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

[Jatin Bhateja]

On Tue, 7 Mar 2023 03:00:34 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Other than the minor comments above, the x86 side changes look good to me.
>
> @sviswa7 I update changes based on your comments. Please, look: [9302d4b](https://github.com/openjdk/jdk/pull/12869/commits/9302d4bc00f8f1d8e774a260eb6aacb2d51a2dd4)

Hi @vnkozlov , There is some discrepancy in results b/w interpreter, C1 and C2 for following case.

public class Foo {
  public static short bar(float f) {return Float.floatToFloat16(f);}
  public static void main(String[] args) {
	 System.out.println(Float.floatToRawIntBits(Float.float16ToFloat((short) 31745)));
	 System.out.println(bar(Float.float16ToFloat((short) 31745)));
  }
}

CPROMPT>java  -Xint -cp . Foo
2143297536                                                       // FP32 QNaN + significand preserved
32257                                                            // FP16 QNaN + significand preserved
CPROMPT>java -Xbatch -Xcomp -cp . Foo
2139103232                                                       // FP32 SNaN + significand preserved
31745                                                            // FP16 SNaN + significand preserved
CPROMPT>java -XX:-TieredCompilation -Xbatch -Xcomp -cp . Foo
2139103232                                                       // FP32  SNaN + significand preserved
32257                                                            // FP16  QNaN + significand preserved.

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PR: https://git.openjdk.org/jdk/pull/12869