pan/bi: Add dual texture fusing pass

Bifrost supports a special "dual texture" instruction, sampling from two
textures at once at the same coordinate. Each subinstruction is highly
restricted (a subset of TEXS_2D); together, they are represented by TEXC
with a special dual texture operation descriptor. Add an optimization
pass to fuse these instructions.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13723>

src/panfrost/bifrost/bi_opt_dual_tex.c

@@ -0,0 +1,154 @@
+/*
+ * Copyright (C) 2021 Collabora, Ltd.
+ *
+ * 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.h"
+#include "bi_builder.h"
+
+#define XXH_INLINE_ALL
+#include "xxhash.h"
+
+/* Fuse pairs of TEXS_2D instructions into a single dual texture TEXC, if both
+ * sample at the same coordinate with the default LOD mode for the shader stage
+ * (computed LOD in fragment shaders, else zero LOD) and immediate
+ * texture/sampler indices 0...3.
+ *
+ * Fusing across basic block boundaries is not expected to be useful, as it
+ * increases register pressure and causes redundant memory traffic. As such, we
+ * use a local optimization pass.
+ *
+ * To pair ops efficiently, we maintain a set (backed by a hash table) using
+ * only the coordinate sources for hashing and equality. Hence the pass runs in
+ * O(n) worst case expected time for n insturctions in a block. We reject
+ * invalid texture instructions quickly to reduce the constant factor.
+ *
+ * Dual texture instructions have skip flags, like normal texture instructions.
+ * Adding a skip flag to an instruction that doesn't have it is illegal, but
+ * removing a skip flag from one that has it is legal. Accordingly, set the
+ * fused TEXC's skip to the logical AND of the unfused TEXS flags. We run the
+ * optimization pass to run after bi_analyze_helper_requirements.
+ */
+
+static inline bool
+bi_can_fuse_dual_tex(bi_instr *I, bool fuse_zero_lod)
+{
+        return (I->op == BI_OPCODE_TEXS_2D_F32 || I->op == BI_OPCODE_TEXS_2D_F16) &&
+               (I->texture_index < 4 && I->sampler_index < 4) &&
+               (I->lod_mode == fuse_zero_lod);
+}
+
+static enum bifrost_texture_format
+bi_format_for_texs_2d(enum bi_opcode op)
+{
+        switch (op) {
+        case BI_OPCODE_TEXS_2D_F32: return BIFROST_TEXTURE_FORMAT_F32;
+        case BI_OPCODE_TEXS_2D_F16: return BIFROST_TEXTURE_FORMAT_F16;
+        default:                    unreachable("Invalid TEXS_2D instruction");
+        }
+}
+
+static void
+bi_fuse_dual(bi_context *ctx, bi_instr *I1, bi_instr *I2)
+{
+        /* Construct a texture operation descriptor for the dual texture */
+        struct bifrost_dual_texture_operation desc = {
+                .mode = BIFROST_TEXTURE_OPERATION_DUAL,
+
+                .primary_texture_index = I1->texture_index,
+                .primary_sampler_index = I1->sampler_index,
+                .primary_format = bi_format_for_texs_2d(I1->op),
+                .primary_mask = 0xF,
+
+                .secondary_texture_index = I2->texture_index,
+                .secondary_sampler_index = I2->sampler_index,
+                .secondary_format = bi_format_for_texs_2d(I2->op),
+                .secondary_mask = 0xF,
+        };
+
+        /* LOD mode is implied in a shader stage */
+        assert(I1->lod_mode == I2->lod_mode);
+
+        /* Insert before the earlier instruction in case its result is consumed
+         * before the later instruction
+         */
+        bi_builder b = bi_init_builder(ctx, bi_before_instr(I1));
+
+        bi_instr *I = bi_texc_to(&b,
+                        I1->dest[0], I2->dest[0], bi_null(), /* staging */
+                        I1->src[0], I1->src[1], /* coordinates */
+                        bi_imm_u32(bi_dual_tex_as_u32(desc)), I1->lod_mode,
+                        bi_count_write_registers(I1, 0),
+                        bi_count_write_registers(I2, 0));
+
+        I->skip = I1->skip && I2->skip;
+
+        bi_remove_instruction(I1);
+        bi_remove_instruction(I2);
+}
+
+#define HASH(hash, data) XXH32(&(data), sizeof(data), hash)
+
+static uint32_t
+coord_hash(const void *key)
+{
+        const bi_instr *I = key;
+
+        return XXH32(&I->src[0], sizeof(I->src[0]) + sizeof(I->src[1]), 0);
+}
+
+static bool
+coord_equal(const void *key1, const void *key2)
+{
+        const bi_instr *I = key1;
+        const bi_instr *J = key2;
+
+        return memcmp(&I->src[0], &J->src[0],
+                      sizeof(I->src[0]) + sizeof(I->src[1])) == 0;
+}
+
+static void
+bi_opt_fuse_dual_texture_block(bi_context *ctx, bi_block *block)
+{
+        struct set *set = _mesa_set_create(ctx, coord_hash, coord_equal);
+        bool fuse_zero_lod = (ctx->stage != MESA_SHADER_FRAGMENT);
+        bool found = false;
+
+        bi_foreach_instr_in_block_safe(block, I) {
+                if (!bi_can_fuse_dual_tex(I, fuse_zero_lod)) continue;
+
+                struct set_entry *ent = _mesa_set_search_or_add(set, I, &found);
+
+                if (found) {
+                        bi_fuse_dual(ctx, (bi_instr *) ent->key, I);
+                        _mesa_set_remove(set, ent);
+                }
+        }
+}
+
+void
+bi_opt_fuse_dual_texture(bi_context *ctx)
+{
+        bi_foreach_block(ctx, block) {
+                bi_opt_fuse_dual_texture_block(ctx, block);
+        }
+
+}

src/panfrost/bifrost/compiler.h

@@ -905,6 +905,7 @@ void bi_opt_cse(bi_context *ctx);
 void bi_opt_mod_prop_forward(bi_context *ctx);
 void bi_opt_mod_prop_backward(bi_context *ctx);
 void bi_opt_dead_code_eliminate(bi_context *ctx);
+void bi_opt_fuse_dual_texture(bi_context *ctx);
 void bi_opt_dce_post_ra(bi_context *ctx);
 void bi_opt_push_ubo(bi_context *ctx);
 void bi_lower_swizzle(bi_context *ctx);

src/panfrost/bifrost/meson.build

@@ -34,6 +34,7 @@ libpanfrost_bifrost_files = files(
   'bi_opt_cse.c',
   'bi_opt_push_ubo.c',
   'bi_opt_mod_props.c',
+  'bi_opt_dual_tex.c',
   'bi_pack.c',
   'bi_ra.c',
   'bi_schedule.c',