[PATCH] D38196: [AArch64] Avoid interleaved SIMD store instructions for Exynos

[Abderrazek Zaafrani via Phabricator via llvm-commits]

az added a comment.



> I thought the "shouldExitEarly" method aims to check if any of the transformations the pass can do can be profitable for the target at all.
>  My understanding is that this can be checked by just examining the instruction latencies, not having to look at the actual code being compiled at all. I assume that the saving of compile time comes from the fact that "shouldExitEarly" needs to do an amount of work proportional to the number of rewriting rules implemented, not proportional to the amount of code being compiled.
>  So, for the pass to work as expected, i.e. always run when for the target at least one of the transformations is profitable, I think shouldExitEarly should check all rewriting rules implemented.
> 
> Does that make sense, or am I misunderstanding something here?

Your understanding of ShouldExitEarly is accurate and I agree that ideally we should put down all rewriting rules. However, ShouldExitEarly is not very cheap as it calls shouldReplaceInstruction. The question is should we put some heuristics into ShouldExitEarly so that we do not check for all rules even though the number of rules is static and does not depend on code? I currently check for one rule and make it a representative of all (st2 in this case) and this may be over-simplification. Maybe, I can check for one representative of st2 and one for st4 (which both have many variants).


https://reviews.llvm.org/D38196