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

[Vladimir Kozlov]

On Wed, 26 Mar 2025 10:11:25 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`

Good.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24250#pullrequestreview-2718342841