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 of
  30  *  - if (cond) discard to discard_if(cond) and
  31  *  - if (cond) demote to demote_if(cond)
  32  */
  33
  34 static bool
  35 nir_opt_conditional_discard_block(nir_builder *b, nir_block *block)
  36 {
  37    if (nir_cf_node_is_first(&block->cf_node))
  38       return false;
  39
  40    nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
  41    if (prev_node->type != nir_cf_node_if)
  42       return false;
  43
  44    nir_if *if_stmt = nir_cf_node_as_if(prev_node);
  45    nir_block *then_block = nir_if_first_then_block(if_stmt);
  46    nir_block *else_block = nir_if_first_else_block(if_stmt);
  47
  48    /* check there is only one else block and it is empty */
  49    if (nir_if_last_else_block(if_stmt) != else_block)
  50       return false;
  51    if (!exec_list_is_empty(&else_block->instr_list))
  52       return false;
  53
  54    /* check there is only one then block and it has only one instruction in it */
  55    if (nir_if_last_then_block(if_stmt) != then_block)
  56       return false;
  57    if (exec_list_is_empty(&then_block->instr_list))
  58       return false;
  59    if (exec_list_length(&then_block->instr_list) > 1)
  60       return false;
  61    /*
  62     * make sure no subsequent phi nodes point at this if.
  63     */
  64    nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
  65    nir_foreach_instr_safe(instr, after) {
  66       if (instr->type != nir_instr_type_phi)
  67          break;
  68       nir_phi_instr *phi = nir_instr_as_phi(instr);
  69
  70       nir_foreach_phi_src(phi_src, phi) {
  71          if (phi_src->pred == then_block ||
  72              phi_src->pred == else_block)
  73             return false;
  74       }
  75    }
  76
  77    /* Get the first instruction in the then block and confirm it is
  78     * a discard or a demote instruction.
  79     */
  80    nir_instr *instr = nir_block_first_instr(then_block);
  81    if (instr->type != nir_instr_type_intrinsic)
  82       return false;
  83
  84    nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  85    nir_intrinsic_op op = intrin->intrinsic;
  86    assert(if_stmt->condition.is_ssa);
  87    nir_ssa_def *cond = if_stmt->condition.ssa;
  88    b->cursor = nir_before_cf_node(prev_node);
  89
  90    switch (intrin->intrinsic) {
  91    case nir_intrinsic_discard:
  92       op = nir_intrinsic_discard_if;
  93       break;
  94    case nir_intrinsic_demote:
  95       op = nir_intrinsic_demote_if;
  96       break;
  97    case nir_intrinsic_discard_if:
  98    case nir_intrinsic_demote_if:
  99       assert(intrin->src[0].is_ssa);
 100       cond = nir_iand(b, cond, intrin->src[0].ssa);
 101       break;
 102    default:
 103       return false;
 104    }
 105
 106    nir_intrinsic_instr *discard_if =
 107       nir_intrinsic_instr_create(b->shader, op);
 108    discard_if->src[0] = nir_src_for_ssa(cond);
 109
 110    nir_instr_insert_before_cf(prev_node, &discard_if->instr);
 111    nir_instr_remove(&intrin->instr);
 112    nir_cf_node_remove(&if_stmt->cf_node);
 113
 114    return true;
 115 }
 116
 117 bool
 118 nir_opt_conditional_discard(nir_shader *shader)
 119 {
 120    bool progress = false;
 121
 122    nir_builder builder;
 123
 124    nir_foreach_function(function, shader) {
 125       if (function->impl) {
 126          nir_builder_init(&builder, function->impl);
 127
 128          bool impl_progress = false;
 129          nir_foreach_block_safe(block, function->impl) {
 130             if (nir_opt_conditional_discard_block(&builder, block))
 131                impl_progress = true;
 132          }
 133
 134          if (impl_progress) {
 135             nir_metadata_preserve(function->impl, nir_metadata_none);
 136             progress = true;
 137          } else {
 138             nir_metadata_preserve(function->impl, nir_metadata_all);
 139          }
 140       }
 141    }
 142    return progress;
 143 }