--- /dev/null
+/*
+ * Copyright (C) 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"
+
+/* Sometimes we can get unreachable blocks from NIR. In particular this happens
+ * for blocks after an if where both sides end in a break/continue. These blocks
+ * are then reachable only via the physical CFG. This pass deletes these blocks
+ * and reroutes the physical edge past it.
+ */
+
+static void
+delete_block(struct ir3 *ir, struct ir3_block *block)
+{
+ struct ir3_instruction *end = NULL;
+ foreach_instr (instr, &block->instr_list) {
+ if (instr->opc == OPC_END) {
+ end = instr;
+ break;
+ }
+ }
+
+ /* The end block can be legitimately unreachable if the shader only exits via
+ * discarding. ir3_legalize will then insert a branch to the end. Keep the
+ * block around but delete all the other instructions and make the end not
+ * take any sources, so that we don't have any dangling references to other
+ * unreachable blocks.
+ */
+ if (end) {
+ foreach_instr_safe (instr, &block->instr_list) {
+ if (instr != end)
+ list_delinit(&instr->node);
+ }
+ end->srcs_count = 0;
+ return;
+ }
+
+ for (unsigned i = 0; i < 2; i++) {
+ struct ir3_block *succ = block->successors[i];
+ if (!succ)
+ continue;
+
+ unsigned pred_idx = ir3_block_get_pred_index(succ, block);
+
+ /* If this isn't the last predecessor, we swap it with the last before
+ * removing it.
+ */
+ bool swap_pred = pred_idx != succ->predecessors_count - 1;
+
+ foreach_instr (phi, &succ->instr_list) {
+ if (phi->opc != OPC_META_PHI)
+ break;
+
+ if (swap_pred)
+ phi->srcs[pred_idx] = phi->srcs[phi->srcs_count - 1];
+ phi->srcs_count--;
+ }
+ if (swap_pred) {
+ succ->predecessors[pred_idx] =
+ succ->predecessors[succ->predecessors_count - 1];
+ }
+ succ->predecessors_count--;
+ }
+
+ for (unsigned i = 0; i < 2; i++) {
+ struct ir3_block *succ = block->physical_successors[i];
+ if (!succ)
+ continue;
+
+ ir3_block_remove_physical_predecessor(succ, block);
+ }
+
+ if (block->physical_predecessors_count != 0) {
+ /* There should be only one physical predecessor, for the fallthrough
+ * edge.
+ */
+ assert(block->physical_predecessors_count == 1);
+ struct ir3_block *pred = block->physical_predecessors[0];
+ assert(block->node.next != &ir->block_list);
+ struct ir3_block *next = LIST_ENTRY(struct ir3_block, block->node.next, node);
+ if (pred->physical_successors[1] == block)
+ pred->physical_successors[1] = next;
+ else
+ pred->physical_successors[0] = next;
+ ir3_block_add_physical_predecessor(next, pred);
+ }
+}
+
+bool
+ir3_remove_unreachable(struct ir3 *ir)
+{
+ bool progress = false;
+ foreach_block_safe (block, &ir->block_list) {
+ if (block != ir3_start_block(ir) && block->predecessors_count == 0) {
+ delete_block(ir, block);
+ list_del(&block->node);
+ progress = true;
+ }
+ }
+
+ return progress;
+}