src/compiler/nir/nir_lower_clip.c

   1 /*
   2  * Copyright © 2015 Red Hat
   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  *    Rob Clark <robclark@freedesktop.org>
  25  */
  26
  27 #include "nir.h"
  28 #include "nir_builder.h"
  29
  30 #define MAX_CLIP_PLANES 8
  31
  32 /* Generates the lowering code for user-clip-planes, generating CLIPDIST
  33  * from UCP[n] + CLIPVERTEX or POSITION.  Additionally, an optional pass
  34  * for fragment shaders to insert conditional kills based on the inter-
  35  * polated CLIPDIST
  36  *
  37  * NOTE: should be run after nir_lower_outputs_to_temporaries() (or at
  38  * least in scenarios where you can count on each output written once
  39  * and only once).
  40  */
  41
  42
  43 static nir_variable *
  44 create_clipdist_var(nir_shader *shader, unsigned drvloc,
  45                     bool output, gl_varying_slot slot, unsigned array_size)
  46 {
  47    nir_variable *var = rzalloc(shader, nir_variable);
  48
  49    var->data.driver_location = drvloc;
  50    var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
  51    var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
  52    var->data.index = 0;
  53    var->data.location = slot;
  54
  55    if (array_size > 0) {
  56       var->type = glsl_array_type(glsl_float_type(), array_size,
  57                                   sizeof(float));
  58       var->data.compact = 1;
  59    } else
  60       var->type = glsl_vec4_type();
  61
  62    if (output) {
  63       exec_list_push_tail(&shader->outputs, &var->node);
  64       shader->num_outputs++; /* TODO use type_size() */
  65    }
  66    else {
  67       exec_list_push_tail(&shader->inputs, &var->node);
  68       shader->num_inputs++;  /* TODO use type_size() */
  69    }
  70    return var;
  71 }
  72
  73 static void
  74 create_clipdist_vars(nir_shader *shader, nir_variable **io_vars,
  75                      unsigned ucp_enables, int *drvloc, bool output,
  76                      bool use_clipdist_array)
  77 {
  78    if (use_clipdist_array) {
  79       io_vars[0] =
  80          create_clipdist_var(shader, ++(*drvloc), true,
  81                              VARYING_SLOT_CLIP_DIST0,
  82                              util_last_bit(ucp_enables));
  83    } else {
  84       if (ucp_enables & 0x0f)
  85          io_vars[0] =
  86             create_clipdist_var(shader, ++(*drvloc), output,
  87                                 VARYING_SLOT_CLIP_DIST0, 0);
  88       if (ucp_enables & 0xf0)
  89          io_vars[1] =
  90             create_clipdist_var(shader, ++(*drvloc), output,
  91                                 VARYING_SLOT_CLIP_DIST1, 0);
  92    }
  93 }
  94
  95 static void
  96 store_clipdist_output(nir_builder *b, nir_variable *out, nir_ssa_def **val)
  97 {
  98    nir_intrinsic_instr *store;
  99
 100    store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
 101    store->num_components = 4;
 102    nir_intrinsic_set_base(store, out->data.driver_location);
 103    nir_intrinsic_set_write_mask(store, 0xf);
 104    store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
 105    store->src[0].is_ssa = true;
 106    store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
 107    nir_builder_instr_insert(b, &store->instr);
 108 }
 109
 110 static void
 111 load_clipdist_input(nir_builder *b, nir_variable *in, nir_ssa_def **val)
 112 {
 113    nir_intrinsic_instr *load;
 114
 115    load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
 116    load->num_components = 4;
 117    nir_intrinsic_set_base(load, in->data.driver_location);
 118    load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
 119    nir_ssa_dest_init(&load->instr, &load->dest, 4, 32, NULL);
 120    nir_builder_instr_insert(b, &load->instr);
 121
 122    val[0] = nir_channel(b, &load->dest.ssa, 0);
 123    val[1] = nir_channel(b, &load->dest.ssa, 1);
 124    val[2] = nir_channel(b, &load->dest.ssa, 2);
 125    val[3] = nir_channel(b, &load->dest.ssa, 3);
 126 }
 127
 128 static nir_ssa_def *
 129 find_output_in_block(nir_block *block, unsigned drvloc)
 130 {
 131    nir_foreach_instr(instr, block) {
 132
 133       if (instr->type == nir_instr_type_intrinsic) {
 134          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
 135          if ((intr->intrinsic == nir_intrinsic_store_output) &&
 136              nir_intrinsic_base(intr) == drvloc) {
 137             assert(intr->src[0].is_ssa);
 138             assert(nir_src_is_const(intr->src[1]));
 139             return intr->src[0].ssa;
 140          }
 141       }
 142    }
 143
 144    return NULL;
 145 }
 146
 147 /* TODO: maybe this would be a useful helper?
 148  * NOTE: assumes each output is written exactly once (and unconditionally)
 149  * so if needed nir_lower_outputs_to_temporaries()
 150  */
 151 static nir_ssa_def *
 152 find_output(nir_shader *shader, unsigned drvloc)
 153 {
 154    nir_ssa_def *def = NULL;
 155    nir_foreach_function(function, shader) {
 156       if (function->impl) {
 157          nir_foreach_block_reverse(block, function->impl) {
 158             nir_ssa_def *new_def = find_output_in_block(block, drvloc);
 159             assert(!(new_def && def));
 160             def = new_def;
 161 #if !defined(DEBUG)
 162             /* for debug builds, scan entire shader to assert
 163              * if output is written multiple times.  For release
 164              * builds just assume all is well and bail when we
 165              * find first:
 166              */
 167             if (def)
 168                break;
 169 #endif
 170          }
 171       }
 172    }
 173
 174    return def;
 175 }
 176
 177 static bool
 178 find_clipvertex_and_position_outputs(nir_shader *shader,
 179                                      nir_variable **clipvertex,
 180                                      nir_variable **position)
 181 {
 182    nir_foreach_variable(var, &shader->outputs) {
 183       switch (var->data.location) {
 184       case VARYING_SLOT_POS:
 185          *position = var;
 186          break;
 187       case VARYING_SLOT_CLIP_VERTEX:
 188          *clipvertex = var;
 189          break;
 190       case VARYING_SLOT_CLIP_DIST0:
 191       case VARYING_SLOT_CLIP_DIST1:
 192          /* if shader is already writing CLIPDIST, then
 193           * there should be no user-clip-planes to deal
 194           * with.
 195           *
 196           * We assume nir_remove_dead_variables has removed the clipdist
 197           * variables if they're not written.
 198           */
 199          return false;
 200       }
 201    }
 202
 203    return *clipvertex || *position;
 204 }
 205
 206 static void
 207 lower_clip_outputs(nir_builder *b, nir_variable *position,
 208                    nir_variable *clipvertex, nir_variable **out,
 209                    unsigned ucp_enables, bool use_vars,
 210                    bool use_clipdist_array)
 211 {
 212    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 213    nir_ssa_def *cv;
 214
 215    if (use_vars) {
 216       cv = nir_load_var(b, clipvertex ? clipvertex : position);
 217
 218       if (clipvertex) {
 219          exec_node_remove(&clipvertex->node);
 220          clipvertex->data.mode = nir_var_shader_temp;
 221          exec_list_push_tail(&b->shader->globals, &clipvertex->node);
 222       }
 223    } else {
 224       if (clipvertex)
 225          cv = find_output(b->shader, clipvertex->data.driver_location);
 226       else {
 227          assert(position);
 228          cv = find_output(b->shader, position->data.driver_location);
 229       }
 230    }
 231
 232    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 233       if (ucp_enables & (1 << plane)) {
 234          nir_ssa_def *ucp = nir_load_user_clip_plane(b, plane);
 235
 236          /* calculate clipdist[plane] - dot(ucp, cv): */
 237          clipdist[plane] = nir_fdot4(b, ucp, cv);
 238       } else {
 239          /* 0.0 == don't-clip == disabled: */
 240          clipdist[plane] = nir_imm_float(b, 0.0);
 241       }
 242       if (use_clipdist_array && plane < util_last_bit(ucp_enables)) {
 243          assert(use_vars);
 244          nir_deref_instr *deref;
 245          deref = nir_build_deref_array_imm(b,
 246                                            nir_build_deref_var(b, out[0]),
 247                                            plane);
 248          nir_store_deref(b, deref, clipdist[plane], 1);
 249       }
 250    }
 251
 252    if (!use_clipdist_array) {
 253       if (use_vars) {
 254          if (ucp_enables & 0x0f)
 255             nir_store_var(b, out[0], nir_vec(b, clipdist, 4), 0xf);
 256          if (ucp_enables & 0xf0)
 257             nir_store_var(b, out[1], nir_vec(b, &clipdist[4], 4), 0xf);
 258       } else {
 259          if (ucp_enables & 0x0f)
 260             store_clipdist_output(b, out[0], &clipdist[0]);
 261          if (ucp_enables & 0xf0)
 262             store_clipdist_output(b, out[1], &clipdist[4]);
 263       }
 264    }
 265 }
 266
 267 /*
 268  * VS lowering
 269  */
 270
 271 /* ucp_enables is bitmask of enabled ucps.  Actual ucp values are
 272  * passed in to shader via user_clip_plane system-values
 273  *
 274  * If use_vars is true, the pass will use variable loads and stores instead
 275  * of working with store_output intrinsics.
 276  *
 277  * If use_clipdist_array is true, the pass will use compact arrays for the
 278  * clipdist output instead of two vec4s.
 279  */
 280 bool
 281 nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables, bool use_vars,
 282                   bool use_clipdist_array)
 283 {
 284    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
 285    nir_builder b;
 286    int maxloc = -1;
 287    nir_variable *position = NULL;
 288    nir_variable *clipvertex = NULL;
 289    nir_variable *out[2] = { NULL };
 290
 291    if (!ucp_enables)
 292       return false;
 293
 294    nir_builder_init(&b, impl);
 295
 296    /* NIR should ensure that, even in case of loops/if-else, there
 297     * should be only a single predecessor block to end_block, which
 298     * makes the perfect place to insert the clipdist calculations.
 299     *
 300     * NOTE: in case of early returns, these would have to be lowered
 301     * to jumps to end_block predecessor in a previous pass.  Not sure
 302     * if there is a good way to sanity check this, but for now the
 303     * users of this pass don't support sub-routines.
 304     */
 305    assert(impl->end_block->predecessors->entries == 1);
 306    b.cursor = nir_after_cf_list(&impl->body);
 307
 308    /* find clipvertex/position outputs */
 309    if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
 310       return false;
 311
 312    /* insert CLIPDIST outputs */
 313    create_clipdist_vars(shader, out, ucp_enables, &maxloc, true,
 314                         use_clipdist_array);
 315
 316    lower_clip_outputs(&b, position, clipvertex, out, ucp_enables, use_vars,
 317                       use_clipdist_array);
 318
 319    nir_metadata_preserve(impl, nir_metadata_dominance);
 320
 321    return true;
 322 }
 323
 324 static void
 325 lower_clip_in_gs_block(nir_builder *b, nir_block *block, nir_variable *position,
 326                        nir_variable *clipvertex, nir_variable **out,
 327                        unsigned ucp_enables, bool use_clipdist_array)
 328 {
 329    nir_foreach_instr_safe(instr, block) {
 330       if (instr->type != nir_instr_type_intrinsic)
 331          continue;
 332
 333       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 334       switch (intrin->intrinsic) {
 335       case nir_intrinsic_emit_vertex_with_counter:
 336       case nir_intrinsic_emit_vertex:
 337          b->cursor = nir_before_instr(instr);
 338          lower_clip_outputs(b, position, clipvertex, out, ucp_enables, true,
 339                             use_clipdist_array);
 340          break;
 341       default:
 342          /* not interesting; skip this */
 343          break;
 344       }
 345    }
 346 }
 347
 348 /*
 349  * GS lowering
 350  */
 351
 352 bool
 353 nir_lower_clip_gs(nir_shader *shader, unsigned ucp_enables,
 354                   bool use_clipdist_array)
 355 {
 356    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
 357    nir_builder b;
 358    int maxloc = -1;
 359    nir_variable *position = NULL;
 360    nir_variable *clipvertex = NULL;
 361    nir_variable *out[2] = { NULL };
 362
 363    if (!ucp_enables)
 364       return false;
 365
 366    /* find clipvertex/position outputs */
 367    if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
 368       return false;
 369
 370    /* insert CLIPDIST outputs */
 371    create_clipdist_vars(shader, out, ucp_enables, &maxloc, true,
 372                         use_clipdist_array);
 373
 374    nir_builder_init(&b, impl);
 375
 376    nir_foreach_block(block, impl)
 377       lower_clip_in_gs_block(&b, block, position, clipvertex, out,
 378                              ucp_enables, use_clipdist_array);
 379
 380    nir_metadata_preserve(impl, nir_metadata_dominance);
 381
 382    return true;
 383 }
 384
 385 /*
 386  * FS lowering
 387  */
 388
 389 static void
 390 lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 391               nir_variable **in)
 392 {
 393    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 394    nir_builder b;
 395
 396    nir_builder_init(&b, impl);
 397    b.cursor = nir_before_cf_list(&impl->body);
 398
 399    if (ucp_enables & 0x0f)
 400       load_clipdist_input(&b, in[0], &clipdist[0]);
 401    if (ucp_enables & 0xf0)
 402       load_clipdist_input(&b, in[1], &clipdist[4]);
 403
 404    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 405       if (ucp_enables & (1 << plane)) {
 406          nir_intrinsic_instr *discard;
 407          nir_ssa_def *cond;
 408
 409          cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));
 410
 411          discard = nir_intrinsic_instr_create(b.shader,
 412                                               nir_intrinsic_discard_if);
 413          discard->src[0] = nir_src_for_ssa(cond);
 414          nir_builder_instr_insert(&b, &discard->instr);
 415
 416          b.shader->info.fs.uses_discard = true;
 417       }
 418    }
 419
 420    nir_metadata_preserve(impl, nir_metadata_dominance);
 421 }
 422
 423 /* insert conditional kill based on interpolated CLIPDIST
 424  */
 425 bool
 426 nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables,
 427                   bool use_clipdist_array)
 428 {
 429    nir_variable *in[2];
 430    int maxloc = -1;
 431
 432    if (!ucp_enables)
 433       return false;
 434
 435    nir_foreach_variable(var, &shader->inputs) {
 436       int loc = var->data.driver_location;
 437
 438       /* keep track of last used driver-location.. we'll be
 439        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 440        * input:
 441        */
 442       maxloc = MAX2(maxloc, loc);
 443    }
 444
 445    /* The shader won't normally have CLIPDIST inputs, so we
 446     * must add our own:
 447     */
 448    /* insert CLIPDIST inputs */
 449    create_clipdist_vars(shader, in, ucp_enables, &maxloc, false,
 450                         use_clipdist_array);
 451
 452    nir_foreach_function(function, shader) {
 453       if (!strcmp(function->name, "main"))
 454          lower_clip_fs(function->impl, ucp_enables, in);
 455    }
 456
 457    return true;
 458 }