pan/bi: Add simple constant folding pass

Cleans up swizzle lowering, and will be used for other cleanup as
well (fancy texturing tends to create a lot of foldable code).

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10392>

src/panfrost/bifrost/bi_opt_constant_fold.c

@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2020 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"
+
+/* Dead simple constant folding to cleanup compiler frontend patterns. Before
+ * adding a new pattern here, check why you need it and whether we can avoid
+ * generating the constant BIR at all. */
+
+static uint32_t
+bi_fold_constant(bi_instr *I, bool *unsupported)
+{
+        uint32_t a = I->src[0].value;
+        uint32_t b = I->src[1].value;
+
+        switch (I->op) {
+        case BI_OPCODE_SWZ_V2I16:
+        {
+                uint16_t lo = (a & 0xFFFF);
+                uint16_t hi = (a >> 16);
+
+                enum bi_swizzle swz = I->src[0].swizzle;
+                assert(swz < BI_SWIZZLE_H11);
+
+                /* Note order is H00, H01, H10, H11 */
+                return (((swz & (1 << 1)) ? hi : lo) << 0) |
+                        (((swz & (1 << 0)) ? hi : lo) << 16);
+        }
+
+        case BI_OPCODE_MKVEC_V2I16:
+        {
+                bool hi_a = I->src[0].swizzle & BI_SWIZZLE_H11;
+                bool hi_b = I->src[1].swizzle & BI_SWIZZLE_H11;
+
+                uint16_t lo = (hi_a ? (a >> 16) : (a & 0xFFFF));
+                uint16_t hi = (hi_b ? (b >> 16) : (b & 0xFFFF));
+
+                return (hi << 16) | lo;
+        }
+
+        default:
+                *unsupported = true;
+                return 0;
+        }
+}
+
+static bool
+bi_all_srcs_const(bi_instr *I)
+{
+        bi_foreach_src(I, s) {
+                enum bi_index_type type = I->src[s].type;
+
+                if (!(type == BI_INDEX_NULL || type == BI_INDEX_CONSTANT))
+                        return false;
+        }
+
+        return true;
+}
+
+void
+bi_opt_constant_fold(bi_context *ctx)
+{
+        bi_foreach_instr_global_safe(ctx, ins) {
+                if (!bi_all_srcs_const(ins)) continue;
+
+                bool unsupported = false;
+                uint32_t replace = bi_fold_constant(ins, &unsupported);
+                if (unsupported) continue;
+
+                /* Replace with constant move, to be copypropped */
+                bi_builder b = bi_init_builder(ctx, bi_after_instr(ins));
+                bi_mov_i32_to(&b, ins->dest[0], bi_imm_u32(replace));
+                bi_remove_instruction(ins);
+        }
+}

src/panfrost/bifrost/bifrost_compile.c

@@ -3078,8 +3078,12 @@ bifrost_compile_shader_nir(nir_shader *nir,
                 block->base.name = block_source_count++;
         }
 
+        /* Runs before constant folding */
+        bi_lower_swizzle(ctx);
+
         /* Runs before copy prop */
         bi_opt_push_ubo(ctx);
+        bi_opt_constant_fold(ctx);
         bi_opt_copy_prop(ctx);
         bi_opt_dead_code_eliminate(ctx, false);
 
@@ -3088,8 +3092,6 @@ bifrost_compile_shader_nir(nir_shader *nir,
                 bi_lower_branch(block);
         }
 
-        bi_lower_swizzle(ctx);
-
         if (bifrost_debug & BIFROST_DBG_SHADERS && !skip_internal)
                 bi_print_shader(ctx, stdout);
         bi_schedule(ctx);

src/panfrost/bifrost/compiler.h

@@ -753,6 +753,7 @@ void bi_print_shader(bi_context *ctx, FILE *fp);
 void bi_opt_copy_prop(bi_context *ctx);
 void bi_opt_dead_code_eliminate(bi_context *ctx, bool soft);
 void bi_opt_push_ubo(bi_context *ctx);
+void bi_opt_constant_fold(bi_context *ctx);
 void bi_lower_swizzle(bi_context *ctx);
 void bi_schedule(bi_context *ctx);
 void bi_assign_scoreboard(bi_context *ctx);

src/panfrost/bifrost/meson.build

@@ -24,6 +24,7 @@ libpanfrost_bifrost_files = files(
   'bi_liveness.c',
   'bi_lower_swizzle.c',
   'bi_print.c',
+  'bi_opt_constant_fold.c',
   'bi_opt_copy_prop.c',
   'bi_opt_dce.c',
   'bi_opt_push_ubo.c',