RFR: 8328528: C2 should optimize long-typed parallel iv in an int counted loop [v8]

[Kangcheng Xu]

On Tue, 23 Jul 2024 09:52:00 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> I'm observing a weird test [failure exposed by GHA](https://github.com/tabjy/jdk/actions/runs/10045677996/job/27764679129) that only happens on Linux x86. While there are no actual loop nodes, `LoopLimit` nodes are matched by the same regex. I'm currently looking into this:
>> 
>> - `LoopLimit` nodes are somehow not eliminated together with counted loops on 32bit Linux
>> - the same binary bundle downloaded from GHA running on my local machine produces only one failure (instead of two) on `testIntCountedLoopWithIntIVWithRandomStrides(int)`
>> - `LoopLimit` and `/(\d+(\s){2}(Loop.*)+(\s){2}===.*)/` being another case of [regex mis-match](https://github.com/openjdk/jdk/pull/18198#issuecomment-2214675206)?
>> 
>> 
>> 2024-07-22T18:16:53.5547051Z One or more @IR rules failed:
>> 2024-07-22T18:16:53.5547411Z 
>> 2024-07-22T18:16:53.5547613Z Failed IR Rules (2) of Methods (2)
>> 2024-07-22T18:16:53.5548249Z ----------------------------------
>> 2024-07-22T18:16:53.5550118Z 1) Method "private static int compiler.loopopts.parallel_iv.TestParallelIvInIntCountedLoop.testIntCountedLoopWithIntIVWithRandomStrides(int)" - [Failed IR rules: 1]:
>> 2024-07-22T18:16:53.5553610Z    * @IR rule 1: "@compiler.lib.ir_framework.IR(phase={DEFAULT}, applyIfPlatformAnd={}, applyIfCPUFeatureOr={}, counts={}, failOn={"_#LOOP#_", "_#COUNTED_LOOP#_"}, applyIfPlatform={}, applyIfPlatformOr={}, applyIfOr={}, applyIfCPUFeatureAnd={}, applyIf={}, applyIfCPUFeature={}, applyIfAnd={}, applyIfNot={})"
>> 2024-07-22T18:16:53.5556263Z      > Phase "PrintIdeal":
>> 2024-07-22T18:16:53.5557150Z        - failOn: Graph contains forbidden nodes:
>> 2024-07-22T18:16:53.5557912Z          * Constraint 1: "(\d+(\s){2}(Loop.*)+(\s){2}===.*)"
>> 2024-07-22T18:16:53.5558668Z            - Matched forbidden node:
>> 2024-07-22T18:16:53.5559308Z              * 127  LoopLimit  === _ 22 10 83  [[ 128 ]] 
>> 2024-07-22T18:16:53.5559791Z 
>> 2024-07-22T18:16:53.5561343Z 2) Method "private static long compiler.loopopts.parallel_iv.TestParallelIvInIntCountedLoop.testIntCountedLoopWithLongIVWithRandomStrides(int)" - [Failed IR rules: 1]:
>> 2024-07-22T18:16:53.5565173Z    * @IR rule 1: "@compiler.lib.ir_framework.IR(phase={DEFAULT}, applyIfPlatformAnd={}, applyIfCPUFeatureOr={}, counts={}, failOn={"_#LOOP#_", "_#COUNTED_LOOP#_"}, applyIfPlatform={}, applyIfPlatformOr={}, applyIfOr={}, applyIfCPUFeatureAnd={}, applyIf={}, applyIfCPUFeature={}, applyIfAnd={}, applyIfNot={})"
>> 2024-07-22T18:16:53.5567518Z      > Phase "PrintIdeal":
>> 2...
>
> @tabjy Yes, looks like the 32-bit VM behaves different. Do you know what makes the difference here?
> Yes, looks like regex-matching is also confused here, we should probably address that.
> If the difference of the 32-bit vs 64-bit turns out to be expected: you can just do this:
> `test/hotspot/jtreg/compiler/loopopts/superword/RedTest_long.java:        applyIfPlatform = {"64-bit", "true"},`

Hi @eme64! Could you kindly give this a quick look if you have the time. Thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/18489#issuecomment-2346386857