[llvm-dev] Enabling Loop Distribution Pass as default in the pipeline of new pass manager

[Jingu Kang via llvm-dev]

Hi Florian,

Thanks for your kind reply.

The loop distribute pass was not triggered with one of below messages on almost all tests.

Skipping; memory operations are safe for vectorization
Skipping; no unsafe dependences to isolate
Skipping; multiple exit blocks

It looks like the first and second message are reasonable.
From third message, we could try to improve the pass to handle loop with the multiple exit blocks… I am not sure how much effort we need for it…

Thanks
JinGu Kang

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Florian Hahn via llvm-dev
Sent: 14 July 2021 13:06
To: Jingu Kang <Jingu.Kang at arm.com>; llvm-dev at lists.llvm.org
Cc: nikic at php.net
Subject: Re: [llvm-dev] Enabling Loop Distribution Pass as default in the pipeline of new pass manager

Hi,


On 5 Jul 2021, at 15:40, Jingu Kang <jingu.kang at arm.com<mailto:jingu.kang at arm.com>> wrote:

Ping.

Additionally, I was not able to see the pass triggered from llvm-test-suite and spec benchmark except hmmer.


Hm, this seems to indicate that the current version of loop-distribute is not very general at all. I’m not sure if we want to enable the pass by default, as long as it effectively only benefits a single benchmark?

Taking a step back, the question this raises for me is *why* it does not trigger anywhere else at all? I doubt there are no other cases in the test-suite and/or various SPEC benchmarks that would benefit from loop distribution. It would at least be helpful to understand *why* the pass misses them at the moment and what kind of changes are needed to make it more general.
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