From: Peter Maydell <peter.maydell@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: qemu-arm <qemu-arm@nongnu.org>, QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [PATCH for-6.2 20/34] target/arm: Implement MVE integer min/max across vector
Date: Tue, 20 Jul 2021 19:21:31 +0100 [thread overview]
Message-ID: <CAFEAcA8scVSuS=Yn0qCssNiS=wBeQSDJTYyL=z2Lm1J=uy_wOg@mail.gmail.com> (raw)
In-Reply-To: <CAFEAcA81nfSPcYDk1FsVqAcxq5D4NXhtXP5c90_0MLtBVxvr0g@mail.gmail.com>
On Mon, 19 Jul 2021 at 16:28, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Sat, 17 Jul 2021 at 21:46, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> >
> > On 7/13/21 6:37 AM, Peter Maydell wrote:
> > > +/* Max and min of absolute values */
> > > +static int64_t do_maxa(int64_t n, int64_t m)
> > > +{
> > > + if (n < 0) {
> > > + n = -n;
> > > + }
> > > + if (m < 0) {
> > > + m = -m;
> > > + }
> > > + return MAX(n, m);
> > > +}
> >
> > This doesn't look quite right. The n operand is extracted unsigned, and only the m
> > operand is subjected to ABS.
>
> Yes, you're right (this patch does always extract ra (here n)
> unsigned, so the only case where it makes a difference is
> VMINAV when the input ra is negative). I noticed this wrinkle
> when implementing the FP variant of this insn, but missed it here.
In fact it doesn't make a difference for this integer version:
because we always extract n as an unsigned value, 'n' is always
positive (either because it's the initial unsigned 'ra' or
because it's the result of a previous do_maxa/do_mina, which
must also always be positive) and so taking the absolute value
of 'n' never affects it. But we might as well delete the unused code.
(For float it *does* make a difference, because there's no
"extract as unsigned" for floats, and so the input 'ra' and
thus the first 'n' can be negative there.)
-- PMM
next prev parent reply other threads:[~2021-07-20 18:23 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-13 13:36 [PATCH for-6.2 00/34] target/arm: Third slice of MVE implementation Peter Maydell
2021-07-13 13:36 ` [PATCH for-6.2 01/34] target/arm: Note that we handle VMOVL as a special case of VSHLL Peter Maydell
2021-07-14 17:02 ` Richard Henderson
2021-07-13 13:36 ` [PATCH for-6.2 02/34] target/arm: Print MVE VPR in CPU dumps Peter Maydell
2021-07-15 1:34 ` Richard Henderson
2021-07-13 13:36 ` [PATCH for-6.2 03/34] target/arm: Fix MVE VSLI by 0 and VSRI by <dt> Peter Maydell
2021-07-16 16:27 ` Richard Henderson
2021-07-13 13:36 ` [PATCH for-6.2 04/34] target/arm: Fix signed VADDV Peter Maydell
2021-07-15 1:37 ` Richard Henderson
2021-07-13 13:36 ` [PATCH for-6.2 05/34] target/arm: Fix mask handling for MVE narrowing operations Peter Maydell
2021-07-16 16:29 ` Richard Henderson
2021-07-13 13:36 ` [PATCH for-6.2 06/34] target/arm: Fix 48-bit saturating shifts Peter Maydell
2021-07-16 16:34 ` Richard Henderson
2021-07-16 16:39 ` Peter Maydell
2021-07-13 13:36 ` [PATCH for-6.2 07/34] target/arm: Fix calculation of LTP mask when LR is 0 Peter Maydell
2021-07-16 16:35 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 08/34] target/arm: Fix VPT advance when ECI is non-zero Peter Maydell
2021-07-16 16:44 ` Richard Henderson
2021-07-16 16:58 ` Richard Henderson
2021-07-19 14:16 ` Peter Maydell
2021-07-13 13:37 ` [PATCH for-6.2 09/34] target/arm: Factor out mve_eci_mask() Peter Maydell
2021-07-16 16:48 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 10/34] target/arm: Fix VLDRB/H/W for predicated elements Peter Maydell
2021-07-16 16:58 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 11/34] target/arm: Implement MVE VMULL (polynomial) Peter Maydell
2021-07-16 17:14 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 12/34] target/arm: Implement MVE incrementing/decrementing dup insns Peter Maydell
2021-07-16 19:57 ` Richard Henderson
2021-07-19 14:25 ` Peter Maydell
2021-07-13 13:37 ` [PATCH for-6.2 13/34] target/arm: Factor out gen_vpst() Peter Maydell
2021-07-16 21:04 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 14/34] target/arm: Implement MVE integer vector comparisons Peter Maydell
2021-07-16 21:55 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 15/34] target/arm: Implement MVE integer vector-vs-scalar comparisons Peter Maydell
2021-07-16 21:58 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 16/34] target/arm: Implement MVE VPSEL Peter Maydell
2021-07-16 22:03 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 17/34] target/arm: Implement MVE VMLAS Peter Maydell
2021-07-16 22:11 ` Richard Henderson
2021-07-17 10:06 ` Peter Maydell
2021-07-17 20:40 ` Richard Henderson
2021-07-20 10:13 ` Peter Maydell
2021-07-13 13:37 ` [PATCH for-6.2 18/34] target/arm: Implement MVE shift-by-scalar Peter Maydell
2021-07-16 22:15 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 19/34] target/arm: Move 'x' and 'a' bit definitions into vmlaldav formats Peter Maydell
2021-07-16 22:16 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 20/34] target/arm: Implement MVE integer min/max across vector Peter Maydell
2021-07-17 20:46 ` Richard Henderson
2021-07-19 15:28 ` Peter Maydell
2021-07-20 18:21 ` Peter Maydell [this message]
2021-07-13 13:37 ` [PATCH for-6.2 21/34] target/arm: Implement MVE VABAV Peter Maydell
2021-07-17 20:50 ` Richard Henderson
2021-07-17 22:13 ` Peter Maydell
2021-07-17 22:18 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 22/34] target/arm: Implement MVE narrowing moves Peter Maydell
2021-07-21 21:45 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 23/34] target/arm: Rename MVEGenDualAccOpFn to MVEGenLongDualAccOpFn Peter Maydell
2021-07-21 21:45 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 24/34] target/arm: Implement MVE VMLADAV and VMLSLDAV Peter Maydell
2021-07-21 22:01 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 25/34] target/arm: Implement MVE VMLA Peter Maydell
2021-07-21 22:03 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 26/34] target/arm: Implement MVE saturating doubling multiply accumulates Peter Maydell
2021-07-21 22:07 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 27/34] target/arm: Implement MVE VQABS, VQNEG Peter Maydell
2021-07-21 22:09 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 28/34] target/arm: Implement MVE VMAXA, VMINA Peter Maydell
2021-07-21 22:12 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 29/34] target/arm: Implement MVE VMOV to/from 2 general-purpose registers Peter Maydell
2021-07-21 22:20 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 30/34] target/arm: Implement MVE VPNOT Peter Maydell
2021-07-21 22:24 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 31/34] target/arm: Implement MVE VCTP Peter Maydell
2021-07-21 22:33 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 32/34] target/arm: Implement MVE scatter-gather insns Peter Maydell
2021-07-22 0:36 ` Richard Henderson
2021-07-22 8:42 ` Peter Maydell
2021-07-13 13:37 ` [PATCH for-6.2 33/34] target/arm: Implement MVE scatter-gather immediate forms Peter Maydell
2021-07-22 0:49 ` Richard Henderson
2021-07-13 13:37 ` [PATCH for-6.2 34/34] target/arm: Implement MVE interleaving loads/stores Peter Maydell
2021-07-22 17:52 ` Richard Henderson
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