RFR: 8288445: AArch64: C2 compilation fails with guarantee(!true || (true && (shift != 0))) failed: impossible encoding [v4]

[Hao Sun]

On Thu, 23 Jun 2022 08:09:36 GMT, Dean Long <dlong at openjdk.org> wrote:

>> The range for aarch64 vector right-shift is 1 to the element width.  This issue fixes the problem in the back-end.  There is a separate problem in the front-end that shift by 0 is not always optimized out.
>
> Dean Long has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - fix comment
>  - Update test/hotspot/jtreg/compiler/codegen/ShiftByZero.java
>    
>    Co-authored-by: Andrew Haley <aph-open at littlepinkcloud.com>

test/hotspot/jtreg/compiler/codegen/ShiftByZero.java line 43:

> 41:         int shift = i32[0];
> 42:         // This loop is to confuse the optimizer, so that "shift" is
> 43:         // optimized to 0 only after loop vectorization. 

It seems that we should remove the trailing whitespace, as suggested by `jcheck`.
Suggestion:

        // optimized to 0 only after loop vectorization.

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