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 ir_if_to_cond_assign.cpp
  26  *
  27  * This attempts to flatten all if statements to conditional
  28  * assignments for GPUs that don't do control flow.
  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
  35 #include "glsl_types.h"
  36 #include "ir.h"
  37
  38 class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
  39 public:
  40    ir_if_to_cond_assign_visitor()
  41    {
  42       this->progress = false;
  43    }
  44
  45    ir_visitor_status visit_leave(ir_if *);
  46
  47    bool progress;
  48 };
  49
  50 bool
  51 do_if_to_cond_assign(exec_list *instructions)
  52 {
  53    ir_if_to_cond_assign_visitor v;
  54
  55    visit_list_elements(&v, instructions);
  56
  57    return v.progress;
  58 }
  59
  60 void
  61 check_control_flow(ir_instruction *ir, void *data)
  62 {
  63    bool *found_control_flow = (bool *)data;
  64    switch (ir->ir_type) {
  65    case ir_type_call:
  66    case ir_type_discard:
  67    case ir_type_loop:
  68    case ir_type_loop_jump:
  69    case ir_type_return:
  70       *found_control_flow = true;
  71       break;
  72    default:
  73       break;
  74    }
  75 }
  76
  77 void
  78 move_block_to_cond_assign(void *mem_ctx,
  79                           ir_if *if_ir, ir_variable *cond_var, bool then)
  80 {
  81    exec_list *instructions;
  82
  83    if (then) {
  84       instructions = &if_ir->then_instructions;
  85    } else {
  86       instructions = &if_ir->else_instructions;
  87    }
  88
  89    foreach_iter(exec_list_iterator, iter, *instructions) {
  90       ir_instruction *ir = (ir_instruction *)iter.get();
  91
  92       if (ir->ir_type == ir_type_assignment) {
  93          ir_assignment *assign = (ir_assignment *)ir;
  94          ir_rvalue *cond_expr;
  95          ir_dereference *deref = new(mem_ctx) ir_dereference_variable(cond_var);
  96
  97          if (then) {
  98             cond_expr = deref;
  99          } else {
 100             cond_expr = new(mem_ctx) ir_expression(ir_unop_logic_not,
 101                                                    glsl_type::bool_type,
 102                                                    deref,
 103                                                    NULL);
 104          }
 105
 106          if (!assign->condition) {
 107             assign->condition = cond_expr;
 108          } else {
 109             assign->condition = new(mem_ctx) ir_expression(ir_binop_logic_and,
 110                                                            glsl_type::bool_type,
 111                                                            cond_expr,
 112                                                            assign->condition);
 113          }
 114       }
 115
 116       /* Now, move from the if block to the block surrounding it. */
 117       ir->remove();
 118       if_ir->insert_before(ir);
 119    }
 120 }
 121
 122 ir_visitor_status
 123 ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
 124 {
 125    bool found_control_flow = false;
 126    ir_variable *cond_var;
 127    ir_assignment *assign;
 128    ir_dereference_variable *deref;
 129
 130    /* Check that both blocks don't contain anything we can't support. */
 131    foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
 132       ir_instruction *then_ir = (ir_instruction *)then_iter.get();
 133       visit_tree(then_ir, check_control_flow, &found_control_flow);
 134    }
 135    foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
 136       ir_instruction *else_ir = (ir_instruction *)else_iter.get();
 137       visit_tree(else_ir, check_control_flow, &found_control_flow);
 138    }
 139    if (found_control_flow)
 140       return visit_continue;
 141
 142    void *mem_ctx = talloc_parent(ir);
 143
 144    /* Store the condition to a variable so the assignment conditions are
 145     * simpler.
 146     */
 147    cond_var = new(mem_ctx) ir_variable(glsl_type::bool_type,
 148                                        "if_to_cond_assign_condition",
 149                                        ir_var_temporary);
 150    ir->insert_before(cond_var);
 151
 152    deref = new(mem_ctx) ir_dereference_variable(cond_var);
 153    assign = new(mem_ctx) ir_assignment(deref,
 154                                        ir->condition, NULL);
 155    ir->insert_before(assign);
 156
 157    /* Now, move all of the instructions out of the if blocks, putting
 158     * conditions on assignments.
 159     */
 160    move_block_to_cond_assign(mem_ctx, ir, cond_var, true);
 161    move_block_to_cond_assign(mem_ctx, ir, cond_var, false);
 162
 163    ir->remove();
 164
 165    this->progress = true;
 166
 167    return visit_continue;
 168 }