Make this more efficient in the following ways:

Make this more efficient in the following ways:
1. Do not statically construct a map when the program starts up, this
   is expensive and cannot be optimized.  Instead, create a list.
2. Do not insert entries for all function in the module into a hashmap
   that lives the full life of the compiler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25512 91177308-0d34-0410-b5e6-96231b3b80d8