Maxime, can you check this code in ir/constprop.js :

var val0 = (v0.type === IRType.box) ? ((v0.value === undefined || v0.value === null) ? 0 : (v0.value << TAG_NUM_BITS_INT)) // FIXME : v0.value; var val1 = (v1.type === IRType.box) ? ((v1.value === undefined || v1.value === null) ? 0 : (v1.value << TAG_NUM_BITS_INT)) // FIXME : v1.value;

It seems that v0.value can be undefined or null. In your original code you directly did a v0.value << TAG_NUM_BITS_INT and this seems like a bug to me (v8 surprisingly returns 0 in those cases).

Marc