reactos/dll/opengl/mesa/src/glsl/lower_if_to_cond_assign.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
  24 /**
  25  * \file lower_if_to_cond_assign.cpp
  26  *
  27  * This attempts to flatten if-statements to conditional assignments for
  28  * GPUs with limited or no flow control support.
  29  *
  30  * It can't handle other control flow being inside of its block, such
  31  * as calls or loops.  Hopefully loop unrolling and inlining will take
  32  * care of those.
  33  *
  34  * Drivers for GPUs with no control flow support should simply call
  35  *
  36  *    lower_if_to_cond_assign(instructions)
  37  *
  38  * to attempt to flatten all if-statements.
  39  *
  40  * Some GPUs (such as i965 prior to gen6) do support control flow, but have a
  41  * maximum nesting depth N.  Drivers for such hardware can call
  42  *
  43  *    lower_if_to_cond_assign(instructions, N)
  44  *
  45  * to attempt to flatten any if-statements appearing at depth > N.
  46  */
  47
  48 #include "glsl_types.h"
  49 #include "ir.h"
  50 #include "program/hash_table.h"
  51
  52 class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
  53 public:
  54    ir_if_to_cond_assign_visitor(unsigned max_depth)
  55    {
  56       this->progress = false;
  57       this->max_depth = max_depth;
  58       this->depth = 0;
  59
  60       this->condition_variables = hash_table_ctor(0, hash_table_pointer_hash,
  61                                                   hash_table_pointer_compare);
  62    }
  63
  64    ~ir_if_to_cond_assign_visitor()
  65    {
  66       hash_table_dtor(this->condition_variables);
  67    }
  68
  69    ir_visitor_status visit_enter(ir_if *);
  70    ir_visitor_status visit_leave(ir_if *);
  71
  72    bool progress;
  73    unsigned max_depth;
  74    unsigned depth;
  75
  76    struct hash_table *condition_variables;
  77 };
  78
  79 bool
  80 lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
  81 {
  82    if (max_depth == UINT_MAX)
  83       return false;
  84
  85    ir_if_to_cond_assign_visitor v(max_depth);
  86
  87    visit_list_elements(&v, instructions);
  88
  89    return v.progress;
  90 }
  91
  92 void
  93 check_control_flow(ir_instruction *ir, void *data)
  94 {
  95    bool *found_control_flow = (bool *)data;
  96    switch (ir->ir_type) {
  97    case ir_type_call:
  98    case ir_type_discard:
  99    case ir_type_loop:
 100    case ir_type_loop_jump:
 101    case ir_type_return:
 102       *found_control_flow = true;
 103       break;
 104    default:
 105       break;
 106    }
 107 }
 108
 109 void
 110 move_block_to_cond_assign(void *mem_ctx,
 111                           ir_if *if_ir, ir_rvalue *cond_expr,
 112                           exec_list *instructions,
 113                           struct hash_table *ht)
 114 {
 115    foreach_list_safe(node, instructions) {
 116       ir_instruction *ir = (ir_instruction *) node;
 117
 118       if (ir->ir_type == ir_type_assignment) {
 119          ir_assignment *assign = (ir_assignment *)ir;
 120
 121          if (hash_table_find(ht, assign) == NULL) {
 122             hash_table_insert(ht, assign, assign);
 123
 124             /* If the LHS of the assignment is a condition variable that was
 125              * previously added, insert an additional assignment of false to
 126              * the variable.
 127              */
 128             const bool assign_to_cv =
 129                hash_table_find(ht, assign->lhs->variable_referenced()) != NULL;
 130
 131             if (!assign->condition) {
 132                if (assign_to_cv) {
 133                   assign->rhs =
 134                      new(mem_ctx) ir_expression(ir_binop_logic_and,
 135                                                 glsl_type::bool_type,
 136                                                 cond_expr->clone(mem_ctx, NULL),
 137                                                 assign->rhs);
 138                } else {
 139                   assign->condition = cond_expr->clone(mem_ctx, NULL);
 140                }
 141             } else {
 142                assign->condition =
 143                   new(mem_ctx) ir_expression(ir_binop_logic_and,
 144                                              glsl_type::bool_type,
 145                                              cond_expr->clone(mem_ctx, NULL),
 146                                              assign->condition);
 147             }
 148          }
 149       }
 150
 151       /* Now, move from the if block to the block surrounding it. */
 152       ir->remove();
 153       if_ir->insert_before(ir);
 154    }
 155 }
 156
 157 ir_visitor_status
 158 ir_if_to_cond_assign_visitor::visit_enter(ir_if *ir)
 159 {
 160    (void) ir;
 161    this->depth++;
 162
 163    return visit_continue;
 164 }
 165
 166 ir_visitor_status
 167 ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
 168 {
 169    /* Only flatten when beyond the GPU's maximum supported nesting depth. */
 170    if (this->depth-- <= this->max_depth)
 171       return visit_continue;
 172
 173    bool found_control_flow = false;
 174    ir_assignment *assign;
 175
 176    /* Check that both blocks don't contain anything we can't support. */
 177    foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
 178       ir_instruction *then_ir = (ir_instruction *)then_iter.get();
 179       visit_tree(then_ir, check_control_flow, &found_control_flow);
 180    }
 181    foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
 182       ir_instruction *else_ir = (ir_instruction *)else_iter.get();
 183       visit_tree(else_ir, check_control_flow, &found_control_flow);
 184    }
 185    if (found_control_flow)
 186       return visit_continue;
 187
 188    void *mem_ctx = ralloc_parent(ir);
 189
 190    /* Store the condition to a variable.  Move all of the instructions from
 191     * the then-clause of the if-statement.  Use the condition variable as a
 192     * condition for all assignments.
 193     */
 194    ir_variable *const then_var =
 195       new(mem_ctx) ir_variable(glsl_type::bool_type,
 196                                "if_to_cond_assign_then",
 197                                ir_var_temporary);
 198    ir->insert_before(then_var);
 199
 200    ir_dereference_variable *then_cond =
 201       new(mem_ctx) ir_dereference_variable(then_var);
 202
 203    assign = new(mem_ctx) ir_assignment(then_cond, ir->condition);
 204    ir->insert_before(assign);
 205
 206    move_block_to_cond_assign(mem_ctx, ir, then_cond,
 207                              &ir->then_instructions,
 208                              this->condition_variables);
 209
 210    /* Add the new condition variable to the hash table.  This allows us to
 211     * find this variable when lowering other (enclosing) if-statements.
 212     */
 213    hash_table_insert(this->condition_variables, then_var, then_var);
 214
 215    /* If there are instructions in the else-clause, store the inverse of the
 216     * condition to a variable.  Move all of the instructions from the
 217     * else-clause if the if-statement.  Use the (inverse) condition variable
 218     * as a condition for all assignments.
 219     */
 220    if (!ir->else_instructions.is_empty()) {
 221       ir_variable *const else_var =
 222          new(mem_ctx) ir_variable(glsl_type::bool_type,
 223                                   "if_to_cond_assign_else",
 224                                   ir_var_temporary);
 225       ir->insert_before(else_var);
 226
 227       ir_dereference_variable *else_cond =
 228          new(mem_ctx) ir_dereference_variable(else_var);
 229
 230       ir_rvalue *inverse =
 231          new(mem_ctx) ir_expression(ir_unop_logic_not,
 232                                     then_cond->clone(mem_ctx, NULL));
 233
 234       assign = new(mem_ctx) ir_assignment(else_cond, inverse);
 235       ir->insert_before(assign);
 236
 237       move_block_to_cond_assign(mem_ctx, ir, else_cond,
 238                                 &ir->else_instructions,
 239                                 this->condition_variables);
 240
 241       /* Add the new condition variable to the hash table.  This allows us to
 242        * find this variable when lowering other (enclosing) if-statements.
 243        */
 244       hash_table_insert(this->condition_variables, else_var, else_var);
 245    }
 246
 247    ir->remove();
 248
 249    this->progress = true;
 250
 251    return visit_continue;
 252 }