IMO this is one of those fragile optimizations. If the optimization is important, it should be explicit (hand-rolled asm) or else you risk breaking it. If it's

IMO this is one of those fragile optimizations. If the optimization is important, it should be explicit (hand-rolled asm) or else you risk breaking it. If it's not important, then nobody cares. Emitting OoB reads dependent on optimization level? Think about ASAN, debugger watchpoints...can't be worth it! clang has a cool feature that highlights missed vectorization opportunities: > clang++ -O3 -c test.cpp -Rpass-analysis=loop-vectorize test.cpp:5:4: remark: loop not vectorized: loop control flow is not understood by vectorizer [-Rpass-analysis=loop-vectorize] love it!