[llvm] [NFC][CodeGen] Add helper function to check SubReg validity (PR #181489)

[Jay Foad via llvm-commits]

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@@ -1078,8 +1078,9 @@ const TargetRegisterClass *MachineInstr::getRegClassConstraintEffect(
       CurRC = TRI->getMatchingSuperRegClass(CurRC, OpRC, SubIdx);
     else
       CurRC = TRI->getSubClassWithSubReg(CurRC, SubIdx);
-  } else if (OpRC)
+  } else if (OpRC) {
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jayfoad wrote:

Nit: unrelated cleanup

https://github.com/llvm/llvm-project/pull/181489