[aarch64-port-dev ] RFR: C2: Canonicalize (x & 16 == 16) [Was: AARCH64 optimization: using TBZ instruction for bit check]

[Andrew Haley]

Hi,

On 19/06/2020 17:49, Boris Ulasevich wrote:
> I added the expression canonicalization in the BoolNode::Ideal method:
> http://cr.openjdk.java.net/~bulasevich/8247408/webrev.02b
>
> The change reduces a number of generated machine instructions on all
> ARM/x86/PPC architectures. Benchmark shows positive results on ARM64 and
> ARM32 with the given change.
>
> On x86 benchmark performance improves from +1% to +13% depending on the
> CPU generation, except of machines affected by Intel Erratum (JDK-8234160)
> issue. Maximum decrease observed is -%11. It does not look like a problem
> with the proposed benchmark though, but rather like an issue with
> Erratum mitigation.
>
> On PowerPC result of the micro-benchmark is also positive. I changed the
> micro-benchmark to make it a little bulkier so that we don't hit the
> limitations of architectures with a less elaborate branch prediction
> mechanism. The original application performance does not change on PowerPC.

Fantastic work, thanks! You've done a remarkably thorough job.  It's
slightly unfortunate that one of the targets regresses. If there had
been no regressions, I'd approve this straight away.

Forwarding to hotspot-compiler-dev for more comments.

VladimirK, what do you think? I guess we could turn this off on the
machines affected by JDK-8234160. Should we?

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