[PATCH] Speed up creation of live ranges for physical registers by using a segment set

[Eric Christopher]

Couple of questions:

a) Compile time results?
b) Why didn't it help/produce a slowdown for computeVirtRegs? 
c) What's the slowdown look like for using it all the time? Is it because we're using find instead of set::upper_bound? Where are we running into issues?
d) It seems like we're duplicating a lot of code to do this, is there any way you can think of to remove that duplication here?

Couple of clean up comments:

a) Comments are a full sentence including captialization.
b) Pull the asserts out of the else blocks.
c) Single statement blocks shouldn't have braces.

-eric

http://reviews.llvm.org/D6013