mesa/src/intel/compiler/brw_vec4_cmod_propagation.cpp

/*
 * Copyright © 2015 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.
 *
 */

/** @file brw_vec4_cmod_propagation.cpp
 *
 * Really similar to brw_fs_cmod_propagation but adapted to vec4 needs. Check
 * brw_fs_cmod_propagation for further details on the rationale behind this
 * optimization.
 */

#include "brw_vec4.h"
#include "brw_cfg.h"
#include "brw_eu.h"

namespace brw {

static bool
writemasks_incompatible(const vec4_instruction *earlier,
                        const vec4_instruction *later)
{
   return (earlier->dst.writemask != WRITEMASK_X &&
           earlier->dst.writemask != WRITEMASK_XYZW) ||
          (earlier->dst.writemask == WRITEMASK_XYZW &&
           later->src[0].swizzle != BRW_SWIZZLE_XYZW) ||
          (later->dst.writemask & ~earlier->dst.writemask) != 0;
}

static bool
opt_cmod_propagation_local(bblock_t *block)
{
   bool progress = false;
   int ip = block->end_ip + 1;

   foreach_inst_in_block_reverse_safe(vec4_instruction, inst, block) {
      ip--;

      if ((inst->opcode != BRW_OPCODE_AND &&
           inst->opcode != BRW_OPCODE_CMP &&
           inst->opcode != BRW_OPCODE_MOV) ||
          inst->predicate != BRW_PREDICATE_NONE ||
          !inst->dst.is_null() ||
          (inst->src[0].file != VGRF && inst->src[0].file != ATTR &&
           inst->src[0].file != UNIFORM))
         continue;

      /* An ABS source modifier can only be handled when processing a compare
       * with a value other than zero.
       */
      if (inst->src[0].abs &&
          (inst->opcode != BRW_OPCODE_CMP || inst->src[1].is_zero()))
         continue;

      if (inst->opcode == BRW_OPCODE_AND &&
          !(inst->src[1].is_one() &&
            inst->conditional_mod == BRW_CONDITIONAL_NZ &&
            !inst->src[0].negate))
         continue;

      if (inst->opcode == BRW_OPCODE_MOV &&
          inst->conditional_mod != BRW_CONDITIONAL_NZ)
         continue;

      bool read_flag = false;
      foreach_inst_in_block_reverse_starting_from(vec4_instruction, scan_inst, inst) {
         /* A CMP with a second source of zero can match with anything.  A CMP
          * with a second source that is not zero can only match with an ADD
          * instruction.
          */
         if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero()) {
            bool negate;

            if (scan_inst->opcode != BRW_OPCODE_ADD)
               goto not_match;

            if (writemasks_incompatible(scan_inst, inst))
               goto not_match;

            /* A CMP is basically a subtraction.  The result of the
             * subtraction must be the same as the result of the addition.
             * This means that one of the operands must be negated.  So (a +
             * b) vs (a == -b) or (a + -b) vs (a == b).
             */
            if ((inst->src[0].equals(scan_inst->src[0]) &&
                 inst->src[1].negative_equals(scan_inst->src[1])) ||
                (inst->src[0].equals(scan_inst->src[1]) &&
                 inst->src[1].negative_equals(scan_inst->src[0]))) {
               negate = false;
            } else if ((inst->src[0].negative_equals(scan_inst->src[0]) &&
                        inst->src[1].equals(scan_inst->src[1])) ||
                       (inst->src[0].negative_equals(scan_inst->src[1]) &&
                        inst->src[1].equals(scan_inst->src[0]))) {
               negate = true;
            } else {
               goto not_match;
            }

            if (scan_inst->exec_size != inst->exec_size ||
                scan_inst->group != inst->group)
               goto not_match;

            /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
             *
             *    * Note that the [post condition signal] bits generated at
             *      the output of a compute are before the .sat.
             *
             * So we don't have to bail if scan_inst has saturate.
             */

            /* Otherwise, try propagating the conditional. */
            const enum brw_conditional_mod cond =
               negate ? brw_swap_cmod(inst->conditional_mod)
                      : inst->conditional_mod;

            if (scan_inst->can_do_cmod() &&
                ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
                 scan_inst->conditional_mod == cond)) {
               scan_inst->conditional_mod = cond;
               inst->remove(block);
               progress = true;
            }
            break;
         }

         if (regions_overlap(inst->src[0], inst->size_read(0),
                             scan_inst->dst, scan_inst->size_written)) {
            if ((scan_inst->predicate && scan_inst->opcode != BRW_OPCODE_SEL) ||
                scan_inst->dst.offset != inst->src[0].offset ||
                writemasks_incompatible(scan_inst, inst) ||
                scan_inst->exec_size != inst->exec_size ||
                scan_inst->group != inst->group) {
               break;
            }

            /* CMP's result is the same regardless of dest type. */
            if (inst->conditional_mod == BRW_CONDITIONAL_NZ &&
                scan_inst->opcode == BRW_OPCODE_CMP &&
                (inst->dst.type == BRW_REGISTER_TYPE_D ||
                 inst->dst.type == BRW_REGISTER_TYPE_UD)) {
               inst->remove(block);
               progress = true;
               break;
            }

            /* If the AND wasn't handled by the previous case, it isn't safe
             * to remove it.
             */
            if (inst->opcode == BRW_OPCODE_AND)
               break;

            /* Comparisons operate differently for ints and floats */
            if (scan_inst->dst.type != inst->dst.type &&
                (scan_inst->dst.type == BRW_REGISTER_TYPE_F ||
                 inst->dst.type == BRW_REGISTER_TYPE_F))
               break;

            /* If the instruction generating inst's source also wrote the
             * flag, and inst is doing a simple .nz comparison, then inst
             * is redundant - the appropriate value is already in the flag
             * register.  Delete inst.
             */
            if (inst->conditional_mod == BRW_CONDITIONAL_NZ &&
                !inst->src[0].negate &&
                scan_inst->writes_flag()) {
               inst->remove(block);
               progress = true;
               break;
            }

            /* The conditional mod of the CMP/CMPN instructions behaves
             * specially because the flag output is not calculated from the
             * result of the instruction, but the other way around, which
             * means that even if the condmod to propagate and the condmod
             * from the CMP instruction are the same they will in general give
             * different results because they are evaluated based on different
             * inputs.
             */
            if (scan_inst->opcode == BRW_OPCODE_CMP ||
                scan_inst->opcode == BRW_OPCODE_CMPN)
               break;

            /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
             *
             *    * Note that the [post condition signal] bits generated at
             *      the output of a compute are before the .sat.
             */
            if (scan_inst->saturate)
               break;

            /* From the Sky Lake PRM, Vol 2a, "Multiply":
             *
             *    "When multiplying integer data types, if one of the sources
             *    is a DW, the resulting full precision data is stored in
             *    the accumulator. However, if the destination data type is
             *    either W or DW, the low bits of the result are written to
             *    the destination register and the remaining high bits are
             *    discarded. This results in undefined Overflow and Sign
             *    flags. Therefore, conditional modifiers and saturation
             *    (.sat) cannot be used in this case.
             *
             * We just disallow cmod propagation on all integer multiplies.
             */
            if (!brw_reg_type_is_floating_point(scan_inst->dst.type) &&
                scan_inst->opcode == BRW_OPCODE_MUL)
               break;

            /* Otherwise, try propagating the conditional. */
            enum brw_conditional_mod cond =
               inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)
                                   : inst->conditional_mod;

            if (scan_inst->can_do_cmod() &&
                ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
                 scan_inst->conditional_mod == cond)) {
               scan_inst->conditional_mod = cond;
               inst->remove(block);
               progress = true;
            }
            break;
         }

      not_match:
         if (scan_inst->writes_flag())
            break;

         read_flag = read_flag || scan_inst->reads_flag();
      }
   }

   return progress;
}

bool
vec4_visitor::opt_cmod_propagation()
{
   bool progress = false;

   foreach_block_reverse(block, cfg) {
      progress = opt_cmod_propagation_local(block) || progress;
   }

   if (progress)
      invalidate_live_intervals();

   return progress;
}

} /* namespace brw */