[ObjCARC] Strength reduce objc_retainBlock -> objc_retain if the objc_retainBlock is optimizable.

If an objc_retainBlock has the copy_on_escape metadata attached to it
AND if the block pointer argument only escapes down the stack, we are
allowed to strength reduce the objc_retainBlock to to an objc_retain and
thus optimize it.

Current there is logic in the ARC data flow analysis to handle
this case which is complicated and involved making distinctions in
between objc_retainBlock and objc_retain in certain places and
considering them the same in others.

This patch simplifies said code by:

1. Performing the strength reduction in the initial ARC peephole
analysis (ObjCARCOpts::OptimizeIndividualCalls).

2. Changes the ARC dataflow analysis (which runs after the peephole
analysis) to consider all objc_retainBlock calls to not be optimizable
(since if the call was optimizable, we would have strength reduced it
already).

This patch leaves in the infrastructure in the ARC dataflow analysis to
handle this case, which due to 2 will just be dead code. I am doing this
on purpose to separate the removal of the old code from the testing of
the new code.

<rdar://problem/13249661>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178284 91177308-0d34-0410-b5e6-96231b3b80d8
Non optimizable objc_retainBlock calls are not forwarding.

Since we handle optimizable objc_retainBlocks through strength reduction
in OptimizableIndividualCalls, we know that all code after that point
will only see non-optimizable objc_retainBlock calls. IsForwarding is
only called by functions after that point, so it is ok to just classify
objc_retainBlock as non-forwarding.

<rdar://problem/13249661>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178285 91177308-0d34-0410-b5e6-96231b3b80d8
Only enable 64-bit bswap DAG combines for PPC64

Compiling in 32-bit mode on a P7 would assert after 64-bit DAG combines were
added for bswap with load/store. This is because these combines are really only
valid in 64-bit mode, regardless of the CPU (and this was not being checked).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178286 91177308-0d34-0410-b5e6-96231b3b80d8
Specify CPUs on the PPC bswap-load-store test

Otherwise, the CHECK-NOT's might trigger depending on the host's CPU.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178287 91177308-0d34-0410-b5e6-96231b3b80d8