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_as_const_value(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 static void
 154 lower_clip_vs(nir_function_impl *impl, unsigned ucp_enables,
 155               nir_ssa_def *cv, nir_variable **out)
 156 {
 157    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 158    nir_builder b;
 159
 160    nir_builder_init(&b, impl);
 161
 162    /* NIR should ensure that, even in case of loops/if-else, there
 163     * should be only a single predecessor block to end_block, which
 164     * makes the perfect place to insert the clipdist calculations.
 165     *
 166     * NOTE: in case of early returns, these would have to be lowered
 167     * to jumps to end_block predecessor in a previous pass.  Not sure
 168     * if there is a good way to sanity check this, but for now the
 169     * users of this pass don't support sub-routines.
 170     */
 171    assert(impl->end_block->predecessors->entries == 1);
 172    b.cursor = nir_after_cf_list(&impl->body);
 173
 174    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 175       if (ucp_enables & (1 << plane)) {
 176          nir_ssa_def *ucp =
 177             nir_load_system_value(&b, nir_intrinsic_load_user_clip_plane, plane);
 178
 179          /* calculate clipdist[plane] - dot(ucp, cv): */
 180          clipdist[plane] = nir_fdot4(&b, ucp, cv);
 181       }
 182       else {
 183          /* 0.0 == don't-clip == disabled: */
 184          clipdist[plane] = nir_imm_float(&b, 0.0);
 185       }
 186    }
 187
 188    if (ucp_enables & 0x0f)
 189       store_clipdist_output(&b, out[0], &clipdist[0]);
 190    if (ucp_enables & 0xf0)
 191       store_clipdist_output(&b, out[1], &clipdist[4]);
 192
 193    nir_metadata_preserve(impl, nir_metadata_dominance);
 194 }
 195
 196 /* ucp_enables is bitmask of enabled ucps.  Actual ucp values are
 197  * passed in to shader via user_clip_plane system-values
 198  */
 199 bool
 200 nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables)
 201 {
 202    int clipvertex = -1;
 203    int position = -1;
 204    int maxloc = -1;
 205    nir_ssa_def *cv;
 206    nir_variable *out[2] = { NULL };
 207
 208    if (!ucp_enables)
 209       return false;
 210
 211    /* find clipvertex/position outputs: */
 212    nir_foreach_variable(var, &shader->outputs) {
 213       int loc = var->data.driver_location;
 214
 215       /* keep track of last used driver-location.. we'll be
 216        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 217        * output:
 218        */
 219       maxloc = MAX2(maxloc, loc);
 220
 221       switch (var->data.location) {
 222       case VARYING_SLOT_POS:
 223          position = loc;
 224          break;
 225       case VARYING_SLOT_CLIP_VERTEX:
 226          clipvertex = loc;
 227          break;
 228       case VARYING_SLOT_CLIP_DIST0:
 229       case VARYING_SLOT_CLIP_DIST1:
 230          /* if shader is already writing CLIPDIST, then
 231           * there should be no user-clip-planes to deal
 232           * with.
 233           */
 234          return false;
 235       }
 236    }
 237
 238    if (clipvertex != -1)
 239       cv = find_output(shader, clipvertex);
 240    else if (position != -1)
 241       cv = find_output(shader, position);
 242    else
 243       return false;
 244
 245    /* insert CLIPDIST outputs: */
 246    if (ucp_enables & 0x0f)
 247       out[0] =
 248          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST0);
 249    if (ucp_enables & 0xf0)
 250       out[1] =
 251          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST1);
 252
 253    nir_foreach_function(function, shader) {
 254       if (!strcmp(function->name, "main"))
 255          lower_clip_vs(function->impl, ucp_enables, cv, out);
 256    }
 257
 258    return true;
 259 }
 260
 261 /*
 262  * FS lowering
 263  */
 264
 265 static void
 266 lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 267               nir_variable **in)
 268 {
 269    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 270    nir_builder b;
 271
 272    nir_builder_init(&b, impl);
 273    b.cursor = nir_before_cf_list(&impl->body);
 274
 275    if (ucp_enables & 0x0f)
 276       load_clipdist_input(&b, in[0], &clipdist[0]);
 277    if (ucp_enables & 0xf0)
 278       load_clipdist_input(&b, in[1], &clipdist[4]);
 279
 280    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 281       if (ucp_enables & (1 << plane)) {
 282          nir_intrinsic_instr *discard;
 283          nir_ssa_def *cond;
 284
 285          cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));
 286
 287          discard = nir_intrinsic_instr_create(b.shader,
 288                                               nir_intrinsic_discard_if);
 289          discard->src[0] = nir_src_for_ssa(cond);
 290          nir_builder_instr_insert(&b, &discard->instr);
 291
 292          b.shader->info.fs.uses_discard = true;
 293       }
 294    }
 295
 296    nir_metadata_preserve(impl, nir_metadata_dominance);
 297 }
 298
 299 /* insert conditional kill based on interpolated CLIPDIST
 300  */
 301 bool
 302 nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables)
 303 {
 304    nir_variable *in[2];
 305    int maxloc = -1;
 306
 307    if (!ucp_enables)
 308       return false;
 309
 310    nir_foreach_variable(var, &shader->inputs) {
 311       int loc = var->data.driver_location;
 312
 313       /* keep track of last used driver-location.. we'll be
 314        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 315        * input:
 316        */
 317       maxloc = MAX2(maxloc, loc);
 318    }
 319
 320    /* The shader won't normally have CLIPDIST inputs, so we
 321     * must add our own:
 322     */
 323    /* insert CLIPDIST outputs: */
 324    if (ucp_enables & 0x0f)
 325       in[0] =
 326          create_clipdist_var(shader, ++maxloc, false,
 327                              VARYING_SLOT_CLIP_DIST0);
 328    if (ucp_enables & 0xf0)
 329       in[1] =
 330          create_clipdist_var(shader, ++maxloc, false,
 331                              VARYING_SLOT_CLIP_DIST1);
 332
 333    nir_foreach_function(function, shader) {
 334       if (!strcmp(function->name, "main"))
 335          lower_clip_fs(function->impl, ucp_enables, in);
 336    }
 337
 338    return true;
 339 }