[llvm] [AMDGPU] Add assembler check for GFX1250 unclaused vmem workaround (PR #209517)

[Jay Foad via llvm-commits]

jayfoad wrote:

I have some criticisms of my own:

1. The warning is not actionable unless you already know exactly what sequence it is checking for. I guess the only solution to that is to make the warning message more verbose.
2. We could significantly relax the checks.

As I understand it, the actual requirements are:

1. The first VMEM instruction executed by the wave must not be in a clause.
2. The first VALU instruction executed by the wave must be "safe". I don't have the exact list of safe instructions, but V_NOP is the canonical example.

So perhaps we could just check that the first two instructions are V_NOP and any VMEM, in either order?

https://github.com/llvm/llvm-project/pull/209517