In bug 654190 I made various functions use the string index value, but there are more. - In Ion somewhere in StringToNumber. I think sometimes we don't even emit optimized code when handling strings just the Value variant. IIRC this happens with +string. - Make sure that we inline the getIndexValue call into ToInt32 etc. Right now these end up calling getIndexValue via ToNumber -> ToNumberSlow -> StringToNumber, maybe we should push the call up. - When parsing string literals we should try to cache the index value. This should speed up the parseInt benchmark in bug 930540. - Code using the DOM will sometimes have snippets like css.width = 100 + "px"; We could potentially optimize this by matching isRope() & leftChild->hasIndexValue() & rightChild == "px"