ARM: fold prologue/epilogue sp updates into push/pop for code size

ARM prologues usually look like:
    push {r7, lr}
    sub sp, sp, #4

If code size is extremely important, this can be optimised to the single
instruction:
    push {r6, r7, lr}

where we don't actually care about the contents of r6, but pushing it subtracts
4 from sp as a side effect.

This should implement such a conversion, predicated on the "minsize" function
attribute (-Oz) since I've yet to find any code it actually makes faster.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194264 91177308-0d34-0410-b5e6-96231b3b80d8
Add ImmutableSet profiling info for 'bool'.

Useful for tri-state maps: true, false, and "no data yet".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194266 91177308-0d34-0410-b5e6-96231b3b80d8
CalculateSpillWeights does not need to be a pass

Based on discussions with Lang Hames and Jakob Stoklund Olesen at the hacker's lab, and in the light of upcoming work on the PBQP register allocator, it was though that CalcSpillWeights does not need to be a pass. This change will enable to customize / tune the spill weight computation depending on the allocator.

Update the documentation style while there.

No functionnal change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194269 91177308-0d34-0410-b5e6-96231b3b80d8