Disable jump threading UnOp::Not for non-bool

Author: compiler-errors

Diff for: compiler/rustc_mir_transform/src/jump_threading.rs

@@ -494,8 +494,16 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             }
             // Transfer the conditions on the copy rhs, after inversing polarity.
             Rvalue::UnaryOp(UnOp::Not, Operand::Move(place) | Operand::Copy(place)) => {
+                if !place.ty(self.body, self.tcx).ty.is_bool() {
+                    // Constructing the conditions by inverting the polarity
+                    // of equality is only correct for bools. That is to say,
+                    // `!a == b` is not `a != b` for integers greater than 1 bit.
+                    return;
+                }
                 let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return };
                 let Some(place) = self.map.find(place.as_ref()) else { return };
+                // FIXME: I think This could be generalized to not bool if we
+                // actually perform a logical not on the condition's value.
                 let conds = conditions.map(self.arena, Condition::inv);
                 state.insert_value_idx(place, conds, &self.map);
             }

Diff for: tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.diff

@@ -22,8 +22,7 @@
           _3 = Not(move _4);
           StorageDead(_4);
           _2 = Eq(move _3, const 0_i32);
--         switchInt(move _2) -> [0: bb2, otherwise: bb1];
-+         goto -> bb1;
+          switchInt(move _2) -> [0: bb2, otherwise: bb1];
       }
 
       bb1: {