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Re: [PATCH v2 03/24] target/mips/cpu: Introduce isa_rel6_available() hel

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 03/24] target/mips/cpu: Introduce isa_rel6_available() helper
Date: Thu, 7 Jan 2021 10:04:52 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 12/16/20 4:14 AM, Jiaxun Yang wrote:
> 在 2020/12/16 上午10:50, Jiaxun Yang 写道:
>> TBH I do think it doesn't sounds like a good idea to make 32-bit
>> and 64-bit different. In fact ISA_MIPS32R6 is always set for targets
>> with ISA_MIPS64R6.
>> We're treating MIPS64R6 as a superset of MIPS32R6, and ISA_MIPS3
>> is used to tell if a CPU supports 64-bit.
>> FYI:
>> https://commons.wikimedia.org/wiki/File:MIPS_instruction_set_family.svg
> Just add more cents here...
> The current method we handle R6 makes me a little bit annoying.
> Given that MIPS is backward compatible until R5, and R6 reorganized a lot
> of opcodes, I do think decoding procdure of R6 should be dedicated from
> the rest,
> otherwise we may fall into the hell of finding difference between R6 and
> previous
> ISAs, also I've heard some R6 only ASEs is occupying opcodes marked as
> "removed in R6", so it doesn't looks like a wise idea to check removed
> in R6
> in helpers.

I think we are in agreement :) Your comment seems what I addressed
last month as this series:
(I'll try to rebase it and post during the week-end.)

> So we may end up having four series of decodetrees for ISA
> Series1: MIPS-II, MIPS32, MIPS32R2, MIPS32R5 (32bit "old" ISAs)
> Series2: MIPS-III, MIPS64, MIPS64R2, MIPS64R5 (64bit "old" ISAs)
> Series3: MIPS32R6 (32bit "new" ISAs)
> Series4: MIPS64R6 (64bit "new" ISAs)
> Thanks
> - Jiaxun

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