cmd/asm: support Advanced Matrix Extensions (AMX) in Go Assembler

[henkjan-sneller]

The Go assembler (shipped with 1.20.5) currently lacks support for Advanced Matrix Extensions (AMX), particularly the sub-extensions AMX-TILE, AMX-INT8, and AMX-BF16.

As a workaround, we have been using byte sequences to generate the required instructions. However, for the sake of our mental stability, we would love to use proper instructions. @golang/compiler could you please add these 12 AMX instructions.

[ianlancetaylor]

This doesn't need to be a proposal, so taking it out of the proposal process.

[cagedmantis]

/cc @golang/compiler

[anton-kuklin]

Would love to work on that.

[cherrymui]

@anton-kuklin that would be great. Thanks! (I don't know of anybody currently working on this.)

[anton-kuklin]

Sure, starting my work.

[anton-kuklin]

Quick update on my progress. During the investigation of how to implement this feature I discovered that there's a tool x86avgen. It generates corresponding optables based on a provided csv file, e.g. this or this. After that I discovered, that there's a tool x86spec which actually downloads the latest intel doc and parses it to generate corresponding csv file mentioned previously.

However, there's a problem. Currently this tool can't parse properly the latest documentation with added AMX commands, due to the unhandled header.
For example:

p.1440: reading TILELOADD/TILELOADDT1-Load Tile: unexpected header: "CPUID Feature\nFlag"
["Opcode/Instruction" "Op/En" "64/32-Bit Mode" "CPUID Feature\nFlag" "Description"]
["VEX.128.F2.0F38.W0 4B !(11):rrr:100\nTILELOADD tmm1, sibmem" "A" "V/N.E." "AMX-TILE" "Load data into tmm1 as specified by information\nin sibmem."]
["VEX.128.66.0F38.W0 4B !(11):rrr:100\nTILELOADDT1 tmm1, sibmem" "A" "V/N.E." "AMX-TILE" "Load data into tmm1 as specified by information\nin sibmem with hint to optimize data caching."]

To add AMX commands I first need to fix this parser (which I will work on). Do I need to create a separate issue for it, or I can fix it as part of this one?

CC: @cherrymui

[gopherbot]

Change https://go.dev/cl/510555 mentions this issue: x86spec: fix header parsing

[anton-kuklin]

Hey @cherrymui, any chance you can give it a look? It should become pretty straightforward, after we will sort out the PR mentioned above.

[gopherbot]

Change https://go.dev/cl/516277 mentions this issue: cmd/asm: add x86 AMX instructions

[anton-kuklin]

I've created an initial PR, however there's a number of questions, which had to be resolved before it will be ready, so it will take some time. I will ask questions in gerrit.