[llvm] [X86][MC] Support Enc/Dec for NF BMI instructions (PR #76709)

[Shengchen Kan via llvm-commits]

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@@ -1134,6 +1134,25 @@ static int getInstructionIDWithAttrMask(uint16_t *instructionID,
   return 0;
 }
 
+static bool isNF(InternalInstruction *insn) {
+  // NF bit is the MSB of aaa.
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KanRobert wrote:

This comment should be moved to line 1191. It's used to explain why we use `else if` for `aaaFromEVEX4of4`

https://github.com/llvm/llvm-project/pull/76709