mesa/src/intel/compiler/brw_opt_saturate_propagation.cpp

/*
 * Copyright © 2013 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 "brw_analysis.h"
#include "brw_fs.h"
#include "brw_cfg.h"

/** @file
 *
 * Implements a pass that propagates the SAT modifier from a MOV.SAT into the
 * instruction that produced the source of the MOV.SAT, thereby allowing the
 * MOV's src and dst to be coalesced and the MOV removed.
 *
 * For instance,
 *
 *    ADD     tmp, src0, src1
 *    MOV.SAT dst, tmp
 *
 * would be transformed into
 *
 *    ADD.SAT tmp, src0, src1
 *    MOV     dst, tmp
 */

static bool
propagate_sat(brw_inst *inst, brw_inst *scan_inst)
{
   if (scan_inst->dst.type != inst->dst.type) {
      scan_inst->dst.type = inst->dst.type;
      for (int i = 0; i < scan_inst->sources; i++) {
         scan_inst->src[i].type = inst->dst.type;
      }
   }

   if (inst->src[0].negate) {
      if (scan_inst->opcode == BRW_OPCODE_MUL) {
         scan_inst->src[0].negate = !scan_inst->src[0].negate;
         inst->src[0].negate = false;
      } else if (scan_inst->opcode == BRW_OPCODE_MAD) {
         for (int i = 0; i < 2; i++) {
            if (scan_inst->src[i].file == IMM) {
               brw_reg_negate_immediate(&scan_inst->src[i]);
            } else {
               scan_inst->src[i].negate = !scan_inst->src[i].negate;
            }
         }
         inst->src[0].negate = false;
      } else if (scan_inst->opcode == BRW_OPCODE_ADD) {
         if (scan_inst->src[1].file == IMM) {
            if (!brw_reg_negate_immediate(&scan_inst->src[1])) {
               return false;
            }
         } else {
            scan_inst->src[1].negate = !scan_inst->src[1].negate;
         }
         scan_inst->src[0].negate = !scan_inst->src[0].negate;
         inst->src[0].negate = false;
      } else {
         return false;
      }
   }

   scan_inst->saturate = true;
   inst->saturate = false;
   return true;
}

static bool
opt_saturate_propagation_local(fs_visitor &s, bblock_t *block)
{
   bool progress = false;
   int ip = block->end_ip + 1;

   foreach_inst_in_block_reverse(brw_inst, inst, block) {
      ip--;

      if (inst->opcode != BRW_OPCODE_MOV ||
          !inst->saturate ||
          inst->dst.file != VGRF ||
          inst->dst.type != inst->src[0].type ||
          inst->src[0].file != VGRF ||
          inst->src[0].abs)
         continue;

      const brw_def_analysis &defs = s.def_analysis.require();
      brw_inst *def = defs.get(inst->src[0]);

      if (def != NULL) {
         if (def->exec_size != inst->exec_size)
            continue;

         if (def->dst.type != inst->dst.type && !def->can_change_types())
            continue;

         if (def->flags_written(s.devinfo) != 0)
            continue;

         if (def->saturate) {
            inst->saturate = false;
            progress = true;
            continue;
         } else if (defs.get_use_count(def->dst) == 1 &&
                    def->can_do_saturate() &&
                    propagate_sat(inst, def)) {
            progress = true;
            continue;
         }

         /* If the def is in a different block the liveness based pass will
          * not be able to make progress, so skip it.
          */
         if (block != defs.get_block(inst->src[0]))
            continue;
      }

      const brw_live_variables &live = s.live_analysis.require();
      int src_var = live.var_from_reg(inst->src[0]);
      int src_end_ip = live.end[src_var];

      bool interfered = false;
      foreach_inst_in_block_reverse_starting_from(brw_inst, scan_inst, inst) {
         if (scan_inst->exec_size == inst->exec_size &&
             regions_overlap(scan_inst->dst, scan_inst->size_written,
                             inst->src[0], inst->size_read(s.devinfo, 0))) {
            if (scan_inst->is_partial_write() ||
                (scan_inst->dst.type != inst->dst.type &&
                 !scan_inst->can_change_types()))
               break;

            if (scan_inst->flags_written(s.devinfo) != 0)
               break;

            if (scan_inst->saturate) {
               inst->saturate = false;
               progress = true;
            } else if (src_end_ip == ip || inst->dst.equals(inst->src[0])) {
               if (scan_inst->can_do_saturate() &&
                   propagate_sat(inst, scan_inst)) {
                  progress = true;
               }
            }
            break;
         }
         for (int i = 0; i < scan_inst->sources; i++) {
            if (scan_inst->src[i].file == VGRF &&
                scan_inst->src[i].nr == inst->src[0].nr &&
                regions_overlap(
                  scan_inst->src[i], scan_inst->size_read(s.devinfo, i),
                  inst->src[0], inst->size_read(s.devinfo, 0))) {
               if (scan_inst->opcode != BRW_OPCODE_MOV ||
                   !scan_inst->saturate ||
                   scan_inst->src[0].abs ||
                   scan_inst->src[0].negate ||
                   scan_inst->src[0].abs != inst->src[0].abs ||
                   scan_inst->src[0].negate != inst->src[0].negate) {
                  interfered = true;
                  break;
               }
            }
         }

         if (interfered)
            break;
      }
   }

   return progress;
}

bool
brw_opt_saturate_propagation(fs_visitor &s)
{
   bool progress = false;

   foreach_block (block, s.cfg) {
      progress = opt_saturate_propagation_local(s, block) || progress;
   }

   /* Live intervals are still valid. */

   return progress;
}