1/*
2 * Copyright © 2020 Microsoft 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
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 */
23
24#include "nir.h"
25#include "nir_builder.h"
26
27static bool
28nir_scale_fdiv_instr(nir_builder *b, nir_instr *instr, UNUSED void *_data)
29{
30   if (instr->type != nir_instr_type_alu)
31      return false;
32
33   nir_alu_instr *alu = nir_instr_as_alu(instr);
34   if (alu->op != nir_op_fdiv || alu->src[0].src.ssa->bit_size != 32)
35      return false;
36
37   b->cursor = nir_before_instr(&alu->instr);
38
39   nir_ssa_def *fabs = nir_fabs(b, alu->src[1].src.ssa);
40   nir_ssa_def *big = nir_flt(b, nir_imm_int(b, 0x7e800000), fabs);
41   nir_ssa_def *small = nir_flt(b, fabs, nir_imm_int(b, 0x00800000));
42
43   nir_ssa_def *scaled_down_a = nir_fmul_imm(b, alu->src[0].src.ssa, 0.25);
44   nir_ssa_def *scaled_down_b = nir_fmul_imm(b, alu->src[1].src.ssa, 0.25);
45   nir_ssa_def *scaled_up_a = nir_fmul_imm(b, alu->src[0].src.ssa, 16777216.0);
46   nir_ssa_def *scaled_up_b = nir_fmul_imm(b, alu->src[1].src.ssa, 16777216.0);
47
48   nir_ssa_def *final_a =
49      nir_bcsel(b, big, scaled_down_a,
50     (nir_bcsel(b, small, scaled_up_a, alu->src[0].src.ssa)));
51   nir_ssa_def *final_b =
52      nir_bcsel(b, big, scaled_down_b,
53     (nir_bcsel(b, small, scaled_up_b, alu->src[1].src.ssa)));
54
55   nir_instr_rewrite_src_ssa(instr, &alu->src[0].src, final_a);
56   nir_instr_rewrite_src_ssa(instr, &alu->src[1].src, final_b);
57
58   return true;
59}
60
61/** Scale both sides of an fdiv if needed to prevent denorm flushing
62 *
63 * This may be needed to satisfy the precision requirements of OpenCL.  When
64 * fdiv is lowered to frcp+fmul, denorm flushing may cause the frcp to return
65 * zero even for finite floats.  This multiplies both sides of an fdiv by a
66 * constant, if needed, to prevent such flushing.
67 */
68bool
69nir_scale_fdiv(nir_shader *shader)
70{
71   return nir_shader_instructions_pass(shader, nir_scale_fdiv_instr,
72                                       nir_metadata_block_index |
73                                       nir_metadata_dominance,
74                                       NULL);
75}
76