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)
  46 {
  47    nir_variable *var = rzalloc(shader, nir_variable);
  48
  49    var->data.driver_location = drvloc;
  50    var->type = glsl_vec4_type();
  51    var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
  52    var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
  53    var->data.index = 0;
  54    var->data.location = slot;
  55
  56    if (output) {
  57       exec_list_push_tail(&shader->outputs, &var->node);
  58       shader->num_outputs++; /* TODO use type_size() */
  59    }
  60    else {
  61       exec_list_push_tail(&shader->inputs, &var->node);
  62       shader->num_inputs++;  /* TODO use type_size() */
  63    }
  64    return var;
  65 }
  66
  67 static void
  68 store_clipdist_output(nir_builder *b, nir_variable *out, nir_ssa_def **val)
  69 {
  70    nir_intrinsic_instr *store;
  71
  72    store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
  73    store->num_components = 4;
  74    nir_intrinsic_set_base(store, out->data.driver_location);
  75    nir_intrinsic_set_write_mask(store, 0xf);
  76    store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
  77    store->src[0].is_ssa = true;
  78    store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
  79    nir_builder_instr_insert(b, &store->instr);
  80 }
  81
  82 static void
  83 load_clipdist_input(nir_builder *b, nir_variable *in, nir_ssa_def **val)
  84 {
  85    nir_intrinsic_instr *load;
  86
  87    load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
  88    load->num_components = 4;
  89    nir_intrinsic_set_base(load, in->data.driver_location);
  90    load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
  91    nir_ssa_dest_init(&load->instr, &load->dest, 4, 32, NULL);
  92    nir_builder_instr_insert(b, &load->instr);
  93
  94    val[0] = nir_channel(b, &load->dest.ssa, 0);
  95    val[1] = nir_channel(b, &load->dest.ssa, 1);
  96    val[2] = nir_channel(b, &load->dest.ssa, 2);
  97    val[3] = nir_channel(b, &load->dest.ssa, 3);
  98 }
  99
 100 static nir_ssa_def *
 101 find_output_in_block(nir_block *block, unsigned drvloc)
 102 {
 103    nir_foreach_instr(instr, block) {
 104
 105       if (instr->type == nir_instr_type_intrinsic) {
 106          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
 107          if ((intr->intrinsic == nir_intrinsic_store_output) &&
 108              nir_intrinsic_base(intr) == drvloc) {
 109             assert(intr->src[0].is_ssa);
 110             assert(nir_src_is_const(intr->src[1]));
 111             return intr->src[0].ssa;
 112          }
 113       }
 114    }
 115
 116    return NULL;
 117 }
 118
 119 /* TODO: maybe this would be a useful helper?
 120  * NOTE: assumes each output is written exactly once (and unconditionally)
 121  * so if needed nir_lower_outputs_to_temporaries()
 122  */
 123 static nir_ssa_def *
 124 find_output(nir_shader *shader, unsigned drvloc)
 125 {
 126    nir_ssa_def *def = NULL;
 127    nir_foreach_function(function, shader) {
 128       if (function->impl) {
 129          nir_foreach_block_reverse(block, function->impl) {
 130             nir_ssa_def *new_def = find_output_in_block(block, drvloc);
 131             assert(!(new_def && def));
 132             def = new_def;
 133 #if !defined(DEBUG)
 134             /* for debug builds, scan entire shader to assert
 135              * if output is written multiple times.  For release
 136              * builds just assume all is well and bail when we
 137              * find first:
 138              */
 139             if (def)
 140                break;
 141 #endif
 142          }
 143       }
 144    }
 145
 146    return def;
 147 }
 148
 149 /*
 150  * VS lowering
 151  */
 152
 153 /* ucp_enables is bitmask of enabled ucps.  Actual ucp values are
 154  * passed in to shader via user_clip_plane system-values
 155  */
 156 bool
 157 nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables)
 158 {
 159    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
 160    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 161    nir_builder b;
 162    int clipvertex = -1;
 163    int position = -1;
 164    int maxloc = -1;
 165    nir_ssa_def *cv;
 166    nir_variable *out[2] = { NULL };
 167
 168    if (!ucp_enables)
 169       return false;
 170
 171    nir_builder_init(&b, impl);
 172
 173    /* NIR should ensure that, even in case of loops/if-else, there
 174     * should be only a single predecessor block to end_block, which
 175     * makes the perfect place to insert the clipdist calculations.
 176     *
 177     * NOTE: in case of early returns, these would have to be lowered
 178     * to jumps to end_block predecessor in a previous pass.  Not sure
 179     * if there is a good way to sanity check this, but for now the
 180     * users of this pass don't support sub-routines.
 181     */
 182    assert(impl->end_block->predecessors->entries == 1);
 183    b.cursor = nir_after_cf_list(&impl->body);
 184
 185    /* find clipvertex/position outputs: */
 186    nir_foreach_variable(var, &shader->outputs) {
 187       int loc = var->data.driver_location;
 188
 189       /* keep track of last used driver-location.. we'll be
 190        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 191        * output:
 192        */
 193       maxloc = MAX2(maxloc, loc);
 194
 195       switch (var->data.location) {
 196       case VARYING_SLOT_POS:
 197          position = loc;
 198          break;
 199       case VARYING_SLOT_CLIP_VERTEX:
 200          clipvertex = loc;
 201          break;
 202       case VARYING_SLOT_CLIP_DIST0:
 203       case VARYING_SLOT_CLIP_DIST1:
 204          /* if shader is already writing CLIPDIST, then
 205           * there should be no user-clip-planes to deal
 206           * with.
 207           */
 208          return false;
 209       }
 210    }
 211
 212    if (clipvertex != -1)
 213       cv = find_output(shader, clipvertex);
 214    else if (position != -1)
 215       cv = find_output(shader, position);
 216    else
 217       return false;
 218
 219    /* insert CLIPDIST outputs: */
 220    if (ucp_enables & 0x0f)
 221       out[0] =
 222          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST0);
 223    if (ucp_enables & 0xf0)
 224       out[1] =
 225          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST1);
 226
 227    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 228       if (ucp_enables & (1 << plane)) {
 229          nir_ssa_def *ucp = nir_load_user_clip_plane(&b, plane);
 230
 231          /* calculate clipdist[plane] - dot(ucp, cv): */
 232          clipdist[plane] = nir_fdot4(&b, ucp, cv);
 233       } else {
 234          /* 0.0 == don't-clip == disabled: */
 235          clipdist[plane] = nir_imm_float(&b, 0.0);
 236       }
 237    }
 238
 239    if (ucp_enables & 0x0f)
 240       store_clipdist_output(&b, out[0], &clipdist[0]);
 241    if (ucp_enables & 0xf0)
 242       store_clipdist_output(&b, out[1], &clipdist[4]);
 243
 244    nir_metadata_preserve(impl, nir_metadata_dominance);
 245
 246    return true;
 247 }
 248
 249 /*
 250  * FS lowering
 251  */
 252
 253 static void
 254 lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 255               nir_variable **in)
 256 {
 257    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 258    nir_builder b;
 259
 260    nir_builder_init(&b, impl);
 261    b.cursor = nir_before_cf_list(&impl->body);
 262
 263    if (ucp_enables & 0x0f)
 264       load_clipdist_input(&b, in[0], &clipdist[0]);
 265    if (ucp_enables & 0xf0)
 266       load_clipdist_input(&b, in[1], &clipdist[4]);
 267
 268    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 269       if (ucp_enables & (1 << plane)) {
 270          nir_intrinsic_instr *discard;
 271          nir_ssa_def *cond;
 272
 273          cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));
 274
 275          discard = nir_intrinsic_instr_create(b.shader,
 276                                               nir_intrinsic_discard_if);
 277          discard->src[0] = nir_src_for_ssa(cond);
 278          nir_builder_instr_insert(&b, &discard->instr);
 279
 280          b.shader->info.fs.uses_discard = true;
 281       }
 282    }
 283
 284    nir_metadata_preserve(impl, nir_metadata_dominance);
 285 }
 286
 287 /* insert conditional kill based on interpolated CLIPDIST
 288  */
 289 bool
 290 nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables)
 291 {
 292    nir_variable *in[2];
 293    int maxloc = -1;
 294
 295    if (!ucp_enables)
 296       return false;
 297
 298    nir_foreach_variable(var, &shader->inputs) {
 299       int loc = var->data.driver_location;
 300
 301       /* keep track of last used driver-location.. we'll be
 302        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 303        * input:
 304        */
 305       maxloc = MAX2(maxloc, loc);
 306    }
 307
 308    /* The shader won't normally have CLIPDIST inputs, so we
 309     * must add our own:
 310     */
 311    /* insert CLIPDIST outputs: */
 312    if (ucp_enables & 0x0f)
 313       in[0] =
 314          create_clipdist_var(shader, ++maxloc, false,
 315                              VARYING_SLOT_CLIP_DIST0);
 316    if (ucp_enables & 0xf0)
 317       in[1] =
 318          create_clipdist_var(shader, ++maxloc, false,
 319                              VARYING_SLOT_CLIP_DIST1);
 320
 321    nir_foreach_function(function, shader) {
 322       if (!strcmp(function->name, "main"))
 323          lower_clip_fs(function->impl, ucp_enables, in);
 324    }
 325
 326    return true;
 327 }