[llvm] [X86][NFC] Share isDispOrCDisp8 between the encoder and CompressEVEX (PR #222591)

[Simon Pilgrim via llvm-commits]

================
@@ -145,14 +137,7 @@ static bool hasShorterEVEXViaCDisp8(const MachineInstr &MI) {
     return false;
 
   int64_t Val = Disp.getImm();
-  // VEX can already use a disp8 in this range, so EVEX offers no saving.
-  if (isInt<8>(Val))
-    return false;
-  // EVEX can use disp8*N only when the value is a multiple of N and the scaled
-  // value fits in a signed byte.
-  if (Val % static_cast<int64_t>(CD8_Scale) != 0)
-    return false;
-  return isInt<8>(Val / static_cast<int64_t>(CD8_Scale));
+  return X86II::isDispOrCDisp8(MI.getDesc().TSFlags, Val) && !isInt<8>(Val);
----------------
RKSimon wrote:

Cheaper test first.
```suggestion
  return !isInt<8>(Val) && X86II::isDispOrCDisp8(MI.getDesc().TSFlags, Val);
```

https://github.com/llvm/llvm-project/pull/222591