https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128208
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- t.c:11:23: note: ==> examining statement: _9 = .MASK_LOAD (_49, 32B, _35, 0); t.c:11:23: note: vect_is_simple_use: operand _4 != 0, type of def: internal t.c:11:23: missed: unsupported masked emulated gather. t.c:14:33: missed: not vectorized: relevant stmt not supported: _9 = .MASK_LOAD (_49, 32B, _35, 0); works with -mtune-ctrl=use_gather, so "expected". We do not attempt to use control flow to emulate this (or masked elementwise scalar loads). clang doesn't seem to be bothered about data[(i*8)].a faulting, not sure with what argument, I believe it generates wrong-code. Not confirming, I'd say WONTFIX.
