[llvm] [AMDGPU] Create AMDGPUMnemonicAlias tablegen class (PR #89288)

[Joe Nash via llvm-commits]

================
@@ -1073,10 +1072,18 @@ multiclass MIMG_Atomic_Addr_Helper_m <mimgopc op, string asm,
         if !empty(renamed) then
           def _V4_gfx12 : VIMAGE_Atomic_gfx12 <op, asm, data_rc, 4, enableDasm>;
         else
-          def _V4_gfx12 : VIMAGE_Atomic_gfx12_Renamed <op, asm, renamed, data_rc, 4, enableDasm>;
+          def _V4_gfx12 : VIMAGE_Atomic_gfx12_Renamed <op, renamed, data_rc, 4, enableDasm>;
       }
     }
   }
+  if !and(op.HAS_GFX12, !not(!empty(renamed))) then
+    def dbg1 : AMDGPUMnemonicAlias<asm, renamed> {
----------------
Sisyph wrote:

The name was for debugging yes. However, it is actually the functional alias.

https://github.com/llvm/llvm-project/pull/89288