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