Re: Re: [PATCH] RISC-V: Add rounding mode operand for floating point instructions

[钟居哲 <juzhe.zhong@rivai.ai>]

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So, you mean I also need to add frm into vsqrt? 
If yes, I am now send another patch to add it.



juzhe.zhong@rivai.ai
 
From: Kito Cheng
Date: 2023-05-15 22:07
To: 钟居哲
CC: Jeff Law; gcc-patches; kito.cheng; palmer; palmer; rdapp.gcc
Subject: Re: Re: [PATCH] RISC-V: Add rounding mode operand for floating point instructions
Oh, Craig says vfrsqrt7.v not have frm but vsqrt.v have frm, and
checked spike that match that.
 
On Mon, May 15, 2023 at 9:55 PM 钟居哲 <juzhe.zhong@rivai.ai> wrote:
>
> I don't know why we should not add frm vfsqrt.v since I saw topper (LLVM maintainer) said we should
> not add frm into vsqrt.v. Maybe kito knows the reason ?
>
> https://github.com/riscv-non-isa/rvv-intrinsic-doc/pull/226
>
>
>
>
> juzhe.zhong@rivai.ai
>
> From: Jeff Law
> Date: 2023-05-15 21:52
> To: juzhe.zhong; gcc-patches
> CC: kito.cheng; kito.cheng; palmer; palmer; rdapp.gcc
> Subject: Re: [PATCH] RISC-V: Add rounding mode operand for floating point instructions
>
>
> On 5/15/23 05:49, juzhe.zhong@rivai.ai wrote:
> > From: Juzhe-Zhong <juzhe.zhong@rivai.ai>
> >
> > This patch is adding rounding mode operand and FRM_REGNUM dependency
> > into floating-point instructions.
> >
> > The floating-point instructions we added FRM and rounding mode operand:
> > 1. vfadd/vfsub
> > 2. vfwadd/vfwsub
> > 3. vfmul
> > 4. vfdiv
> > 5. vfwmul
> > 6. vfwmacc/vfwnmacc/vfwmsac/vfwnmsac
> > 7. vfsqrt7/vfrec7
> > 8. floating-point conversions.
> > 9. floating-point reductions.
> >
> > The floating-point instructions we did NOT add FRM and rounding mode operand:
> > 1. vfsqrt/vfneg
> Assuming vfsqrt is actually an estimator the best place to handle
> rounding modes is at the last step(s) after N-R or Goldschmidt
> refinement steps.  I haven't paid too much attention to FP yet, but this
> is an area I've got fairly extensive experience.
>
> Sadly RISC-V's estimator is fairly poor and the single instance FMACs
> are going to result in an implementation that may not actually be any
> better than what glibc can do.
>
> Jeff
>