RFR: 8346787: Fix two C2 IR matching tests for RISC-V

[Damon Fenacci]

On Tue, 24 Dec 2024 05:23:42 GMT, Fei Yang <fyang at openjdk.org> wrote:

> Two IR matching tests added by [JDK-8332268](https://bugs.openjdk.org/browse/JDK-8332268) are failing on RISC-V:
>   TEST: compiler/c2/irTests/ModINodeIdealizationTests.java
>   TEST: compiler/c2/irTests/ModLNodeIdealizationTests.java
> 
> These two tests require conditional move support. See ModLNode::Ideal & ModLNode::Ideal [1][2]. But RISC-V base ISA (RV64GCV) does not support conditional move, so we set `ConditionalMoveLimit` to 0 for this CPU platform. This change simply skips these two tests for now.
> 
> Some further information:
> An initial version of conditional move based on RISC-V `Zicond` extension has been added by: [JDK-8344306](https://bugs.openjdk.org/browse/JDK-8344306). But that still lacks performance tunning and we will reconsider and adjust this `ConditionalMoveLimit` parameter as we go. New issue: [JDK-8346786](https://bugs.openjdk.org/browse/JDK-8346786).
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/divnode.cpp#L993
> [2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/divnode.cpp#L1253

This looks good as temporary fix. Thanks @RealFYang (you might just want to change the copyright date: it's that time of the year again 😉)

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

PR Review: https://git.openjdk.org/jdk/pull/22874#pullrequestreview-2531562276