[qznc]

I'd say both statements are correct.

Compiler implementers are happy when they don't have to care about some edge case because then the code is simpler. Thus, only for unsigned counters there is the extra logic to compile them correctly.

That is my interpretation of "The opposite is the case". Writing a compiler is easier with lots of undefined behavior.

[ender341341]

But that's backwards, the compiler writers are writing special cases to erase checks in the signed case. Doing the 'dumb' thing and mindlessly going through the written check is simpler which is why that's what compilers did for decades as de facto standard on x86.

[qznc]

The dump thing is a non optimizing compiler. GCC and LLVM contain many optimization phases. It is probably some normal optimization which is only "wrong" in the context of loop conditions.