[libc] [flang] [compiler-rt] [llvm] [clang-tools-extra] [lldb] [clang] [libcxx] [lld] [AMDGPU][GFX12] VOP encoding and codegen - add support for v_cvt fp8/… (PR #78414)

[Mirko Brkušanin via libcxx-commits]

mbrkusanin wrote:

> > Why is so there so much special casing in the assembler/disassembler?
> 
> I'm not an original author of these change, but from what I understand it is a workaround to handle VOP3 instructions which have a single source but require the use of two bits from OPSEL. `V_CVT_F32_FP8` has one source but is using two bits from OPSEL to specify which part from 32 bit register to convert ([7:0], [15:8], [23: 16] or 31 : 24]). And since OPSELs are correlated with sources/destination (one bit from OPSEL with one soruce/destination) these is required without any deeper changes to TableGen.
> 
> I'm open to change TableGen, but I would prefer to create new ticket and do it with new PR. These change may take longer than one day and we would like to have these PR merged before LLVM branching.

Correct some of these instructions use opsel[1] which in LLVM in stored in src1_modifiers so a dummy src1 is used. And as far as I know we can not have src1_modfiers without src1 operand.

https://github.com/llvm/llvm-project/pull/78414