[llvm] [GlobalISel] Drop nuw/nsw/disjoint when widening a result with G_ANYEXT (PR #218558)

[Chinmay Deshpande via llvm-commits]

================
@@ -3006,6 +3006,11 @@ LegalizerHelper::widenScalar(MachineInstr &MI, unsigned TypeIdx, LLT WideTy) {
     // don't affect the result) and then truncate the result back to the
     // original type.
     Observer.changingInstr(MI);
+    // The G_ANYEXTs below leave the new high bits unconstrained, so no-wrap and
+    // disjoint claims proved at the narrow width no longer hold. Paths that
+    // widen with value-preserving G_ZEXT/G_SEXT keep their flags.
+    MI.clearFlags(MachineInstr::NoUWrap | MachineInstr::NoSWrap |
+                  MachineInstr::Disjoint);
----------------
chinmaydd wrote:

I wonder if a cleaner fix is to do something like:

```
void LegalizerHelper::widenScalarSrc(MachineInstr &MI, LLT WideTy,
                                     unsigned OpIdx, unsigned ExtOpcode) {
  if (ExtOpcode == TargetOpcode::G_ANYEXT)
    // clear flags
  ...
}
```

Also, this seems to be missing a dedicated MIR tests for opcodes such as `G_ADD`, `G_AND`, etc..

https://github.com/llvm/llvm-project/pull/218558