Hoist the rest of the logic for fully promoting allocas with all uses in
a single block into the helper routine. This takes advantage of the fact
that we can directly replace uses prior to any store with undef to
simplify matters and unconditionally promote allocas only used within
one block.

I've removed the special handling for the case of no stores existing.
This has no semantic effect but might slow things down. I'll fix that in
a later patch when I refactor this entire thing to be easier to manage
the different cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186783 91177308-0d34-0410-b5e6-96231b3b80d8
Hoist the rest of the logic for promoting single-store allocas into the
helper function. This leaves both trivial cases handled entirely in
helper functions and merely manages the list of allocas to process in
the run method.

The next step will be to handle all of the trivial promotion work prior
to even creating the core class and the subsequent simplifications that
enables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186784 91177308-0d34-0410-b5e6-96231b3b80d8