Replace three "strip & accumulate" implementations with a single one

Replace three "strip & accumulate" implementations with a single one

This patch replaces the three almost identical "strip & accumulate"
implementations for constant pointer offsets with a single one,
combining the respective functionalities. The old interfaces are kept
for now.

Differential Revision: https://reviews.llvm.org/D64468

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365723 91177308-0d34-0410-b5e6-96231b3b80d8