Optional args are no longer allocated as they are discovered.

Optional args are no longer allocated as they are discovered.
(This can be improved to avoid making the initial pass over the method.)
Also, ensure automatic vars and reg. spills areas are not extended
if their sizes are used for computing some other offset.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2319 91177308-0d34-0410-b5e6-96231b3b80d8