No useful and reliable way to detect integer overflow in C/C++?

Question

No, this is not a duplicate of How to detect integer overflow?. The issue is the same but the question is different.

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The gcc compiler can optimize away an

Answer 1

int a, b;
b = abs(a); // will overflow if a = 0x80000000
if (b < 0) printf("overflow");  // optimized away 

(You seem to be assuming 2s complement... let's run with that)

Who says abs(a) "overflows" if a has that binary pattern (more accurately, if a is INT_MIN)? The Linux man page for abs(int) says:

Trying to take the absolute value of the most negative integer is not defined.

Not defined doesn't necessarily mean overflow.

So, your premise that b could ever be less than 0, and that's somehow a test for "overflow", is fundamentally flawed from the start. If you want to test, you can not do it on the result that may have undefined behaviour - do it before the operation instead!

If you care about this, you can use C++'s user-defined types (i.e. classes) to implement your own set of tests around the operations you need (or find a library that already does that). The language does not need inbuilt support for this as it can be implemented equally efficiently in such a library, with the resulting semantics of use unchanged. That's fundamental power is one of the great things about C++.