https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- So it still parallelizes the loop(s) but at one level deeper (line 176 vs. 173). This is because dependence analysis does not handle calls and loop distribution distributed a memset. ISL dependence analysis will have the same issue. I've quickly tried replacing memset with *p = {} which somewhat works when wrapping the LHS with a WITH_SIZE_EXPR. It later ICEs, but well. RTL expansion suggests we expect it on the RHS, so *p = WITH_SIZE_EXPR <{}, n} but that doesn't parallelize again (dependence analysis is confused). I think the proper fix is to dependence analysis in get_references_in_stmt, similar to how we handle masked loads/stores.