src/glsl/lower_clip_distance.cpp

   1 /*
   2  * Copyright © 2011 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
  24 /**
  25  * \file lower_clip_distance.cpp
  26  *
  27  * This pass accounts for the difference between the way
  28  * gl_ClipDistance is declared in standard GLSL (as an array of
  29  * floats), and the way it is frequently implemented in hardware (as
  30  * a pair of vec4s, with four clip distances packed into each).
  31  *
  32  * The declaration of gl_ClipDistance is replaced with a declaration
  33  * of gl_ClipDistanceMESA, and any references to gl_ClipDistance are
  34  * translated to refer to gl_ClipDistanceMESA with the appropriate
  35  * swizzling of array indices.  For instance:
  36  *
  37  *   gl_ClipDistance[i]
  38  *
  39  * is translated into:
  40  *
  41  *   gl_ClipDistanceMESA[i>>2][i&3]
  42  *
  43  * Since some hardware may not internally represent gl_ClipDistance as a pair
  44  * of vec4's, this lowering pass is optional.  To enable it, set the
  45  * LowerClipDistance flag in gl_shader_compiler_options to true.
  46  */
  47
  48 #include "glsl_symbol_table.h"
  49 #include "ir_rvalue_visitor.h"
  50 #include "ir.h"
  51
  52 class lower_clip_distance_visitor : public ir_rvalue_visitor {
  53 public:
  54    lower_clip_distance_visitor()
  55       : progress(false), old_clip_distance_var(NULL),
  56         new_clip_distance_var(NULL)
  57    {
  58    }
  59
  60    virtual ir_visitor_status visit(ir_variable *);
  61    void create_indices(ir_rvalue*, ir_rvalue *&, ir_rvalue *&);
  62    virtual ir_visitor_status visit_leave(ir_assignment *);
  63    void visit_new_assignment(ir_assignment *ir);
  64    virtual ir_visitor_status visit_leave(ir_call *);
  65
  66    virtual void handle_rvalue(ir_rvalue **rvalue);
  67
  68    bool progress;
  69
  70    /**
  71     * Pointer to the declaration of gl_ClipDistance, if found.
  72     */
  73    ir_variable *old_clip_distance_var;
  74
  75    /**
  76     * Pointer to the newly-created gl_ClipDistanceMESA variable.
  77     */
  78    ir_variable *new_clip_distance_var;
  79 };
  80
  81
  82 /**
  83  * Replace any declaration of gl_ClipDistance as an array of floats with a
  84  * declaration of gl_ClipDistanceMESA as an array of vec4's.
  85  */
  86 ir_visitor_status
  87 lower_clip_distance_visitor::visit(ir_variable *ir)
  88 {
  89    /* No point in looking for the declaration of gl_ClipDistance if
  90     * we've already found it.
  91     */
  92    if (this->old_clip_distance_var)
  93       return visit_continue;
  94
  95    if (ir->name && strcmp(ir->name, "gl_ClipDistance") == 0) {
  96       this->progress = true;
  97       this->old_clip_distance_var = ir;
  98       assert (ir->type->is_array());
  99       assert (ir->type->element_type() == glsl_type::float_type);
 100       unsigned new_size = (ir->type->array_size() + 3) / 4;
 101
 102       /* Clone the old var so that we inherit all of its properties */
 103       this->new_clip_distance_var = ir->clone(ralloc_parent(ir), NULL);
 104
 105       /* And change the properties that we need to change */
 106       this->new_clip_distance_var->name
 107          = ralloc_strdup(this->new_clip_distance_var, "gl_ClipDistanceMESA");
 108       this->new_clip_distance_var->type
 109          = glsl_type::get_array_instance(glsl_type::vec4_type, new_size);
 110       this->new_clip_distance_var->max_array_access = ir->max_array_access / 4;
 111
 112       ir->replace_with(this->new_clip_distance_var);
 113    }
 114    return visit_continue;
 115 }
 116
 117
 118 /**
 119  * Create the necessary GLSL rvalues to index into gl_ClipDistanceMESA based
 120  * on the rvalue previously used to index into gl_ClipDistance.
 121  *
 122  * \param array_index Selects one of the vec4's in gl_ClipDistanceMESA
 123  * \param swizzle_index Selects a component within the vec4 selected by
 124  *        array_index.
 125  */
 126 void
 127 lower_clip_distance_visitor::create_indices(ir_rvalue *old_index,
 128                                             ir_rvalue *&array_index,
 129                                             ir_rvalue *&swizzle_index)
 130 {
 131    void *ctx = ralloc_parent(old_index);
 132
 133    /* Make sure old_index is a signed int so that the bitwise "shift" and
 134     * "and" operations below type check properly.
 135     */
 136    if (old_index->type != glsl_type::int_type) {
 137       assert (old_index->type == glsl_type::uint_type);
 138       old_index = new(ctx) ir_expression(ir_unop_u2i, old_index);
 139    }
 140
 141    ir_constant *old_index_constant = old_index->constant_expression_value();
 142    if (old_index_constant) {
 143       /* gl_ClipDistance is being accessed via a constant index.  Don't bother
 144        * creating expressions to calculate the lowered indices.  Just create
 145        * constants.
 146        */
 147       int const_val = old_index_constant->get_int_component(0);
 148       array_index = new(ctx) ir_constant(const_val / 4);
 149       swizzle_index = new(ctx) ir_constant(const_val % 4);
 150    } else {
 151       /* Create a variable to hold the value of old_index (so that we
 152        * don't compute it twice).
 153        */
 154       ir_variable *old_index_var = new(ctx) ir_variable(
 155          glsl_type::int_type, "clip_distance_index", ir_var_temporary);
 156       this->base_ir->insert_before(old_index_var);
 157       this->base_ir->insert_before(new(ctx) ir_assignment(
 158          new(ctx) ir_dereference_variable(old_index_var), old_index));
 159
 160       /* Create the expression clip_distance_index / 4.  Do this as a bit
 161        * shift because that's likely to be more efficient.
 162        */
 163       array_index = new(ctx) ir_expression(
 164          ir_binop_rshift, new(ctx) ir_dereference_variable(old_index_var),
 165          new(ctx) ir_constant(2));
 166
 167       /* Create the expression clip_distance_index % 4.  Do this as a bitwise
 168        * AND because that's likely to be more efficient.
 169        */
 170       swizzle_index = new(ctx) ir_expression(
 171          ir_binop_bit_and, new(ctx) ir_dereference_variable(old_index_var),
 172          new(ctx) ir_constant(3));
 173    }
 174 }
 175
 176
 177 void
 178 lower_clip_distance_visitor::handle_rvalue(ir_rvalue **rv)
 179 {
 180    /* If the gl_ClipDistance var hasn't been declared yet, then
 181     * there's no way this deref can refer to it.
 182     */
 183    if (!this->old_clip_distance_var || *rv == NULL)
 184       return;
 185
 186    ir_dereference_array *const array_deref = (*rv)->as_dereference_array();
 187    if (array_deref == NULL)
 188       return;
 189
 190    /* Replace any expression that indexes into the gl_ClipDistance array
 191     * with an expression that indexes into one of the vec4's in
 192     * gl_ClipDistanceMESA and accesses the appropriate component.
 193     */
 194    ir_dereference_variable *old_var_ref =
 195       array_deref->array->as_dereference_variable();
 196    if (old_var_ref && old_var_ref->var == this->old_clip_distance_var) {
 197       this->progress = true;
 198       ir_rvalue *array_index;
 199       ir_rvalue *swizzle_index;
 200       this->create_indices(array_deref->array_index, array_index, swizzle_index);
 201       void *mem_ctx = ralloc_parent(array_deref);
 202       array_deref->array = new(mem_ctx) ir_dereference_array(
 203          this->new_clip_distance_var, array_index);
 204       array_deref->array_index = swizzle_index;
 205    }
 206 }
 207
 208
 209 /**
 210  * Replace any assignment having gl_ClipDistance (undereferenced) as its LHS
 211  * or RHS with a sequence of assignments, one for each component of the array.
 212  * Each of these assignments is lowered to refer to gl_ClipDistanceMESA as
 213  * appropriate.
 214  */
 215 ir_visitor_status
 216 lower_clip_distance_visitor::visit_leave(ir_assignment *ir)
 217 {
 218    ir_dereference_variable *lhs_var = ir->lhs->as_dereference_variable();
 219    ir_dereference_variable *rhs_var = ir->rhs->as_dereference_variable();
 220    if ((lhs_var && lhs_var->var == this->old_clip_distance_var)
 221        || (rhs_var && rhs_var->var == this->old_clip_distance_var)) {
 222       /* LHS or RHS of the assignment is the entire gl_ClipDistance array.
 223        * Since we are reshaping gl_ClipDistance from an array of floats to an
 224        * array of vec4's, this isn't going to work as a bulk assignment
 225        * anymore, so unroll it to element-by-element assignments and lower
 226        * each of them.
 227        *
 228        * Note: to unroll into element-by-element assignments, we need to make
 229        * clones of the LHS and RHS.  This is only safe if the LHS and RHS are
 230        * side-effect free.  Fortunately, we know that they are, because the
 231        * only kind of rvalue that can have side effects is an ir_call, and
 232        * ir_calls only appear (a) as a statement on their own, or (b) as the
 233        * RHS of an assignment that stores the result of the call in a
 234        * temporary variable.
 235        */
 236       void *ctx = ralloc_parent(ir);
 237       int array_size = this->old_clip_distance_var->type->array_size();
 238       for (int i = 0; i < array_size; ++i) {
 239          ir_dereference_array *new_lhs = new(ctx) ir_dereference_array(
 240             ir->lhs->clone(ctx, NULL), new(ctx) ir_constant(i));
 241          this->handle_rvalue((ir_rvalue **) &new_lhs);
 242          ir_dereference_array *new_rhs = new(ctx) ir_dereference_array(
 243             ir->rhs->clone(ctx, NULL), new(ctx) ir_constant(i));
 244          this->handle_rvalue((ir_rvalue **) &new_rhs);
 245          this->base_ir->insert_before(
 246             new(ctx) ir_assignment(new_lhs, new_rhs));
 247       }
 248       ir->remove();
 249
 250       return visit_continue;
 251    }
 252
 253    /* Handle the LHS as if it were an r-value.  Normally
 254     * rvalue_visit(ir_assignment *) only visits the RHS, but we need to lower
 255     * expressions in the LHS as well.
 256     */
 257    handle_rvalue((ir_rvalue **)&ir->lhs);
 258    return rvalue_visit(ir);
 259 }
 260
 261
 262 /**
 263  * Set up base_ir properly and call visit_leave() on a newly created
 264  * ir_assignment node.  This is used in cases where we have to insert an
 265  * ir_assignment in a place where we know the hierarchical visitor won't see
 266  * it.
 267  */
 268 void
 269 lower_clip_distance_visitor::visit_new_assignment(ir_assignment *ir)
 270 {
 271    ir_instruction *old_base_ir = this->base_ir;
 272    this->base_ir = ir;
 273    ir->accept(this);
 274    this->base_ir = old_base_ir;
 275 }
 276
 277
 278 /**
 279  * If gl_ClipDistance appears as an argument in an ir_call expression, replace
 280  * it with a temporary variable, and make sure the ir_call is preceded and/or
 281  * followed by assignments that copy the contents of the temporary variable to
 282  * and/or from gl_ClipDistance.  Each of these assignments is then lowered to
 283  * refer to gl_ClipDistanceMESA.
 284  */
 285 ir_visitor_status
 286 lower_clip_distance_visitor::visit_leave(ir_call *ir)
 287 {
 288    void *ctx = ralloc_parent(ir);
 289
 290    const exec_node *formal_param_node = ir->callee->parameters.head;
 291    const exec_node *actual_param_node = ir->actual_parameters.head;
 292    while (!actual_param_node->is_tail_sentinel()) {
 293       ir_variable *formal_param = (ir_variable *) formal_param_node;
 294       ir_rvalue *actual_param = (ir_rvalue *) actual_param_node;
 295
 296       /* Advance formal_param_node and actual_param_node now so that we can
 297        * safely replace actual_param with another node, if necessary, below.
 298        */
 299       formal_param_node = formal_param_node->next;
 300       actual_param_node = actual_param_node->next;
 301
 302       ir_dereference_variable *deref = actual_param->as_dereference_variable();
 303       if (deref && deref->var == this->old_clip_distance_var) {
 304          /* User is trying to pass the whole gl_ClipDistance array to a
 305           * function call.  Since we are reshaping gl_ClipDistance from an
 306           * array of floats to an array of vec4's, this isn't going to work
 307           * anymore, so use a temporary array instead.
 308           */
 309          ir_variable *temp_clip_distance = new(ctx) ir_variable(
 310             actual_param->type, "temp_clip_distance", ir_var_temporary);
 311          this->base_ir->insert_before(temp_clip_distance);
 312          actual_param->replace_with(
 313             new(ctx) ir_dereference_variable(temp_clip_distance));
 314          if (formal_param->mode == ir_var_function_in
 315              || formal_param->mode == ir_var_function_inout) {
 316             /* Copy from gl_ClipDistance to the temporary before the call.
 317              * Since we are going to insert this copy before the current
 318              * instruction, we need to visit it afterwards to make sure it
 319              * gets lowered.
 320              */
 321             ir_assignment *new_assignment = new(ctx) ir_assignment(
 322                new(ctx) ir_dereference_variable(temp_clip_distance),
 323                new(ctx) ir_dereference_variable(old_clip_distance_var));
 324             this->base_ir->insert_before(new_assignment);
 325             this->visit_new_assignment(new_assignment);
 326          }
 327          if (formal_param->mode == ir_var_function_out
 328              || formal_param->mode == ir_var_function_inout) {
 329             /* Copy from the temporary to gl_ClipDistance after the call.
 330              * Since visit_list_elements() has already decided which
 331              * instruction it's going to visit next, we need to visit
 332              * afterwards to make sure it gets lowered.
 333              */
 334             ir_assignment *new_assignment = new(ctx) ir_assignment(
 335                new(ctx) ir_dereference_variable(old_clip_distance_var),
 336                new(ctx) ir_dereference_variable(temp_clip_distance));
 337             this->base_ir->insert_after(new_assignment);
 338             this->visit_new_assignment(new_assignment);
 339          }
 340       }
 341    }
 342
 343    return rvalue_visit(ir);
 344 }
 345
 346
 347 bool
 348 lower_clip_distance(gl_shader *shader)
 349 {
 350    lower_clip_distance_visitor v;
 351
 352    visit_list_elements(&v, shader->ir);
 353
 354    if (v.new_clip_distance_var)
 355       shader->symbols->add_variable(v.new_clip_distance_var);
 356
 357    return v.progress;
 358 }