[aarch64-port-dev ] RFR(S): 8239914: AArch64: Combine add/sub with comparison against zero

[Andrew Haley]

Hi,

On 2/27/20 3:41 AM, Pengfei Li wrote:

> This is a small enhancement in AArch64 C2 matching rules.
> 
> For Java code like "if (a + b > 0) {...}", C2 AArch64 backend generates
> instructions like below.
>   add     w10, w2, w1
>   cmp     w10, #0x0
>   b.gt    0x0000ffff790d5274
> 
> Please let me know if this enhancement is valuable or not.

This looks good, but it's hard to say without JMH tests. We really can't
say very much about performance enhancements without measurements.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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