nir: factor out nir_verts_in_output_prim helper

very useful for geometry shader lowering code.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34638>

src/compiler/nir/nir.h

@@ -6447,6 +6447,13 @@ void nir_print_use_dominators(nir_use_dominance_state *state,
                               nir_instr **instructions,
                               unsigned num_instructions);
 
+static inline unsigned
+nir_verts_in_output_prim(nir_shader *gs)
+{
+   assert(gs->info.stage == MESA_SHADER_GEOMETRY);
+   return mesa_vertices_per_prim(gs->info.gs.output_primitive);
+}
+
 #include "nir_inline_helpers.h"
 
 #ifdef __cplusplus

src/compiler/nir/nir_lower_gs_intrinsics.c

@@ -142,8 +142,7 @@ rewrite_emit_vertex(nir_intrinsic_instr *intrin, struct state *state)
       /* We form a new primitive for every vertex emitted after the first
        * complete primitive (since we're outputting strips).
        */
-      unsigned min_verts =
-         mesa_vertices_per_prim(b->shader->info.gs.output_primitive);
+      unsigned min_verts = nir_verts_in_output_prim(b->shader);
       nir_def *new_prim = nir_uge_imm(b, vtx_per_prim_cnt, min_verts);
 
       /* Increment the decomposed primitive count by 1 if we formed a complete
@@ -185,8 +184,6 @@ overwrite_incomplete_primitives(struct state *state, unsigned stream)
    assert(state->count_vtx_per_prim);
 
    nir_builder *b = state->builder;
-   unsigned outprim_min_vertices =
-      mesa_vertices_per_prim(b->shader->info.gs.output_primitive);
 
    /* Total count of vertices emitted so far. */
    nir_def *vtxcnt_total =
@@ -198,7 +195,7 @@ overwrite_incomplete_primitives(struct state *state, unsigned stream)
 
    /* See if the current primitive is a incomplete */
    nir_def *is_inc_prim =
-      nir_ilt_imm(b, vtxcnt_per_primitive, outprim_min_vertices);
+      nir_ilt_imm(b, vtxcnt_per_primitive, nir_verts_in_output_prim(b->shader));
 
    /* Number of vertices in the incomplete primitive */
    nir_def *num_inc_vtx =