revision refers to this bug:
  https://swiftshader.googlesource.com/SwiftShader.git/+/e8d42ae19d9c8433a728fb1b1382a3ff0258926c

commit e8d42ae19d9c8433a728fb1b1382a3ff0258926c
Author: Robert Liao <robliao@chromium.org>
Date: Mon Aug 14 19:24:44 2017

Remove /RTC1 for Windows Debug Builds

SwiftShader requests the optimized flags for debug buidls for
performance. This leads to an incompatible use of /O1 and /RTC1.

BUG= chromium:755195 

Change-Id: I53b6f99a67d0b8d5fc5932b677ee278aca300702
Reviewed-on: https://swiftshader-review.googlesource.com/11594
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Robert Liao <robliao@chromium.org>

[modify] https://crrev.com/e8d42ae19d9c8433a728fb1b1382a3ff0258926c/BUILD.gn

Change submitted from
https://swiftshader-review.googlesource.com/#/c/SwiftShader/+/11594/

> Are there bug filed for whatever shortcomings you see?
They're already tracked in http://crbug.com/636111

The main problem here is we don't exercise the debugging system to completeness every day. It depends on the problem we're trying to solve. When something is missing, we won't find out until someone hits that case.

Clang has some of the basics down, but as we've discovered it's definitely not up to par for debug information. In fact, in some cases, it's debugger hostile (e.g. the hang on  http://crbug.com/753032 , causing us to lose control of the process for minutes at a time).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fe528e14b412bf3dc1b5879a004d870735311ed0

commit fe528e14b412bf3dc1b5879a004d870735311ed0
Author: Nico Weber <thakis@chromium.org>
Date: Mon Aug 14 19:51:49 2017

win: Unbreak msvc unofficial release builds a bit.


Bug:  755195 
Cq-Include-Trybots: master.tryserver.chromium.win:win10_chromium_x64_rel_ng
Change-Id: Ie1b24b0ad37a1c4fe82386a39f132f92dbfa8c2a
Reviewed-on: https://chromium-review.googlesource.com/614148
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494142}
[modify] https://crrev.com/fe528e14b412bf3dc1b5879a004d870735311ed0/sandbox/win/src/lpc_policy_test.cc

'all' builds locally for me with your swiftshader fix and my sandbox one, so things should be fine after swiftshader rolls forward.

https://build.chromium.org/p/chromium.fyi/console?category=win%20clang (all msvc bots) looks like it's slowly greening up already.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/693c11eab0ea3cdb8b4f14643769a10a2eba827b

commit 693c11eab0ea3cdb8b4f14643769a10a2eba827b
Author: Alexis Hetu <sugoi@google.com>
Date: Tue Aug 15 05:28:37 2017

Roll SwiftShader 5bf72ee..e8d42ae

https://swiftshader.googlesource.com/SwiftShader.git/+log/5bf72ee..e8d42ae

BUG= chromium:755195 

TBR=kbr@chromium.org

TEST=bots

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel,linux_chromium_cfi_rel_ng;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Change-Id: Ifffea9273cf79c8048cbf95003f7eb29b98a17ef
Reviewed-on: https://chromium-review.googlesource.com/615027
Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494328}
[modify] https://crrev.com/693c11eab0ea3cdb8b4f14643769a10a2eba827b/DEPS