1/*
2 * Copyright (C) 2019 Collabora, Ltd.
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
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 *
23 * Authors (Collabora):
24 *   Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
25 */
26
27/**
28 * @file
29 *
30 * Flushes undefined SSA values to a zero vector fo the appropriate component
31 * count, to avoid undefined behaviour in the resulting shader. Not required
32 * for conformance as use of uninitialized variables is explicitly left
33 * undefined by the spec.  Works around buggy apps, however.
34 *
35 * Call immediately after nir_opt_undef. If called before, larger optimization
36 * opportunities from the former pass will be missed. If called outside of an
37 * optimization loop, constant propagation and algebraic optimizations won't be
38 * able to kick in to reduce stuff consuming the zero.
39 */
40
41#include "nir_builder.h"
42
43static bool
44lower_undef_instr_to_zero(nir_builder *b, nir_instr *instr, UNUSED void *_state)
45{
46   if (instr->type != nir_instr_type_ssa_undef)
47      return false;
48
49   nir_ssa_undef_instr *und = nir_instr_as_ssa_undef(instr);
50   b->cursor = nir_instr_remove(&und->instr);
51   nir_ssa_def *zero = nir_imm_zero(b, und->def.num_components,
52                                       und->def.bit_size);
53   nir_ssa_def_rewrite_uses(&und->def, zero);
54   return true;
55}
56
57bool
58nir_lower_undef_to_zero(nir_shader *shader)
59{
60   return nir_shader_instructions_pass(shader, lower_undef_instr_to_zero,
61                                       nir_metadata_block_index |
62                                       nir_metadata_dominance, NULL);
63}
64