[llvm] [VirtRegMap] Remove unsupported sub-registers during rewrite (PR #201550)

[Jay Foad via llvm-commits]

================
@@ -696,13 +696,30 @@ void VirtRegRewriter::rewrite() {
                 LaneBitmask LiveOutUndefLanes =
                     liveOutUndefPhiLanesForUndefSubregDef(LI, *MBBI, SubReg,
                                                           PhysReg, MI);
+                const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
+
+                // FIXME: Incorrect sub-regsiters should never make it into
----------------
jayfoad wrote:

```suggestion
                // FIXME: Incorrect sub-registers should never make it into
```

https://github.com/llvm/llvm-project/pull/201550