This is addressing PR43371. When optimizing for size, and SCEV runtime checks
need to be emitted to check overflow behaviour, the loop vectorizer can run in this
LoopVectorize.cpp:2699: void llvm::InnerLoopVectorizer::emitSCEVChecks( llvm::Loop *, llvm::BasicBlock *): Assertion `!BB->getParent()->hasOptSize() && "Cannot SCEV check stride or overflow when optimizing for size"'
SCEV should not generate predicates while optimising for size, because
code will be generated for predicates, such as these SCEV overflow runtime