RFR: 8294729: [s390] Implement nmethod entry barriers

[Erik Österlund]

On Tue, 4 Oct 2022 14:27:09 GMT, Tyler Steele <tsteele at openjdk.org> wrote:

> This draft PR implements native method barriers on s390. When complete, this will fix the build, and bring the other benefits of [JDK-8290025](https://bugs.openjdk.org/browse/JDK-8290025) to that platform.

Looks like you missed implementing the c2i entry barrier that comes hand in hand with the nmethod entry barriers. Once you implemented that it looks like you need to spill more registers in g1_write_barrier_pre() in g1BarrierSetAssembler_s390.cpp with this change as well, as all java arguments are live at that point and with G1 the phantom load of the method holder will call the pre_write barrier which occasionally will call the runtime. At that point, even floating point arguments must be saved. The current s390 g1 pre write barrier seems to assume it is only called from the interpreter, I believe. All other platforms went through the same dance when adding nmethod entry barriers.

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Changes requested by eosterlund (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10558