1/*
2 * Copyright (C) 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io>
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 "agx_compiler.h"
25
26/* SSA-based scalar dead code elimination */
27
28void
29agx_dce(agx_context *ctx)
30{
31   bool progress;
32   do {
33      progress = false;
34
35      BITSET_WORD *seen = calloc(BITSET_WORDS(ctx->alloc), sizeof(BITSET_WORD));
36
37      agx_foreach_instr_global(ctx, I) {
38         agx_foreach_src(I, s) {
39            if (I->src[s].type == AGX_INDEX_NORMAL)
40               BITSET_SET(seen, I->src[s].value);
41         }
42      }
43
44      agx_foreach_instr_global_safe_rev(ctx, I) {
45         if (!agx_opcodes_info[I->op].can_eliminate) continue;
46
47         bool needed = false;
48
49         agx_foreach_dest(I, d) {
50            if (I->dest[d].type == AGX_INDEX_NORMAL)
51               needed |= BITSET_TEST(seen, I->dest[d].value);
52            else if (I->dest[d].type != AGX_INDEX_NULL)
53               needed = true;
54         }
55
56         if (!needed) {
57            agx_remove_instruction(I);
58            progress = true;
59         }
60      }
61
62      free(seen);
63   } while (progress);
64}
65