src/compiler/nir/nir_opt_conditional_discard.c

   1 /*
   2  * Copyright © 2016 Red Hat
   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
  27 /** @file nir_opt_conditional_discard.c
  28  *
  29  * Handles optimization of lowering if (cond) discard to discard_if(cond).
  30  */
  31
  32 static bool
  33 nir_opt_conditional_discard_block(nir_builder *b, nir_block *block)
  34 {
  35    if (nir_cf_node_is_first(&block->cf_node))
  36       return false;
  37
  38    nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
  39    if (prev_node->type != nir_cf_node_if)
  40       return false;
  41
  42    nir_if *if_stmt = nir_cf_node_as_if(prev_node);
  43    nir_block *then_block = nir_if_first_then_block(if_stmt);
  44    nir_block *else_block = nir_if_first_else_block(if_stmt);
  45
  46    /* check there is only one else block and it is empty */
  47    if (nir_if_last_else_block(if_stmt) != else_block)
  48       return false;
  49    if (!exec_list_is_empty(&else_block->instr_list))
  50       return false;
  51
  52    /* check there is only one then block and it has only one instruction in it */
  53    if (nir_if_last_then_block(if_stmt) != then_block)
  54       return false;
  55    if (exec_list_is_empty(&then_block->instr_list))
  56       return false;
  57    if (exec_list_length(&then_block->instr_list) > 1)
  58       return false;
  59    /*
  60     * make sure no subsequent phi nodes point at this if.
  61     */
  62    nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
  63    nir_foreach_instr_safe(instr, after) {
  64       if (instr->type != nir_instr_type_phi)
  65          break;
  66       nir_phi_instr *phi = nir_instr_as_phi(instr);
  67
  68       nir_foreach_phi_src(phi_src, phi) {
  69          if (phi_src->pred == then_block ||
  70              phi_src->pred == else_block)
  71             return false;
  72       }
  73    }
  74
  75    /* Get the first instruction in the then block and confirm it is
  76     * a discard or a discard_if
  77     */
  78    nir_instr *instr = nir_block_first_instr(then_block);
  79    if (instr->type != nir_instr_type_intrinsic)
  80       return false;
  81
  82    nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  83    if (intrin->intrinsic != nir_intrinsic_discard &&
  84        intrin->intrinsic != nir_intrinsic_discard_if)
  85       return false;
  86
  87    nir_src cond;
  88
  89    b->cursor = nir_before_cf_node(prev_node);
  90    if (intrin->intrinsic == nir_intrinsic_discard)
  91       cond = if_stmt->condition;
  92    else
  93       cond = nir_src_for_ssa(nir_iand(b,
  94                                       nir_ssa_for_src(b, if_stmt->condition, 1),
  95                                       nir_ssa_for_src(b, intrin->src[0], 1)));
  96
  97    nir_intrinsic_instr *discard_if =
  98       nir_intrinsic_instr_create(b->shader, nir_intrinsic_discard_if);
  99    nir_src_copy(&discard_if->src[0], &cond, discard_if);
 100
 101    nir_instr_insert_before_cf(prev_node, &discard_if->instr);
 102    nir_instr_remove(&intrin->instr);
 103    nir_cf_node_remove(&if_stmt->cf_node);
 104
 105    return true;
 106 }
 107
 108 bool
 109 nir_opt_conditional_discard(nir_shader *shader)
 110 {
 111    bool progress = false;
 112
 113    nir_builder builder;
 114
 115    nir_foreach_function(function, shader) {
 116       if (function->impl) {
 117          nir_builder_init(&builder, function->impl);
 118          nir_foreach_block_safe(block, function->impl) {
 119             progress |= nir_opt_conditional_discard_block(&builder, block);
 120          }
 121       }
 122    }
 123    return progress;
 124 }