[llvm] r295378 - [LSR] Prevent formula with SCEVAddRecExpr type of Reg from Sibling loops

[Davide Italiano via llvm-commits]

On Wed, Feb 22, 2017 at 5:03 PM, Wei Mi <wmi at google.com> wrote:
>
>
> On Wed, Feb 22, 2017 at 4:08 PM, Wei Mi <wmi at google.com> wrote:
>>
>>
>>
>> On Wed, Feb 22, 2017 at 3:46 PM, Davide Italiano <davide at freebsd.org>
>> wrote:
>>>
>>> On Thu, Feb 16, 2017 at 1:27 PM, Wei Mi via llvm-commits
>>> <llvm-commits at lists.llvm.org> wrote:
>>> > Author: wmi
>>> > Date: Thu Feb 16 15:27:31 2017
>>> > New Revision: 295378
>>> >
>>> > URL: http://llvm.org/viewvc/llvm-project?rev=295378&view=rev
>>> > Log:
>>> > [LSR] Prevent formula with SCEVAddRecExpr type of Reg from Sibling
>>> > loops
>>> >
>>>
>>> Sorry if I'm late, but our downstream branch was a little bit behind.
>>> With this test LTO time of some of our internal codebases skyrockets.
>>> running `llc` on the test attached takes ~7 seconds with the change
>>> reverted and I had to kill it after 10 minutes with the change in. Can
>>> you please take a look, and see if you can fix this easily (or
>>> revert?) I'd like to get our bots green again.
>>>
>>
>> Sorry to break your bot. I can reproduce the problem and am looking at it.
>> Thanks for the testcase.
>>
>> Wei.
>
>
> Hi Davide,
>
> I found the problem was there for a long time (I reproduce the same problem
> since r290782. I cannot try earlier versions because they cannot digest the
> IR). rL294814 just hided the problem and rL295378 exposed the problem again.
>

This is unfortunate, maybe it's time to bite the bullet and
analyze/fix the underlying problem?

> Is this the first time you see the problem? I am curious why it doesn't
> break the bot before.
>

This is a bot I just set up recently (mid January, to test NewGVN with
some of our internal codebases).
r290782 (by Dan, cc:ed) is unlikely to be the culprit, FWIW.


-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare