[PATCH] D22639: Add flag to PassManagerBuilder to disable GVN Hoist Pass.

[Daniel Berlin via llvm-commits]

+george

On Thu, Jul 21, 2016 at 12:49 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

>
>
> On Thu, Jul 21, 2016 at 12:43 PM, Benjamin Kramer <benny.kra at gmail.com>
> wrote:
>
>> bkramer added a subscriber: bkramer.
>> bkramer added a comment.
>>
>> The problem is not a Halide test but a scalability issue in MemorySSA
>> that's making Halide unusable, consuming gigabytes of memory and taking
>> forever.
>
>
>
> Personally, I don't think the GVNHoist pass is ready for prime time yet
>> and needs more testing, like we did for other passes that were first
>> rigorously tested under a flag before being enabled by default. Going
>> directly from zero to default with a major new optimization infrastructure
>> (MemSSA) is a recipe for disaster.
>>
>
> I agree that GVNHoist probably should not be on by default yet regardless
> of anything else.
>
> George recently (IE this week) replaced the walker in MemorySSA because
> we've known from the beginning that there were significant scaling issues
> in the original impl (it could use N^2 memory and time easily with the
> caching scheme it used) .
>
> It's likely you just hit one of these cases.
>
>
>> Sadly the test case is fairly large and being a compile time regression
>> reduction is difficult, I believe Alina is working on that.
>>
>> Can you send me the testcase, even if large?
>
> Alternatively, i'm curious if it's still an issue with George's latest
> walker commit.
>
>
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