RFR: 8351155: C1/C2: Remove 32-bit x86 specific FP rounding support [v2]

[Aleksey Shipilev]

On Thu, 27 Mar 2025 08:45:49 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> C1 and C2 have support for rounding double/floats, to support awkward rounding modes of x87 FPU. With 32-bit x86 port removed, we can remove those parts. This basically deletes all the code that uses `strict_fp_requires_explicit_rounding`, which is now universally `false` for all supported platforms.
>> 
>> For C1, we remove `RoundFP` op, its associated `lir_roundfp` and related utility methods that insert these nodes in the graph.
>> 
>> For C2, we remove `RoundDouble` and `RoundFloat` nodes (note there is a confusingly named `RoundDoubleMode` nodes that are not related to this), associated utility methods, AD match rules that reference these nodes (as nops!), and some `Ideal`-s that are no longer needed.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `tier1`
>>  - [x] Linux x86_64 server fastdebug, `all`
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Minor leftover

Need a quick re-review after a minor leftover removal.

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PR Comment: https://git.openjdk.org/jdk/pull/24250#issuecomment-2758809458