RFR: 8365841: RISC-V: Several IR verification tests fail after JDK-8350960 without Zvfh

[Fei Yang]

On Wed, 20 Aug 2025 07:01:59 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi,
> Can you help to review this patch? Thanks!
> 
> The error in both cases is caused by the same reason: the target IR, MulReductionVI, is not matched.
> This is because the match_rule_supported_vector in riscv_v.ad is missing a break. If the if condition in `case MulReductionVI` evaluates to false, the loop will not exit until the `return UseZvfh`.
> 
> Failed IR tests:
> compiler/loopopts/superword/ProdRed_Int.java
> compiler/loopopts/superword/RedTest_int.java
> 
> ### Test (fastdebug)
> - [x] Run compiler/loopopts/superword/ProdRed_Int.java on k1 and k230
> - [x] Run compiler/loopopts/superword/RedTest_int.java on k1 and k230

Good catch! Thanks.

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26854#pullrequestreview-3135122539