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

[Emanuel Peter]

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`

Nice, that was quick!
Do we not need to restrict the IR rules? Or will that not fail on `IA32`?

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PR Comment: https://git.openjdk.org/jdk/pull/22446#issuecomment-2516685436