Integrated: 8321308: AArch64: Fix matching predication for cbz/cbnz

[Fei Gao]

On Wed, 6 Dec 2023 01:54:59 GMT, Fei Gao <fgao at openjdk.org> wrote:

> For array length check like:
> 
>   if (a.length > 0) {
>     [Block 1]
>   } else {
>     [Block 2]
>   }
> 
> 
> Since `a.length` is unsigned, it's semantically equivalent to:
> 
>   if (a.length != 0) {
>     [Block 1]
>   } else {
>     [Block 2]
>   }
> 
> 
> On aarch64 port, we can do the conversion like above, during c2 compiler instruction matching, for certain unsigned integral comparisons.
> 
> For example,
> 
> cmpw  w11, #0 # unsigned
> bls   label   # unsigned
> [Block 1]
> 
> label:
> [Block 2]
> 
> 
> can be converted to:
> 
> cbz  w11, label
> [Block 1]
> 
> label:
> [Block 2]
> 
> 
> Currently, we have some matching rules to do the conversion [[1]](https://github.com/openjdk/jdk/blob/4f1a10f84bcfadef263a0890b6834ccd3d5bb52f/src/hotspot/cpu/aarch64/aarch64.ad#L15688). But the predicate here [[2]](https://github.com/openjdk/jdk/blob/4f1a10f84bcfadef263a0890b6834ccd3d5bb52f/src/hotspot/cpu/aarch64/aarch64.ad#L5631) matches wrong `BoolTest` masks, so these rules fail to convert. I guess it's a typo introduced in [JDK-8160006](https://bugs.openjdk.org/browse/JDK-8160006). The patch fixes it.

This pull request has now been integrated.

Changeset: 2c9185eb
Author:    Fei Gao <fgao at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/2c9185eb81c9dfcc30d160a6254089c474b56b0d
Stats:     131 lines in 3 files changed: 116 ins; 0 del; 15 mod

8321308: AArch64: Fix matching predication for cbz/cbnz

Reviewed-by: fyang, adinn, aph

-------------

PR: https://git.openjdk.org/jdk/pull/16989