[PATCH] D99205: Add jump-threading optimization for deterministic finite automata

[Alan Phipps via Phabricator via llvm-commits]

alanphipps added a comment.

In D99205#2802936 <https://reviews.llvm.org/D99205#2802936>, @alexey.zhikhar wrote:

> In D99205#2792215 <https://reviews.llvm.org/D99205#2792215>, @alanphipps wrote:
>
>> Thanks for all of the effort!  On our downstream Cortex-R5 compiler, I'm seeing a 20.4% speedup on Coremark with this patch, which is good, however, the older patch (https://reviews.llvm.org/D88307) gave me a 21.6% speedup. Any idea what could account for the difference there?
>
> It would be very hard for us to explain the difference without having access to both the downstream compiler and the hardware but something that comes to mind is:
>
> (1) were the two experiments performed on the same baseline compiler?
> (2) 1% could be within noise and might be due to trivial changes in the generated code (change of alignment, change of branch addresses and branch target addresses, etc.)
> (3) were both passes in the same place in the pipeline in both experiments?
>
> From the information provided, it is not possible to understand the root cause of the difference.

Thanks, and understood. I'll see if I can do some more digging here, but I suspect it may be noise.  I wasn't sure if there was an obvious difference in the algorithms here that might account for a degradation.  I'm pretty sure both passes are not in the same place in the pipeline (just taking the patch from the other review).


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