Improve constant pool support

Investigate and improve the current constant pool generation and code.

The current constant pool placement code doesn't take profile info into consideration or whether something gets placed in the inner most kerrnel of a loop etc. There are a few cases when it does get placed in the middle of the inner most loop in which case we might see some weird cache effects. A long term plan should be to try and share constant pools across functions and make it work with hot-cold partitioning of functions.