agx: Add agx_nir_opt_preamble pass

This pass creates preamble shaders. The heavylifting is done by
nir_opt_preamble. We do need to define the cost model for nir_opt_preamble, set
up 16-bit units for the register file, and scalarize the resulting
load/store_preamble intrinsics.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18813>

src/asahi/compiler/agx_compiler.h

@@ -790,6 +790,7 @@ void agx_liveness_ins_update(BITSET_WORD *live, agx_instr *I);
 
 bool agx_lower_resinfo(nir_shader *s);
 bool agx_nir_lower_array_texture(nir_shader *s);
+bool agx_nir_opt_preamble(nir_shader *s, unsigned *preamble_size);
 
 #ifdef __cplusplus
 } /* extern C */

src/asahi/compiler/agx_nir_opt_preamble.c

@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2022 Alyssa Rosenzweig <alyssa@rosenzweig.io>
+ * Copyright © 2021 Valve Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "compiler/nir/nir_builder.h"
+#include "agx_compiler.h"
+
+static bool
+nir_scalarize_preamble(struct nir_builder *b, nir_instr *instr, UNUSED void *data)
+{
+   if (instr->type != nir_instr_type_intrinsic)
+      return false;
+
+   nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+   if (intr->intrinsic != nir_intrinsic_load_preamble &&
+       intr->intrinsic != nir_intrinsic_store_preamble)
+      return false;
+
+   bool is_load = (intr->intrinsic == nir_intrinsic_load_preamble);
+
+   nir_ssa_def *v = is_load ? &intr->dest.ssa :
+                    nir_ssa_for_src(b, intr->src[0], nir_src_num_components(intr->src[0]));
+
+   if (v->num_components == 1)
+      return false;
+
+   /* Scalarize */
+   b->cursor = nir_before_instr(&intr->instr);
+   unsigned stride = MAX2(v->bit_size / 16, 1);
+   unsigned base = nir_intrinsic_base(intr);
+
+   if (is_load) {
+      nir_ssa_def *comps[NIR_MAX_VEC_COMPONENTS];
+      for (unsigned i = 0; i < v->num_components; ++i)
+         comps[i] = nir_load_preamble(b, 1, v->bit_size, .base = base + (i * stride));
+
+      nir_ssa_def_rewrite_uses(v, nir_vec(b, comps, v->num_components));
+   } else {
+      for (unsigned i = 0; i < v->num_components; ++i)
+         nir_store_preamble(b, nir_channel(b, v, i), .base = base + (i * stride));
+
+      nir_instr_remove(instr);
+   }
+
+   return true;
+}
+
+static void
+def_size(nir_ssa_def *def, unsigned *size, unsigned *align)
+{
+   unsigned bit_size = MAX2(def->bit_size, 16);
+
+   *size = (bit_size * def->num_components) / 16;
+   *align = bit_size / 16;
+}
+
+static float
+instr_cost(nir_instr *instr, const void *data)
+{
+   switch (instr->type) {
+   case nir_instr_type_intrinsic:
+      switch (nir_instr_as_intrinsic(instr)->intrinsic) {
+      case nir_intrinsic_load_global:
+      case nir_intrinsic_load_global_constant:
+      case nir_intrinsic_load_ubo:
+         return 10.0;
+      default:
+         /* Assume it's a sysval or something */
+         return 0.0;
+      }
+
+   case nir_instr_type_tex:
+      /* Texturing involes lots of memory bandwidth */
+      return 20.0;
+
+   case nir_instr_type_alu:
+      /* We optimistically assume that moves get coalesced */
+      if (nir_op_is_vec(nir_instr_as_alu(instr)->op))
+         return 0.0;
+      else
+         return 2.0;
+
+   default:
+      return 1.0;
+   }
+}
+
+static float
+rewrite_cost(nir_ssa_def *def, const void *data)
+{
+   bool mov_needed = false;
+   nir_foreach_use (use, def) {
+      nir_instr *parent_instr = use->parent_instr;
+      if (parent_instr->type != nir_instr_type_alu) {
+         mov_needed = true;
+         break;
+      } else {
+         nir_alu_instr *alu = nir_instr_as_alu(parent_instr);
+         if (alu->op == nir_op_vec2 ||
+             alu->op == nir_op_vec3 ||
+             alu->op == nir_op_vec4 ||
+             alu->op == nir_op_mov) {
+            mov_needed = true;
+            break;
+         } else {
+            /* Assume for non-moves that the const is folded into the src */
+         }
+      }
+   }
+
+   return mov_needed ? def->num_components : 0;
+}
+
+static bool
+avoid_instr(const nir_instr *instr, const void *data)
+{
+   return false;
+}
+
+static const nir_opt_preamble_options preamble_options = {
+   .drawid_uniform = true,
+   .subgroup_size_uniform = true,
+   .def_size = def_size,
+   .instr_cost_cb = instr_cost,
+   .rewrite_cost_cb = rewrite_cost,
+   .avoid_instr_cb = avoid_instr,
+
+   /* Storage size 16-bit words. Should be 512, but we push some sysvals ad hoc
+    * in the backend compiler, so we need to reserve space. When we move UBO and
+    * VBO lowering to NIR, this can be bumped up to 512.
+    */
+   .preamble_storage_size = 256,
+};
+
+bool
+agx_nir_opt_preamble(nir_shader *nir, unsigned *preamble_size)
+{
+   bool progress = nir_opt_preamble(nir, &preamble_options, preamble_size);
+
+   /* If nir_opt_preamble made progress, the shader now has
+    * load_preamble/store_preamble intrinsics in it. These need to be
+    * scalarized for the backend to process them appropriately.
+    */
+   if (progress) {
+      nir_shader_instructions_pass(nir, nir_scalarize_preamble,
+                                   nir_metadata_block_index |
+                                   nir_metadata_dominance, NULL);
+   }
+
+   return progress;
+}

src/asahi/compiler/meson.build

@@ -24,6 +24,7 @@ libasahi_agx_files = files(
   'agx_dce.c',
   'agx_liveness.c',
   'agx_nir_lower_array_texture.c',
+  'agx_nir_opt_preamble.c',
   'agx_lower_64bit.c',
   'agx_lower_resinfo.c',
   'agx_lower_parallel_copy.c',