https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80080
--- Comment #7 from Dominik Vogt <vogt at linux dot vnet.ibm.com> --- (In reply to Jakub Jelinek from comment #6) > I think it depends on what > (success, old_reg) = compare-and-swap(mem, old_reg, new_reg) > sets if success is true. Is there a guarantee that old_reg will be assigned > whatever has been passed as the second argument in that case on all targets? Isn't that part of the interface of the atomic_compare_and_swap pattern? Gccinternals: > Operand 1 is an output operand which is set to the contents of the memory > before the operation was attempted. Operand 3 is the value that is > expected to be in memory. If the CS instruction on a target does not overwrite the register old_reg with the memory value before swapping, the target's backend must do that manually, I think.
