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Date: Thu, 29 Sep 2022 10:56:57 +0100
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Subject: Re: [PATCH] vect: while_ult for integer mask
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To: Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org>, Richard Biener
	<richard.guenther@gmail.com>, <juzhe.zhong@rivai.ai>,
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On 29/09/2022 10:24, Richard Sandiford wrote:
> Otherwise:
> 
>    operand0[0] = operand1 < operand2;
>    for (i = 1; i < operand3; i++)
>      operand0[i] = operand0[i - 1] && (operand1 + i < operand2);
> 
> looks like a "length and mask" operation, which IIUC is also what
> RVV wanted?  (Wasn't at the Cauldron, so not entirely sure.)
> 
> Perhaps the difference is that in this case the length must be constant.
> (Or is that true for RVV as well?)

I too saw that presentation and I have compared notes with Juzhe before 
posting this.

As he has posted, what they want is different because their config 
register has an explicit length field whereas GCN just uses a mask to 
limit the length (more like AArch64, I think).

The RVV solution uses different logic in the gimple IR; this proposal is 
indistinguishable from the status quo at that point.

Andrew