Re: Re: [PATCH] RISC-V: Implement vector "average" autovec pattern.

[钟居哲 <juzhe.zhong@rivai.ai>]

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Plz put your testcases into:

# widening operation only test on LMUL < 8
set AUTOVEC_TEST_OPTS [list \
  {-ftree-vectorize -O3 --param riscv-autovec-lmul=m1} \
  {-ftree-vectorize -O3 --param riscv-autovec-lmul=m2} \
  {-ftree-vectorize -O3 --param riscv-autovec-lmul=m4} \
  {-ftree-vectorize -O2 --param riscv-autovec-lmul=m1} \
  {-ftree-vectorize -O2 --param riscv-autovec-lmul=m2} \
  {-ftree-vectorize -O2 --param riscv-autovec-lmul=m4} ]
foreach op $AUTOVEC_TEST_OPTS {
  dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/autovec/widen/*.\[cS\]]] \
    "" "$op"
}

You could either simpilfy put them into "widen" directory or create a new directly.
Anyway, make sure you have fully tested it with LMUL = 1/2/4.



juzhe.zhong@rivai.ai
 
From: Robin Dapp
Date: 2023-08-03 02:49
To: 钟居哲; gcc-patches; palmer; kito.cheng; Jeff Law
CC: rdapp.gcc
Subject: Re: [PATCH] RISC-V: Implement vector "average" autovec pattern.
> 1. How do you model round to +Inf (avg_floor) and round to -Inf (avg_ceil) ?
 
That's just specified by the +1 or the lack of it in the original pattern.
Actually the IFN is just a detour because we would create perfect code
if not for the fallback.  But as there is currently now way to check for
the existence of a narrowing shift we cannot circumvent the fallback.
 
> 2. Is it possible we could use vaadd[u] to model avg ?
In principle yes (I first read it wrong that overflow must not happen but the
specs actually say that it does not happen).
However, we would need to set a rounding mode before vaadd or check its current
value and provide a fallback.  Off the spot I can't imagine a workaround like
two vaadds or so.
 
Regards
Robin