Signed integer overflow check optimized away in C

Signed integer overflow guard disappears after optimization

ISO C defines signed integer overflow as undefined behavior. A compiler may assume the overflow never occurs and remove an explicit overflow check, even when the source appears to guard against it. I need to know whether a bounds check written for signed arithmetic can be relied upon across common C toolchains.

The uncertainty centers on optimization level, compiler version, and language standard from C99 through C23. Unsigned overflow is defined to wrap modulo 2 to the power of N, but signed overflow has no required errno, diagnostic, or trap. I am looking for a portable way to express the intent without depending on wraparound semantics, and per-toolchain verification would be needed before deployment.

• Does ISO C permit a compiler to delete a signed overflow check that is provably unreachable only because overflow is undefined?
• Which compiler flags or language-standard selections affect whether the check survives?
• Is there a standards-conforming C idiom for detecting signed overflow before it occurs?