[titzer]

Exactly. The irony in all of this is that C is not a portable assembler. It'd be better if it were[1]!

If you want the exact semantics of a hardware instruction, you cannot get it, because the compiler reasons with C's abstract machine that assumes your program doesn't have undefined behavior, like signed wraparound, when in some situations you in fact do want signed wraparound, since that's what literally every modern CPU does.

[1] If the standard said that "the integer addition operator maps to the XYZ instruction on this target", that'd be something! But then compilers would have to reason about machine-level semantics to make optimizations. In reality, C's spec is designed by compiler writers for compiler writers, not for programs, and not for hardware.