RFR: 8288445: AArch64: C2 compilation fails with guarantee(!true || (true && (shift != 0))) failed: impossible encoding

[Hao Sun]

On Wed, 22 Jun 2022 03:40:14 GMT, Dean Long <dlong at openjdk.org> wrote:

> > Instead of introducing immI_positive, I wonder if we can generate orr dst src for zero shift count, just as the SVE part does
> 
> I considered using left-shift by 0, but I don't think it's worth it to optimize this case in the back-end. If we really want to optimize shift by 0, I think it should be done in the front-end.

Okay.

I think we may want to make the same update to the corresponding SVE part, e.g. https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/aarch64/aarch64_sve.ad*L3662__;Iw!!ACWV5N9M2RV99hQ!KfV6TCMgPvv6TBAs13_7o6shZKffk3wZF2Wn7gPCbA3vzCiFZJgNknz-Q9bfnJt5PxOMM3vBSQWCpLNp89qa7VQKREbtiA$ , as it's better to align with the NEON and SVE implementations.

It may deserve one separate patch, not in this bugfix one.

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PR: https://git.openjdk.org/jdk19/pull/40