RFR: 8275167: x86 intrinsic for unsignedMultiplyHigh

[Vamsi Parasa]

On Fri, 15 Oct 2021 20:19:31 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> > > How you verified correctness of results? I suggest to extend `test/jdk//java/lang/Math/MultiplicationTests.java` test to cover unsigned method.
> > 
> > 
> > Tests for unsignedMultiplyHigh were already added in test/jdk//java/lang/Math/MultiplicationTests.java (in July 2021 by Brian Burkhalter). Used that test to verify the correctness of the results.
> 
> Good. It seems I have old version of the test. Did you run it with -Xcomp? How you verified that intrinsic is used?

The tests were not run with -Xcomp. Looked at the generated x86 code using the disassembler (hsdis) and verified that that correct instruction (mul) instead of (imul, without the intrinsic) was being generated.

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PR: https://git.openjdk.java.net/jdk/pull/5933