[llvm] [X86] Support EVEX compression for EGPR (PR #77202)

[Phoebe Wang via llvm-commits]

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@@ -29,8 +29,10 @@ class X86Subtarget;
 namespace X86 {
 
 enum AsmComments {
+  // For instr that was compressed from EVEX to LEGACY.
+  AC_EVEX_2_LEGACY = MachineInstr::TAsmComments,
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phoebewang wrote:

Why we need to associate with this value? Will it be a problem if there's new Flag added after `MachineInstr::TAsmComments`?

https://github.com/llvm/llvm-project/pull/77202