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      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  * Authors:
     24  *    Jason Ekstrand (jason (at) jlekstrand.net)
     25  *
     26  */
     27 
     28 #include "brw_nir.h"
     29 #include "compiler/nir/nir_builder.h"
     30 
     31 /*
     32  * Implements a small peephole optimization that looks for a multiply that
     33  * is only ever used in an add and replaces both with an fma.
     34  */
     35 
     36 static inline bool
     37 are_all_uses_fadd(nir_ssa_def *def)
     38 {
     39    if (!list_empty(&def->if_uses))
     40       return false;
     41 
     42    nir_foreach_use(use_src, def) {
     43       nir_instr *use_instr = use_src->parent_instr;
     44 
     45       if (use_instr->type != nir_instr_type_alu)
     46          return false;
     47 
     48       nir_alu_instr *use_alu = nir_instr_as_alu(use_instr);
     49       switch (use_alu->op) {
     50       case nir_op_fadd:
     51          break; /* This one's ok */
     52 
     53       case nir_op_imov:
     54       case nir_op_fmov:
     55       case nir_op_fneg:
     56       case nir_op_fabs:
     57          assert(use_alu->dest.dest.is_ssa);
     58          if (!are_all_uses_fadd(&use_alu->dest.dest.ssa))
     59             return false;
     60          break;
     61 
     62       default:
     63          return false;
     64       }
     65    }
     66 
     67    return true;
     68 }
     69 
     70 static nir_alu_instr *
     71 get_mul_for_src(nir_alu_src *src, int num_components,
     72                 uint8_t swizzle[4], bool *negate, bool *abs)
     73 {
     74    uint8_t swizzle_tmp[4];
     75    assert(src->src.is_ssa && !src->abs && !src->negate);
     76 
     77    nir_instr *instr = src->src.ssa->parent_instr;
     78    if (instr->type != nir_instr_type_alu)
     79       return NULL;
     80 
     81    nir_alu_instr *alu = nir_instr_as_alu(instr);
     82 
     83    /* We want to bail if any of the other ALU operations involved is labled
     84     * exact.  One reason for this is that, while the value that is changing is
     85     * actually the result of the add and not the multiply, the intention of
     86     * the user when they specify an exact multiply is that they want *that*
     87     * value and what they don't care about is the add.  Another reason is that
     88     * SPIR-V explicitly requires this behaviour.
     89     */
     90    if (alu->exact)
     91       return NULL;
     92 
     93    switch (alu->op) {
     94    case nir_op_imov:
     95    case nir_op_fmov:
     96       alu = get_mul_for_src(&alu->src[0], num_components, swizzle, negate, abs);
     97       break;
     98 
     99    case nir_op_fneg:
    100       alu = get_mul_for_src(&alu->src[0], num_components, swizzle, negate, abs);
    101       *negate = !*negate;
    102       break;
    103 
    104    case nir_op_fabs:
    105       alu = get_mul_for_src(&alu->src[0], num_components, swizzle, negate, abs);
    106       *negate = false;
    107       *abs = true;
    108       break;
    109 
    110    case nir_op_fmul:
    111       /* Only absorb a fmul into a ffma if the fmul is only used in fadd
    112        * operations.  This prevents us from being too aggressive with our
    113        * fusing which can actually lead to more instructions.
    114        */
    115       if (!are_all_uses_fadd(&alu->dest.dest.ssa))
    116          return NULL;
    117       break;
    118 
    119    default:
    120       return NULL;
    121    }
    122 
    123    if (!alu)
    124       return NULL;
    125 
    126    /* Copy swizzle data before overwriting it to avoid setting a wrong swizzle.
    127     *
    128     * Example:
    129     *   Former swizzle[] = xyzw
    130     *   src->swizzle[] = zyxx
    131     *
    132     *   Expected output swizzle = zyxx
    133     *   If we reuse swizzle in the loop, then output swizzle would be zyzz.
    134     */
    135    memcpy(swizzle_tmp, swizzle, 4*sizeof(uint8_t));
    136    for (int i = 0; i < num_components; i++)
    137       swizzle[i] = swizzle_tmp[src->swizzle[i]];
    138 
    139    return alu;
    140 }
    141 
    142 /**
    143  * Given a list of (at least two) nir_alu_src's, tells if any of them is a
    144  * constant value and is used only once.
    145  */
    146 static bool
    147 any_alu_src_is_a_constant(nir_alu_src srcs[])
    148 {
    149    for (unsigned i = 0; i < 2; i++) {
    150       if (srcs[i].src.ssa->parent_instr->type == nir_instr_type_load_const) {
    151          nir_load_const_instr *load_const =
    152             nir_instr_as_load_const (srcs[i].src.ssa->parent_instr);
    153 
    154          if (list_is_singular(&load_const->def.uses) &&
    155              list_empty(&load_const->def.if_uses)) {
    156             return true;
    157          }
    158       }
    159    }
    160 
    161    return false;
    162 }
    163 
    164 static bool
    165 brw_nir_opt_peephole_ffma_block(nir_builder *b, nir_block *block)
    166 {
    167    bool progress = false;
    168 
    169    nir_foreach_instr_safe(instr, block) {
    170       if (instr->type != nir_instr_type_alu)
    171          continue;
    172 
    173       nir_alu_instr *add = nir_instr_as_alu(instr);
    174       if (add->op != nir_op_fadd)
    175          continue;
    176 
    177       assert(add->dest.dest.is_ssa);
    178       if (add->exact)
    179          continue;
    180 
    181       assert(add->src[0].src.is_ssa && add->src[1].src.is_ssa);
    182 
    183       /* This, is the case a + a.  We would rather handle this with an
    184        * algebraic reduction than fuse it.  Also, we want to only fuse
    185        * things where the multiply is used only once and, in this case,
    186        * it would be used twice by the same instruction.
    187        */
    188       if (add->src[0].src.ssa == add->src[1].src.ssa)
    189          continue;
    190 
    191       nir_alu_instr *mul;
    192       uint8_t add_mul_src, swizzle[4];
    193       bool negate, abs;
    194       for (add_mul_src = 0; add_mul_src < 2; add_mul_src++) {
    195          for (unsigned i = 0; i < 4; i++)
    196             swizzle[i] = i;
    197 
    198          negate = false;
    199          abs = false;
    200 
    201          mul = get_mul_for_src(&add->src[add_mul_src],
    202                                add->dest.dest.ssa.num_components,
    203                                swizzle, &negate, &abs);
    204 
    205          if (mul != NULL)
    206             break;
    207       }
    208 
    209       if (mul == NULL)
    210          continue;
    211 
    212       unsigned bit_size = add->dest.dest.ssa.bit_size;
    213 
    214       nir_ssa_def *mul_src[2];
    215       mul_src[0] = mul->src[0].src.ssa;
    216       mul_src[1] = mul->src[1].src.ssa;
    217 
    218       /* If any of the operands of the fmul and any of the fadd is a constant,
    219        * we bypass because it will be more efficient as the constants will be
    220        * propagated as operands, potentially saving two load_const instructions.
    221        */
    222       if (any_alu_src_is_a_constant(mul->src) &&
    223           any_alu_src_is_a_constant(add->src)) {
    224          continue;
    225       }
    226 
    227       b->cursor = nir_before_instr(&add->instr);
    228 
    229       if (abs) {
    230          for (unsigned i = 0; i < 2; i++)
    231             mul_src[i] = nir_fabs(b, mul_src[i]);
    232       }
    233 
    234       if (negate)
    235          mul_src[0] = nir_fneg(b, mul_src[0]);
    236 
    237       nir_alu_instr *ffma = nir_alu_instr_create(b->shader, nir_op_ffma);
    238       ffma->dest.saturate = add->dest.saturate;
    239       ffma->dest.write_mask = add->dest.write_mask;
    240 
    241       for (unsigned i = 0; i < 2; i++) {
    242          ffma->src[i].src = nir_src_for_ssa(mul_src[i]);
    243          for (unsigned j = 0; j < add->dest.dest.ssa.num_components; j++)
    244             ffma->src[i].swizzle[j] = mul->src[i].swizzle[swizzle[j]];
    245       }
    246       nir_alu_src_copy(&ffma->src[2], &add->src[1 - add_mul_src], ffma);
    247 
    248       assert(add->dest.dest.is_ssa);
    249 
    250       nir_ssa_dest_init(&ffma->instr, &ffma->dest.dest,
    251                         add->dest.dest.ssa.num_components,
    252                         bit_size,
    253                         add->dest.dest.ssa.name);
    254       nir_ssa_def_rewrite_uses(&add->dest.dest.ssa,
    255                                nir_src_for_ssa(&ffma->dest.dest.ssa));
    256 
    257       nir_builder_instr_insert(b, &ffma->instr);
    258       assert(list_empty(&add->dest.dest.ssa.uses));
    259       nir_instr_remove(&add->instr);
    260 
    261       progress = true;
    262    }
    263 
    264    return progress;
    265 }
    266 
    267 static bool
    268 brw_nir_opt_peephole_ffma_impl(nir_function_impl *impl)
    269 {
    270    bool progress = false;
    271 
    272    nir_builder builder;
    273    nir_builder_init(&builder, impl);
    274 
    275    nir_foreach_block(block, impl) {
    276       progress |= brw_nir_opt_peephole_ffma_block(&builder, block);
    277    }
    278 
    279    if (progress)
    280       nir_metadata_preserve(impl, nir_metadata_block_index |
    281                                   nir_metadata_dominance);
    282 
    283    return progress;
    284 }
    285 
    286 bool
    287 brw_nir_opt_peephole_ffma(nir_shader *shader)
    288 {
    289    bool progress = false;
    290 
    291    nir_foreach_function(function, shader) {
    292       if (function->impl)
    293          progress |= brw_nir_opt_peephole_ffma_impl(function->impl);
    294    }
    295 
    296    return progress;
    297 }
    298