Add MIPS extensions

[djtodoro]

Adding extensions for MIPS vendor:
1. xmipscmov
2. xmipslsp
3. xmipscbop
4. xmipsexectl

The official product page here:
https://mips.com/products/hardware/p8700/

Upstreaming of this in LLVM and binutils is in progress.

[djtodoro]

cc @asb :)

[lenary]

This looks good to me, and uncontroversial :)

[cmuellner]

Thanks for the PR!

I see that the references to the two new extensions go to the product description of the MIPS P8700 Series.
If that product retires, will the extensions also retire? If not (which I assume), is there a reference for a description of the extensions independent of the product they implement?

Also, the docs on the product page don't mention the two extensions (Xmipscmov and Xmipslsp). The appendix of the P8700 programmer's guide only lists nine custom instructions (ccmov, ehb, ihb, ldp, lwp, mtlbwr, pref, sdp, swp). This repo is not the right place to define extensions. Instead, a document should be referenced where the extensions are defined (incl. CSRs, instructions, etc).

A specification of a custom extension should also include the vendor prefix (e.g. mips.ccmov).

[djtodoro]

Thanks for the PR!

I see that the references to the two new extensions go to the product description of the MIPS P8700 Series. If that product retires, will the extensions also retire? If not (which I assume), is there a reference for a description of the extensions independent of the product they implement?

Also, the docs on the product page don't mention the two extensions (Xmipscmov and Xmipslsp). The appendix of the P8700 programmer's guide only lists nine custom instructions (ccmov, ehb, ihb, ldp, lwp, mtlbwr, pref, sdp, swp). This repo is not the right place to define extensions. Instead, a document should be referenced where the extensions are defined (incl. CSRs, instructions, etc).

A specification of a custom extension should also include the vendor prefix (e.g. mips.ccmov).

@cmuellner thanks for the comment! Sorry for the delay here. We have updated the document at [0], and in the MIPS Defined Instructions section, you can see that we have added the mips.* prefix to all of our extensions.

https://mips.com/wp-content/uploads/2025/03/P8700-F_Programmers_Reference_Manual_Rev1.81_3-3-2025.pdf

[djtodoro]

Do you have any comment on this?

[apazos]

LGTM, @cmuellner any final comments?

[djtodoro]

Ping. :) Any comments?

[djtodoro]

Ping. :)

[kito-cheng]

LGTM as a RISC-V GCC maintainer

[cmuellner]

The links are already out-of-date. On the referenced page are "Product Brief", "Programmer's Guide", and "Data Sheet". However, the PR states "MIPS p8700 specification", which is not on the linked page.
I assume that the "Programmer's Guide" is the relevant document.
So, I suggest changing the text in the brackets to "MIPS P8700 Programmer's Guide".

Another thing that I noticed is that the PR introduces an extension with the name "xmipscmove," but the document names it "xmipscmov" (without the e at the end).

If these two items are addressed, we can land this.

[djtodoro]

@cmuellner thanks for the comment. I have addressed it and updated the links. Thank you.

[cmuellner]

LGTM