nir: Add ability to overwrite incomplete GS primitives.
After each end_primitive and at the end of the shader before emitting
set_vertex_and_primitive_count, we check if the primitive that is being
emitted has enough vertices or not, and we adjust the vertex and
primitive counters accordingly.
As a result, if the backend uses this option, the backend compiler
will not have to worry about discarding the unneeded vertices
and primitives.
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6964>
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index e712c6d..989f39f 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -4730,6 +4730,7 @@
nir_lower_gs_intrinsics_per_stream = 1 << 0,
nir_lower_gs_intrinsics_count_primitives = 1 << 1,
nir_lower_gs_intrinsics_count_vertices_per_primitive = 1 << 2,
+ nir_lower_gs_intrinsics_overwrite_incomplete = 1 << 3,
} nir_lower_gs_intrinsics_flags;
bool nir_lower_gs_intrinsics(nir_shader *shader, nir_lower_gs_intrinsics_flags options);
diff --git a/src/compiler/nir/nir_lower_gs_intrinsics.c b/src/compiler/nir/nir_lower_gs_intrinsics.c
index a514551..e83034b 100644
--- a/src/compiler/nir/nir_lower_gs_intrinsics.c
+++ b/src/compiler/nir/nir_lower_gs_intrinsics.c
@@ -62,6 +62,7 @@
bool per_stream;
bool count_prims;
bool count_vtx_per_prim;
+ bool overwrite_incomplete;
bool progress;
};
@@ -131,6 +132,73 @@
}
/**
+ * Emits code that overwrites incomplete primitives and their vertices.
+ *
+ * A primitive is considered incomplete when it doesn't have enough vertices.
+ * For example, a triangle strip that has 2 or fewer vertices, or a line strip
+ * with 1 vertex are considered incomplete.
+ *
+ * After each end_primitive and at the end of the shader before emitting
+ * set_vertex_and_primitive_count, we check if the primitive that is being
+ * emitted has enough vertices or not, and we adjust the vertex and primitive
+ * counters accordingly.
+ *
+ * This means that the following emit_vertex can reuse the vertex index of
+ * a previous vertex, if the previous primitive was incomplete, so the compiler
+ * backend is expected to simply overwrite any data that belonged to those.
+ */
+static void
+overwrite_incomplete_primitives(struct state *state, unsigned stream)
+{
+ assert(state->count_vtx_per_prim);
+
+ nir_builder *b = state->builder;
+ unsigned outprim = b->shader->info.gs.output_primitive;
+ unsigned outprim_min_vertices;
+
+ if (outprim == GL_POINTS)
+ outprim_min_vertices = 1;
+ else if (outprim == GL_LINE_STRIP)
+ outprim_min_vertices = 2;
+ else if (outprim == GL_TRIANGLE_STRIP)
+ outprim_min_vertices = 3;
+ else
+ unreachable("Invalid GS output primitive type.");
+
+ /* Total count of vertices emitted so far. */
+ nir_ssa_def *vtxcnt_total =
+ nir_load_var(b, state->vertex_count_vars[stream]);
+
+ /* Number of vertices emitted for the last primitive */
+ nir_ssa_def *vtxcnt_per_primitive =
+ nir_load_var(b, state->vtxcnt_per_prim_vars[stream]);
+
+ /* See if the current primitive is a incomplete */
+ nir_ssa_def *is_inc_prim =
+ nir_ilt(b, vtxcnt_per_primitive, nir_imm_int(b, outprim_min_vertices));
+
+ /* Number of vertices in the incomplete primitive */
+ nir_ssa_def *num_inc_vtx =
+ nir_bcsel(b, is_inc_prim, vtxcnt_per_primitive, nir_imm_int(b, 0));
+
+ /* Store corrected total vertex count */
+ nir_store_var(b, state->vertex_count_vars[stream],
+ nir_isub(b, vtxcnt_total, num_inc_vtx),
+ 0x1); /* .x */
+
+ if (state->count_prims) {
+ /* Number of incomplete primitives (0 or 1) */
+ nir_ssa_def *num_inc_prim = nir_b2i32(b, is_inc_prim);
+
+ /* Store corrected primitive count */
+ nir_ssa_def *prim_cnt = nir_load_var(b, state->primitive_count_vars[stream]);
+ nir_store_var(b, state->primitive_count_vars[stream],
+ nir_isub(b, prim_cnt, num_inc_prim),
+ 0x1); /* .x */
+ }
+}
+
+/**
* Replace end_primitive with end_primitive_with_counter.
*/
static void
@@ -166,6 +234,9 @@
}
if (state->count_vtx_per_prim) {
+ if (state->overwrite_incomplete)
+ overwrite_incomplete_primitives(state, stream);
+
/* Store 0 to per-primitive vertex count */
nir_store_var(b, state->vtxcnt_per_prim_vars[stream],
nir_imm_int(b, 0),
@@ -226,6 +297,9 @@
if (state->per_stream && !(shader->info.gs.active_stream_mask & (1 << stream)))
continue;
+ if (state->overwrite_incomplete)
+ overwrite_incomplete_primitives(state, stream);
+
nir_ssa_def *vtx_cnt = nir_load_var(b, state->vertex_count_vars[stream]);
nir_ssa_def *prim_cnt;
@@ -251,13 +325,16 @@
{
bool per_stream = options & nir_lower_gs_intrinsics_per_stream;
bool count_primitives = options & nir_lower_gs_intrinsics_count_primitives;
+ bool overwrite_incomplete = options & nir_lower_gs_intrinsics_overwrite_incomplete;
bool count_vtx_per_prim =
- options & nir_lower_gs_intrinsics_count_vertices_per_primitive;
+ overwrite_incomplete ||
+ (options & nir_lower_gs_intrinsics_count_vertices_per_primitive);
struct state state;
state.progress = false;
state.count_prims = count_primitives;
state.count_vtx_per_prim = count_vtx_per_prim;
+ state.overwrite_incomplete = overwrite_incomplete;
state.per_stream = per_stream;
nir_function_impl *impl = nir_shader_get_entrypoint(shader);
