src/glsl/nir/nir_opt_peephole_ffma.c

   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@jlekstrand.net)
  25  *
  26  */
  27
  28 #include "nir.h"
  29
  30 /*
  31  * Implements a small peephole optimization that looks for a multiply that
  32  * is only ever used in an add and replaces both with an fma.
  33  */
  34
  35 struct peephole_ffma_state {
  36    void *mem_ctx;
  37    nir_function_impl *impl;
  38    bool progress;
  39 };
  40
  41 static inline bool
  42 are_all_uses_fadd(nir_ssa_def *def)
  43 {
  44    if (def->if_uses->entries > 0)
  45       return false;
  46
  47    struct set_entry *use_iter;
  48    set_foreach(def->uses, use_iter) {
  49       nir_instr *use_instr = (nir_instr *)use_iter->key;
  50
  51       if (use_instr->type != nir_instr_type_alu)
  52          return false;
  53
  54       nir_alu_instr *use_alu = nir_instr_as_alu(use_instr);
  55       switch (use_alu->op) {
  56       case nir_op_fadd:
  57          break; /* This one's ok */
  58
  59       case nir_op_imov:
  60       case nir_op_fmov:
  61       case nir_op_fneg:
  62       case nir_op_fabs:
  63          assert(use_alu->dest.dest.is_ssa);
  64          if (!are_all_uses_fadd(&use_alu->dest.dest.ssa))
  65             return false;
  66          break;
  67
  68       default:
  69          return false;
  70       }
  71    }
  72
  73    return true;
  74 }
  75
  76 static nir_alu_instr *
  77 get_mul_for_src(nir_alu_src *src, uint8_t swizzle[4], bool *negate, bool *abs)
  78 {
  79    assert(src->src.is_ssa && !src->abs && !src->negate);
  80
  81    nir_instr *instr = src->src.ssa->parent_instr;
  82    if (instr->type != nir_instr_type_alu)
  83       return NULL;
  84
  85    nir_alu_instr *alu = nir_instr_as_alu(instr);
  86    switch (alu->op) {
  87    case nir_op_imov:
  88    case nir_op_fmov:
  89       alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
  90       break;
  91
  92    case nir_op_fneg:
  93       alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
  94       *negate = !*negate;
  95       break;
  96
  97    case nir_op_fabs:
  98       alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
  99       *negate = false;
 100       *abs = true;
 101       break;
 102
 103    case nir_op_fmul:
 104       /* Only absorb a fmul into a ffma if the fmul is is only used in fadd
 105        * operations.  This prevents us from being too aggressive with our
 106        * fusing which can actually lead to more instructions.
 107        */
 108       if (!are_all_uses_fadd(&alu->dest.dest.ssa))
 109          return NULL;
 110       break;
 111
 112    default:
 113       return NULL;
 114    }
 115
 116    if (!alu)
 117       return NULL;
 118
 119    for (unsigned i = 0; i < 4; i++) {
 120       if (!(alu->dest.write_mask & (1 << i)))
 121          break;
 122
 123       swizzle[i] = swizzle[src->swizzle[i]];
 124    }
 125
 126    return alu;
 127 }
 128
 129 static bool
 130 nir_opt_peephole_ffma_block(nir_block *block, void *void_state)
 131 {
 132    struct peephole_ffma_state *state = void_state;
 133
 134    nir_foreach_instr_safe(block, instr) {
 135       if (instr->type != nir_instr_type_alu)
 136          continue;
 137
 138       nir_alu_instr *add = nir_instr_as_alu(instr);
 139       if (add->op != nir_op_fadd)
 140          continue;
 141
 142       /* TODO: Maybe bail if this expression is considered "precise"? */
 143
 144       assert(add->src[0].src.is_ssa && add->src[1].src.is_ssa);
 145
 146       /* This, is the case a + a.  We would rather handle this with an
 147        * algebraic reduction than fuse it.  Also, we want to only fuse
 148        * things where the multiply is used only once and, in this case,
 149        * it would be used twice by the same instruction.
 150        */
 151       if (add->src[0].src.ssa == add->src[1].src.ssa)
 152          continue;
 153
 154       nir_alu_instr *mul;
 155       uint8_t add_mul_src, swizzle[4];
 156       bool negate, abs;
 157       for (add_mul_src = 0; add_mul_src < 2; add_mul_src++) {
 158          for (unsigned i = 0; i < 4; i++)
 159             swizzle[i] = i;
 160
 161          negate = false;
 162          abs = false;
 163
 164          mul = get_mul_for_src(&add->src[add_mul_src], swizzle, &negate, &abs);
 165
 166          if (mul != NULL)
 167             break;
 168       }
 169
 170       if (mul == NULL)
 171          continue;
 172
 173       nir_ssa_def *mul_src[2];
 174       mul_src[0] = mul->src[0].src.ssa;
 175       mul_src[1] = mul->src[1].src.ssa;
 176
 177       if (abs) {
 178          for (unsigned i = 0; i < 2; i++) {
 179             nir_alu_instr *abs = nir_alu_instr_create(state->mem_ctx,
 180                                                       nir_op_fabs);
 181             abs->src[0].src = nir_src_for_ssa(mul_src[i]);
 182             nir_ssa_dest_init(&abs->instr, &abs->dest.dest,
 183                               mul_src[i]->num_components, NULL);
 184             abs->dest.write_mask = (1 << mul_src[i]->num_components) - 1;
 185             nir_instr_insert_before(&add->instr, &abs->instr);
 186             mul_src[i] = &abs->dest.dest.ssa;
 187          }
 188       }
 189
 190       if (negate) {
 191          nir_alu_instr *neg = nir_alu_instr_create(state->mem_ctx,
 192                                                    nir_op_fneg);
 193          neg->src[0].src = nir_src_for_ssa(mul_src[0]);
 194          nir_ssa_dest_init(&neg->instr, &neg->dest.dest,
 195                            mul_src[0]->num_components, NULL);
 196          neg->dest.write_mask = (1 << mul_src[0]->num_components) - 1;
 197          nir_instr_insert_before(&add->instr, &neg->instr);
 198          mul_src[0] = &neg->dest.dest.ssa;
 199       }
 200
 201       nir_alu_instr *ffma = nir_alu_instr_create(state->mem_ctx, nir_op_ffma);
 202       ffma->dest.saturate = add->dest.saturate;
 203       ffma->dest.write_mask = add->dest.write_mask;
 204
 205       for (unsigned i = 0; i < 2; i++) {
 206          ffma->src[i].src = nir_src_for_ssa(mul_src[i]);
 207          for (unsigned j = 0; j < add->dest.dest.ssa.num_components; j++)
 208             ffma->src[i].swizzle[j] = mul->src[i].swizzle[swizzle[j]];
 209       }
 210       nir_alu_src_copy(&ffma->src[2], &add->src[1 - add_mul_src],
 211                        state->mem_ctx);
 212
 213       assert(add->dest.dest.is_ssa);
 214
 215       nir_ssa_dest_init(&ffma->instr, &ffma->dest.dest,
 216                         add->dest.dest.ssa.num_components,
 217                         add->dest.dest.ssa.name);
 218       nir_ssa_def_rewrite_uses(&add->dest.dest.ssa,
 219                                nir_src_for_ssa(&ffma->dest.dest.ssa),
 220                                state->mem_ctx);
 221
 222       nir_instr_insert_before(&add->instr, &ffma->instr);
 223       assert(add->dest.dest.ssa.uses->entries == 0);
 224       nir_instr_remove(&add->instr);
 225
 226       state->progress = true;
 227    }
 228
 229    return true;
 230 }
 231
 232 static bool
 233 nir_opt_peephole_ffma_impl(nir_function_impl *impl)
 234 {
 235    struct peephole_ffma_state state;
 236
 237    state.mem_ctx = ralloc_parent(impl);
 238    state.impl = impl;
 239    state.progress = false;
 240
 241    nir_foreach_block(impl, nir_opt_peephole_ffma_block, &state);
 242
 243    if (state.progress)
 244       nir_metadata_preserve(impl, nir_metadata_block_index |
 245                                   nir_metadata_dominance);
 246
 247    return state.progress;
 248 }
 249
 250 bool
 251 nir_opt_peephole_ffma(nir_shader *shader)
 252 {
 253    bool progress = false;
 254
 255    nir_foreach_overload(shader, overload) {
 256       if (overload->impl)
 257          progress |= nir_opt_peephole_ffma_impl(overload->impl);
 258    }
 259
 260    return progress;
 261 }