On 01/05/2015 08:51 AM, Stefan Monnier wrote:
> For the USE_LSB_TAG case,
> that's not a problem, but for the case where we use the MSB for the tag,
> a negative number will not have the expected 000 in the MSB.

Thanks, good catch.  This is a problem on !USE_LSB_TAG platforms where 
heap memory lives below statically-allocated memory.  That should be 
rare (I don't know of such a platform offhand), but for now the simplest 
fix is to avoid this optimization on !USE_LSB_TAG platforms.  Revised 
patches attached, updated to match the latest master.