1/* 2 * Copyright © 2015 Connor Abbott 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: 24 * Connor Abbott (cwabbott0@gmail.com) 25 * 26 */ 27 28#include "nir.h" 29#include "nir_builder.h" 30 31static nir_alu_instr * 32get_parent_mov(nir_ssa_def *ssa) 33{ 34 if (ssa->parent_instr->type != nir_instr_type_alu) 35 return NULL; 36 37 nir_alu_instr *alu = nir_instr_as_alu(ssa->parent_instr); 38 return (alu->op == nir_op_imov || alu->op == nir_op_fmov) ? alu : NULL; 39} 40 41static bool 42matching_mov(nir_alu_instr *mov1, nir_ssa_def *ssa) 43{ 44 if (!mov1) 45 return false; 46 47 nir_alu_instr *mov2 = get_parent_mov(ssa); 48 return mov2 && nir_alu_srcs_equal(mov1, mov2, 0, 0); 49} 50 51/* 52 * This is a pass for removing phi nodes that look like: 53 * a = phi(b, b, b, ...) 54 * 55 * Note that we can't ignore undef sources here, or else we may create a 56 * situation where the definition of b isn't dominated by its uses. We're 57 * allowed to do this since the definition of b must dominate all of the 58 * phi node's predecessors, which means it must dominate the phi node as well 59 * as all of the phi node's uses. In essence, the phi node acts as a copy 60 * instruction. b can't be another phi node in the same block, since the only 61 * time when phi nodes can source other phi nodes defined in the same block is 62 * at the loop header, and in that case one of the sources of the phi has to 63 * be from before the loop and that source can't be b. 64 */ 65 66static bool 67remove_phis_block(nir_block *block, nir_builder *b) 68{ 69 bool progress = false; 70 71 nir_foreach_instr_safe(instr, block) { 72 if (instr->type != nir_instr_type_phi) 73 break; 74 75 nir_phi_instr *phi = nir_instr_as_phi(instr); 76 77 nir_ssa_def *def = NULL; 78 nir_alu_instr *mov = NULL; 79 bool srcs_same = true; 80 81 nir_foreach_phi_src(src, phi) { 82 assert(src->src.is_ssa); 83 84 /* For phi nodes at the beginning of loops, we may encounter some 85 * sources from backedges that point back to the destination of the 86 * same phi, i.e. something like: 87 * 88 * a = phi(a, b, ...) 89 * 90 * We can safely ignore these sources, since if all of the normal 91 * sources point to the same definition, then that definition must 92 * still dominate the phi node, and the phi will still always take 93 * the value of that definition. 94 */ 95 if (src->src.ssa == &phi->dest.ssa) 96 continue; 97 98 if (def == NULL) { 99 def = src->src.ssa; 100 mov = get_parent_mov(def); 101 } else { 102 if (src->src.ssa != def && !matching_mov(mov, src->src.ssa)) { 103 srcs_same = false; 104 break; 105 } 106 } 107 } 108 109 if (!srcs_same) 110 continue; 111 112 /* We must have found at least one definition, since there must be at 113 * least one forward edge. 114 */ 115 assert(def != NULL); 116 117 if (mov) { 118 /* If the sources were all mov's from the same source with the same 119 * swizzle, then we can't just pick a random move because it may not 120 * dominate the phi node. Instead, we need to emit our own move after 121 * the phi which uses the shared source, and rewrite uses of the phi 122 * to use the move instead. This is ok, because while the mov's may 123 * not all dominate the phi node, their shared source does. 124 */ 125 126 b->cursor = nir_after_phis(block); 127 def = mov->op == nir_op_imov ? 128 nir_imov_alu(b, mov->src[0], def->num_components) : 129 nir_fmov_alu(b, mov->src[0], def->num_components); 130 } 131 132 assert(phi->dest.is_ssa); 133 nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def)); 134 nir_instr_remove(instr); 135 136 progress = true; 137 } 138 139 return progress; 140} 141 142static bool 143remove_phis_impl(nir_function_impl *impl) 144{ 145 bool progress = false; 146 nir_builder bld; 147 nir_builder_init(&bld, impl); 148 149 nir_foreach_block(block, impl) { 150 progress |= remove_phis_block(block, &bld); 151 } 152 153 if (progress) { 154 nir_metadata_preserve(impl, nir_metadata_block_index | 155 nir_metadata_dominance); 156 } 157 158 return progress; 159} 160 161bool 162nir_opt_remove_phis(nir_shader *shader) 163{ 164 bool progress = false; 165 166 nir_foreach_function(function, shader) 167 if (function->impl) 168 progress = remove_phis_impl(function->impl) || progress; 169 170 return progress; 171} 172 173