src/compiler/nir/nir_lower_to_source_mods.c

   1 /*
   2  * Copyright © 2014 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  * Authors:
  24  *    Jason Ekstrand (jason@jlekstrand.net)
  25  *
  26  */
  27
  28 #include "nir.h"
  29
  30 /*
  31  * This pass lowers the neg, abs, and sat operations to source modifiers on
  32  * ALU operations to make things nicer for the backend.  It's just much
  33  * easier to not have them when we're doing optimizations.
  34  */
  35
  36 static bool
  37 nir_lower_to_source_mods_block(nir_block *block)
  38 {
  39    nir_foreach_instr(instr, block) {
  40       if (instr->type != nir_instr_type_alu)
  41          continue;
  42
  43       nir_alu_instr *alu = nir_instr_as_alu(instr);
  44
  45       for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
  46          if (!alu->src[i].src.is_ssa)
  47             continue;
  48
  49          if (alu->src[i].src.ssa->parent_instr->type != nir_instr_type_alu)
  50             continue;
  51
  52          nir_alu_instr *parent = nir_instr_as_alu(alu->src[i].src.ssa->parent_instr);
  53
  54          if (parent->dest.saturate)
  55             continue;
  56
  57          switch (nir_alu_type_get_base_type(nir_op_infos[alu->op].input_types[i])) {
  58          case nir_type_float:
  59             if (parent->op != nir_op_fmov)
  60                continue;
  61             break;
  62          case nir_type_int:
  63             if (parent->op != nir_op_imov)
  64                continue;
  65             break;
  66          default:
  67             continue;
  68          }
  69
  70          /* We can only do a rewrite if the source we are copying is SSA.
  71           * Otherwise, moving the read might invalidly reorder reads/writes
  72           * on a register.
  73           */
  74          if (!parent->src[0].src.is_ssa)
  75             continue;
  76
  77          nir_instr_rewrite_src(instr, &alu->src[i].src, parent->src[0].src);
  78          if (alu->src[i].abs) {
  79             /* abs trumps both neg and abs, do nothing */
  80          } else {
  81             alu->src[i].negate = (alu->src[i].negate != parent->src[0].negate);
  82             alu->src[i].abs |= parent->src[0].abs;
  83          }
  84
  85          for (int j = 0; j < 4; ++j) {
  86             if (!nir_alu_instr_channel_used(alu, i, j))
  87                continue;
  88             alu->src[i].swizzle[j] = parent->src[0].swizzle[alu->src[i].swizzle[j]];
  89          }
  90
  91          if (list_empty(&parent->dest.dest.ssa.uses) &&
  92              list_empty(&parent->dest.dest.ssa.if_uses))
  93             nir_instr_remove(&parent->instr);
  94       }
  95
  96       switch (alu->op) {
  97       case nir_op_fsat:
  98          alu->op = nir_op_fmov;
  99          alu->dest.saturate = true;
 100          break;
 101       case nir_op_ineg:
 102          alu->op = nir_op_imov;
 103          alu->src[0].negate = !alu->src[0].negate;
 104          break;
 105       case nir_op_fneg:
 106          alu->op = nir_op_fmov;
 107          alu->src[0].negate = !alu->src[0].negate;
 108          break;
 109       case nir_op_iabs:
 110          alu->op = nir_op_imov;
 111          alu->src[0].abs = true;
 112          alu->src[0].negate = false;
 113          break;
 114       case nir_op_fabs:
 115          alu->op = nir_op_fmov;
 116          alu->src[0].abs = true;
 117          alu->src[0].negate = false;
 118          break;
 119       default:
 120          break;
 121       }
 122
 123       /* We've covered sources.  Now we're going to try and saturate the
 124        * destination if we can.
 125        */
 126
 127       if (!alu->dest.dest.is_ssa)
 128          continue;
 129
 130       /* We can only saturate float destinations */
 131       if (nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type) !=
 132           nir_type_float)
 133          continue;
 134
 135       if (!list_empty(&alu->dest.dest.ssa.if_uses))
 136          continue;
 137
 138       bool all_children_are_sat = true;
 139       nir_foreach_use(&alu->dest.dest.ssa, child_src) {
 140          assert(child_src->is_ssa);
 141          nir_instr *child = child_src->parent_instr;
 142          if (child->type != nir_instr_type_alu) {
 143             all_children_are_sat = false;
 144             continue;
 145          }
 146
 147          nir_alu_instr *child_alu = nir_instr_as_alu(child);
 148          if (child_alu->src[0].negate || child_alu->src[0].abs) {
 149             all_children_are_sat = false;
 150             continue;
 151          }
 152
 153          if (child_alu->op != nir_op_fsat &&
 154              !(child_alu->op == nir_op_fmov && child_alu->dest.saturate)) {
 155             all_children_are_sat = false;
 156             continue;
 157          }
 158       }
 159
 160       if (!all_children_are_sat)
 161          continue;
 162
 163       alu->dest.saturate = true;
 164
 165       nir_foreach_use(&alu->dest.dest.ssa, child_src) {
 166          assert(child_src->is_ssa);
 167          nir_instr *child = child_src->parent_instr;
 168          assert(child->type == nir_instr_type_alu);
 169          nir_alu_instr *child_alu = nir_instr_as_alu(child);
 170
 171          child_alu->op = nir_op_fmov;
 172          child_alu->dest.saturate = false;
 173          /* We could propagate the dest of our instruction to the
 174           * destinations of the uses here.  However, one quick round of
 175           * copy propagation will clean that all up and then we don't have
 176           * the complexity.
 177           */
 178       }
 179    }
 180
 181    return true;
 182 }
 183
 184 void
 185 nir_lower_to_source_mods(nir_shader *shader)
 186 {
 187    nir_foreach_function(function, shader) {
 188       if (function->impl) {
 189          nir_foreach_block(block, function->impl) {
 190             nir_lower_to_source_mods_block(block);
 191          }
 192       }
 193    }
 194 }