* Merge get_GVInitializer and getCharArrayLength into a single function

* Merge get_GVInitializer and getCharArrayLength into a single function
  named getConstantStringLength. This is the common part of StrCpy and
  StrLen optimizations and probably several others, yet to be written. It
  performs all the validity checks for looking at constant arrays that are
  supposed to be null-terminated strings and then computes the actual
  length of the string.
* Implement the MemCpyOptimization class. This just turns memcpy of 1, 2, 4
  and 8 byte data blocks that are properly aligned on those boundaries into
  a load and a store. Much more could be done here but alignment
  restrictions and lack of knowledge of the target instruction set prevent
  use from doing significantly more. That will have to be delegated to the
  code generators as they lower llvm.memcpy calls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21562 91177308-0d34-0410-b5e6-96231b3b80d8