RFR: 8350182: [s390x] Relativize locals in interpreter frames

[Lutz Schmidt]

On Mon, 17 Feb 2025 09:53:37 GMT, Amit Kumar <amitkumar at openjdk.org> wrote:

> Port for [JDK-8299795](https://bugs.openjdk.org/browse/JDK-8299795) Relativize Z_locals in interpreter frame for s390x.
> 
> Tier1  test with fastdebug vm are clean.

Looks good overall.
One "hazy" performance concern.

src/hotspot/cpu/s390/templateInterpreterGenerator_s390.cpp line 1138:

> 1136:   // z_ijava_state->locals = Z_esp + parameter_count bytes
> 1137: 
> 1138:   __ z_ldgr(Z_F1, Z_R1); // preserve Z_R1, holding cache offset

How expensive is this?
I remember those GPR <-> FPR transfers to be convenient, but inefficient. But that my have changed.
Would Z_R0 be available or is it occupied as well?

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PR Review: https://git.openjdk.org/jdk/pull/23660#pullrequestreview-2640023331
PR Review Comment: https://git.openjdk.org/jdk/pull/23660#discussion_r1969221075