[AMDGPU][MC][GFX11] Assembly of v_fmac_.*_e64_dpp is broken

[Sisyph]

The e32 version works. The combination of operand list, asmString, and or conversion function cvtVOP3DPP are not right for this instruction.
It has string Constraints = "$src2 = $vdst"; and string DisableEncoding = "$src2"; which is different than other vop3 dpp.

[llvmbot]

@llvm/issue-subscribers-backend-amdgpu

[dpreobra]

https://reviews.llvm.org/D134961

[dpreobra]

Fixed by 8f8e4e3

[dpreobra]

It looks like the fix is incomplete - there is a special case not handled by the patch.

An example of failed test:

v_fmac_f16_e64_dpp v5, v1, v2       // dpp modifiers are optional!

Expected output:

0x05,0x00,0x36,0xd5,0xe9,0x04,0x02,0x00,0x01,0x00,0x00,0x00

Actual result:

An exception

A fix is pending.

[dpreobra]

Hopefully https://reviews.llvm.org/D137549 will handle this case. The problem here is that an optional clamp modifier is followed by a mandatory DPP8/DPPCtrl modifier. As a result, the instruction w/o modifiers is accepted by the parser though it should not.

[dpreobra]

Not reproducible after ef848f2. Kudos to @kosarev.