throws subtraction overflow error for floats

compiler/gen/src/llvm/build.rs

@@ -3424,7 +3424,29 @@ fn build_float_binop<'a, 'ctx, 'env>(
             struct_value.into()
         }
         NumAddWrap => unreachable!("wrapping addition is not defined on floats"),
-        NumSub => bd.build_float_sub(lhs, rhs, "sub_float").into(),
+        NumSub => {
+            let builder = env.builder;
+            let context = env.context;
+
+            let result = bd.build_float_sub(lhs, rhs, "sub_float");
+
+            let is_finite =
+                call_bitcode_fn(env, &[result.into()], &bitcode::NUM_IS_FINITE).into_int_value();
+
+            let then_block = context.append_basic_block(parent, "then_block");
+            let throw_block = context.append_basic_block(parent, "throw_block");
+
+            builder.build_conditional_branch(is_finite, then_block, throw_block);
+
+            builder.position_at_end(throw_block);
+
+            throw_exception(env, "float subtraction overflowed!");
+
+            builder.position_at_end(then_block);
+
+            result.into()
+        }
+        NumSubWrap => unreachable!("wrapping subtraction is not defined on floats"),
         NumMul => bd.build_float_mul(lhs, rhs, "mul_float").into(),
         NumGt => bd.build_float_compare(OGT, lhs, rhs, "float_gt").into(),
         NumGte => bd.build_float_compare(OGE, lhs, rhs, "float_gte").into(),

compiler/gen/tests/gen_num.rs

@@ -704,19 +704,19 @@ mod gen_num {
         );
     }
 
-    //     #[test]
+    #[test]
-    //     #[should_panic(expected = r#"Roc failed with message: "float addition overflowed!"#)]
+    #[should_panic(expected = r#"Roc failed with message: "float addition overflowed!"#)]
-    //     fn float_overflow() {
+    fn float_add_overflow() {
-    //         assert_evals_to!(
+        assert_evals_to!(
-    //             indoc!(
+            indoc!(
-    //                 r#"
+                r#"
-    //                 1.7976931348623157e308 + 1.7976931348623157e308
+                    1.7976931348623157e308 + 1.7976931348623157e308
-    //                 "#
+                    "#
-    //             ),
+            ),
-    //             0.0,
+            0.0,
-    //             f64
+            f64
-    //         );
+        );
-    //     }
+    }
 
     #[test]
     fn num_max_int() {
@@ -770,4 +770,18 @@ mod gen_num {
             i64
         );
     }
+
+    #[test]
+    #[should_panic(expected = r#"Roc failed with message: "float subtraction overflowed!"#)]
+    fn float_sub_overflow() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                    -1.7976931348623157e308 - 1.7976931348623157e308
+                    "#
+            ),
+            0.0,
+            f64
+        );
+    }
 }