Hi all, expand_atomic_load in optabs.c tries to expand a wide atomic load using an atomic_compare_and_swap with the comment saying that sometimes a redundant harmless store may be performed. Is the store really valid if the memory is read-only?
I've been looking at implementing a similar compare-and-swap strategy for atomic_loaddi for some arm targets and this concern came up. I don't think GCC can statically prove that a particular piece of memory is guaranteed to be writeable at runtime in all cases, so emitting a spurious store would not be always valid. I see this concern was already raised in https://gcc.gnu.org/ml/gcc-patches/2011-11/msg00278.html but that doesn't seem to have gone anywhere. Any thoughts? Should we remove the assumption that atomic loads always access writeable memory? Thanks, Kyrill
