Use mask in gather proxy behaviour

Moved from Phys@92b16926

Phys/ParticleCombiners/include/CombKernel/ThOrCombiner.h

@@ -690,7 +690,7 @@ namespace ThOr {
         auto const fit_success_mask = m_vertex_fitter.fitComposite(
             tmp_storage, mask, new_composite_pids,
             Sel::ParticleCombination{detail::Combiner::invoke_or_visit_returning_variant(
-                [&]( auto const& container ) { return container.gather( indices[IInput] ); },
+                [&]( auto const& container ) { return container.gather( indices[IInput], mask ); },
                 std::get<IInput>( in ) )...} );
         if ( tmp_storage.size() != simd_t::size ) {
           throw exception( "tmp_storage didn't have simd_t::size elements." );
@@ -840,9 +840,10 @@ namespace ThOr {
           auto const particles1_mask = simd_t::loop_mask( i1, indices1.size() );
           // Note that this is only *not* reading from beyond the end of
           // indices1 because of the convoluted .resize() in get_indices()
-          auto const p1_inds = select( particles1_mask, int_v{std::next( indices1.data(), i1 )}, int_v{indices1[i1]} );
+          auto const p1_inds    = int_v{std::next( indices1.data(), i1 )};
           auto const particles1 = detail::Combiner::invoke_or_visit_returning_variant(
-              [&]( auto const& container ) { return container.gather( p1_inds ); }, std::get<1>( in ) );
+              [&]( auto const& container ) { return container.gather( p1_inds, particles1_mask ); },
+              std::get<1>( in ) );
           // The "triangle" inefficiency comes in from the `loop_mask`:
           //         d
           //       c d
@@ -1026,7 +1027,7 @@ namespace ThOr {
         // one
         new_comb_t const comb{
             detail::Combiner::invoke_or_visit_returning_variant(
-                [inds = indices[Particle]]( auto const& container ) { return container.gather( inds ); },
+                [inds = indices[Particle], mask]( auto const& container ) { return container.gather( inds, mask ); },
                 std::get<Particle>( in ) )...,
             detail::Combiner::invoke_or_visit_returning_variant(
                 [&]( auto const& container ) { return container.scalar_fill( new_indices[i] ); },