RFR: 8302976: C2 intrinsification of Float.floatToFloat16 and Float.float16ToFloat yields different result than the interpreter

[Vladimir Kozlov]

On Wed, 22 Feb 2023 02:08:27 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

> Change the java/lang/float.java and the corresponding shared runtime constant expression evaluation to generate QNaN.
> The HW instructions generate QNaNs and not SNaNs for floating point instructions. This happens across double, float, and float16 data types. The most significant bit of mantissa is set to 1 for QNaNs.

The proposed fix do exactly what everyone asked - the same result from Java code (Interpreter), runtime (C++ code) and intrinsic (HW instruction). Since HW instruction is already produces QNaNs, PR fixes only Java code (Interpreter) and runtime (C++) code to produce QNaNs.

@TobiHartmann created test which covers all cases and should be added to this PR.

-------------

PR: https://git.openjdk.org/jdk/pull/12704