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      1 /*
      2  * Copyright  2016 Broadcom
      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 /**
     25  * @file vc4_opt_peephole_sf.c
     26  *
     27  * Quick optimization to eliminate unused or identical SF updates.
     28  */
     29 
     30 #include "vc4_qir.h"
     31 #include "util/u_math.h"
     32 
     33 static bool debug;
     34 
     35 static void
     36 dump_from(struct vc4_compile *c, struct qinst *inst, const char *type)
     37 {
     38         if (!debug)
     39                 return;
     40 
     41         fprintf(stderr, "optimizing %s: ", type);
     42         qir_dump_inst(c, inst);
     43         fprintf(stderr, "\n");
     44 }
     45 
     46 static void
     47 dump_to(struct vc4_compile *c, struct qinst *inst)
     48 {
     49         if (!debug)
     50                 return;
     51 
     52         fprintf(stderr, "to: ");
     53         qir_dump_inst(c, inst);
     54         fprintf(stderr, "\n");
     55 }
     56 
     57 static bool
     58 inst_srcs_updated(struct qinst *inst, struct qinst *writer)
     59 {
     60         /* If the sources get overwritten, stop tracking the
     61          * last instruction writing SF.
     62          */
     63         switch (writer->dst.file) {
     64         case QFILE_TEMP:
     65                 for (int i = 0; i < qir_get_nsrc(inst); i++) {
     66                         if (inst->src[i].file == QFILE_TEMP &&
     67                             inst->src[i].index == writer->dst.index) {
     68                                 return true;
     69                         }
     70                 }
     71                 return false;
     72         default:
     73                 return false;
     74         }
     75 }
     76 
     77 static bool
     78 src_file_varies_on_reread(struct qreg reg)
     79 {
     80         switch (reg.file) {
     81         case QFILE_VARY:
     82         case QFILE_VPM:
     83                 return true;
     84         default:
     85                 return false;
     86         }
     87 }
     88 
     89 static bool
     90 inst_result_equals(struct qinst *a, struct qinst *b)
     91 {
     92         if (a->op != b->op ||
     93             qir_depends_on_flags(a) ||
     94             qir_depends_on_flags(b)) {
     95                 return false;
     96         }
     97 
     98         for (int i = 0; i < qir_get_nsrc(a); i++) {
     99                 if (!qir_reg_equals(a->src[i], b->src[i]) ||
    100                     src_file_varies_on_reread(a->src[i]) ||
    101                     src_file_varies_on_reread(b->src[i])) {
    102                         return false;
    103                 }
    104         }
    105 
    106         return true;
    107 }
    108 
    109 static bool
    110 qir_opt_peephole_sf_block(struct vc4_compile *c, struct qblock *block)
    111 {
    112         bool progress = false;
    113         /* We don't have liveness dataflow analysis for flags, but we also
    114          * never generate a use of flags across control flow, so just treat
    115          * them as unused at block exit.
    116          */
    117         bool sf_live = false;
    118         struct qinst *last_sf = NULL;
    119 
    120         /* Walk the block from bottom to top, tracking if the SF is used, and
    121          * removing unused or repeated ones.
    122          */
    123         qir_for_each_inst_rev(inst, block) {
    124                 if (inst->sf) {
    125                         if (!sf_live) {
    126                                 /* Our instruction's SF isn't read, so drop it.
    127                                  */
    128                                 dump_from(c, inst, "dead SF");
    129                                 inst->sf = false;
    130                                 dump_to(c, inst);
    131                                 progress = true;
    132                         } else if (last_sf &&
    133                                    inst_result_equals(last_sf, inst)) {
    134                                 /* The last_sf sets up same value as inst, so
    135                                  * just drop the later one.
    136                                  */
    137                                 dump_from(c, last_sf, "repeated SF");
    138                                 last_sf->sf = false;
    139                                 dump_to(c, last_sf);
    140                                 progress = true;
    141                                 last_sf = inst;
    142                         } else {
    143                                 last_sf = inst;
    144                         }
    145                         sf_live = false;
    146                 }
    147 
    148                 if (last_sf) {
    149                         if (inst_srcs_updated(last_sf, inst))
    150                                 last_sf = NULL;
    151                 }
    152 
    153                 if (qir_depends_on_flags(inst))
    154                         sf_live = true;
    155         }
    156 
    157         return progress;
    158 }
    159 
    160 bool
    161 qir_opt_peephole_sf(struct vc4_compile *c)
    162 {
    163         bool progress = false;
    164 
    165         qir_for_each_block(block, c)
    166                 progress = qir_opt_peephole_sf_block(c, block) || progress;
    167 
    168         return progress;
    169 }
    170