Rewrite all the 'PromoteLocallyUsedAlloca[s]' logic. With the power of

Rewrite all the 'PromoteLocallyUsedAlloca[s]' logic.  With the power of
LargeBlockInfo, we can now dramatically simplify their implementation
and speed them up at the same time.  Now the code has time proportional
to the number of uses of the alloca, not the size of the block.

This also eliminates code that tried to batch up different allocas which
are used in the same blocks, and eliminates the 'retry list' logic which
was baroque and no unneccesary.  In addition to being a speedup for crazy
cases, this is also a nice cleanup:

PromoteMemoryToRegister.cpp |  270 +++++++++++++++-----------------------------
 1 file changed, 96 insertions(+), 174 deletions(-)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@58229 91177308-0d34-0410-b5e6-96231b3b80d8