insn length attribute and code size optimization

[fanqifei]

According to the internal manual, insn length attribute can be used to
to calculate the length of emitted code chunks when verifying branch
distances.
Can it be used in code size optimization?
I may change TARGET_RTX_COSTS in my gcc port and return costs
regarding the ins lengths.  I can see code snippets for this purpose
in i386/i386.c, however, the insn sizes are hard coded in array
size_cost.
Are there any other places where the insn length impacts insn selection?

-- 
-Qifei Fan