src/compiler/nir/nir_divergence_analysis.c

   1 /*
   2  * Copyright © 2018 Valve 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
  25 #include "nir.h"
  26
  27 /* This pass computes for each ssa definition if it is uniform.
  28  * That is, the variable has the same value for all invocations
  29  * of the group.
  30  *
  31  * This divergence analysis pass expects the shader to be in LCSSA-form.
  32  *
  33  * This algorithm implements "The Simple Divergence Analysis" from
  34  * Diogo Sampaio, Rafael De Souza, Sylvain Collange, Fernando Magno Quintão Pereira.
  35  * Divergence Analysis.  ACM Transactions on Programming Languages and Systems (TOPLAS),
  36  * ACM, 2013, 35 (4), pp.13:1-13:36. <10.1145/2523815>. <hal-00909072v2>
  37  */
  38
  39 struct divergence_state {
  40    const nir_divergence_options options;
  41    const gl_shader_stage stage;
  42
  43    /** current control flow state */
  44    /* True if some loop-active invocations might take a different control-flow path.
  45     * A divergent break does not cause subsequent control-flow to be considered
  46     * divergent because those invocations are no longer active in the loop.
  47     * For a divergent if, both sides are considered divergent flow because
  48     * the other side is still loop-active. */
  49    bool divergent_loop_cf;
  50    /* True if a divergent continue happened since the loop header */
  51    bool divergent_loop_continue;
  52    /* True if a divergent break happened since the loop header */
  53    bool divergent_loop_break;
  54
  55    /* True if we visit the block for the fist time */
  56    bool first_visit;
  57 };
  58
  59 static bool
  60 visit_cf_list(struct exec_list *list, struct divergence_state *state);
  61
  62 static bool
  63 visit_alu(nir_alu_instr *instr)
  64 {
  65    if (instr->dest.dest.ssa.divergent)
  66       return false;
  67
  68    unsigned num_src = nir_op_infos[instr->op].num_inputs;
  69
  70    for (unsigned i = 0; i < num_src; i++) {
  71       if (instr->src[i].src.ssa->divergent) {
  72          instr->dest.dest.ssa.divergent = true;
  73          return true;
  74       }
  75    }
  76
  77    return false;
  78 }
  79
  80 static bool
  81 visit_intrinsic(nir_intrinsic_instr *instr, struct divergence_state *state)
  82 {
  83    if (!nir_intrinsic_infos[instr->intrinsic].has_dest)
  84       return false;
  85
  86    if (instr->dest.ssa.divergent)
  87       return false;
  88
  89    nir_divergence_options options = state->options;
  90    gl_shader_stage stage = state->stage;
  91    bool is_divergent = false;
  92    switch (instr->intrinsic) {
  93    /* Intrinsics which are always uniform */
  94    case nir_intrinsic_shader_clock:
  95    case nir_intrinsic_ballot:
  96    case nir_intrinsic_read_invocation:
  97    case nir_intrinsic_read_first_invocation:
  98    case nir_intrinsic_vote_any:
  99    case nir_intrinsic_vote_all:
 100    case nir_intrinsic_vote_feq:
 101    case nir_intrinsic_vote_ieq:
 102    case nir_intrinsic_load_work_dim:
 103    case nir_intrinsic_load_work_group_id:
 104    case nir_intrinsic_load_num_work_groups:
 105    case nir_intrinsic_load_local_group_size:
 106    case nir_intrinsic_load_subgroup_id:
 107    case nir_intrinsic_load_num_subgroups:
 108    case nir_intrinsic_load_subgroup_size:
 109    case nir_intrinsic_load_subgroup_eq_mask:
 110    case nir_intrinsic_load_subgroup_ge_mask:
 111    case nir_intrinsic_load_subgroup_gt_mask:
 112    case nir_intrinsic_load_subgroup_le_mask:
 113    case nir_intrinsic_load_subgroup_lt_mask:
 114    case nir_intrinsic_first_invocation:
 115    case nir_intrinsic_load_base_instance:
 116    case nir_intrinsic_load_base_vertex:
 117    case nir_intrinsic_load_first_vertex:
 118    case nir_intrinsic_load_draw_id:
 119    case nir_intrinsic_load_is_indexed_draw:
 120    case nir_intrinsic_load_viewport_scale:
 121    case nir_intrinsic_load_alpha_ref_float:
 122    case nir_intrinsic_load_user_clip_plane:
 123    case nir_intrinsic_load_viewport_x_scale:
 124    case nir_intrinsic_load_viewport_y_scale:
 125    case nir_intrinsic_load_viewport_z_scale:
 126    case nir_intrinsic_load_viewport_offset:
 127    case nir_intrinsic_load_viewport_z_offset:
 128    case nir_intrinsic_load_blend_const_color_a_float:
 129    case nir_intrinsic_load_blend_const_color_b_float:
 130    case nir_intrinsic_load_blend_const_color_g_float:
 131    case nir_intrinsic_load_blend_const_color_r_float:
 132    case nir_intrinsic_load_blend_const_color_rgba:
 133    case nir_intrinsic_load_blend_const_color_aaaa8888_unorm:
 134    case nir_intrinsic_load_blend_const_color_rgba8888_unorm:
 135       is_divergent = false;
 136       break;
 137
 138    /* Intrinsics with divergence depending on shader stage and hardware */
 139    case nir_intrinsic_load_input:
 140       is_divergent = instr->src[0].ssa->divergent;
 141       if (stage == MESA_SHADER_FRAGMENT)
 142          is_divergent |= !(options & nir_divergence_single_prim_per_subgroup);
 143       else if (stage == MESA_SHADER_TESS_EVAL)
 144          is_divergent |= !(options & nir_divergence_single_patch_per_tes_subgroup);
 145       else
 146          is_divergent = true;
 147       break;
 148    case nir_intrinsic_load_input_vertex:
 149       is_divergent = instr->src[1].ssa->divergent;
 150       assert(stage == MESA_SHADER_FRAGMENT);
 151       is_divergent |= !(options & nir_divergence_single_prim_per_subgroup);
 152       break;
 153    case nir_intrinsic_load_output:
 154       assert(stage == MESA_SHADER_TESS_CTRL || stage == MESA_SHADER_FRAGMENT);
 155       is_divergent = instr->src[0].ssa->divergent;
 156       if (stage == MESA_SHADER_TESS_CTRL)
 157          is_divergent |= !(options & nir_divergence_single_patch_per_tcs_subgroup);
 158       else
 159          is_divergent = true;
 160       break;
 161    case nir_intrinsic_load_layer_id:
 162    case nir_intrinsic_load_front_face:
 163       assert(stage == MESA_SHADER_FRAGMENT);
 164       is_divergent = !(options & nir_divergence_single_prim_per_subgroup);
 165       break;
 166    case nir_intrinsic_load_view_index:
 167       assert(stage != MESA_SHADER_COMPUTE && stage != MESA_SHADER_KERNEL);
 168       if (options & nir_divergence_view_index_uniform)
 169          is_divergent = false;
 170       else if (stage == MESA_SHADER_FRAGMENT)
 171          is_divergent = !(options & nir_divergence_single_prim_per_subgroup);
 172       break;
 173    case nir_intrinsic_load_fs_input_interp_deltas:
 174       assert(stage == MESA_SHADER_FRAGMENT);
 175       is_divergent = instr->src[0].ssa->divergent;
 176       is_divergent |= !(options & nir_divergence_single_prim_per_subgroup);
 177       break;
 178    case nir_intrinsic_load_primitive_id:
 179       if (stage == MESA_SHADER_FRAGMENT)
 180          is_divergent = !(options & nir_divergence_single_prim_per_subgroup);
 181       else if (stage == MESA_SHADER_TESS_CTRL)
 182          is_divergent = !(options & nir_divergence_single_patch_per_tcs_subgroup);
 183       else if (stage == MESA_SHADER_TESS_EVAL)
 184          is_divergent = !(options & nir_divergence_single_patch_per_tes_subgroup);
 185       else if (stage == MESA_SHADER_GEOMETRY)
 186          is_divergent = true;
 187       else
 188          unreachable("Invalid stage for load_primitive_id");
 189       break;
 190    case nir_intrinsic_load_tess_level_inner:
 191    case nir_intrinsic_load_tess_level_outer:
 192       if (stage == MESA_SHADER_TESS_CTRL)
 193          is_divergent = !(options & nir_divergence_single_patch_per_tcs_subgroup);
 194       else if (stage == MESA_SHADER_TESS_EVAL)
 195          is_divergent = !(options & nir_divergence_single_patch_per_tes_subgroup);
 196       else
 197          unreachable("Invalid stage for load_primitive_tess_level_*");
 198       break;
 199    case nir_intrinsic_load_patch_vertices_in:
 200       if (stage == MESA_SHADER_TESS_EVAL)
 201          is_divergent = !(options & nir_divergence_single_patch_per_tes_subgroup);
 202       else
 203          assert(stage == MESA_SHADER_TESS_CTRL);
 204       break;
 205
 206    /* Clustered reductions are uniform if cluster_size == subgroup_size or
 207     * the source is uniform and the operation is invariant.
 208     * Inclusive scans are uniform if
 209     * the source is uniform and the operation is invariant
 210     */
 211    case nir_intrinsic_reduce:
 212       if (nir_intrinsic_cluster_size(instr) == 0)
 213          return false;
 214       /* fallthrough */
 215    case nir_intrinsic_inclusive_scan: {
 216       nir_op op = nir_intrinsic_reduction_op(instr);
 217       is_divergent = instr->src[0].ssa->divergent;
 218       if (op != nir_op_umin && op != nir_op_imin && op != nir_op_fmin &&
 219           op != nir_op_umax && op != nir_op_imax && op != nir_op_fmax &&
 220           op != nir_op_iand && op != nir_op_ior)
 221          is_divergent = true;
 222       break;
 223    }
 224
 225    /* Intrinsics with divergence depending on sources */
 226    case nir_intrinsic_ballot_bitfield_extract:
 227    case nir_intrinsic_ballot_find_lsb:
 228    case nir_intrinsic_ballot_find_msb:
 229    case nir_intrinsic_ballot_bit_count_reduce:
 230    case nir_intrinsic_shuffle_xor:
 231    case nir_intrinsic_shuffle_up:
 232    case nir_intrinsic_shuffle_down:
 233    case nir_intrinsic_quad_broadcast:
 234    case nir_intrinsic_quad_swap_horizontal:
 235    case nir_intrinsic_quad_swap_vertical:
 236    case nir_intrinsic_quad_swap_diagonal:
 237    case nir_intrinsic_load_deref:
 238    case nir_intrinsic_load_ubo:
 239    case nir_intrinsic_load_ssbo:
 240    case nir_intrinsic_load_shared:
 241    case nir_intrinsic_load_global:
 242    case nir_intrinsic_load_uniform:
 243    case nir_intrinsic_load_push_constant:
 244    case nir_intrinsic_load_constant:
 245    case nir_intrinsic_load_sample_pos_from_id:
 246    case nir_intrinsic_load_kernel_input:
 247    case nir_intrinsic_image_load:
 248    case nir_intrinsic_image_deref_load:
 249    case nir_intrinsic_bindless_image_load:
 250    case nir_intrinsic_image_samples:
 251    case nir_intrinsic_image_deref_samples:
 252    case nir_intrinsic_bindless_image_samples:
 253    case nir_intrinsic_get_buffer_size:
 254    case nir_intrinsic_image_size:
 255    case nir_intrinsic_image_deref_size:
 256    case nir_intrinsic_bindless_image_size:
 257    case nir_intrinsic_copy_deref:
 258    case nir_intrinsic_deref_buffer_array_length:
 259    case nir_intrinsic_vulkan_resource_index:
 260    case nir_intrinsic_vulkan_resource_reindex:
 261    case nir_intrinsic_load_vulkan_descriptor:
 262    case nir_intrinsic_atomic_counter_read:
 263    case nir_intrinsic_atomic_counter_read_deref:
 264    case nir_intrinsic_quad_swizzle_amd:
 265    case nir_intrinsic_masked_swizzle_amd: {
 266       unsigned num_srcs = nir_intrinsic_infos[instr->intrinsic].num_srcs;
 267       for (unsigned i = 0; i < num_srcs; i++) {
 268          if (instr->src[i].ssa->divergent) {
 269             is_divergent = true;
 270             break;
 271          }
 272       }
 273       break;
 274    }
 275
 276    case nir_intrinsic_shuffle:
 277       is_divergent = instr->src[0].ssa->divergent &&
 278                      instr->src[1].ssa->divergent;
 279       break;
 280
 281    /* Intrinsics which are always divergent */
 282    case nir_intrinsic_load_color0:
 283    case nir_intrinsic_load_color1:
 284    case nir_intrinsic_load_param:
 285    case nir_intrinsic_load_sample_id:
 286    case nir_intrinsic_load_sample_id_no_per_sample:
 287    case nir_intrinsic_load_sample_mask_in:
 288    case nir_intrinsic_load_interpolated_input:
 289    case nir_intrinsic_load_barycentric_pixel:
 290    case nir_intrinsic_load_barycentric_centroid:
 291    case nir_intrinsic_load_barycentric_sample:
 292    case nir_intrinsic_load_barycentric_model:
 293    case nir_intrinsic_load_barycentric_at_sample:
 294    case nir_intrinsic_load_barycentric_at_offset:
 295    case nir_intrinsic_interp_deref_at_offset:
 296    case nir_intrinsic_interp_deref_at_sample:
 297    case nir_intrinsic_interp_deref_at_centroid:
 298    case nir_intrinsic_interp_deref_at_vertex:
 299    case nir_intrinsic_load_tess_coord:
 300    case nir_intrinsic_load_point_coord:
 301    case nir_intrinsic_load_frag_coord:
 302    case nir_intrinsic_load_sample_pos:
 303    case nir_intrinsic_load_vertex_id_zero_base:
 304    case nir_intrinsic_load_vertex_id:
 305    case nir_intrinsic_load_per_vertex_input:
 306    case nir_intrinsic_load_per_vertex_output:
 307    case nir_intrinsic_load_instance_id:
 308    case nir_intrinsic_load_invocation_id:
 309    case nir_intrinsic_load_local_invocation_id:
 310    case nir_intrinsic_load_local_invocation_index:
 311    case nir_intrinsic_load_global_invocation_id:
 312    case nir_intrinsic_load_global_invocation_index:
 313    case nir_intrinsic_load_subgroup_invocation:
 314    case nir_intrinsic_load_helper_invocation:
 315    case nir_intrinsic_is_helper_invocation:
 316    case nir_intrinsic_load_scratch:
 317    case nir_intrinsic_deref_atomic_add:
 318    case nir_intrinsic_deref_atomic_imin:
 319    case nir_intrinsic_deref_atomic_umin:
 320    case nir_intrinsic_deref_atomic_imax:
 321    case nir_intrinsic_deref_atomic_umax:
 322    case nir_intrinsic_deref_atomic_and:
 323    case nir_intrinsic_deref_atomic_or:
 324    case nir_intrinsic_deref_atomic_xor:
 325    case nir_intrinsic_deref_atomic_exchange:
 326    case nir_intrinsic_deref_atomic_comp_swap:
 327    case nir_intrinsic_deref_atomic_fadd:
 328    case nir_intrinsic_deref_atomic_fmin:
 329    case nir_intrinsic_deref_atomic_fmax:
 330    case nir_intrinsic_deref_atomic_fcomp_swap:
 331    case nir_intrinsic_ssbo_atomic_add:
 332    case nir_intrinsic_ssbo_atomic_imin:
 333    case nir_intrinsic_ssbo_atomic_umin:
 334    case nir_intrinsic_ssbo_atomic_imax:
 335    case nir_intrinsic_ssbo_atomic_umax:
 336    case nir_intrinsic_ssbo_atomic_and:
 337    case nir_intrinsic_ssbo_atomic_or:
 338    case nir_intrinsic_ssbo_atomic_xor:
 339    case nir_intrinsic_ssbo_atomic_exchange:
 340    case nir_intrinsic_ssbo_atomic_comp_swap:
 341    case nir_intrinsic_ssbo_atomic_fadd:
 342    case nir_intrinsic_ssbo_atomic_fmax:
 343    case nir_intrinsic_ssbo_atomic_fmin:
 344    case nir_intrinsic_ssbo_atomic_fcomp_swap:
 345    case nir_intrinsic_image_deref_atomic_add:
 346    case nir_intrinsic_image_deref_atomic_imin:
 347    case nir_intrinsic_image_deref_atomic_umin:
 348    case nir_intrinsic_image_deref_atomic_imax:
 349    case nir_intrinsic_image_deref_atomic_umax:
 350    case nir_intrinsic_image_deref_atomic_and:
 351    case nir_intrinsic_image_deref_atomic_or:
 352    case nir_intrinsic_image_deref_atomic_xor:
 353    case nir_intrinsic_image_deref_atomic_exchange:
 354    case nir_intrinsic_image_deref_atomic_comp_swap:
 355    case nir_intrinsic_image_deref_atomic_fadd:
 356    case nir_intrinsic_image_atomic_add:
 357    case nir_intrinsic_image_atomic_imin:
 358    case nir_intrinsic_image_atomic_umin:
 359    case nir_intrinsic_image_atomic_imax:
 360    case nir_intrinsic_image_atomic_umax:
 361    case nir_intrinsic_image_atomic_and:
 362    case nir_intrinsic_image_atomic_or:
 363    case nir_intrinsic_image_atomic_xor:
 364    case nir_intrinsic_image_atomic_exchange:
 365    case nir_intrinsic_image_atomic_comp_swap:
 366    case nir_intrinsic_image_atomic_fadd:
 367    case nir_intrinsic_bindless_image_atomic_add:
 368    case nir_intrinsic_bindless_image_atomic_imin:
 369    case nir_intrinsic_bindless_image_atomic_umin:
 370    case nir_intrinsic_bindless_image_atomic_imax:
 371    case nir_intrinsic_bindless_image_atomic_umax:
 372    case nir_intrinsic_bindless_image_atomic_and:
 373    case nir_intrinsic_bindless_image_atomic_or:
 374    case nir_intrinsic_bindless_image_atomic_xor:
 375    case nir_intrinsic_bindless_image_atomic_exchange:
 376    case nir_intrinsic_bindless_image_atomic_comp_swap:
 377    case nir_intrinsic_bindless_image_atomic_fadd:
 378    case nir_intrinsic_shared_atomic_add:
 379    case nir_intrinsic_shared_atomic_imin:
 380    case nir_intrinsic_shared_atomic_umin:
 381    case nir_intrinsic_shared_atomic_imax:
 382    case nir_intrinsic_shared_atomic_umax:
 383    case nir_intrinsic_shared_atomic_and:
 384    case nir_intrinsic_shared_atomic_or:
 385    case nir_intrinsic_shared_atomic_xor:
 386    case nir_intrinsic_shared_atomic_exchange:
 387    case nir_intrinsic_shared_atomic_comp_swap:
 388    case nir_intrinsic_shared_atomic_fadd:
 389    case nir_intrinsic_shared_atomic_fmin:
 390    case nir_intrinsic_shared_atomic_fmax:
 391    case nir_intrinsic_shared_atomic_fcomp_swap:
 392    case nir_intrinsic_global_atomic_add:
 393    case nir_intrinsic_global_atomic_imin:
 394    case nir_intrinsic_global_atomic_umin:
 395    case nir_intrinsic_global_atomic_imax:
 396    case nir_intrinsic_global_atomic_umax:
 397    case nir_intrinsic_global_atomic_and:
 398    case nir_intrinsic_global_atomic_or:
 399    case nir_intrinsic_global_atomic_xor:
 400    case nir_intrinsic_global_atomic_exchange:
 401    case nir_intrinsic_global_atomic_comp_swap:
 402    case nir_intrinsic_global_atomic_fadd:
 403    case nir_intrinsic_global_atomic_fmin:
 404    case nir_intrinsic_global_atomic_fmax:
 405    case nir_intrinsic_global_atomic_fcomp_swap:
 406    case nir_intrinsic_atomic_counter_add:
 407    case nir_intrinsic_atomic_counter_min:
 408    case nir_intrinsic_atomic_counter_max:
 409    case nir_intrinsic_atomic_counter_and:
 410    case nir_intrinsic_atomic_counter_or:
 411    case nir_intrinsic_atomic_counter_xor:
 412    case nir_intrinsic_atomic_counter_inc:
 413    case nir_intrinsic_atomic_counter_pre_dec:
 414    case nir_intrinsic_atomic_counter_post_dec:
 415    case nir_intrinsic_atomic_counter_exchange:
 416    case nir_intrinsic_atomic_counter_comp_swap:
 417    case nir_intrinsic_atomic_counter_add_deref:
 418    case nir_intrinsic_atomic_counter_min_deref:
 419    case nir_intrinsic_atomic_counter_max_deref:
 420    case nir_intrinsic_atomic_counter_and_deref:
 421    case nir_intrinsic_atomic_counter_or_deref:
 422    case nir_intrinsic_atomic_counter_xor_deref:
 423    case nir_intrinsic_atomic_counter_inc_deref:
 424    case nir_intrinsic_atomic_counter_pre_dec_deref:
 425    case nir_intrinsic_atomic_counter_post_dec_deref:
 426    case nir_intrinsic_atomic_counter_exchange_deref:
 427    case nir_intrinsic_atomic_counter_comp_swap_deref:
 428    case nir_intrinsic_exclusive_scan:
 429    case nir_intrinsic_ballot_bit_count_exclusive:
 430    case nir_intrinsic_ballot_bit_count_inclusive:
 431    case nir_intrinsic_write_invocation_amd:
 432    case nir_intrinsic_mbcnt_amd:
 433    case nir_intrinsic_elect:
 434       is_divergent = true;
 435       break;
 436
 437    default:
 438 #ifdef NDEBUG
 439       is_divergent = true;
 440       break;
 441 #else
 442       nir_print_instr(&instr->instr, stderr);
 443       unreachable("\nNIR divergence analysis: Unhandled intrinsic.");
 444 #endif
 445    }
 446
 447    instr->dest.ssa.divergent = is_divergent;
 448    return is_divergent;
 449 }
 450
 451 static bool
 452 visit_tex(nir_tex_instr *instr)
 453 {
 454    if (instr->dest.ssa.divergent)
 455       return false;
 456
 457    bool is_divergent = false;
 458
 459    for (unsigned i = 0; i < instr->num_srcs; i++) {
 460       switch (instr->src[i].src_type) {
 461       case nir_tex_src_sampler_deref:
 462       case nir_tex_src_sampler_handle:
 463       case nir_tex_src_sampler_offset:
 464          is_divergent |= instr->src[i].src.ssa->divergent &&
 465                          instr->sampler_non_uniform;
 466          break;
 467       case nir_tex_src_texture_deref:
 468       case nir_tex_src_texture_handle:
 469       case nir_tex_src_texture_offset:
 470          is_divergent |= instr->src[i].src.ssa->divergent &&
 471                          instr->texture_non_uniform;
 472          break;
 473       default:
 474          is_divergent |= instr->src[i].src.ssa->divergent;
 475          break;
 476       }
 477    }
 478
 479    instr->dest.ssa.divergent = is_divergent;
 480    return is_divergent;
 481 }
 482
 483 static bool
 484 visit_load_const(nir_load_const_instr *instr)
 485 {
 486    return false;
 487 }
 488
 489 static bool
 490 visit_ssa_undef(nir_ssa_undef_instr *instr)
 491 {
 492    return false;
 493 }
 494
 495 static bool
 496 nir_variable_mode_is_uniform(nir_variable_mode mode) {
 497    switch (mode) {
 498    case nir_var_uniform:
 499    case nir_var_mem_ubo:
 500    case nir_var_mem_ssbo:
 501    case nir_var_mem_shared:
 502    case nir_var_mem_global:
 503       return true;
 504    default:
 505       return false;
 506    }
 507 }
 508
 509 static bool
 510 nir_variable_is_uniform(nir_variable *var, struct divergence_state *state)
 511 {
 512    if (nir_variable_mode_is_uniform(var->data.mode))
 513       return true;
 514
 515    if (state->stage == MESA_SHADER_FRAGMENT &&
 516        (state->options & nir_divergence_single_prim_per_subgroup) &&
 517        var->data.mode == nir_var_shader_in &&
 518        var->data.interpolation == INTERP_MODE_FLAT)
 519       return true;
 520
 521    if (state->stage == MESA_SHADER_TESS_CTRL &&
 522        (state->options & nir_divergence_single_patch_per_tcs_subgroup) &&
 523        var->data.mode == nir_var_shader_out && var->data.patch)
 524       return true;
 525
 526    if (state->stage == MESA_SHADER_TESS_EVAL &&
 527        (state->options & nir_divergence_single_patch_per_tes_subgroup) &&
 528        var->data.mode == nir_var_shader_in && var->data.patch)
 529       return true;
 530
 531    return false;
 532 }
 533
 534 static bool
 535 visit_deref(nir_deref_instr *deref, struct divergence_state *state)
 536 {
 537    if (deref->dest.ssa.divergent)
 538       return false;
 539
 540    bool is_divergent = false;
 541    switch (deref->deref_type) {
 542    case nir_deref_type_var:
 543       is_divergent = !nir_variable_is_uniform(deref->var, state);
 544       break;
 545    case nir_deref_type_array:
 546    case nir_deref_type_ptr_as_array:
 547       is_divergent = deref->arr.index.ssa->divergent;
 548       /* fallthrough */
 549    case nir_deref_type_struct:
 550    case nir_deref_type_array_wildcard:
 551       is_divergent |= deref->parent.ssa->divergent;
 552       break;
 553    case nir_deref_type_cast:
 554       is_divergent = !nir_variable_mode_is_uniform(deref->var->data.mode) ||
 555                      deref->parent.ssa->divergent;
 556       break;
 557    }
 558
 559    deref->dest.ssa.divergent = is_divergent;
 560    return is_divergent;
 561 }
 562
 563 static bool
 564 visit_jump(nir_jump_instr *jump, struct divergence_state *state)
 565 {
 566    switch (jump->type) {
 567    case nir_jump_continue:
 568       if (state->divergent_loop_continue)
 569          return false;
 570       if (state->divergent_loop_cf)
 571          state->divergent_loop_continue = true;
 572       return state->divergent_loop_continue;
 573    case nir_jump_break:
 574       if (state->divergent_loop_break)
 575          return false;
 576       if (state->divergent_loop_cf)
 577          state->divergent_loop_break = true;
 578       return state->divergent_loop_break;
 579    case nir_jump_return:
 580       unreachable("NIR divergence analysis: Unsupported return instruction.");
 581    }
 582    return false;
 583 }
 584
 585 static bool
 586 set_ssa_def_not_divergent(nir_ssa_def *def, UNUSED void *_state)
 587 {
 588    def->divergent = false;
 589    return true;
 590 }
 591
 592 static bool
 593 visit_block(nir_block *block, struct divergence_state *state)
 594 {
 595    bool has_changed = false;
 596
 597    nir_foreach_instr(instr, block) {
 598       /* phis are handled when processing the branches */
 599       if (instr->type == nir_instr_type_phi)
 600          continue;
 601
 602       if (state->first_visit)
 603          nir_foreach_ssa_def(instr, set_ssa_def_not_divergent, NULL);
 604
 605       switch (instr->type) {
 606       case nir_instr_type_alu:
 607          has_changed |= visit_alu(nir_instr_as_alu(instr));
 608          break;
 609       case nir_instr_type_intrinsic:
 610          has_changed |= visit_intrinsic(nir_instr_as_intrinsic(instr), state);
 611          break;
 612       case nir_instr_type_tex:
 613          has_changed |= visit_tex(nir_instr_as_tex(instr));
 614          break;
 615       case nir_instr_type_load_const:
 616          has_changed |= visit_load_const(nir_instr_as_load_const(instr));
 617          break;
 618       case nir_instr_type_ssa_undef:
 619          has_changed |= visit_ssa_undef(nir_instr_as_ssa_undef(instr));
 620          break;
 621       case nir_instr_type_deref:
 622          has_changed |= visit_deref(nir_instr_as_deref(instr), state);
 623          break;
 624       case nir_instr_type_jump:
 625          has_changed |= visit_jump(nir_instr_as_jump(instr), state);
 626          break;
 627       case nir_instr_type_phi:
 628       case nir_instr_type_call:
 629       case nir_instr_type_parallel_copy:
 630          unreachable("NIR divergence analysis: Unsupported instruction type.");
 631       }
 632    }
 633
 634    return has_changed;
 635 }
 636
 637 /* There are 3 types of phi instructions:
 638  * (1) gamma: represent the joining point of different paths
 639  *     created by an “if-then-else” branch.
 640  *     The resulting value is divergent if the branch condition
 641  *     or any of the source values is divergent. */
 642 static bool
 643 visit_if_merge_phi(nir_phi_instr *phi, bool if_cond_divergent)
 644 {
 645    if (phi->dest.ssa.divergent)
 646       return false;
 647
 648    unsigned defined_srcs = 0;
 649    nir_foreach_phi_src(src, phi) {
 650       /* if any source value is divergent, the resulting value is divergent */
 651       if (src->src.ssa->divergent) {
 652          phi->dest.ssa.divergent = true;
 653          return true;
 654       }
 655       if (src->src.ssa->parent_instr->type != nir_instr_type_ssa_undef) {
 656          defined_srcs++;
 657       }
 658    }
 659
 660    /* if the condition is divergent and two sources defined, the definition is divergent */
 661    if (defined_srcs > 1 && if_cond_divergent) {
 662       phi->dest.ssa.divergent = true;
 663       return true;
 664    }
 665
 666    return false;
 667 }
 668
 669 /* There are 3 types of phi instructions:
 670  * (2) mu: which only exist at loop headers,
 671  *     merge initial and loop-carried values.
 672  *     The resulting value is divergent if any source value
 673  *     is divergent or a divergent loop continue condition
 674  *     is associated with a different ssa-def. */
 675 static bool
 676 visit_loop_header_phi(nir_phi_instr *phi, nir_block *preheader, bool divergent_continue)
 677 {
 678    if (phi->dest.ssa.divergent)
 679       return false;
 680
 681    nir_ssa_def* same = NULL;
 682    nir_foreach_phi_src(src, phi) {
 683       /* if any source value is divergent, the resulting value is divergent */
 684       if (src->src.ssa->divergent) {
 685          phi->dest.ssa.divergent = true;
 686          return true;
 687       }
 688       /* if this loop is uniform, we're done here */
 689       if (!divergent_continue)
 690          continue;
 691       /* skip the loop preheader */
 692       if (src->pred == preheader)
 693          continue;
 694       /* skip undef values */
 695       if (src->src.ssa->parent_instr->type == nir_instr_type_ssa_undef)
 696          continue;
 697
 698       /* check if all loop-carried values are from the same ssa-def */
 699       if (!same)
 700          same = src->src.ssa;
 701       else if (same != src->src.ssa) {
 702          phi->dest.ssa.divergent = true;
 703          return true;
 704       }
 705    }
 706
 707    return false;
 708 }
 709
 710 /* There are 3 types of phi instructions:
 711  * (3) eta: represent values that leave a loop.
 712  *     The resulting value is divergent if the source value is divergent
 713  *     or any loop exit condition is divergent for a value which is
 714  *     not loop-invariant.
 715  *     (note: there should be no phi for loop-invariant variables.) */
 716 static bool
 717 visit_loop_exit_phi(nir_phi_instr *phi, bool divergent_break)
 718 {
 719    if (phi->dest.ssa.divergent)
 720       return false;
 721
 722    if (divergent_break) {
 723       phi->dest.ssa.divergent = true;
 724       return true;
 725    }
 726
 727    /* if any source value is divergent, the resulting value is divergent */
 728    nir_foreach_phi_src(src, phi) {
 729       if (src->src.ssa->divergent) {
 730          phi->dest.ssa.divergent = true;
 731          return true;
 732       }
 733    }
 734
 735    return false;
 736 }
 737
 738 static bool
 739 visit_if(nir_if *if_stmt, struct divergence_state *state)
 740 {
 741    bool progress = false;
 742
 743    struct divergence_state then_state = *state;
 744    then_state.divergent_loop_cf |= if_stmt->condition.ssa->divergent;
 745    progress |= visit_cf_list(&if_stmt->then_list, &then_state);
 746
 747    struct divergence_state else_state = *state;
 748    else_state.divergent_loop_cf |= if_stmt->condition.ssa->divergent;
 749    progress |= visit_cf_list(&if_stmt->else_list, &else_state);
 750
 751    /* handle phis after the IF */
 752    nir_foreach_instr(instr, nir_cf_node_cf_tree_next(&if_stmt->cf_node)) {
 753       if (instr->type != nir_instr_type_phi)
 754          break;
 755
 756       if (state->first_visit)
 757          nir_instr_as_phi(instr)->dest.ssa.divergent = false;
 758       progress |= visit_if_merge_phi(nir_instr_as_phi(instr),
 759                                      if_stmt->condition.ssa->divergent);
 760    }
 761
 762    /* join loop divergence information from both branch legs */
 763    state->divergent_loop_continue |= then_state.divergent_loop_continue ||
 764                                      else_state.divergent_loop_continue;
 765    state->divergent_loop_break |= then_state.divergent_loop_break ||
 766                                   else_state.divergent_loop_break;
 767
 768    /* A divergent continue makes succeeding loop CF divergent:
 769     * not all loop-active invocations participate in the remaining loop-body
 770     * which means that a following break might be taken by some invocations, only */
 771    state->divergent_loop_cf |= state->divergent_loop_continue;
 772
 773    return progress;
 774 }
 775
 776 static bool
 777 visit_loop(nir_loop *loop, struct divergence_state *state)
 778 {
 779    bool progress = false;
 780    nir_block *loop_header = nir_loop_first_block(loop);
 781    nir_block *loop_preheader = nir_block_cf_tree_prev(loop_header);
 782
 783    /* handle loop header phis first: we have no knowledge yet about
 784     * the loop's control flow or any loop-carried sources. */
 785    nir_foreach_instr(instr, loop_header) {
 786       if (instr->type != nir_instr_type_phi)
 787          break;
 788
 789       nir_phi_instr *phi = nir_instr_as_phi(instr);
 790       if (!state->first_visit && phi->dest.ssa.divergent)
 791          continue;
 792
 793       nir_foreach_phi_src(src, phi) {
 794          if (src->pred == loop_preheader) {
 795             phi->dest.ssa.divergent = src->src.ssa->divergent;
 796             break;
 797          }
 798       }
 799       progress |= phi->dest.ssa.divergent;
 800    }
 801
 802    /* setup loop state */
 803    struct divergence_state loop_state = *state;
 804    loop_state.divergent_loop_cf = false;
 805    loop_state.divergent_loop_continue = false;
 806    loop_state.divergent_loop_break = false;
 807
 808    /* process loop body until no further changes are made */
 809    bool repeat;
 810    do {
 811       progress |= visit_cf_list(&loop->body, &loop_state);
 812       repeat = false;
 813
 814       /* revisit loop header phis to see if something has changed */
 815       nir_foreach_instr(instr, loop_header) {
 816          if (instr->type != nir_instr_type_phi)
 817             break;
 818
 819          repeat |= visit_loop_header_phi(nir_instr_as_phi(instr),
 820                                          loop_preheader,
 821                                          loop_state.divergent_loop_continue);
 822       }
 823
 824       loop_state.divergent_loop_cf = false;
 825       loop_state.first_visit = false;
 826    } while (repeat);
 827
 828    /* handle phis after the loop */
 829    nir_foreach_instr(instr, nir_cf_node_cf_tree_next(&loop->cf_node)) {
 830       if (instr->type != nir_instr_type_phi)
 831          break;
 832
 833       if (state->first_visit)
 834          nir_instr_as_phi(instr)->dest.ssa.divergent = false;
 835       progress |= visit_loop_exit_phi(nir_instr_as_phi(instr),
 836                                       loop_state.divergent_loop_break);
 837    }
 838
 839    return progress;
 840 }
 841
 842 static bool
 843 visit_cf_list(struct exec_list *list, struct divergence_state *state)
 844 {
 845    bool has_changed = false;
 846
 847    foreach_list_typed(nir_cf_node, node, node, list) {
 848       switch (node->type) {
 849       case nir_cf_node_block:
 850          has_changed |= visit_block(nir_cf_node_as_block(node), state);
 851          break;
 852       case nir_cf_node_if:
 853          has_changed |= visit_if(nir_cf_node_as_if(node), state);
 854          break;
 855       case nir_cf_node_loop:
 856          has_changed |= visit_loop(nir_cf_node_as_loop(node), state);
 857          break;
 858       case nir_cf_node_function:
 859          unreachable("NIR divergence analysis: Unsupported cf_node type.");
 860       }
 861    }
 862
 863    return has_changed;
 864 }
 865
 866 void
 867 nir_divergence_analysis(nir_shader *shader, nir_divergence_options options)
 868 {
 869    struct divergence_state state = {
 870       .options = options,
 871       .stage = shader->info.stage,
 872       .divergent_loop_cf = false,
 873       .divergent_loop_continue = false,
 874       .divergent_loop_break = false,
 875       .first_visit = true,
 876    };
 877
 878    visit_cf_list(&nir_shader_get_entrypoint(shader)->body, &state);
 879 }
 880