1. we'd run simplifycfg at the very start, even though
the per function passes have already cleaned this up.
2. In the main per-function pipeline that is interlaced with inlining
etc, we would do instcombine, jump threading, simplifycfg *before*
doing SROA. SROA is much more likely to expose opportunities for
these passes than they are for SROA, so move SRoA up earlier.
also add some comments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85742 91177308-0d34-0410-b5e6-96231b3b80d8
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