Re: [PATCH] Canonicalize vec_merge when mask is constant.

[Jeff Law <jeffreyalaw@gmail.com>]

On 4/19/23 21:58, liuhongt via Gcc-patches wrote:
> Use swap_communattive_operands_p for canonicalization. When both value
> has same operand precedence value, then first bit in the mask should
> select first operand.
> 
> The canonicalization should help backends for pattern match. .i.e. x86
> backend has lots of vec_merge patterns, combine will create any form
> of vec_merge(mask, or inverted mask), then backend need to add 2
> patterns to match exact 1 instruction. The canonicalization can
> simplify 2 patterns to 1.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}, aarch64-linux-gnu.
> Ok for trunk?
> 
> gcc/ChangeLog:
> 
> 	* combine.cc (maybe_swap_commutative_operands): Canonicalize
> 	vec_merge when mask is constant.
ISTM that if we're going to call this the canonical form, then we should 
document it in rtl.texi.

Otherwise it looks pretty good to me.  So let's get the docs updated and 
get this installed.

jeff