RFR: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does [v9]

[Emanuel Peter]

On Tue, 25 Feb 2025 12:23:58 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> test/hotspot/jtreg/compiler/c2/irTests/RShiftLNodeIdealizationTests.java line 145:
>> 
>>> 143:     public long test9(long x) {
>>> 144:         x = Integer.max(Integer.min((int)x, (int)test7Max), (int)(test7Min-1));
>>> 145:         return ((x << test7Shift) >> test7Shift);
>> 
>> It could be nice to have some test cases where both shift values are completely randomized.
>
> The transformation only happens if the amounts we shift left and right are the same. So if they are random, the transformation won't apply most of the time and, rarely, it will (because they will turn out to be the same). I'm not sure how to write an IR test then.

You would not have to assert anything about the IR, just do value verification in that case.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23438#discussion_r1969666205