Integrated: 8345219: C2: x86_64 should not go to interpreter stubs for NaNs handling

[Aleksey Shipilev]

On Thu, 28 Nov 2024 18:22:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Found this while cleaning up x86_32 code for removal.
> 
> In our current code there is a block added by [JDK-8076373](https://bugs.openjdk.org/browse/JDK-8076373):
> https://github.com/openjdk/jdk/blob/3b21a298c29d88720f6bfb2dc1f3305b6a3db307/src/hotspot/share/compiler/compileBroker.cpp#L1451-L1473
> 
> Ostensibly, that block is for x86_32 handling of signalling NaNs -- x87 FPU has a peculiarity with them. See other funky bugs we seen with it: [JDK-8285985](https://bugs.openjdk.org/browse/JDK-8285985), [JDK-8293991](https://bugs.openjdk.org/browse/JDK-8293991).
> 
> But the way current block is coded, it is enabled for X86 wholesale, which also means x86_64! In fact, it is likely even worse on x86_64, because the related "fast" entries are generated only for x86_32:
> https://github.com/openjdk/jdk/blob/3b21a298c29d88720f6bfb2dc1f3305b6a3db307/src/hotspot/share/interpreter/templateInterpreterGenerator.cpp#L493-L502
> 
> This can be solved by checking `IA32` instead of `X86`. This block would be gone completely once we remove x86_32 port. Meanwhile, we can make it right by x86_64, and make eventual x86_32 removal less confusing. This issue seems to only affect the compilation of native methods, while most of the hot code is riding on compiler intrinsics. I'll put performance data in comments.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `all`

This pull request has now been integrated.

Changeset: f3b4350e
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/f3b4350e0f14d3b0c551e0d24563788f379111d6
Stats:     355 lines in 5 files changed: 353 ins; 0 del; 2 mod

8345219: C2: x86_64 should not go to interpreter stubs for NaNs handling

Reviewed-by: epeter, kvn

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PR: https://git.openjdk.org/jdk/pull/22446