[llvm] [AMDGPU][MC] GFX9 - Support NV bit in FLAT instructions in pre-GFX90A (PR #154237)

[Stanislav Mekhanoshin via llvm-commits]

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@@ -2481,7 +2481,28 @@ class FLAT_Real_vi <bits<7> op, FLAT_Pseudo ps, bit has_sccb = ps.has_sccb> :
                   !subst("$sccb", !if(has_sccb, "$sccb",""), ps.AsmOperands);
 }
 
+class FLAT_Real_gfx9 <bits<7> op, FLAT_Pseudo ps, bit has_sccb = ps.has_sccb> :
+  FLAT_Real_vi <op, ps, has_sccb> {
+  let AssemblerPredicate = isGFX9NotGFX90A;
+  let Subtarget = SIEncodingFamily.GFX9;
+  let DecoderNamespace = "GFX9";
+  let Inst{55} = cpol{5}; // nv - GFX9 (pre-90A) uses bit 55 as the non-volatile bit.
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rampitec wrote:

`let Inst{55} = cpol{CPolBit.NV};`

https://github.com/llvm/llvm-project/pull/154237