To be clear here, overflow is a "program error" in Rust; it's specified to panic in debug builds, and any build where it doesn't panic is defined as wrapping two's compliment.

I tried to toss this into godbolt, but the optimizer is too good of course, it will optimize away the entire if if my_signed_int is a literal. Here's one without optimizations: https://godbolt.org/g/tBZcTA

It seems to compare 1 to 1, and then branch. My guess, though this isn't my area of specialty, is that this is because it is also assuming that overflow can't happen, making this always true.

Clang, interestingly enough, does the load, add, and compare https://godbolt.org/g/gPjgVc