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      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 }
    125