[llvm] [AMDGPU] Machine-CP is deleting incorrect copy instr. (PR #114773)

[Jay Foad via llvm-commits]

jayfoad wrote:

> $vgpr254 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit-def $agpr0_agpr1

That implicit def looks completely wrong to me. If anything, it should be an implicit def of `$vgpr254_vgpr255`, i.e. the entire tuple of which this instruction is only explicitly deffing one part.

https://github.com/llvm/llvm-project/pull/114773