ir_reader.cpp

   1 /*
   2  * Copyright © 2010 Intel 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
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23 #include <cstdio>
  24 #include <cstdarg>
  25 #include "ir_reader.h"
  26 #include "glsl_parser_extras.h"
  27 #include "glsl_types.h"
  28 #include "s_expression.h"
  29
  30 static void ir_read_error(s_expression *expr, const char *fmt, ...);
  31 static const glsl_type *read_type(_mesa_glsl_parse_state *, s_expression *);
  32
  33 static void read_instructions(_mesa_glsl_parse_state *, exec_list *,
  34                               s_expression *, ir_loop *);
  35 static ir_instruction *read_instruction(_mesa_glsl_parse_state *,
  36                                         s_expression *, ir_loop *);
  37 static ir_variable *read_declaration(_mesa_glsl_parse_state *, s_list *);
  38 static ir_if *read_if(_mesa_glsl_parse_state *, s_list *, ir_loop *);
  39 static ir_loop *read_loop(_mesa_glsl_parse_state *st, s_list *list);
  40 static ir_return *read_return(_mesa_glsl_parse_state *, s_list *);
  41
  42 static ir_rvalue *read_rvalue(_mesa_glsl_parse_state *, s_expression *);
  43 static ir_assignment *read_assignment(_mesa_glsl_parse_state *, s_list *);
  44 static ir_expression *read_expression(_mesa_glsl_parse_state *, s_list *);
  45 static ir_swizzle *read_swizzle(_mesa_glsl_parse_state *, s_list *);
  46 static ir_constant *read_constant(_mesa_glsl_parse_state *, s_list *);
  47 static ir_dereference *read_var_ref(_mesa_glsl_parse_state *, s_list *);
  48 static ir_dereference *read_array_ref(_mesa_glsl_parse_state *, s_list *);
  49 static ir_dereference *read_record_ref(_mesa_glsl_parse_state *, s_list *);
  50
  51 void
  52 _mesa_glsl_read_ir(_mesa_glsl_parse_state *state, exec_list *instructions,
  53                    const char *src)
  54 {
  55    s_expression *expr = s_expression::read_expression(src);
  56    if (expr == NULL) {
  57       ir_read_error(NULL, "couldn't parse S-Expression.");
  58       state->error = true;
  59       return;
  60    }
  61    printf("S-Expression:\n");
  62    expr->print();
  63    printf("\n-------------\n");
  64
  65    _mesa_glsl_initialize_types(state);
  66    _mesa_glsl_initialize_variables(instructions, state);
  67    _mesa_glsl_initialize_constructors(instructions, state);
  68    _mesa_glsl_initialize_functions(instructions, state);
  69
  70    read_instructions(state, instructions, expr, NULL);
  71 }
  72
  73 static void
  74 ir_read_error(s_expression *expr, const char *fmt, ...)
  75 {
  76    char buf[1024];
  77    int len;
  78    va_list ap;
  79
  80    // FIXME: state->error = true;
  81
  82    len = snprintf(buf, sizeof(buf), "error: ");
  83
  84    va_start(ap, fmt);
  85    vsnprintf(buf + len, sizeof(buf) - len, fmt, ap);
  86    va_end(ap);
  87
  88    printf("%s\n", buf);
  89 }
  90
  91 static const glsl_type *
  92 read_type(_mesa_glsl_parse_state *st, s_expression *expr)
  93 {
  94    s_list *list = SX_AS_LIST(expr);
  95    if (list != NULL) {
  96       s_symbol *type_sym = SX_AS_SYMBOL(list->subexpressions.get_head());
  97       if (type_sym == NULL) {
  98          ir_read_error(expr, "expected type (array ...) or (struct ...)");
  99          return NULL;
 100       }
 101       if (strcmp(type_sym->value(), "array") == 0) {
 102          if (list->length() != 3) {
 103             ir_read_error(expr, "expected type (array <type> <int>)");
 104             return NULL;
 105          }
 106
 107          // Read base type
 108          s_expression *base_expr = (s_expression*) type_sym->next;
 109          const glsl_type *base_type = read_type(st, base_expr);
 110          if (base_type == NULL) {
 111             ir_read_error(expr, "when reading base type of array");
 112             return NULL;
 113          }
 114
 115          // Read array size
 116          s_int *size = SX_AS_INT(base_expr->next);
 117          if (size == NULL) {
 118             ir_read_error(expr, "found non-integer array size");
 119             return NULL;
 120          }
 121
 122          return glsl_type::get_array_instance(base_type, size->value());
 123       } else if (strcmp(type_sym->value(), "struct") == 0) {
 124          assert(false); // FINISHME
 125       } else {
 126          ir_read_error(expr, "expected (array ...) or (struct ...); found (%s ...)", type_sym->value());
 127          return NULL;
 128       }
 129    }
 130
 131    s_symbol *type_sym = SX_AS_SYMBOL(expr);
 132    if (type_sym == NULL) {
 133       ir_read_error(expr, "expected <type> (symbol or list)");
 134       return NULL;
 135    }
 136
 137    const glsl_type *type = st->symbols->get_type(type_sym->value());
 138    if (type == NULL)
 139       ir_read_error(expr, "invalid type: %s", type_sym->value());
 140
 141    return type;
 142 }
 143
 144
 145 static void
 146 read_instructions(_mesa_glsl_parse_state *st, exec_list *instructions,
 147                   s_expression *expr, ir_loop *loop_ctx)
 148 {
 149    // Read in a list of instructions
 150    s_list *list = SX_AS_LIST(expr);
 151    if (list == NULL) {
 152       ir_read_error(expr, "Expected (<instruction> ...); found an atom.");
 153       st->error = true;
 154       return;
 155    }
 156
 157    foreach_iter(exec_list_iterator, it, list->subexpressions) {
 158       s_expression *sub = (s_expression*) it.get();
 159       ir_instruction *ir = read_instruction(st, sub, loop_ctx);
 160       if (ir == NULL) {
 161          ir_read_error(sub, "Invalid instruction.\n");
 162          st->error = true;
 163          return;
 164       }
 165       instructions->push_tail(ir);
 166    }
 167 }
 168
 169
 170 static ir_instruction *
 171 read_instruction(_mesa_glsl_parse_state *st, s_expression *expr,
 172                  ir_loop *loop_ctx)
 173 {
 174    s_symbol *symbol = SX_AS_SYMBOL(expr);
 175    if (symbol != NULL) {
 176       if (strcmp(symbol->value(), "break") == 0 && loop_ctx != NULL)
 177          return new ir_loop_jump(loop_ctx, ir_loop_jump::jump_break);
 178       if (strcmp(symbol->value(), "continue") == 0 && loop_ctx != NULL)
 179          return new ir_loop_jump(loop_ctx, ir_loop_jump::jump_continue);
 180    }
 181
 182    s_list *list = SX_AS_LIST(expr);
 183    if (list == NULL || list->subexpressions.is_empty())
 184       return NULL;
 185
 186    s_symbol *tag = SX_AS_SYMBOL(list->subexpressions.get_head());
 187    if (tag == NULL) {
 188       ir_read_error(expr, "expected instruction tag");
 189       return NULL;
 190    }
 191
 192    ir_instruction *inst = NULL;
 193    if (strcmp(tag->value(), "declare") == 0) {
 194       inst = read_declaration(st, list);
 195    } else if (strcmp(tag->value(), "if") == 0) {
 196       inst = read_if(st, list, loop_ctx);
 197    } else if (strcmp(tag->value(), "loop") == 0) {
 198       inst = read_loop(st, list);
 199    } else if (strcmp(tag->value(), "return") == 0) {
 200       inst = read_return(st, list);
 201    } else {
 202       inst = read_rvalue(st, list);
 203       if (inst == NULL)
 204          ir_read_error(list, "when reading instruction");
 205    }
 206    return inst;
 207 }
 208
 209
 210 static ir_variable *
 211 read_declaration(_mesa_glsl_parse_state *st, s_list *list)
 212 {
 213    if (list->length() != 4) {
 214       ir_read_error(list, "expected (declare (<qualifiers>) <type> <name>)");
 215       return NULL;
 216    }
 217
 218    s_list *quals = SX_AS_LIST(list->subexpressions.head->next);
 219    if (quals == NULL) {
 220       ir_read_error(list, "expected a list of variable qualifiers");
 221       return NULL;
 222    }
 223
 224    s_expression *type_expr = (s_expression*) quals->next;
 225    const glsl_type *type = read_type(st, type_expr);
 226    if (type == NULL)
 227       return NULL;
 228
 229    s_symbol *var_name = SX_AS_SYMBOL(type_expr->next);
 230    if (var_name == NULL) {
 231       ir_read_error(list, "expected variable name, found non-symbol");
 232       return NULL;
 233    }
 234
 235    ir_variable *var = new ir_variable(type, var_name->value());
 236
 237    foreach_iter(exec_list_iterator, it, quals->subexpressions) {
 238       s_symbol *qualifier = SX_AS_SYMBOL(it.get());
 239       if (qualifier == NULL) {
 240          ir_read_error(list, "qualifier list must contain only symbols");
 241          delete var;
 242          return NULL;
 243       }
 244
 245       // FINISHME: Check for duplicate/conflicting qualifiers.
 246       if (strcmp(qualifier->value(), "centroid") == 0) {
 247          var->centroid = 1;
 248       } else if (strcmp(qualifier->value(), "invariant") == 0) {
 249          var->invariant = 1;
 250       } else if (strcmp(qualifier->value(), "uniform") == 0) {
 251          var->mode = ir_var_uniform;
 252       } else if (strcmp(qualifier->value(), "auto") == 0) {
 253          var->mode = ir_var_auto;
 254       } else if (strcmp(qualifier->value(), "in") == 0) {
 255          var->mode = ir_var_in;
 256       } else if (strcmp(qualifier->value(), "out") == 0) {
 257          var->mode = ir_var_out;
 258       } else if (strcmp(qualifier->value(), "inout") == 0) {
 259          var->mode = ir_var_inout;
 260       } else if (strcmp(qualifier->value(), "smooth") == 0) {
 261          var->interpolation = ir_var_smooth;
 262       } else if (strcmp(qualifier->value(), "flat") == 0) {
 263          var->interpolation = ir_var_flat;
 264       } else if (strcmp(qualifier->value(), "noperspective") == 0) {
 265          var->interpolation = ir_var_noperspective;
 266       } else {
 267          ir_read_error(list, "unknown qualifier: %s", qualifier->value());
 268          delete var;
 269          return NULL;
 270       }
 271    }
 272
 273    // Add the variable to the symbol table
 274    st->symbols->add_variable(var_name->value(), var);
 275
 276    return var;
 277 }
 278
 279
 280 static ir_if *
 281 read_if(_mesa_glsl_parse_state *st, s_list *list, ir_loop *loop_ctx)
 282 {
 283    if (list->length() != 4) {
 284       ir_read_error(list, "expected (if <condition> (<then> ...) "
 285                           "(<else> ...))");
 286       return NULL;
 287    }
 288
 289    s_expression *cond_expr = (s_expression*) list->subexpressions.head->next;
 290    ir_rvalue *condition = read_rvalue(st, cond_expr);
 291    if (condition == NULL) {
 292       ir_read_error(list, "when reading condition of (if ...)");
 293       return NULL;
 294    }
 295
 296    s_expression *then_expr = (s_expression*) cond_expr->next;
 297    s_expression *else_expr = (s_expression*) then_expr->next;
 298
 299    ir_if *iff = new ir_if(condition);
 300
 301    read_instructions(st, &iff->then_instructions, then_expr, loop_ctx);
 302    read_instructions(st, &iff->else_instructions, else_expr, loop_ctx);
 303    if (st->error) {
 304       delete iff;
 305       iff = NULL;
 306    }
 307    return iff;
 308 }
 309
 310
 311 static ir_loop *
 312 read_loop(_mesa_glsl_parse_state *st, s_list *list)
 313 {
 314    if (list->length() != 6) {
 315       ir_read_error(list, "expected (loop <counter> <from> <to> <increment> "
 316                           "<body>)");
 317       return NULL;
 318    }
 319
 320    s_expression *count_expr = (s_expression*) list->subexpressions.head->next;
 321    s_expression *from_expr  = (s_expression*) count_expr->next;
 322    s_expression *to_expr    = (s_expression*) from_expr->next;
 323    s_expression *inc_expr   = (s_expression*) to_expr->next;
 324    s_expression *body_expr  = (s_expression*) inc_expr->next;
 325
 326    // FINISHME: actually read the count/from/to fields.
 327
 328    ir_loop *loop = new ir_loop;
 329    read_instructions(st, &loop->body_instructions, body_expr, loop);
 330    if (st->error) {
 331       delete loop;
 332       loop = NULL;
 333    }
 334    return loop;
 335 }
 336
 337
 338 static ir_return *
 339 read_return(_mesa_glsl_parse_state *st, s_list *list)
 340 {
 341    if (list->length() != 2) {
 342       ir_read_error(list, "expected (return <rvalue>)");
 343       return NULL;
 344    }
 345
 346    s_expression *expr = (s_expression*) list->subexpressions.head->next;
 347
 348    ir_rvalue *retval = read_rvalue(st, expr);
 349    if (retval == NULL) {
 350       ir_read_error(list, "when reading return value");
 351       return NULL;
 352    }
 353
 354    return new ir_return(retval);
 355 }
 356
 357
 358 static ir_rvalue *
 359 read_rvalue(_mesa_glsl_parse_state *st, s_expression *expr)
 360 {
 361    s_list *list = SX_AS_LIST(expr);
 362    if (list == NULL || list->subexpressions.is_empty())
 363       return NULL;
 364
 365    s_symbol *tag = SX_AS_SYMBOL(list->subexpressions.get_head());
 366    if (tag == NULL) {
 367       ir_read_error(expr, "expected rvalue tag");
 368       return NULL;
 369    }
 370
 371    ir_rvalue *rvalue = NULL;
 372    if (strcmp(tag->value(), "swiz") == 0) {
 373       rvalue = read_swizzle(st, list);
 374    } else if (strcmp(tag->value(), "assign") == 0) {
 375       rvalue = read_assignment(st, list);
 376    } else if (strcmp(tag->value(), "expression") == 0) {
 377       rvalue = read_expression(st, list);
 378    // FINISHME: ir_call
 379    } else if (strcmp(tag->value(), "constant") == 0) {
 380       rvalue = read_constant(st, list);
 381    } else if (strcmp(tag->value(), "var_ref") == 0) {
 382       rvalue = read_var_ref(st, list);
 383    } else if (strcmp(tag->value(), "array_ref") == 0) {
 384       rvalue = read_array_ref(st, list);
 385    } else if (strcmp(tag->value(), "record_ref") == 0) {
 386       rvalue = read_record_ref(st, list);
 387    } else {
 388       ir_read_error(expr, "unrecognized rvalue tag: %s", tag->value());
 389    }
 390
 391    return rvalue;
 392 }
 393
 394 static ir_assignment *
 395 read_assignment(_mesa_glsl_parse_state *st, s_list *list)
 396 {
 397    if (list->length() != 4) {
 398       ir_read_error(list, "expected (assign <condition> <lhs> <rhs>)");
 399       return NULL;
 400    }
 401
 402    s_expression *cond_expr = (s_expression*) list->subexpressions.head->next;
 403    s_expression *lhs_expr  = (s_expression*) cond_expr->next;
 404    s_expression *rhs_expr  = (s_expression*) lhs_expr->next;
 405
 406    // FINISHME: Deal with "true" condition
 407    ir_rvalue *condition = read_rvalue(st, cond_expr);
 408    if (condition == NULL) {
 409       ir_read_error(list, "when reading condition of assignment");
 410       return NULL;
 411    }
 412
 413    ir_rvalue *lhs = read_rvalue(st, lhs_expr);
 414    if (lhs == NULL) {
 415       ir_read_error(list, "when reading left-hand side of assignment");
 416       return NULL;
 417    }
 418
 419    ir_rvalue *rhs = read_rvalue(st, rhs_expr);
 420    if (rhs == NULL) {
 421       ir_read_error(list, "when reading right-hand side of assignment");
 422       return NULL;
 423    }
 424
 425    return new ir_assignment(lhs, rhs, condition);
 426 }
 427
 428
 429 static ir_expression *
 430 read_expression(_mesa_glsl_parse_state *st, s_list *list)
 431 {
 432    const unsigned list_length = list->length();
 433    if (list_length < 4) {
 434       ir_read_error(list, "expected (expression <type> <operator> <operand> "
 435                           "[<operand>])");
 436       return NULL;
 437    }
 438
 439    s_expression *type_expr = (s_expression*) list->subexpressions.head->next;
 440    const glsl_type *type = read_type(st, type_expr);
 441    if (type == NULL)
 442       return NULL;
 443
 444    /* Read the operator */
 445    s_symbol *op_sym = SX_AS_SYMBOL(type_expr->next);
 446    if (op_sym == NULL) {
 447       ir_read_error(list, "expected operator, found non-symbol");
 448       return NULL;
 449    }
 450
 451    ir_expression_operation op = ir_expression::get_operator(op_sym->value());
 452    if (op == (ir_expression_operation) -1) {
 453       ir_read_error(list, "invalid operator: %s", op_sym->value());
 454       return NULL;
 455    }
 456
 457    /* Now that we know the operator, check for the right number of operands */
 458    if (ir_expression::get_num_operands(op) == 2) {
 459       if (list_length != 5) {
 460          ir_read_error(list, "expected (expression %s <operand1> <operand2>)",
 461                        op_sym->value());
 462          return NULL;
 463       }
 464    } else {
 465       if (list_length != 4) {
 466          ir_read_error(list, "expected (expression %s <operand>)",
 467                        op_sym->value());
 468          return NULL;
 469       }
 470    }
 471
 472    s_expression *exp1 = (s_expression*) (op_sym->next);
 473    ir_rvalue *arg1 = read_rvalue(st, exp1);
 474    if (arg1 == NULL) {
 475       ir_read_error(list, "when reading first operand of %s", op_sym->value());
 476       return NULL;
 477    }
 478
 479    ir_rvalue *arg2 = NULL;
 480    if (ir_expression::get_num_operands(op) == 2) {
 481       s_expression *exp2 = (s_expression*) (exp1->next);
 482       arg2 = read_rvalue(st, exp2);
 483       if (arg2 == NULL) {
 484          ir_read_error(list, "when reading second operand of %s",
 485                        op_sym->value());
 486          return NULL;
 487       }
 488    }
 489
 490    return new ir_expression(op, type, arg1, arg2);
 491 }
 492
 493 static ir_swizzle *
 494 read_swizzle(_mesa_glsl_parse_state *st, s_list *list)
 495 {
 496    if (list->length() != 3) {
 497       ir_read_error(list, "expected (swiz <swizzle> <rvalue>)");
 498       return NULL;
 499    }
 500
 501    s_symbol *swiz = SX_AS_SYMBOL(list->subexpressions.head->next);
 502    if (swiz == NULL) {
 503       ir_read_error(list, "expected a valid swizzle; found non-symbol");
 504       return NULL;
 505    }
 506
 507    unsigned num_components = strlen(swiz->value());
 508    if (num_components > 4) {
 509       ir_read_error(list, "expected a valid swizzle; found %s", swiz->value());
 510       return NULL;
 511    }
 512
 513    s_expression *sub = (s_expression*) swiz->next;
 514    if (sub == NULL) {
 515       ir_read_error(list, "expected rvalue: (swizzle %s <rvalue>)", swiz->value());
 516       return NULL;
 517    }
 518
 519    ir_rvalue *rvalue = read_rvalue(st, sub);
 520    if (rvalue == NULL)
 521       return NULL;
 522
 523    return ir_swizzle::create(rvalue, swiz->value(), num_components);
 524 }
 525
 526 static ir_constant *
 527 read_constant(_mesa_glsl_parse_state *st, s_list *list)
 528 {
 529    if (list->length() != 3) {
 530       ir_read_error(list, "expected (constant <type> (<num> ... <num>))");
 531       return NULL;
 532    }
 533
 534    s_expression *type_expr = (s_expression*) list->subexpressions.head->next;
 535    const glsl_type *type = read_type(st, type_expr);
 536    if (type == NULL)
 537       return NULL;
 538
 539    s_list *values = SX_AS_LIST(type_expr->next);
 540    if (values == NULL) {
 541       ir_read_error(list, "expected (constant <type> (<num> ... <num>))");
 542       return NULL;
 543    }
 544
 545    const glsl_type *const base_type = type->get_base_type();
 546
 547    unsigned u[16];
 548    int i[16];
 549    float f[16];
 550    bool b[16];
 551
 552    // Read in list of values (at most 16).
 553    int k = 0;
 554    foreach_iter(exec_list_iterator, it, values->subexpressions) {
 555       if (k >= 16) {
 556          ir_read_error(values, "expected at most 16 numbers");
 557          return NULL;
 558       }
 559
 560       s_expression *expr = (s_expression*) it.get();
 561
 562       if (base_type->base_type == GLSL_TYPE_FLOAT) {
 563          s_number *value = SX_AS_NUMBER(expr);
 564          if (value == NULL) {
 565             ir_read_error(values, "expected numbers");
 566             return NULL;
 567          }
 568          f[k] = value->fvalue();
 569       } else {
 570          s_int *value = SX_AS_INT(expr);
 571          if (value == NULL) {
 572             ir_read_error(values, "expected integers");
 573             return NULL;
 574          }
 575
 576          switch (base_type->base_type) {
 577          case GLSL_TYPE_UINT: {
 578             u[k] = value->value();
 579             break;
 580          }
 581          case GLSL_TYPE_INT: {
 582             i[k] = value->value();
 583             break;
 584          }
 585          case GLSL_TYPE_BOOL: {
 586             b[k] = value->value();
 587             break;
 588          }
 589          default:
 590             ir_read_error(values, "unsupported constant type");
 591             return NULL;
 592          }
 593       }
 594       ++k;
 595    }
 596    switch (base_type->base_type) {
 597    case GLSL_TYPE_UINT:
 598       return new ir_constant(type, u);
 599    case GLSL_TYPE_INT:
 600       return new ir_constant(type, i);
 601    case GLSL_TYPE_BOOL:
 602       return new ir_constant(type, b);
 603    case GLSL_TYPE_FLOAT:
 604       return new ir_constant(type, f);
 605    }
 606    return NULL; // should not be reached
 607 }
 608
 609 static ir_instruction *
 610 read_dereferencable(_mesa_glsl_parse_state *st, s_expression *expr)
 611 {
 612    // Read the subject of a dereference - either a variable name or a swizzle
 613    s_symbol *var_name = SX_AS_SYMBOL(expr);
 614    if (var_name != NULL) {
 615       ir_variable *var = st->symbols->get_variable(var_name->value());
 616       if (var == NULL) {
 617          ir_read_error(expr, "undeclared variable: %s", var_name->value());
 618       }
 619       return var;
 620    } else {
 621       // Hopefully a (swiz ...)
 622       s_list *list = SX_AS_LIST(expr);
 623       if (list != NULL && !list->subexpressions.is_empty()) {
 624          s_symbol *tag = SX_AS_SYMBOL(list->subexpressions.head);
 625          if (tag != NULL && strcmp(tag->value(), "swiz") == 0)
 626             return read_swizzle(st, list);
 627       }
 628    }
 629    ir_read_error(expr, "expected variable name or (swiz ...)");
 630    return NULL;
 631 }
 632
 633 static ir_dereference *
 634 read_var_ref(_mesa_glsl_parse_state *st, s_list *list)
 635 {
 636    if (list->length() != 2) {
 637       ir_read_error(list, "expected (var_ref <variable name or (swiz)>)");
 638       return NULL;
 639    }
 640    s_expression *subj_expr = (s_expression*) list->subexpressions.head->next;
 641    ir_instruction *subject = read_dereferencable(st, subj_expr);
 642    if (subject == NULL)
 643       return NULL;
 644    return new ir_dereference(subject);
 645 }
 646
 647 static ir_dereference *
 648 read_array_ref(_mesa_glsl_parse_state *st, s_list *list)
 649 {
 650    if (list->length() != 3) {
 651       ir_read_error(list, "expected (array_ref <variable name or (swiz)> "
 652                           "<rvalue>)");
 653       return NULL;
 654    }
 655
 656    s_expression *subj_expr = (s_expression*) list->subexpressions.head->next;
 657    ir_instruction *subject = read_dereferencable(st, subj_expr);
 658    if (subject == NULL)
 659       return NULL;
 660
 661    s_expression *idx_expr = (s_expression*) subj_expr->next;
 662    ir_rvalue *idx = read_rvalue(st, idx_expr);
 663    return new ir_dereference(subject, idx);
 664 }
 665
 666 static ir_dereference *
 667 read_record_ref(_mesa_glsl_parse_state *st, s_list *list)
 668 {
 669    ir_read_error(list, "FINISHME: record refs not yet supported.");
 670    return NULL;
 671 }