May RTX code grow faster than machine mode ?
Since RTX code grows target independent wheras 
machine mode grows target dependent.

In the future, we may easily have more and more targets that some target may have a lot of machine mode.
Maybe Richard Sandiford suggestion is a good idea to fix it?

Thanks for all comments.


juzhe.zhong@rivai.ai
 
From: Jakub Jelinek
Date: 2023-04-11 17:59
To: juzhe.zhong; Jeff Law; gcc-patches; kito.cheng; palmer; rguenther; richard.sandiford
Subject: Re: [PATCH] machine_mode type size: Extend enum size from 8-bit to 16-bit
On Tue, Apr 11, 2023 at 10:46:25AM +0100, Richard Sandiford wrote:
> I agree with all the comments about the danger of growing the number of
> modes too much.  But it looks like rtx_def should be easy to rearrange.
> Unless I'm missing something, there are less than 256 rtx codes at
> present.  So one simple option would be to make the code 8 bits and
> the machine_mode 16 bits (and swap them, so that they stay well-aligned
> wrt their size).
> 
> That of course would create new problem if we want more than 256 codes
> in future.  But then there would be the option of a non-power-of-2
> split (12/12 or whatever).  Also, it's possible to multiplex operations
> into a single code by adding an extra operand, whereas it's harder to
> multiplex modes.
 
We have 151 rtx codes if not a generator, 201 otherwise.  That is closer to
the limit except for the RISCV proposed changes.
 
Jakub