LoopVectorize: LoopSimplify can't canonicalize loops with an
indirectbr in it, don't assert on those cases.
Fixes PR16139.
This should fix clang assertion failures when optimizing at -O3, similar
to:
Assertion failed: (TheLoop->getLoopPreheader() && "No preheader!!"),
function canVectorize, file
contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp, line 2171.
Reported by: O. Hartmann <ohartman@zedat.fu-berlin.de>
PR: ports/178332, ports/178977
MFC after: 3 days
b3eb0ffbc9