pan/midgard: Turn Z/S stores into zs_output_pan intrinsics

Midgard can't write depth and stencil separately. It has to happen in
a single store operation containing both. Let's add a panfrost specific
intrinsic and turn all depth/stencil stores into a packed depth+stencil
one.

Note that this intrinsic is not yet handled in emit_intrinsic(), but
we'll address that later.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3697>

src/compiler/nir/nir_intrinsics.py

@@ -858,6 +858,7 @@ intrinsic("load_global_ir3", [2, 1], dest_comp=0, indices=[ACCESS, ALIGN_MUL, AL
 
 # src[] = { value }
 store("raw_output_pan", 1, [])
+store("zs_output_pan", 1, [COMPONENT])
 load("raw_output_pan", 0, [], [CAN_ELIMINATE, CAN_REORDER])
 load("output_u8_as_fp16_pan", 0, [], [CAN_ELIMINATE, CAN_REORDER])
 

src/panfrost/midgard/midgard_compile.c

@@ -446,6 +446,103 @@ midgard_nir_lower_fdot2(nir_shader *shader)
         return progress;
 }
 
+/* Midgard can't write depth and stencil separately. It has to happen in a
+ * single store operation containing both. Let's add a panfrost specific
+ * intrinsic and turn all depth/stencil stores into a packed depth+stencil
+ * one.
+ */
+static bool
+midgard_nir_lower_zs_store(nir_shader *nir)
+{
+        if (nir->info.stage != MESA_SHADER_FRAGMENT)
+                return false;
+
+        nir_variable *z_var = NULL, *s_var = NULL;
+
+        nir_foreach_variable(var, &nir->outputs) {
+                if (var->data.location == FRAG_RESULT_DEPTH)
+                        z_var = var;
+                else if (var->data.location == FRAG_RESULT_STENCIL)
+                        s_var = var;
+        }
+
+        if (!z_var && !s_var)
+                return false;
+
+        bool progress = false;
+
+        nir_foreach_function(function, nir) {
+                if (!function->impl) continue;
+
+                nir_intrinsic_instr *z_store = NULL, *s_store = NULL, *last_store = NULL;
+
+                nir_foreach_block(block, function->impl) {
+                        nir_foreach_instr_safe(instr, block) {
+                                if (instr->type != nir_instr_type_intrinsic)
+                                        continue;
+
+                                nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+                                if (intr->intrinsic != nir_intrinsic_store_output)
+                                        continue;
+
+                                if (z_var && nir_intrinsic_base(intr) == z_var->data.driver_location) {
+                                        assert(!z_store);
+                                        z_store = intr;
+                                        last_store = intr;
+                                }
+
+                                if (s_var && nir_intrinsic_base(intr) == s_var->data.driver_location) {
+                                        assert(!s_store);
+                                        s_store = intr;
+                                        last_store = intr;
+                                }
+                        }
+                }
+
+                if (!z_store && !s_store) continue;
+
+                nir_builder b;
+                nir_builder_init(&b, function->impl);
+
+                b.cursor = nir_before_instr(&last_store->instr);
+
+		nir_ssa_def *zs_store_src;
+
+                if (z_store && s_store) {
+                        nir_ssa_def *srcs[2] = {
+                                nir_ssa_for_src(&b, z_store->src[0], 1),
+                                nir_ssa_for_src(&b, s_store->src[0], 1),
+                        };
+
+                        zs_store_src = nir_vec(&b, srcs, 2);
+                } else {
+                        zs_store_src = nir_ssa_for_src(&b, last_store->src[0], 1);
+                }
+
+                nir_intrinsic_instr *zs_store;
+
+                zs_store = nir_intrinsic_instr_create(b.shader,
+                                                      nir_intrinsic_store_zs_output_pan);
+                zs_store->src[0] = nir_src_for_ssa(zs_store_src);
+                zs_store->num_components = z_store && s_store ? 2 : 1;
+                nir_intrinsic_set_component(zs_store, z_store ? 0 : 1);
+
+                /* Replace the Z and S store by a ZS store */
+                nir_builder_instr_insert(&b, &zs_store->instr);
+
+                if (z_store)
+                        nir_instr_remove(&z_store->instr);
+
+                if (s_store)
+                        nir_instr_remove(&s_store->instr);
+
+                nir_metadata_preserve(function->impl, nir_metadata_block_index | nir_metadata_dominance);
+                progress = true;
+        }
+
+        return progress;
+}
+
 /* Flushes undefined values to zero */
 
 static void
@@ -2708,6 +2805,7 @@ midgard_compile_shader_nir(nir_shader *nir, midgard_program *program, bool is_bl
         NIR_PASS_V(nir, nir_lower_vars_to_ssa);
 
         NIR_PASS_V(nir, nir_lower_io, nir_var_all, glsl_type_size, 0);
+        NIR_PASS_V(nir, midgard_nir_lower_zs_store);
 
         /* Optimisation passes */