give branch folding a simple heuristic to decide which block to split so that
it inserts an uncond branch where it is less likely to cause a problem.  This
fixes some perf issues on ppc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31354 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed