[llvm] r229584 - We require MSVC 2013 Update 4 due to previous versions miscompiling ASTMatchers

[Aaron Ballman]

On Tue, Feb 17, 2015 at 7:54 PM, Kaylor, Andrew <andrew.kaylor at intel.com> wrote:
> I have been seeing some problems where some clang regression tests
> intermittently fail -- most often Format/style-on-command-line.  I have no
> idea if that’s related.

No, that's a long-standing bug we have with lit tests that try to
delete files on Windows (the file sometimes stays open by another
process such as AV software, or the test itself, and so it gets a
Permission Denied error when the delete is attempted). Very annoying.

> I don’t know what to say about reverting this change.  This change seems
> like the kind of thing that needs to happen sooner or later.  If it stays,
> I’m going to be forced to use a local change to enable builds until I can
> get the techs here to update a couple of systems for me.  I can live with
> that, but it is inconvenient.  Mainly I just wanted to start a conversation
> to see how many other people were in my position and to explore the
> possibility that there are other ways around whatever issues forced this
> change.

My biggest concern is ensuring that users are not blocked, so we can
revert this change to unblock you. However, that greatly increases the
likelihood of dealing with odd miscompiles, which wastes a lot of time
for very little benefit. My personal preference is for us to be able
to rely on the latest updates to any major compiler revision being
installed, but not at the expense of other people's workflows.

~Aaron