Add sub-types to existing instruction formats

[AFOliveira]

Summary

Track progress on introducing sub-types for our R-, I-, B-, S-, U-type instruction formats to improve clarity, tooling and testing.

Motivation

• Mixed encodings in each format (e.g. immediates vs. hard-coded bits)
• Ambiguous docs some instructions don't match any type
• Coarse tests that can’t target specific bit-patterns

Proposal

1. Add a subtype field to our instruction schema.
2. Example sub-types:
   • R.aqrl — acquire release Rtype
3. Annotate existing instructions.
4. Create test suite to validate schema in UDB

Next Steps

• Create full list in a readable format to ask for reviews

[AFOliveira]

@Unique-Usman can we discuss this topic here from now on? Please comment this so I can assign it to you

[Unique-Usman]

Hi @AFOliveira, Got stuck in college activities. I am back now. I suggest we use this Github thread instead of excel. People Can also see it and easily drop comment here ? What do you think ?

[AFOliveira]

Hi @AFOliveira, Got stuck in college activities. I am back now. I suggest we use this Github thread instead of excel. People Can also see it and easily drop comment here ? What do you think ?

That's fine, but how? 1000+ lines is not readable as you posted, so maybe you will need to format it in github, which may be a lot of work.

[Unique-Usman]

I think we should use Divide and Conquer approach, I think we should go extension by extension as some of the instruction subtypes are similar across extension. what do you think?

[AFOliveira]

Problem is that won't be easy even for people who may come just to review. Also, the same sub-type may exist in several extensions, but I think it's your call, just try to make it readable, and I'll try to review and ask people to review it

[Unique-Usman]

Yeah, Subtypes exist in different extensions actually. Maybe we can have it in excel. The question is, how do we make it synchronized. For excel, if we have everything inside the excel file, people can come randomly and review. It will be add to know what has been reviewed and what has not been ? If we have in a thread, we can go extension by extension. Have discussion on it, then go to the next extension. If someone comes they can view what has been discussed and proposed. And they can dropped their own idea. Will this be easy to do in excel ?

[Unique-Usman]

This is the sample of what I am saying for example starting with A Extension

A - Extension

R-aq-rl type - suggested type

• Instructions: 20
• Encoding:
  • Match: 00000------------011-----0101111
  • Variables:
    • aq (location: 26)
    • rl (location: 25)
    • rs2 (location: 24-20)
    • rs1 (location: 19-15)
    • rd (location: 11-7)
• Sample Instruction: amomax.w.yaml

R-aq-rl-ls type - suggested type

• Instructions: 2
• Encoding:
  • Match: 00010--00000-----011-----0101111
  • Variables:
    • aq (location: 26)
    • rl (location: 25)
    • rs1 (location: 19-15)
    • rd (location: 11-7)
• Sample Instruction: lr.d.yaml

[Unique-Usman]

We can have people, review the above A extensions and the suggested type. After it has been reviewed, we can now add it to the excel or some other file extension. We can go four extension instead of a single extension for faster review. @AFOliveira what do you think ?

[ThinkOpenly]

As a reference that I find useful, here is a representation of one of the top-level instruction formats supported by the OpenPOWER ISA:

I like how the subtypes are all listed together in a compact table, so you can easily see the differences among them.

@Unique-Usman: pick an extension that has a small to moderate number of subtypes, and within the list of that extensions instructions, pick just one top-level format, say "I-type" or "R-type". Create a table similar to the image above, and let's review that. These tables should probably have a list of associated instructions (from just the one extension) with each row. This information will make the review much easier.

Then we can add, one-by-one, the additional top-level formats covered by that one extension.

Then, we can move, one-by-one, to the other extensions.

How does that sound?

[Unique-Usman]

@ThinkOpenly, that sounds very good. I think we can create the table using the excel format. The question now is where the I post the table for review and discussion here or in the excel format (I do not think this is easier or possible though)?