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Re: [PATCH for-6.2 05/34] target/arm: Fix mask handling for MVE narrowin

From: Richard Henderson
Subject: Re: [PATCH for-6.2 05/34] target/arm: Fix mask handling for MVE narrowing operations
Date: Fri, 16 Jul 2021 09:29:36 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/13/21 6:36 AM, Peter Maydell wrote:
In the MVE helpers for the narrowing operations (DO_VSHRN and
DO_VSHRN_SAT) we were using the wrong bits of the predicate mask for
the 'top' versions of the insn.  This is because the loop works over
the double-sized input elements and shifts the predicate mask by that
many bits each time, but when we write out the half-sized output we
must look at the mask bits for whichever half of the element we are
writing to.

Correct this by shifting the whole mask right by ESIZE bits for the
'top' insns.  This allows us also to simplify the saturation bit
checking (where we had noticed that we needed to look at a different
mask bit for the 'top' insn.)

Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
  target/arm/mve_helper.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


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