[mat_epice]

EDIT: This comment is wrong, see fsmv’s comment below. Leaving for posterity because I’m no coward!

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Undefined behavior only means that the spec leaves a particular situation undefined and that the compiler implementor can do whatever they want. Every compiler defines undefined behavior, whether it’s documented (or easy to qualify, or deterministic) or not.

It is in poor taste that gcc has had widely used, documented behaviors that are changing, especially in a point release.

[fsmv]

I think you're confusing unspecified and undefined behavior. UB could do something randomly different every time and unspecified must chose an option.

In a lot of cases in optimizing compilers they just assume UB doesn't exist. Yes technically the compiler does do something but there's still a big difference between the two.

[mat_epice]

Thanks, you’re right, I was mistaken.