Matt Godbolt <m...@godbolt.org> writes: > GCC's code generation uses a "load; add; store" for volatiles, instead > of a single "add 1, [metric]".
GCC doesn't know if a target's load/add/store patterns are volatile-safe, so it must avoid them. There are a few targets that have been audited for volatile-safe-ness such that gcc *can* use the combined load/add/store when the backend says it's OK. x86 is not yet one of those targets. Also, note that the standard says the physical target must do the same operations that the "model" target does, but it does not require that these operations be in separate opcodes. A single opcode that performs the correct operations in the correct order complies with the standard; but you have to tell gcc which opcodes comply.
