1/*
2 * Copyright (C) 2021 Valve Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21 * SOFTWARE.
22 */
23
24#include "ir3.h"
25
26/* Sometimes we can get unreachable blocks from NIR. In particular this happens
27 * for blocks after an if where both sides end in a break/continue. These blocks
28 * are then reachable only via the physical CFG. This pass deletes these blocks
29 * and reroutes the physical edge past it.
30 */
31
32static void
33delete_block(struct ir3 *ir, struct ir3_block *block)
34{
35   struct ir3_instruction *end = NULL;
36   foreach_instr (instr, &block->instr_list) {
37      if (instr->opc == OPC_END) {
38         end = instr;
39         break;
40      }
41   }
42
43   /* The end block can be legitimately unreachable if the shader only exits via
44    * discarding. ir3_legalize will then insert a branch to the end. Keep the
45    * block around but delete all the other instructions and make the end not
46    * take any sources, so that we don't have any dangling references to other
47    * unreachable blocks.
48    */
49   if (end) {
50      foreach_instr_safe (instr, &block->instr_list) {
51         if (instr != end)
52            list_delinit(&instr->node);
53      }
54      end->srcs_count = 0;
55      return;
56   }
57
58   for (unsigned i = 0; i < 2; i++) {
59      struct ir3_block *succ = block->successors[i];
60      if (!succ)
61         continue;
62
63      unsigned pred_idx = ir3_block_get_pred_index(succ, block);
64
65      /* If this isn't the last predecessor, we swap it with the last before
66       * removing it.
67       */
68      bool swap_pred = pred_idx != succ->predecessors_count - 1;
69
70      foreach_instr (phi, &succ->instr_list) {
71         if (phi->opc != OPC_META_PHI)
72            break;
73
74         if (swap_pred)
75            phi->srcs[pred_idx] = phi->srcs[phi->srcs_count - 1];
76         phi->srcs_count--;
77      }
78      if (swap_pred) {
79         succ->predecessors[pred_idx] =
80            succ->predecessors[succ->predecessors_count - 1];
81      }
82      succ->predecessors_count--;
83   }
84
85   for (unsigned i = 0; i < 2; i++) {
86      struct ir3_block *succ = block->physical_successors[i];
87      if (!succ)
88         continue;
89
90      ir3_block_remove_physical_predecessor(succ, block);
91   }
92
93   if (block->physical_predecessors_count != 0) {
94      /* There should be only one physical predecessor, for the fallthrough
95       * edge.
96       */
97      assert(block->physical_predecessors_count == 1);
98      struct ir3_block *pred = block->physical_predecessors[0];
99      assert(block->node.next != &ir->block_list);
100      struct ir3_block *next = list_entry(block->node.next, struct ir3_block, node);
101      if (pred->physical_successors[1] == block)
102         pred->physical_successors[1] = next;
103      else
104         pred->physical_successors[0] = next;
105      ir3_block_add_physical_predecessor(next, pred);
106   }
107}
108
109bool
110ir3_remove_unreachable(struct ir3 *ir)
111{
112   bool progress = false;
113   foreach_block_safe (block, &ir->block_list) {
114      if (block != ir3_start_block(ir) && block->predecessors_count == 0) {
115         delete_block(ir, block);
116         list_del(&block->node);
117         progress = true;
118      }
119   }
120
121   return progress;
122}
123