src/freedreno/ir3/ir3_nir_lower_io_offsets.c

   1 /*
   2  * Copyright © 2018-2019 Igalia S.L.
   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 "ir3_nir.h"
  25 #include "compiler/nir/nir_builder.h"
  26
  27 /**
  28  * This pass moves to NIR certain offset computations for different I/O
  29  * ops that are currently implemented on the IR3 backend compiler, to
  30  * give NIR a chance to optimize them:
  31  *
  32  * - Dword-offset for SSBO load, store and atomics: A new, similar intrinsic
  33  *   is emitted that replaces the original one, adding a new source that
  34  *   holds the result of the original byte-offset source divided by 4.
  35  */
  36
  37
  38 /* Returns the ir3-specific intrinsic opcode corresponding to an SSBO
  39  * instruction that is handled by this pass. It also conveniently returns
  40  * the offset source index in @offset_src_idx.
  41  *
  42  * If @intrinsic is not SSBO, or it is not handled by the pass, -1 is
  43  * returned.
  44  */
  45 static int
  46 get_ir3_intrinsic_for_ssbo_intrinsic(unsigned intrinsic,
  47                                                                          uint8_t *offset_src_idx)
  48 {
  49         debug_assert(offset_src_idx);
  50
  51         *offset_src_idx = 1;
  52
  53         switch (intrinsic) {
  54         case nir_intrinsic_store_ssbo:
  55                 *offset_src_idx = 2;
  56                 return nir_intrinsic_store_ssbo_ir3;
  57         case nir_intrinsic_load_ssbo:
  58                 return nir_intrinsic_load_ssbo_ir3;
  59         case nir_intrinsic_ssbo_atomic_add:
  60                 return nir_intrinsic_ssbo_atomic_add_ir3;
  61         case nir_intrinsic_ssbo_atomic_imin:
  62                 return nir_intrinsic_ssbo_atomic_imin_ir3;
  63         case nir_intrinsic_ssbo_atomic_umin:
  64                 return nir_intrinsic_ssbo_atomic_umin_ir3;
  65         case nir_intrinsic_ssbo_atomic_imax:
  66                 return nir_intrinsic_ssbo_atomic_imax_ir3;
  67         case nir_intrinsic_ssbo_atomic_umax:
  68                 return nir_intrinsic_ssbo_atomic_umax_ir3;
  69         case nir_intrinsic_ssbo_atomic_and:
  70                 return nir_intrinsic_ssbo_atomic_and_ir3;
  71         case nir_intrinsic_ssbo_atomic_or:
  72                 return nir_intrinsic_ssbo_atomic_or_ir3;
  73         case nir_intrinsic_ssbo_atomic_xor:
  74                 return nir_intrinsic_ssbo_atomic_xor_ir3;
  75         case nir_intrinsic_ssbo_atomic_exchange:
  76                 return nir_intrinsic_ssbo_atomic_exchange_ir3;
  77         case nir_intrinsic_ssbo_atomic_comp_swap:
  78                 return nir_intrinsic_ssbo_atomic_comp_swap_ir3;
  79         default:
  80                 break;
  81         }
  82
  83         return -1;
  84 }
  85
  86 static nir_ssa_def *
  87 check_and_propagate_bit_shift32(nir_builder *b, nir_alu_instr *alu_instr,
  88                                                                 int32_t direction, int32_t shift)
  89 {
  90         debug_assert(alu_instr->src[1].src.is_ssa);
  91         nir_ssa_def *shift_ssa = alu_instr->src[1].src.ssa;
  92
  93         /* Only propagate if the shift is a const value so we can check value range
  94          * statically.
  95          */
  96         nir_const_value *const_val = nir_src_as_const_value(alu_instr->src[1].src);
  97         if (!const_val)
  98                 return NULL;
  99
 100         int32_t current_shift = const_val[0].i32 * direction;
 101         int32_t new_shift = current_shift + shift;
 102
 103         /* If the merge would reverse the direction, bail out.
 104          * e.g, 'x << 2' then 'x >> 4' is not 'x >> 2'.
 105          */
 106         if (current_shift * new_shift < 0)
 107                 return NULL;
 108
 109         /* If the propagation would overflow an int32_t, bail out too to be on the
 110          * safe side.
 111          */
 112         if (new_shift < -31 || new_shift > 31)
 113                 return NULL;
 114
 115         b->cursor = nir_before_instr(&alu_instr->instr);
 116
 117         /* Add or substract shift depending on the final direction (SHR vs. SHL). */
 118         if (shift * direction < 0)
 119                 shift_ssa = nir_isub(b, shift_ssa, nir_imm_int(b, abs(shift)));
 120         else
 121                 shift_ssa = nir_iadd(b, shift_ssa, nir_imm_int(b, abs(shift)));
 122
 123         return shift_ssa;
 124 }
 125
 126 nir_ssa_def *
 127 ir3_nir_try_propagate_bit_shift(nir_builder *b, nir_ssa_def *offset, int32_t shift)
 128 {
 129         nir_instr *offset_instr = offset->parent_instr;
 130         if (offset_instr->type != nir_instr_type_alu)
 131                 return NULL;
 132
 133         nir_alu_instr *alu = nir_instr_as_alu(offset_instr);
 134         nir_ssa_def *shift_ssa;
 135         nir_ssa_def *new_offset = NULL;
 136
 137         switch (alu->op) {
 138         case nir_op_ishl:
 139                 shift_ssa = check_and_propagate_bit_shift32(b, alu, 1, shift);
 140                 if (shift_ssa)
 141                         new_offset = nir_ishl(b, alu->src[0].src.ssa, shift_ssa);
 142                 break;
 143         case nir_op_ishr:
 144                 shift_ssa = check_and_propagate_bit_shift32(b, alu, -1, shift);
 145                 if (shift_ssa)
 146                         new_offset = nir_ishr(b, alu->src[0].src.ssa, shift_ssa);
 147                 break;
 148         case nir_op_ushr:
 149                 shift_ssa = check_and_propagate_bit_shift32(b, alu, -1, shift);
 150                 if (shift_ssa)
 151                         new_offset = nir_ushr(b, alu->src[0].src.ssa, shift_ssa);
 152                 break;
 153         default:
 154                 return NULL;
 155         }
 156
 157         return new_offset;
 158 }
 159
 160 static bool
 161 lower_offset_for_ssbo(nir_intrinsic_instr *intrinsic, nir_builder *b,
 162                                           unsigned ir3_ssbo_opcode, uint8_t offset_src_idx)
 163 {
 164         unsigned num_srcs = nir_intrinsic_infos[intrinsic->intrinsic].num_srcs;
 165
 166         bool has_dest = nir_intrinsic_infos[intrinsic->intrinsic].has_dest;
 167         nir_ssa_def *new_dest = NULL;
 168
 169         /* Here we create a new intrinsic and copy over all contents from the old one. */
 170
 171         nir_intrinsic_instr *new_intrinsic;
 172         nir_src *target_src;
 173
 174         /* 'offset_src_idx' holds the index of the source that represent the offset. */
 175         new_intrinsic =
 176                 nir_intrinsic_instr_create(b->shader, ir3_ssbo_opcode);
 177
 178         debug_assert(intrinsic->src[offset_src_idx].is_ssa);
 179         nir_ssa_def *offset = intrinsic->src[offset_src_idx].ssa;
 180
 181         /* Since we don't have value range checking, we first try to propagate
 182          * the division by 4 ('offset >> 2') into another bit-shift instruction that
 183          * possibly defines the offset. If that's the case, we emit a similar
 184          * instructions adjusting (merging) the shift value.
 185          *
 186          * Here we use the convention that shifting right is negative while shifting
 187          * left is positive. So 'x / 4' ~ 'x >> 2' or 'x << -2'.
 188          */
 189         nir_ssa_def *new_offset = ir3_nir_try_propagate_bit_shift(b, offset, -2);
 190
 191         /* The new source that will hold the dword-offset is always the last
 192          * one for every intrinsic.
 193          */
 194         target_src = &new_intrinsic->src[num_srcs];
 195         *target_src = nir_src_for_ssa(offset);
 196
 197         if (has_dest) {
 198                 debug_assert(intrinsic->dest.is_ssa);
 199                 nir_ssa_def *dest = &intrinsic->dest.ssa;
 200                 nir_ssa_dest_init(&new_intrinsic->instr, &new_intrinsic->dest,
 201                                                   dest->num_components, dest->bit_size, NULL);
 202                 new_dest = &new_intrinsic->dest.ssa;
 203         }
 204
 205         for (unsigned i = 0; i < num_srcs; i++)
 206                 new_intrinsic->src[i] = nir_src_for_ssa(intrinsic->src[i].ssa);
 207
 208         for (unsigned i = 0; i < NIR_INTRINSIC_MAX_CONST_INDEX; i++)
 209                 new_intrinsic->const_index[i] = intrinsic->const_index[i];
 210
 211         new_intrinsic->num_components = intrinsic->num_components;
 212
 213         b->cursor = nir_before_instr(&intrinsic->instr);
 214
 215         /* If we managed to propagate the division by 4, just use the new offset
 216          * register and don't emit the SHR.
 217          */
 218         if (new_offset)
 219                 offset = new_offset;
 220         else
 221                 offset = nir_ushr(b, offset, nir_imm_int(b, 2));
 222
 223         /* Insert the new intrinsic right before the old one. */
 224         nir_builder_instr_insert(b, &new_intrinsic->instr);
 225
 226         /* Replace the last source of the new intrinsic by the result of
 227          * the offset divided by 4.
 228          */
 229         nir_instr_rewrite_src(&new_intrinsic->instr,
 230                                                   target_src,
 231                                                   nir_src_for_ssa(offset));
 232
 233         if (has_dest) {
 234                 /* Replace the uses of the original destination by that
 235                  * of the new intrinsic.
 236                  */
 237                 nir_ssa_def_rewrite_uses(&intrinsic->dest.ssa,
 238                                                                  nir_src_for_ssa(new_dest));
 239         }
 240
 241         /* Finally remove the original intrinsic. */
 242         nir_instr_remove(&intrinsic->instr);
 243
 244         return true;
 245 }
 246
 247 static bool
 248 lower_io_offsets_block(nir_block *block, nir_builder *b, void *mem_ctx)
 249 {
 250         bool progress = false;
 251
 252         nir_foreach_instr_safe(instr, block) {
 253                 if (instr->type != nir_instr_type_intrinsic)
 254                         continue;
 255
 256                 nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
 257
 258                 /* SSBO */
 259                 int ir3_intrinsic;
 260                 uint8_t offset_src_idx;
 261                 ir3_intrinsic = get_ir3_intrinsic_for_ssbo_intrinsic(intr->intrinsic,
 262                                                                                                                          &offset_src_idx);
 263                 if (ir3_intrinsic != -1) {
 264                         progress |= lower_offset_for_ssbo(intr, b, (unsigned) ir3_intrinsic,
 265                                                                                           offset_src_idx);
 266                 }
 267         }
 268
 269         return progress;
 270 }
 271
 272 static bool
 273 lower_io_offsets_func(nir_function_impl *impl)
 274 {
 275         void *mem_ctx = ralloc_parent(impl);
 276         nir_builder b;
 277         nir_builder_init(&b, impl);
 278
 279         bool progress = false;
 280         nir_foreach_block_safe(block, impl) {
 281                 progress |= lower_io_offsets_block(block, &b, mem_ctx);
 282         }
 283
 284         if (progress) {
 285                 nir_metadata_preserve(impl, nir_metadata_block_index |
 286                                                                         nir_metadata_dominance);
 287         }
 288
 289         return progress;
 290 }
 291
 292 bool
 293 ir3_nir_lower_io_offsets(nir_shader *shader)
 294 {
 295         bool progress = false;
 296
 297         nir_foreach_function(function, shader) {
 298                 if (function->impl)
 299                         progress |= lower_io_offsets_func(function->impl);
 300         }
 301
 302         return progress;
 303 }