If you do have hidden thread safety bugs you are only one compile away from failure, even on x86. Some function gets vectorized and a variable shifts in or out

If you do have hidden thread safety bugs you are only one compile away from failure, even on x86. Some function gets vectorized and a variable shifts in or out of a register? Or one of your libraries gets rebuilt with LTO / LTCG and its functions are inlined. If your code was wrong, any of that can ruin it and you're left trying to figure it out, and requiring your developers to use exactly one point release of Visual Studio and never, ever upgrade the SDK install.