pan/bi: Add dead code elimination pass

Now that we have liveness analysis, we can cleanup the IR considerably.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4150>

src/panfrost/bifrost/bi_opt_dce.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2018 Alyssa Rosenzweig
+ * Copyright (C) 2019-2020 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 "util/u_memory.h"
+
+bool
+bi_opt_dead_code_eliminate(bi_context *ctx, bi_block *block)
+{
+        bool progress = false;
+        unsigned temp_count = bi_max_temp(ctx);
+
+        bi_invalidate_liveness(ctx);
+        bi_compute_liveness(ctx);
+
+        uint16_t *live = mem_dup(block->base.live_out, temp_count * sizeof(uint16_t));
+
+        bi_foreach_instr_in_block_safe_rev(block, ins) {
+                if (ins->dest && !(ins->dest & BIR_SPECIAL)) {
+                        if (!live[ins->dest]) {
+                                bi_remove_instruction(ins);
+                                progress |= true;
+                        }
+                }
+
+                bi_liveness_ins_update(live, ins, temp_count);
+        }
+
+        free(live);
+
+        return progress;
+}

src/panfrost/bifrost/bifrost_compile.c

@@ -841,6 +841,17 @@ bifrost_compile_shader_nir(nir_shader *nir, panfrost_program *program, unsigned
                 break; /* TODO: Multi-function shaders */
         }
 
+        bool progress = false;
+
+        do {
+                progress = false;
+
+                bi_foreach_block(ctx, _block) {
+                        bi_block *block = (bi_block *) _block;
+                        progress |= bi_opt_dead_code_eliminate(ctx, block);
+                }
+        } while(progress);
+
         bi_print_shader(ctx, stdout);
         bi_schedule(ctx);
 

src/panfrost/bifrost/compiler.h

@@ -378,7 +378,7 @@ bi_remove_instruction(bi_instruction *ins)
 /* Keep me synced please so we can check src & BIR_SPECIAL */
 
 #define BIR_SPECIAL        ((BIR_INDEX_REGISTER | BIR_INDEX_UNIFORM) | \
-        (BIR_INDEX_CONSTANT | BIR_INDEX_ZERO)
+        (BIR_INDEX_CONSTANT | BIR_INDEX_ZERO))
 
 static inline unsigned
 bi_max_temp(bi_context *ctx)
@@ -501,6 +501,7 @@ uint16_t bi_bytemask_of_read_components(bi_instruction *ins, unsigned node);
 
 /* BIR passes */
 
+bool bi_opt_dead_code_eliminate(bi_context *ctx, bi_block *block);
 void bi_schedule(bi_context *ctx);
 
 /* Liveness */

src/panfrost/bifrost/meson.build

@@ -23,6 +23,7 @@ libpanfrost_bifrost_files = files(
   'disassemble.c',
   'bi_liveness.c',
   'bi_print.c',
+  'bi_opt_dce.c',
   'bi_schedule.c',
   'bi_tables.c',
   'bir.c',