[Bug target/116782] New: x86 backend cannot control vectorization of gather and masked gather (and scatter) separately

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116782

            Bug ID: 116782
           Summary: x86 backend cannot control vectorization of gather and
                    masked gather (and scatter) separately
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

The x86 backend still uses the builtin_{gather,scatter} hooks (PR85919) but
those do not distinguish between masked and non-masked use.  Masked gathers
and scatters are vectorization enabler and not only needed for performance
as we cannot open-code them easily.

The proposal would be to implement mask_gather_load_optab and
mask_scatter_store_optab, partially transitioning to IFNs and thereby
have a set of patterns to enable separately.