The CTR loops pass will insert the decrementing branch instruction in an exiting
block for the loop being transformed. However if that block is part of another
loop as well (whether a nested loop or with irreducible CFG), it is not valid
to use that exiting block. In fact, if the loop hass irreducible CFG, we don't
bother analyzing it and we just bail on the transformation. In practice, this
doesn't lead to a noticeable reduction in the number of loops transformed by
this pass.
Fixes https://bugs.llvm.org/show_bug.cgi?id=37229
Differential Revision: https://reviews.llvm.org/D46162
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331410 91177308-0d34-0410-b5e6-96231b3b80d8
