mesa/src/compiler/nir/nir_lower_to_source_mods.c

/*
 * Copyright © 2014 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "nir.h"
#include "nir_builder.h"

/*
 * This pass lowers the neg, abs, and sat operations to source modifiers on
 * ALU operations to make things nicer for the backend.  It's just much
 * easier to not have them when we're doing optimizations.
 */

static void
alu_src_consume_abs(nir_alu_src *src)
{
   src->abs = true;
}

static void
alu_src_consume_negate(nir_alu_src *src)
{
   /* If abs is set on the source, the negate goes away */
   if (!src->abs)
      src->negate = !src->negate;
}

static bool
nir_lower_to_source_mods_instr(nir_builder *b, nir_instr *instr,
                               void *data)
{
   nir_lower_to_source_mods_flags options =
      *((nir_lower_to_source_mods_flags*) data);

   bool progress = false;

   if (instr->type != nir_instr_type_alu)
      return false;

   nir_alu_instr *alu = nir_instr_as_alu(instr);

   bool lower_abs = (nir_op_infos[alu->op].num_inputs < 3) ||
         (options & nir_lower_triop_abs);

   for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
      if (!alu->src[i].src.is_ssa)
         continue;

      if (alu->src[i].src.ssa->parent_instr->type != nir_instr_type_alu)
         continue;

      nir_alu_instr *parent = nir_instr_as_alu(alu->src[i].src.ssa->parent_instr);

      if (parent->dest.saturate)
         continue;

      if (nir_alu_type_get_base_type(nir_op_infos[alu->op].input_types[i]) != nir_type_float)
         continue;

      if (!(parent->op == nir_op_fabs && (options & nir_lower_fabs_source_mods)) &&
          !(parent->op == nir_op_fneg && (options & nir_lower_fneg_source_mods))) {
         continue;
      }

      if (nir_src_bit_size(alu->src[i].src) == 64)
         continue;

      /* We can only do a rewrite if the source we are copying is SSA.
       * Otherwise, moving the read might invalidly reorder reads/writes
       * on a register.
       */
      if (!parent->src[0].src.is_ssa)
         continue;

      if (!lower_abs && (parent->op == nir_op_fabs || parent->src[0].abs))
         continue;

      nir_instr_rewrite_src(instr, &alu->src[i].src, parent->src[0].src);

      /* Apply any modifiers that come from the parent opcode */
      if (parent->op == nir_op_fneg)
         alu_src_consume_negate(&alu->src[i]);
      if (parent->op == nir_op_fabs)
         alu_src_consume_abs(&alu->src[i]);

      /* Apply modifiers from the parent source */
      if (parent->src[0].negate)
         alu_src_consume_negate(&alu->src[i]);
      if (parent->src[0].abs)
         alu_src_consume_abs(&alu->src[i]);

      for (int j = 0; j < 4; ++j) {
         if (!nir_alu_instr_channel_used(alu, i, j))
            continue;
         alu->src[i].swizzle[j] = parent->src[0].swizzle[alu->src[i].swizzle[j]];
      }

      if (nir_ssa_def_is_unused(&parent->dest.dest.ssa))
         nir_instr_remove(&parent->instr);

      progress = true;
   }

   /* We've covered sources.  Now we're going to try and saturate the
    * destination if we can.
    */

   if (!alu->dest.dest.is_ssa)
      return progress;

   if (nir_dest_bit_size(alu->dest.dest) == 64)
      return progress;

   /* We can only saturate float destinations */
   if (nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type) !=
       nir_type_float)
      return progress;

   bool all_children_are_sat = true;
   nir_foreach_use_including_if(child_src, &alu->dest.dest.ssa) {
      if (child_src->is_if) {
         all_children_are_sat = false;
         break;
      }
  
      assert(child_src->is_ssa);
      nir_instr *child = child_src->parent_instr;
      if (child->type != nir_instr_type_alu) {
         all_children_are_sat = false;
         continue;
      }

      nir_alu_instr *child_alu = nir_instr_as_alu(child);
      if (child_alu->src[0].negate || child_alu->src[0].abs) {
         all_children_are_sat = false;
         continue;
      }

      if (child_alu->op != nir_op_fsat) {
         all_children_are_sat = false;
         continue;
      }
   }

   if (!all_children_are_sat)
      return progress;

   alu->dest.saturate = true;
   progress = true;

   nir_foreach_use(child_src, &alu->dest.dest.ssa) {
      assert(child_src->is_ssa);
      nir_alu_instr *child_alu = nir_instr_as_alu(child_src->parent_instr);

      child_alu->op = nir_op_mov;
      child_alu->dest.saturate = false;
      /* We could propagate the dest of our instruction to the
       * destinations of the uses here.  However, one quick round of
       * copy propagation will clean that all up and then we don't have
       * the complexity.
       */
   }

   return progress;
}

bool
nir_lower_to_source_mods(nir_shader *shader,
                         nir_lower_to_source_mods_flags options)
{
   return nir_shader_instructions_pass(shader,
                                       nir_lower_to_source_mods_instr,
                                       nir_metadata_block_index |
                                       nir_metadata_dominance,
                                       &options);
}