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Date: Fri, 15 Jan 2021 13:01:12 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: HAO CHEN GUI <guihaoc@linux.ibm.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Add a new pattern in 4-insn combine
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On Mon, Nov 30, 2020 at 11:08:22AM +0800, HAO CHEN GUI wrote:
>   This patch adds a new pattern(combine 4 insns to 3 insns) in 4-insn 
> combine. In the patch, newpat is split twice. The newpat, newi2pat and 

As I said before, that has a lot of problems, and is only suitable for
stage 1 (after many fixes!)

I don't think this is a good idea at all, fwiw.  Before we even should
think about doing 4->3 combinations, we should stop severely limiting
what combinations of 4 insns we allow; and we do that because it will
slow down the compiler a lot, for no big gain.


Segher