src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp

   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
  24 #include "brw_fs.h"
  25 #include "brw_fs_live_variables.h"
  26 #include "brw_cfg.h"
  27
  28 /** @file brw_fs_cmod_propagation.cpp
  29  *
  30  * Implements a pass that propagates the conditional modifier from a CMP x 0.0
  31  * instruction into the instruction that generated x. For instance, in this
  32  * sequence
  33  *
  34  *    add(8)          g70<1>F    g69<8,8,1>F    4096F
  35  *    cmp.ge.f0(8)    null       g70<8,8,1>F    0F
  36  *
  37  * we can do the comparison as part of the ADD instruction directly:
  38  *
  39  *    add.ge.f0(8)    g70<1>F    g69<8,8,1>F    4096F
  40  *
  41  * If there had been a use of the flag register and another CMP using g70
  42  *
  43  *    add.ge.f0(8)    g70<1>F    g69<8,8,1>F    4096F
  44  *    (+f0) sel(8)    g71<F>     g72<8,8,1>F    g73<8,8,1>F
  45  *    cmp.ge.f0(8)    null       g70<8,8,1>F    0F
  46  *
  47  * we can recognize that the CMP is generating the flag value that already
  48  * exists and therefore remove the instruction.
  49  */
  50
  51 static bool
  52 opt_cmod_propagation_local(bblock_t *block)
  53 {
  54    bool progress = false;
  55    int ip = block->end_ip + 1;
  56
  57    foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
  58       ip--;
  59
  60       if ((inst->opcode != BRW_OPCODE_AND &&
  61            inst->opcode != BRW_OPCODE_CMP &&
  62            inst->opcode != BRW_OPCODE_MOV) ||
  63           inst->predicate != BRW_PREDICATE_NONE ||
  64           !inst->dst.is_null() ||
  65           inst->src[0].file != GRF ||
  66           inst->src[0].abs)
  67          continue;
  68
  69       /* Only an AND.NZ can be propagated.  Many AND.Z instructions are
  70        * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
  71        * Propagating those would require inverting the condition on the CMP.
  72        * This changes both the flag value and the register destination of the
  73        * CMP.  That result may be used elsewhere, so we can't change its value
  74        * on a whim.
  75        */
  76       if (inst->opcode == BRW_OPCODE_AND &&
  77           !(inst->src[1].is_one() &&
  78             inst->conditional_mod == BRW_CONDITIONAL_NZ &&
  79             !inst->src[0].negate))
  80          continue;
  81
  82       if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero())
  83          continue;
  84
  85       if (inst->opcode == BRW_OPCODE_MOV &&
  86           inst->conditional_mod != BRW_CONDITIONAL_NZ)
  87          continue;
  88
  89       bool read_flag = false;
  90       foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst,
  91                                                   block) {
  92          if (scan_inst->overwrites_reg(inst->src[0])) {
  93             if (scan_inst->is_partial_write() ||
  94                 scan_inst->dst.reg_offset != inst->src[0].reg_offset)
  95                break;
  96
  97             /* This must be done before the dst.type check because the result
  98              * type of the AND will always be D, but the result of the CMP
  99              * could be anything.  The assumption is that the AND is just
 100              * figuring out what the result of the previous comparison was
 101              * instead of doing a new comparison with a different type.
 102              */
 103             if (inst->opcode == BRW_OPCODE_AND) {
 104                if (scan_inst->opcode == BRW_OPCODE_CMP) {
 105                   inst->remove(block);
 106                   progress = true;
 107                }
 108
 109                break;
 110             }
 111
 112             /* Comparisons operate differently for ints and floats */
 113             if (scan_inst->dst.type != inst->dst.type)
 114                break;
 115
 116             /* If the instruction generating inst's source also wrote the
 117              * flag, and inst is doing a simple .nz comparison, then inst
 118              * is redundant - the appropriate value is already in the flag
 119              * register.  Delete inst.
 120              */
 121             if (inst->conditional_mod == BRW_CONDITIONAL_NZ &&
 122                 !inst->src[0].negate &&
 123                 scan_inst->writes_flag()) {
 124                inst->remove(block);
 125                progress = true;
 126                break;
 127             }
 128
 129             /* Otherwise, try propagating the conditional. */
 130             enum brw_conditional_mod cond =
 131                inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)
 132                                    : inst->conditional_mod;
 133
 134             if (scan_inst->can_do_cmod() &&
 135                 ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
 136                  scan_inst->conditional_mod == cond)) {
 137                scan_inst->conditional_mod = cond;
 138                inst->remove(block);
 139                progress = true;
 140             }
 141             break;
 142          }
 143
 144          if (scan_inst->writes_flag())
 145             break;
 146
 147          read_flag = read_flag || scan_inst->reads_flag();
 148       }
 149    }
 150
 151    return progress;
 152 }
 153
 154 bool
 155 fs_visitor::opt_cmod_propagation()
 156 {
 157    bool progress = false;
 158
 159    foreach_block_reverse(block, cfg) {
 160       progress = opt_cmod_propagation_local(block) || progress;
 161    }
 162
 163    if (progress)
 164       invalidate_live_intervals();
 165
 166    return progress;
 167 }