Path: ...!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Robert Finch <robfi680@gmail.com>
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Fri, 20 Sep 2024 01:55:47 -0400
Organization: A noiseless patient Spider
Lines: 69
Message-ID: <vcj2p6$vg4a$1@dont-email.me>
References: <vaqgtl$3526$1@dont-email.me>
 <2024Sep11.123824@mips.complang.tuwien.ac.at> <vbsoro$3ol1a$1@dont-email.me>
 <867cbhgozo.fsf@linuxsc.com> <20240912142948.00002757@yahoo.com>
 <vbuu5n$9tue$1@dont-email.me> <20240915001153.000029bf@yahoo.com>
 <vc6jbk$5v9f$1@paganini.bofh.team> <20240915154038.0000016e@yahoo.com>
 <vc70sl$285g2$4@dont-email.me> <vc73bl$28v0v$1@dont-email.me>
 <OvEFO.70694$EEm7.38286@fx16.iad>
 <32a15246310ea544570564a6ea100cab@www.novabbs.org>
 <vc7a6h$2afrl$2@dont-email.me>
 <50cd3ba7c0cbb587a55dd67ae46fc9ce@www.novabbs.org>
 <vc8qic$2od19$1@dont-email.me> <fCXFO.4617$9Rk4.4393@fx37.iad>
 <vcb730$3ci7o$1@dont-email.me> <7cBGO.169512$_o_3.43954@fx17.iad>
 <vcffub$77jk$1@dont-email.me> <n7XGO.89096$15a6.87061@fx12.iad>
 <35b8ff2e6baa54c7aa22ec4edf45c3f9@www.novabbs.org>
 <vcht39$mbru$1@dont-email.me>
 <790b8efbbbb95a6e56ea52bc004f466a@www.novabbs.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Fri, 20 Sep 2024 07:55:50 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="2aa1eff26a0609aa43eb8e70fd231bb3";
	logging-data="1032330"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/jPjiTzihWugQLHeUSb+mrx9lB8nz7xYo="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:hJDM4ZfYYd468grdOUYIaY3dBTY=
In-Reply-To: <790b8efbbbb95a6e56ea52bc004f466a@www.novabbs.org>
Content-Language: en-US
Bytes: 4336

On 2024-09-19 4:21 p.m., MitchAlsup1 wrote:
> On Thu, 19 Sep 2024 19:12:41 +0000, Brett wrote:
> 
>> MitchAlsup1 <mitchalsup@aol.com> wrote:
>>> On Thu, 19 Sep 2024 15:07:11 +0000, EricP wrote:
>>
>>
>>>> - register specifier fields are either source or dest, never both
>>>
>>> I happen to be wishywashy on this
>>
>>
>> This is deeply interesting, can you expound on why it is fine a register
>> field can be shared by loads and stores, and sometimes both like x86.
> 
> My 66000 encodes store data register in the same field position as it
> encodes "what kind of branch" is being performed, and the same position
> as all calculation (and load) results.
> 
> I started doing this in 1982 with Mc88100 ISA, and never found a problem
> with the encoding nor in the decoding nor with the pipelining of it.
> 
> Let me be clear, I do not support necessarily damaging a source operand
> to fit in another destination as::
> 
>      ADD     SP,SP,#0x40
> 
> by specifying SP only once in the instruction.
> 
> So,
> 
>      +------+-----+-----+----------------+
>      | major| Rd  | Rs1 | whatever       |
>      +------+-----+-----+----------------+
>      |  BC  | cnd | Rs1 | label  offset  |
>      +------+-----+-----+----------------+
>      |  LD  | Rd  | Rb  | displacement   |
>      +------+-----+-----+----------------+
>      | ST   | Rs0 | Rb  | displacement   |
>      +------+-----+-----+----------------+
> 
> Is:
> a) no burden in encoding
> b) no burden in decoding
> c) no burden in pipelining
> d) no burden in stealing the Store data port late in the pipeline
>    {in particular, this saves lots of flip-flops deferring store
>     data until after cache hit, TLB hit, and data has arrived at
>     cache.}
> 
> I disagree with things like::
> 
>      +------+-----+-----+----------------+
>      | big OpCode | Rds | whatever       |
>      +------+-----+-----+----------------+
> 
> Where Rds means the specifier is used as both a source and destination.
> 
> Notice in my encoding one can ALWAYS take the register specification
> fields and wire them directly into the RF/renamer decoder ports.
> You lose this property the other way around.
> 
??? I am not sure about this. It is in the Q+ ISA. Is the decoder output 
registered before feeding the renamer?