RFR: 8341137: Optimize long vector multiplication using x86 VPMUL[U]DQ instruction

[Jatin Bhateja]

On Thu, 17 Oct 2024 21:53:16 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> > > MulVL (VectorCastI2X src1) (VectorCastI2X src2)
> 
> > It looks unsafe to me, since VectorCastI2L sign-extends integer lanes, ...
> 
> Hm, I don't see any problems with it if `VPMULDQ` is used. Sign extension becomes redundant when 64-bit multiplication is strength-reduced to 32-bit one (32x32->64). Am I missing something important here?

@iwanowww , Agree!, I missed noticing that you were talking about **VPMULDQ**, its a  signed doubleword multiplier with quadword saturation, so it should be ok to include suggested pattern.

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PR Comment: https://git.openjdk.org/jdk/pull/21244#issuecomment-2421132055