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From: Jan Beulich <>
To: im Kiva <>, Nelson Chu <>
Subject: Re: [RISCV] [GNU AS] Possible `vmsge{u}.vx` instruction lowering bug?
Date: Tue, 29 Aug 2023 09:43:21 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 29.08.2023 08:52, im Kiva via Binutils wrote:
> Hi maintainers,
> I discovered that GNU Assembler (as) lowers `vmsge.vx` and `vmsgeu.vx` (pseudo
> instructions from RISC-V Vector Extension [1]) when the destination
> register is v0 as follows:
> vmsge{u}.vx v0, v4, a0, v0.t, v2
> will be expanded to:
> vmslt{u}.vx v2, v4, a0, v0.t
> v0, v0, v2
> You can inspect the lowering result with Godbolt [2].
> However, according to the Vector specification [1] page 52. The "desugared"
> `vmslt{u}.vx` is not masked:
>> masked va >= x, vd == v0
>>   pseudoinstruction: vmsge{u}.vx vd, va, x, v0.t, vt
>>   expansion: vmslt{u}.vx vt, va, x; vd, vd, vt
> So the spec-expected result of the example above should be:
> vmslt{u}.vx v2, v4, a0 <-- no v0.t here
> v0, v0, v2
> I thus submitted a patch to the LLVM [3], and it was accepted recently.
> I am wondering if binutils considers it a bug, or if it is just intentional
> because of some historical and compatibility reasons.

I think this wants fixing alike in binutils: From looking at vector_macro(),
it appears that emitting the masked form is merely an accident resulting
from the inverted encoding of "masking". In particular, if masking was
indeed meant, I expect code there would be

		  if (vd == vm)
		      macro_build (NULL, "vmslt.vx", "Vd,Vt,sVm", vtemp, vs2, vs1, vm);
		      macro_build (NULL, "", "Vd,Vt,Vs", vd, vm, vtemp);

much like it is a few lines down from there. (Apparently the "else" path
omitted above is similarly affected.)


  reply	other threads:[~2023-08-29  7:43 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-29  6:52 im Kiva
2023-08-29  7:43 ` Jan Beulich [this message]
2023-08-29  7:59   ` Nelson Chu
2023-08-29  8:52     ` Jan Beulich
2023-08-30  2:51       ` Nelson Chu
2023-08-30  5:50         ` Jan Beulich
2023-09-01  6:37           ` Kiva Oyama
2023-09-01  8:03             ` Nelson Chu

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