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

[Matt Arsenault via llvm-commits]

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@@ -822,6 +822,19 @@ DecodeStatus AMDGPUDisassembler::getInstruction(MCInst &MI, uint64_t &Size,
     }
   }
 
+  if (MCII->get(MI.getOpcode()).TSFlags & SIInstrFlags::FLAT) {
+    if (isGFX9() && !isGFX90A()) {
+      // Pre-GFX90A GFX9's use bit 55 as NV.
+      assert(Bytes_.size() >= 8);
+      if (Bytes_[6] & 0x80) { // check bit 55
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arsenm wrote:

We should have less special case code like this. It would be preferable to have a separate instruction definition 

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