avoid potentially undefined behavior and make valgrind happy (bnoordhuis) (github issue #153)

quickjs.c

@@ -7905,47 +7905,45 @@ static JSValue JS_GetPropertyValue(JSContext *ctx, JSValueConst this_obj,
     if (likely(JS_VALUE_GET_TAG(this_obj) == JS_TAG_OBJECT &&
                JS_VALUE_GET_TAG(prop) == JS_TAG_INT)) {
         JSObject *p;
-        uint32_t idx, len;
+        uint32_t idx;
         /* fast path for array access */
         p = JS_VALUE_GET_OBJ(this_obj);
         idx = JS_VALUE_GET_INT(prop);
-        /* Note: this code works even if 'p->u.array.count' is not
-           initialized. There are two cases:
-           - 'p' is an array-like object. 'p->u.array.count' is
-             initialized so the slow_path is taken when the index is
-             out of bounds.
-           - 'p' is not an array-like object. 'p->u.array.count' has
-           any value and potentially not initialized. In all the cases
-           (idx >= len or idx < len) the slow path is taken as
-           expected.
-        */
-        len = (uint32_t)p->u.array.count;
-        if (unlikely(idx >= len))
-            goto slow_path;
         switch(p->class_id) {
         case JS_CLASS_ARRAY:
         case JS_CLASS_ARGUMENTS:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_DupValue(ctx, p->u.array.u.values[idx]);
         case JS_CLASS_INT8_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewInt32(ctx, p->u.array.u.int8_ptr[idx]);
         case JS_CLASS_UINT8C_ARRAY:
         case JS_CLASS_UINT8_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewInt32(ctx, p->u.array.u.uint8_ptr[idx]);
         case JS_CLASS_INT16_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewInt32(ctx, p->u.array.u.int16_ptr[idx]);
         case JS_CLASS_UINT16_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewInt32(ctx, p->u.array.u.uint16_ptr[idx]);
         case JS_CLASS_INT32_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewInt32(ctx, p->u.array.u.int32_ptr[idx]);
         case JS_CLASS_UINT32_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewUint32(ctx, p->u.array.u.uint32_ptr[idx]);
         case JS_CLASS_BIG_INT64_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewBigInt64(ctx, p->u.array.u.int64_ptr[idx]);
         case JS_CLASS_BIG_UINT64_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return JS_NewBigUint64(ctx, p->u.array.u.uint64_ptr[idx]);
         case JS_CLASS_FLOAT32_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return __JS_NewFloat64(ctx, p->u.array.u.float_ptr[idx]);
         case JS_CLASS_FLOAT64_ARRAY:
+            if (unlikely(idx >= p->u.array.count)) goto slow_path;
             return __JS_NewFloat64(ctx, p->u.array.u.double_ptr[idx]);
         default:
             goto slow_path;