src/compiler/nir/nir_lower_bit_size.c

   1 /*
   2  * Copyright © 2018 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 "nir_builder.h"
  25
  26 /**
  27  * Some ALU operations may not be supported in hardware in specific bit-sizes.
  28  * This pass allows implementations to selectively lower such operations to
  29  * a bit-size that is supported natively and then converts the result back to
  30  * the original bit-size.
  31  */
  32
  33 static nir_ssa_def *convert_to_bit_size(nir_builder *bld, nir_ssa_def *src,
  34                                         nir_alu_type type, unsigned bit_size)
  35 {
  36    assert(src->bit_size < bit_size);
  37
  38    /* create b2i32(a) instead of i2i32(b2i8(a))/i2i32(b2i16(a)) */
  39    nir_alu_instr *alu = nir_src_as_alu_instr(nir_src_for_ssa(src));
  40    if ((type & (nir_type_uint | nir_type_int)) && bit_size == 32 &&
  41        alu && (alu->op == nir_op_b2i8 || alu->op == nir_op_b2i16)) {
  42       nir_alu_instr *instr = nir_alu_instr_create(bld->shader, nir_op_b2i32);
  43       nir_alu_src_copy(&instr->src[0], &alu->src[0], instr);
  44       return nir_builder_alu_instr_finish_and_insert(bld, instr);
  45    }
  46
  47    return nir_convert_to_bit_size(bld, src, type, bit_size);
  48 }
  49
  50 static void
  51 lower_alu_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
  52 {
  53    const nir_op op = alu->op;
  54    unsigned dst_bit_size = alu->dest.dest.ssa.bit_size;
  55
  56    bld->cursor = nir_before_instr(&alu->instr);
  57
  58    /* Convert each source to the requested bit-size */
  59    nir_ssa_def *srcs[NIR_MAX_VEC_COMPONENTS] = { NULL };
  60    for (unsigned i = 0; i < nir_op_infos[op].num_inputs; i++) {
  61       nir_ssa_def *src = nir_ssa_for_alu_src(bld, alu, i);
  62
  63       nir_alu_type type = nir_op_infos[op].input_types[i];
  64       if (nir_alu_type_get_type_size(type) == 0)
  65          src = convert_to_bit_size(bld, src, type, bit_size);
  66
  67       if (i == 1 && (op == nir_op_ishl || op == nir_op_ishr || op == nir_op_ushr)) {
  68          assert(util_is_power_of_two_nonzero(dst_bit_size));
  69          src = nir_iand(bld, src, nir_imm_int(bld, dst_bit_size - 1));
  70       }
  71
  72       srcs[i] = src;
  73    }
  74
  75    /* Emit the lowered ALU instruction */
  76    nir_ssa_def *lowered_dst = NULL;
  77    if (op == nir_op_imul_high || op == nir_op_umul_high) {
  78       assert(dst_bit_size * 2 <= bit_size);
  79       lowered_dst = nir_imul(bld, srcs[0], srcs[1]);
  80       if (nir_op_infos[op].output_type & nir_type_uint)
  81          lowered_dst = nir_ushr_imm(bld, lowered_dst, dst_bit_size);
  82       else
  83          lowered_dst = nir_ishr_imm(bld, lowered_dst, dst_bit_size);
  84    } else if (op == nir_op_iadd_sat || op == nir_op_isub_sat || op == nir_op_uadd_sat ||
  85               op == nir_op_uadd_carry) {
  86       if (op == nir_op_isub_sat)
  87          lowered_dst = nir_isub(bld, srcs[0], srcs[1]);
  88       else
  89          lowered_dst = nir_iadd(bld, srcs[0], srcs[1]);
  90
  91       /* The add_sat and sub_sat instructions need to clamp the result to the
  92        * range of the original type.
  93        */
  94       if (op == nir_op_iadd_sat || op == nir_op_isub_sat) {
  95          const int64_t int_max = u_intN_max(dst_bit_size);
  96          const int64_t int_min = u_intN_min(dst_bit_size);
  97
  98          lowered_dst = nir_iclamp(bld, lowered_dst,
  99                                   nir_imm_intN_t(bld, int_min, bit_size),
 100                                   nir_imm_intN_t(bld, int_max, bit_size));
 101       } else if (op == nir_op_uadd_sat) {
 102          const uint64_t uint_max = u_uintN_max(dst_bit_size);
 103
 104          lowered_dst = nir_umin(bld, lowered_dst,
 105                                 nir_imm_intN_t(bld, uint_max, bit_size));
 106       } else {
 107          assert(op == nir_op_uadd_carry);
 108          lowered_dst = nir_ushr_imm(bld, lowered_dst, dst_bit_size);
 109       }
 110    } else {
 111       lowered_dst = nir_build_alu_src_arr(bld, op, srcs);
 112    }
 113
 114
 115    /* Convert result back to the original bit-size */
 116    if (nir_alu_type_get_type_size(nir_op_infos[op].output_type) == 0 &&
 117        dst_bit_size != bit_size) {
 118       nir_alu_type type = nir_op_infos[op].output_type;
 119       nir_ssa_def *dst = nir_convert_to_bit_size(bld, lowered_dst, type, dst_bit_size);
 120       nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, dst);
 121    } else {
 122       nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, lowered_dst);
 123    }
 124 }
 125
 126 static void
 127 lower_intrinsic_instr(nir_builder *b, nir_intrinsic_instr *intrin,
 128                       unsigned bit_size)
 129 {
 130    switch (intrin->intrinsic) {
 131    case nir_intrinsic_read_invocation:
 132    case nir_intrinsic_read_first_invocation:
 133    case nir_intrinsic_vote_feq:
 134    case nir_intrinsic_vote_ieq:
 135    case nir_intrinsic_shuffle:
 136    case nir_intrinsic_shuffle_xor:
 137    case nir_intrinsic_shuffle_up:
 138    case nir_intrinsic_shuffle_down:
 139    case nir_intrinsic_quad_broadcast:
 140    case nir_intrinsic_quad_swap_horizontal:
 141    case nir_intrinsic_quad_swap_vertical:
 142    case nir_intrinsic_quad_swap_diagonal:
 143    case nir_intrinsic_reduce:
 144    case nir_intrinsic_inclusive_scan:
 145    case nir_intrinsic_exclusive_scan: {
 146       assert(intrin->src[0].is_ssa && intrin->dest.is_ssa);
 147       const unsigned old_bit_size = intrin->dest.ssa.bit_size;
 148       assert(old_bit_size < bit_size);
 149
 150       nir_alu_type type = nir_type_uint;
 151       if (nir_intrinsic_has_reduction_op(intrin))
 152          type = nir_op_infos[nir_intrinsic_reduction_op(intrin)].input_types[0];
 153       else if (intrin->intrinsic == nir_intrinsic_vote_feq)
 154          type = nir_type_float;
 155
 156       b->cursor = nir_before_instr(&intrin->instr);
 157       nir_intrinsic_instr *new_intrin =
 158          nir_instr_as_intrinsic(nir_instr_clone(b->shader, &intrin->instr));
 159
 160       nir_ssa_def *new_src = nir_convert_to_bit_size(b, intrin->src[0].ssa,
 161                                                      type, bit_size);
 162       new_intrin->src[0] = nir_src_for_ssa(new_src);
 163
 164       if (intrin->intrinsic == nir_intrinsic_vote_feq ||
 165           intrin->intrinsic == nir_intrinsic_vote_ieq) {
 166          /* These return a Boolean; it's always 1-bit */
 167          assert(new_intrin->dest.ssa.bit_size == 1);
 168       } else {
 169          /* These return the same bit size as the source; we need to adjust
 170           * the size and then we'll have to emit a down-cast.
 171           */
 172          assert(intrin->src[0].ssa->bit_size == intrin->dest.ssa.bit_size);
 173          new_intrin->dest.ssa.bit_size = bit_size;
 174       }
 175
 176       nir_builder_instr_insert(b, &new_intrin->instr);
 177
 178       nir_ssa_def *res = &new_intrin->dest.ssa;
 179       if (intrin->intrinsic == nir_intrinsic_exclusive_scan) {
 180          /* For exclusive scan, we have to be careful because the identity
 181           * value for the higher bit size may get added into the mix by
 182           * disabled channels.  For some cases (imin/imax in particular),
 183           * this value won't convert to the right identity value when we
 184           * down-cast so we have to clamp it.
 185           */
 186          switch (nir_intrinsic_reduction_op(intrin)) {
 187          case nir_op_imin: {
 188             int64_t int_max = (1ull << (old_bit_size - 1)) - 1;
 189             res = nir_imin(b, res, nir_imm_intN_t(b, int_max, bit_size));
 190             break;
 191          }
 192          case nir_op_imax: {
 193             int64_t int_min = -(int64_t)(1ull << (old_bit_size - 1));
 194             res = nir_imax(b, res, nir_imm_intN_t(b, int_min, bit_size));
 195             break;
 196          }
 197          default:
 198             break;
 199          }
 200       }
 201
 202       if (intrin->intrinsic != nir_intrinsic_vote_feq &&
 203           intrin->intrinsic != nir_intrinsic_vote_ieq)
 204          res = nir_u2uN(b, res, old_bit_size);
 205
 206       nir_ssa_def_rewrite_uses(&intrin->dest.ssa, res);
 207       break;
 208    }
 209
 210    default:
 211       unreachable("Unsupported instruction");
 212    }
 213 }
 214
 215 static void
 216 lower_phi_instr(nir_builder *b, nir_phi_instr *phi, unsigned bit_size,
 217                 nir_phi_instr *last_phi)
 218 {
 219    assert(phi->dest.is_ssa);
 220    unsigned old_bit_size = phi->dest.ssa.bit_size;
 221    assert(old_bit_size < bit_size);
 222
 223    nir_foreach_phi_src(src, phi) {
 224       b->cursor = nir_after_block_before_jump(src->pred);
 225       assert(src->src.is_ssa);
 226       nir_ssa_def *new_src = nir_u2uN(b, src->src.ssa, bit_size);
 227
 228       nir_instr_rewrite_src(&phi->instr, &src->src, nir_src_for_ssa(new_src));
 229    }
 230
 231    phi->dest.ssa.bit_size = bit_size;
 232
 233    b->cursor = nir_after_instr(&last_phi->instr);
 234
 235    nir_ssa_def *new_dest = nir_u2uN(b, &phi->dest.ssa, old_bit_size);
 236    nir_ssa_def_rewrite_uses_after(&phi->dest.ssa, new_dest,
 237                                   new_dest->parent_instr);
 238 }
 239
 240 static bool
 241 lower_impl(nir_function_impl *impl,
 242            nir_lower_bit_size_callback callback,
 243            void *callback_data)
 244 {
 245    nir_builder b = nir_builder_create(impl);
 246    bool progress = false;
 247
 248    nir_foreach_block(block, impl) {
 249       /* Stash this so we can rewrite phi destinations quickly. */
 250       nir_phi_instr *last_phi = nir_block_last_phi_instr(block);
 251
 252       nir_foreach_instr_safe(instr, block) {
 253          unsigned lower_bit_size = callback(instr, callback_data);
 254          if (lower_bit_size == 0)
 255             continue;
 256
 257          switch (instr->type) {
 258          case nir_instr_type_alu:
 259             lower_alu_instr(&b, nir_instr_as_alu(instr), lower_bit_size);
 260             break;
 261
 262          case nir_instr_type_intrinsic:
 263             lower_intrinsic_instr(&b, nir_instr_as_intrinsic(instr),
 264                                   lower_bit_size);
 265             break;
 266
 267          case nir_instr_type_phi:
 268             lower_phi_instr(&b, nir_instr_as_phi(instr),
 269                             lower_bit_size, last_phi);
 270             break;
 271
 272          default:
 273             unreachable("Unsupported instruction type");
 274          }
 275          progress = true;
 276       }
 277    }
 278
 279    if (progress) {
 280       nir_metadata_preserve(impl, nir_metadata_block_index |
 281                                   nir_metadata_dominance);
 282    } else {
 283       nir_metadata_preserve(impl, nir_metadata_all);
 284    }
 285
 286    return progress;
 287 }
 288
 289 bool
 290 nir_lower_bit_size(nir_shader *shader,
 291                    nir_lower_bit_size_callback callback,
 292                    void *callback_data)
 293 {
 294    bool progress = false;
 295
 296    nir_foreach_function_impl(impl, shader) {
 297       progress |= lower_impl(impl, callback, callback_data);
 298    }
 299
 300    return progress;
 301 }
 302
 303 static void
 304 split_phi(nir_builder *b, nir_phi_instr *phi)
 305 {
 306    nir_phi_instr *lowered[2] = {
 307       nir_phi_instr_create(b->shader),
 308       nir_phi_instr_create(b->shader)
 309    };
 310    int num_components = phi->dest.ssa.num_components;
 311    assert(phi->dest.ssa.bit_size == 64);
 312
 313    nir_foreach_phi_src(src, phi) {
 314       assert(num_components == src->src.ssa->num_components);
 315
 316       b->cursor = nir_before_src(&src->src);
 317
 318       nir_ssa_def *x = nir_unpack_64_2x32_split_x(b, src->src.ssa);
 319       nir_ssa_def *y = nir_unpack_64_2x32_split_y(b, src->src.ssa);
 320
 321       nir_phi_instr_add_src(lowered[0], src->pred, nir_src_for_ssa(x));
 322       nir_phi_instr_add_src(lowered[1], src->pred, nir_src_for_ssa(y));
 323    }
 324
 325    nir_ssa_dest_init(&lowered[0]->instr, &lowered[0]->dest, num_components,
 326                      32);
 327    nir_ssa_dest_init(&lowered[1]->instr, &lowered[1]->dest, num_components,
 328                      32);
 329
 330    b->cursor = nir_before_instr(&phi->instr);
 331    nir_builder_instr_insert(b, &lowered[0]->instr);
 332    nir_builder_instr_insert(b, &lowered[1]->instr);
 333
 334    b->cursor = nir_after_phis(nir_cursor_current_block(b->cursor));
 335    nir_ssa_def *merged = nir_pack_64_2x32_split(b, &lowered[0]->dest.ssa, &lowered[1]->dest.ssa);
 336    nir_ssa_def_rewrite_uses(&phi->dest.ssa, merged);
 337    nir_instr_remove(&phi->instr);
 338 }
 339
 340 static bool
 341 lower_64bit_phi_instr(nir_builder *b, nir_instr *instr, UNUSED void *cb_data)
 342 {
 343    if (instr->type != nir_instr_type_phi)
 344       return false;
 345
 346    nir_phi_instr *phi = nir_instr_as_phi(instr);
 347    assert(phi->dest.is_ssa);
 348
 349    if (phi->dest.ssa.bit_size <= 32)
 350       return false;
 351
 352    split_phi(b, phi);
 353    return true;
 354 }
 355
 356 bool
 357 nir_lower_64bit_phis(nir_shader *shader)
 358 {
 359    return nir_shader_instructions_pass(shader, lower_64bit_phi_instr,
 360                                        nir_metadata_block_index |
 361                                        nir_metadata_dominance,
 362                                        NULL);
 363 }