Rollup merge of #143273 - 1c3t3a:enum-check-negative, r=SparrowLii

Make the enum check work for negative discriminants

The discriminant check was not working correctly for negative numbers. This change fixes that by masking out the relevant bits correctly.

Fixes rust-lang/rust#143218.

compiler/rustc_mir_transform/src/check_enums.rs

@@ -120,6 +120,7 @@ enum EnumCheckType<'tcx> {
     },
 }
 
+#[derive(Debug, Copy, Clone)]
 struct TyAndSize<'tcx> {
     pub ty: Ty<'tcx>,
     pub size: Size,
@@ -337,7 +338,7 @@ fn insert_direct_enum_check<'tcx>(
     let invalid_discr_block_data = BasicBlockData::new(None, false);
     let invalid_discr_block = basic_blocks.push(invalid_discr_block_data);
     let block_data = &mut basic_blocks[current_block];
-    let discr = insert_discr_cast_to_u128(
+    let discr_place = insert_discr_cast_to_u128(
         tcx,
         local_decls,
         block_data,
@@ -348,13 +349,34 @@ fn insert_direct_enum_check<'tcx>(
         source_info,
     );
 
+    // Mask out the bits of the discriminant type.
+    let mask = discr.size.unsigned_int_max();
+    let discr_masked =
+        local_decls.push(LocalDecl::with_source_info(tcx.types.u128, source_info)).into();
+    let rvalue = Rvalue::BinaryOp(
+        BinOp::BitAnd,
+        Box::new((
+            Operand::Copy(discr_place),
+            Operand::Constant(Box::new(ConstOperand {
+                span: source_info.span,
+                user_ty: None,
+                const_: Const::Val(ConstValue::from_u128(mask), tcx.types.u128),
+            })),
+        )),
+    );
+    block_data
+        .statements
+        .push(Statement::new(source_info, StatementKind::Assign(Box::new((discr_masked, rvalue)))));
+
     // Branch based on the discriminant value.
     block_data.terminator = Some(Terminator {
         source_info,
         kind: TerminatorKind::SwitchInt {
-            discr: Operand::Copy(discr),
+            discr: Operand::Copy(discr_masked),
             targets: SwitchTargets::new(
-                discriminants.into_iter().map(|discr| (discr, new_block)),
+                discriminants
+                    .into_iter()
+                    .map(|discr_val| (discr.size.truncate(discr_val), new_block)),
                 invalid_discr_block,
             ),
         },
@@ -371,7 +393,7 @@ fn insert_direct_enum_check<'tcx>(
             })),
             expected: true,
             target: new_block,
-            msg: Box::new(AssertKind::InvalidEnumConstruction(Operand::Copy(discr))),
+            msg: Box::new(AssertKind::InvalidEnumConstruction(Operand::Copy(discr_masked))),
             // This calls panic_invalid_enum_construction, which is #[rustc_nounwind].
             // We never want to insert an unwind into unsafe code, because unwinding could
             // make a failing UB check turn into much worse UB when we start unwinding.