[titzer]

One issue is that an optimization like this could have resulted from many prior inlinings and foldings that had to work together to create the pattern that was finally matched, so it's not obvious to point the user to what they should change their code to. Maybe they actually intended that the code get folded at the end by the compiler, but all of those optimizations were done by templates that will get folded a different, but equally cool way, under different specializations.

Generally I think some of LLVM's optimizations are trying too hard for the amount of complexity and compilation overhead they create. All that complexity comes at the risk of bugs. With optimizations around UB, it becomes downright mind-boggling what could go wrong. But I'm not an LLVM maintainer so what the heck do I know.