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 namespace {
  53
  54 class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
  55 public:
  56    ir_if_to_cond_assign_visitor(unsigned max_depth)
  57    {
  58       this->progress = false;
  59       this->max_depth = max_depth;
  60       this->depth = 0;
  61
  62       this->condition_variables = hash_table_ctor(0, hash_table_pointer_hash,
  63                                                   hash_table_pointer_compare);
  64    }
  65
  66    ~ir_if_to_cond_assign_visitor()
  67    {
  68       hash_table_dtor(this->condition_variables);
  69    }
  70
  71    ir_visitor_status visit_enter(ir_if *);
  72    ir_visitor_status visit_leave(ir_if *);
  73
  74    bool progress;
  75    unsigned max_depth;
  76    unsigned depth;
  77
  78    struct hash_table *condition_variables;
  79 };
  80
  81 } /* anonymous namespace */
  82
  83 bool
  84 lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
  85 {
  86    if (max_depth == UINT_MAX)
  87       return false;
  88
  89    ir_if_to_cond_assign_visitor v(max_depth);
  90
  91    visit_list_elements(&v, instructions);
  92
  93    return v.progress;
  94 }
  95
  96 void
  97 check_control_flow(ir_instruction *ir, void *data)
  98 {
  99    bool *found_control_flow = (bool *)data;
 100    switch (ir->ir_type) {
 101    case ir_type_call:
 102    case ir_type_discard:
 103    case ir_type_loop:
 104    case ir_type_loop_jump:
 105    case ir_type_return:
 106       *found_control_flow = true;
 107       break;
 108    default:
 109       break;
 110    }
 111 }
 112
 113 void
 114 move_block_to_cond_assign(void *mem_ctx,
 115                           ir_if *if_ir, ir_rvalue *cond_expr,
 116                           exec_list *instructions,
 117                           struct hash_table *ht)
 118 {
 119    foreach_list_safe(node, instructions) {
 120       ir_instruction *ir = (ir_instruction *) node;
 121
 122       if (ir->ir_type == ir_type_assignment) {
 123          ir_assignment *assign = (ir_assignment *)ir;
 124
 125          if (hash_table_find(ht, assign) == NULL) {
 126             hash_table_insert(ht, assign, assign);
 127
 128             /* If the LHS of the assignment is a condition variable that was
 129              * previously added, insert an additional assignment of false to
 130              * the variable.
 131              */
 132             const bool assign_to_cv =
 133                hash_table_find(ht, assign->lhs->variable_referenced()) != NULL;
 134
 135             if (!assign->condition) {
 136                if (assign_to_cv) {
 137                   assign->rhs =
 138                      new(mem_ctx) ir_expression(ir_binop_logic_and,
 139                                                 glsl_type::bool_type,
 140                                                 cond_expr->clone(mem_ctx, NULL),
 141                                                 assign->rhs);
 142                } else {
 143                   assign->condition = cond_expr->clone(mem_ctx, NULL);
 144                }
 145             } else {
 146                assign->condition =
 147                   new(mem_ctx) ir_expression(ir_binop_logic_and,
 148                                              glsl_type::bool_type,
 149                                              cond_expr->clone(mem_ctx, NULL),
 150                                              assign->condition);
 151             }
 152          }
 153       }
 154
 155       /* Now, move from the if block to the block surrounding it. */
 156       ir->remove();
 157       if_ir->insert_before(ir);
 158    }
 159 }
 160
 161 ir_visitor_status
 162 ir_if_to_cond_assign_visitor::visit_enter(ir_if *ir)
 163 {
 164    (void) ir;
 165    this->depth++;
 166
 167    return visit_continue;
 168 }
 169
 170 ir_visitor_status
 171 ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
 172 {
 173    /* Only flatten when beyond the GPU's maximum supported nesting depth. */
 174    if (this->depth-- <= this->max_depth)
 175       return visit_continue;
 176
 177    bool found_control_flow = false;
 178    ir_assignment *assign;
 179
 180    /* Check that both blocks don't contain anything we can't support. */
 181    foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
 182       ir_instruction *then_ir = (ir_instruction *)then_iter.get();
 183       visit_tree(then_ir, check_control_flow, &found_control_flow);
 184    }
 185    foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
 186       ir_instruction *else_ir = (ir_instruction *)else_iter.get();
 187       visit_tree(else_ir, check_control_flow, &found_control_flow);
 188    }
 189    if (found_control_flow)
 190       return visit_continue;
 191
 192    void *mem_ctx = ralloc_parent(ir);
 193
 194    /* Store the condition to a variable.  Move all of the instructions from
 195     * the then-clause of the if-statement.  Use the condition variable as a
 196     * condition for all assignments.
 197     */
 198    ir_variable *const then_var =
 199       new(mem_ctx) ir_variable(glsl_type::bool_type,
 200                                "if_to_cond_assign_then",
 201                                ir_var_temporary);
 202    ir->insert_before(then_var);
 203
 204    ir_dereference_variable *then_cond =
 205       new(mem_ctx) ir_dereference_variable(then_var);
 206
 207    assign = new(mem_ctx) ir_assignment(then_cond, ir->condition);
 208    ir->insert_before(assign);
 209
 210    move_block_to_cond_assign(mem_ctx, ir, then_cond,
 211                              &ir->then_instructions,
 212                              this->condition_variables);
 213
 214    /* Add the new condition variable to the hash table.  This allows us to
 215     * find this variable when lowering other (enclosing) if-statements.
 216     */
 217    hash_table_insert(this->condition_variables, then_var, then_var);
 218
 219    /* If there are instructions in the else-clause, store the inverse of the
 220     * condition to a variable.  Move all of the instructions from the
 221     * else-clause if the if-statement.  Use the (inverse) condition variable
 222     * as a condition for all assignments.
 223     */
 224    if (!ir->else_instructions.is_empty()) {
 225       ir_variable *const else_var =
 226          new(mem_ctx) ir_variable(glsl_type::bool_type,
 227                                   "if_to_cond_assign_else",
 228                                   ir_var_temporary);
 229       ir->insert_before(else_var);
 230
 231       ir_dereference_variable *else_cond =
 232          new(mem_ctx) ir_dereference_variable(else_var);
 233
 234       ir_rvalue *inverse =
 235          new(mem_ctx) ir_expression(ir_unop_logic_not,
 236                                     then_cond->clone(mem_ctx, NULL));
 237
 238       assign = new(mem_ctx) ir_assignment(else_cond, inverse);
 239       ir->insert_before(assign);
 240
 241       move_block_to_cond_assign(mem_ctx, ir, else_cond,
 242                                 &ir->else_instructions,
 243                                 this->condition_variables);
 244
 245       /* Add the new condition variable to the hash table.  This allows us to
 246        * find this variable when lowering other (enclosing) if-statements.
 247        */
 248       hash_table_insert(this->condition_variables, else_var, else_var);
 249    }
 250
 251    ir->remove();
 252
 253    this->progress = true;
 254
 255    return visit_continue;
 256 }