ir3: Add dominance infrastructure

Mostly lifted from nir.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9842>

src/freedreno/ir3/ir3.h

@@ -577,6 +577,14 @@ struct ir3_block {
 	 */
 	void *data;
 
+	uint32_t index;
+
+	struct ir3_block *imm_dom;
+	DECLARE_ARRAY(struct ir3_block *, dom_children);
+
+	uint32_t dom_pre_index;
+	uint32_t dom_post_index;
+
 #ifdef DEBUG
 	uint32_t serialno;
 #endif
@@ -602,6 +610,9 @@ void ir3_block_add_predecessor(struct ir3_block *block, struct ir3_block *pred);
 void ir3_block_remove_predecessor(struct ir3_block *block, struct ir3_block *pred);
 unsigned ir3_block_get_pred_index(struct ir3_block *block, struct ir3_block *pred);
 
+void ir3_calc_dominance(struct ir3 *ir);
+bool ir3_block_dominates(struct ir3_block *a, struct ir3_block *b);
+
 struct ir3_shader_variant;
 
 struct ir3 * ir3_create(struct ir3_compiler *compiler, struct ir3_shader_variant *v);

src/freedreno/ir3/ir3_dominance.c

@@ -0,0 +1,126 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ * 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 "ir3.h"
+#include "ralloc.h"
+
+/*
+ * Implements the algorithms for computing the dominance tree and the
+ * dominance frontier from "A Simple, Fast Dominance Algorithm" by Cooper,
+ * Harvey, and Kennedy.
+ */
+
+static struct ir3_block *
+intersect(struct ir3_block *b1, struct ir3_block *b2)
+{
+	while (b1 != b2) {
+		/*
+		 * Note, the comparisons here are the opposite of what the paper says
+		 * because we index blocks from beginning -> end (i.e. reverse
+		 * post-order) instead of post-order like they assume.
+		 */
+		while (b1->index > b2->index)
+			b1 = b1->imm_dom;
+		while (b2->index > b1->index)
+			b2 = b2->imm_dom;
+	}
+
+	return b1;
+}
+
+
+static bool
+calc_dominance(struct ir3_block *block)
+{
+	struct ir3_block *new_idom = NULL;
+	for (unsigned i = 0; i < block->predecessors_count; i++) {
+		struct ir3_block *pred = block->predecessors[i];
+
+		if (pred->imm_dom) {
+			if (new_idom)
+				new_idom = intersect(pred, new_idom);
+			else
+				new_idom = pred;
+		}
+	}
+
+	if (block->imm_dom != new_idom) {
+		block->imm_dom = new_idom;
+		return true;
+	}
+
+	return false;
+}
+
+static unsigned
+calc_dfs_indices(struct ir3_block *block, unsigned index)
+{
+	block->dom_pre_index = index++;
+	for (unsigned i = 0; i < block->dom_children_count; i++)
+		index = calc_dfs_indices(block->dom_children[i], index);
+	block->dom_post_index = index++;
+	return index;
+}
+
+void
+ir3_calc_dominance(struct ir3 *ir)
+{
+	unsigned i = 0;
+	foreach_block (block, &ir->block_list) {
+		block->index = i++;
+		if (block == ir3_start_block(ir))
+			block->imm_dom = block;
+		else
+			block->imm_dom = NULL;
+		block->dom_children = NULL;
+		block->dom_children_count = block->dom_children_sz = 0;
+	}
+
+	bool progress = true;
+	while (progress) {
+		progress = false;
+		foreach_block (block, &ir->block_list) {
+			if (block != ir3_start_block(ir))
+				progress |= calc_dominance(block);
+		}
+	}
+
+	ir3_start_block(ir)->imm_dom = NULL;
+
+	foreach_block (block, &ir->block_list) {
+		if (block->imm_dom)
+			array_insert(block->imm_dom, block->imm_dom->dom_children, block);
+	}
+
+	calc_dfs_indices(ir3_start_block(ir), 0);
+}
+
+/* Return true if a dominates b. This includes if a == b. */
+bool ir3_block_dominates(struct ir3_block *a, struct ir3_block *b)
+{
+	return a->dom_pre_index <= b->dom_pre_index &&
+		   a->dom_post_index >= b->dom_post_index;
+}
+

src/freedreno/ir3/meson.build

@@ -78,6 +78,7 @@ libfreedreno_ir3_files = files(
   'ir3_cp_postsched.c',
   'ir3_dce.c',
   'ir3_delay.c',
+  'ir3_dominance.c',
   'ir3_disk_cache.c',
   'ir3_group.c',
   'ir3_image.c',