src/glsl/nir/nir_gs_count_vertices.c

   1 /*
   2  * Copyright © 2015 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 #include "nir_builder.h"
  26
  27 static nir_intrinsic_instr *
  28 as_intrinsic(nir_instr *instr, nir_intrinsic_op op)
  29 {
  30    if (instr->type != nir_instr_type_intrinsic)
  31       return NULL;
  32
  33    nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  34    if (intrin->intrinsic != op)
  35       return NULL;
  36
  37    return intrin;
  38 }
  39
  40 static nir_intrinsic_instr *
  41 as_set_vertex_count(nir_instr *instr)
  42 {
  43    return as_intrinsic(instr, nir_intrinsic_set_vertex_count);
  44 }
  45
  46 /**
  47  * If a geometry shader emits a constant number of vertices, return the
  48  * number of vertices.  Otherwise, return -1 (unknown).
  49  *
  50  * This only works if you've used nir_lower_gs_intrinsics() to do vertex
  51  * counting at the NIR level.
  52  */
  53 int
  54 nir_gs_count_vertices(nir_shader *shader)
  55 {
  56    int count = -1;
  57
  58    nir_foreach_overload(shader, overload) {
  59       if (!overload->impl)
  60          continue;
  61
  62       /* set_vertex_count intrinsics only appear in predecessors of the
  63        * end block.  So we don't need to walk all of them.
  64        */
  65       struct set_entry *entry;
  66       set_foreach(overload->impl->end_block->predecessors, entry) {
  67          nir_block *block = (nir_block *) entry->key;
  68
  69          nir_foreach_instr_reverse(block, instr) {
  70             nir_intrinsic_instr *intrin = as_set_vertex_count(instr);
  71             if (!intrin)
  72                continue;
  73
  74             nir_const_value *val = nir_src_as_const_value(intrin->src[0]);
  75             /* We've found a non-constant value.  Bail. */
  76             if (!val)
  77                return -1;
  78
  79             if (count == -1)
  80                count = val->i[0];
  81
  82             /* We've found contradictory set_vertex_count intrinsics.
  83              * This can happen if there are early-returns in main() and
  84              * different paths emit different numbers of vertices.
  85              */
  86             if (count != val->i[0])
  87                return -1;
  88          }
  89       }
  90    }
  91
  92    return count;
  93 }