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by throwaway294566
1293 days ago
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Out-of-order execution isn't the reason for this. The C standard assumes an abstract machine that allows OoOE, of course, but even with strict in-order hardware UB can hit you at any time, even before you'd think it could. That is because the C standard doesn't limit UB to any constraints like "following lines" or "subsequently executed instructions". Independent of the hardware, the compiler is allowed quite a bit of reordering of instructions. The standard just requires that (some) effects of those executions are ordered as written, but that doesn't include UB. So if you have UB in your future path of execution, the compiler might just do whatever _right now_. |
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