RFR: 8303415: Add VM_Version::is_intrinsic_supported(id)

[David Holmes]

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On Fri, 3 Mar 2023 16:16:08 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Currently we check VM flags, directives and JIT compiler support when we generate intrinsics. 
> We have *product* VM flags for most intrinsics and set them in VM based on HW support. 
> But not all intrinsics have such flags and it is not scalable to add new *product* flag for each new intrinsic. 
> Also we have `-XX:DisableIntrinsic=<id>` and `-XX:ControlIntrinsic=<id>` flags to control intrinsics from command line. We don't need specific flags for that. 
> 
> I propose to add new `VM_Version::is_intrinsic_supported(id)` method to check platform support for intrinsic without adding new flag. I used it for `_floatToFloat16` intrinsic for my work on [JDK-8302976](https://bugs.openjdk.org/browse/JDK-8302976).
> 
> Additional fixes:
> Fixed Interpreter to skip intrinsics if they are disabled with flag.
> Moved Interpreter's `InlineIntrinsics` flag check into one place in shared code.
> Added separate interpreter id for `_dsqrt_strict` so it could be disabled separately from regular `_dsqrt`.
> Added missing `native` mark to `_currentThread`.
> Removed unused `AbstractInterpreter::in_native_entry()`.
> Cleanup C2 intrinsic checks code.
> 
> Tested tier1-4,xcomp,stress. Also ran tier1-3,xcomp with `-XX:-InlineIntrinsics`.

Just a couple of drive-by comments. I'm a bit confused about the core issue of "
Add VM_Version::is_intrinsic_supported(id)" because AFAICS this was only added for x86 ??

src/hotspot/cpu/x86/vm_version_x86.cpp line 3230:

> 3228:   case vmIntrinsics::_floatToFloat16:
> 3229:   case vmIntrinsics::_float16ToFloat:
> 3230:     if (!supports_f16c() && !supports_avx512vl()) return false;

Please put the return on a new line - it is too easy to just see the break.

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PR: https://git.openjdk.org/jdk/pull/12858