1 /* 2 * Copyright 2016 Intel 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 26 static bool 27 instr_is_continue(nir_instr *instr) 28 { 29 if (instr->type != nir_instr_type_jump) 30 return false; 31 32 return nir_instr_as_jump(instr)->type == nir_jump_continue; 33 } 34 35 static bool 36 lower_trivial_continues_block(nir_block *block, nir_loop *loop) 37 { 38 bool progress = false; 39 nir_instr *first_instr = nir_block_first_instr(block); 40 if (!first_instr || instr_is_continue(first_instr)) { 41 /* The block contains only a continue if anything */ 42 nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node); 43 if (prev_node && prev_node->type == nir_cf_node_if) { 44 nir_if *prev_if = nir_cf_node_as_if(prev_node); 45 progress |= lower_trivial_continues_block( 46 nir_if_last_then_block(prev_if), loop); 47 progress |= lower_trivial_continues_block( 48 nir_if_last_else_block(prev_if), loop); 49 } 50 51 /* The lower_phis_to_regs helper is smart enough to push phi sources as 52 * far up if-ladders as it possibly can. In other words, the recursive 53 * calls above shouldn't be adding instructions to this block since it 54 * follows an if statement. 55 */ 56 first_instr = nir_block_first_instr(block); 57 assert(!first_instr || instr_is_continue(first_instr)); 58 } 59 60 nir_instr *last_instr = nir_block_last_instr(block); 61 if (!last_instr || !instr_is_continue(last_instr)) 62 return progress; 63 64 /* We're at the end of a block that goes straight through to the end of the 65 * loop and continues to the top. We can exit normally instead of jump. 66 */ 67 nir_lower_phis_to_regs_block(nir_loop_first_block(loop)); 68 nir_instr_remove(last_instr); 69 return true; 70 } 71 72 static bool 73 lower_trivial_continues_list(struct exec_list *cf_list, 74 bool list_ends_at_loop_tail, 75 nir_loop *loop) 76 { 77 bool progress = false; 78 foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { 79 bool at_loop_tail = list_ends_at_loop_tail && 80 &cf_node->node == exec_list_get_tail(cf_list); 81 switch (cf_node->type) { 82 case nir_cf_node_block: 83 break; 84 85 case nir_cf_node_if: { 86 nir_if *nif = nir_cf_node_as_if(cf_node); 87 if (lower_trivial_continues_list(&nif->then_list, at_loop_tail, loop)) 88 progress = true; 89 if (lower_trivial_continues_list(&nif->else_list, at_loop_tail, loop)) 90 progress = true; 91 break; 92 } 93 94 case nir_cf_node_loop: { 95 nir_loop *loop = nir_cf_node_as_loop(cf_node); 96 if (lower_trivial_continues_list(&loop->body, true, loop)) 97 progress = true; 98 if (lower_trivial_continues_block(nir_loop_last_block(loop), loop)) 99 progress = true; 100 break; 101 } 102 103 case nir_cf_node_function: 104 unreachable("Invalid cf type"); 105 } 106 } 107 108 return progress; 109 } 110 111 /** 112 * This simple pass gets rid of any "trivial" continues, i.e. those that are 113 * at the tail of a loop where we can just delete the continue instruction and 114 * control-flow will naturally and harmlessly take us back to the top of the 115 * loop. 116 */ 117 bool 118 nir_opt_trivial_continues(nir_shader *shader) 119 { 120 bool progress = false; 121 122 nir_foreach_function(function, shader) { 123 if (function->impl == NULL) 124 continue; 125 126 /* First we run the simple pass to get rid of pesky continues */ 127 if (lower_trivial_continues_list(&function->impl->body, false, NULL)) { 128 nir_metadata_preserve(function->impl, nir_metadata_none); 129 130 /* If that made progress, we're no longer really in SSA form. */ 131 nir_lower_regs_to_ssa_impl(function->impl); 132 progress = true; 133 } 134 } 135 136 return progress; 137 } 138