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25 * \file lower_if_to_cond_assign.cpp
27 * This attempts to flatten if-statements to conditional assignments for
28 * GPUs with limited or no flow control support.
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
34 * Drivers for GPUs with no control flow support should simply call
36 * lower_if_to_cond_assign(instructions)
38 * to attempt to flatten all if-statements.
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
43 * lower_if_to_cond_assign(instructions, N)
45 * to attempt to flatten any if-statements appearing at depth > N.
48 #include "glsl_types.h"
50 #include "program/hash_table.h"
52 class ir_if_to_cond_assign_visitor
: public ir_hierarchical_visitor
{
54 ir_if_to_cond_assign_visitor(unsigned max_depth
)
56 this->progress
= false;
57 this->max_depth
= max_depth
;
60 this->condition_variables
= hash_table_ctor(0, hash_table_pointer_hash
,
61 hash_table_pointer_compare
);
64 ~ir_if_to_cond_assign_visitor()
66 hash_table_dtor(this->condition_variables
);
69 ir_visitor_status
visit_enter(ir_if
*);
70 ir_visitor_status
visit_leave(ir_if
*);
76 struct hash_table
*condition_variables
;
80 lower_if_to_cond_assign(exec_list
*instructions
, unsigned max_depth
)
82 ir_if_to_cond_assign_visitor
v(max_depth
);
84 visit_list_elements(&v
, instructions
);
90 check_control_flow(ir_instruction
*ir
, void *data
)
92 bool *found_control_flow
= (bool *)data
;
93 switch (ir
->ir_type
) {
97 case ir_type_loop_jump
:
99 *found_control_flow
= true;
107 move_block_to_cond_assign(void *mem_ctx
,
108 ir_if
*if_ir
, ir_rvalue
*cond_expr
,
109 exec_list
*instructions
,
110 struct hash_table
*ht
)
112 foreach_list_safe(node
, instructions
) {
113 ir_instruction
*ir
= (ir_instruction
*) node
;
115 if (ir
->ir_type
== ir_type_assignment
) {
116 ir_assignment
*assign
= (ir_assignment
*)ir
;
118 if (hash_table_find(ht
, assign
) == NULL
) {
119 hash_table_insert(ht
, assign
, assign
);
121 /* If the LHS of the assignment is a condition variable that was
122 * previously added, insert an additional assignment of false to
125 const bool assign_to_cv
=
126 hash_table_find(ht
, assign
->lhs
->variable_referenced()) != NULL
;
128 if (!assign
->condition
) {
131 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
132 glsl_type::bool_type
,
133 cond_expr
->clone(mem_ctx
, NULL
),
136 assign
->condition
= cond_expr
->clone(mem_ctx
, NULL
);
140 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
141 glsl_type::bool_type
,
142 cond_expr
->clone(mem_ctx
, NULL
),
148 /* Now, move from the if block to the block surrounding it. */
150 if_ir
->insert_before(ir
);
155 ir_if_to_cond_assign_visitor::visit_enter(ir_if
*ir
)
160 return visit_continue
;
164 ir_if_to_cond_assign_visitor::visit_leave(ir_if
*ir
)
166 /* Only flatten when beyond the GPU's maximum supported nesting depth. */
167 if (this->depth
-- <= this->max_depth
)
168 return visit_continue
;
170 bool found_control_flow
= false;
171 ir_assignment
*assign
;
172 ir_dereference_variable
*deref
;
174 /* Check that both blocks don't contain anything we can't support. */
175 foreach_iter(exec_list_iterator
, then_iter
, ir
->then_instructions
) {
176 ir_instruction
*then_ir
= (ir_instruction
*)then_iter
.get();
177 visit_tree(then_ir
, check_control_flow
, &found_control_flow
);
179 foreach_iter(exec_list_iterator
, else_iter
, ir
->else_instructions
) {
180 ir_instruction
*else_ir
= (ir_instruction
*)else_iter
.get();
181 visit_tree(else_ir
, check_control_flow
, &found_control_flow
);
183 if (found_control_flow
)
184 return visit_continue
;
186 void *mem_ctx
= ralloc_parent(ir
);
188 /* Store the condition to a variable. Move all of the instructions from
189 * the then-clause of the if-statement. Use the condition variable as a
190 * condition for all assignments.
192 ir_variable
*const then_var
=
193 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
194 "if_to_cond_assign_then",
196 ir
->insert_before(then_var
);
198 ir_dereference_variable
*then_cond
=
199 new(mem_ctx
) ir_dereference_variable(then_var
);
201 assign
= new(mem_ctx
) ir_assignment(then_cond
, ir
->condition
);
202 ir
->insert_before(assign
);
204 move_block_to_cond_assign(mem_ctx
, ir
, then_cond
,
205 &ir
->then_instructions
,
206 this->condition_variables
);
208 /* Add the new condition variable to the hash table. This allows us to
209 * find this variable when lowering other (enclosing) if-statements.
211 hash_table_insert(this->condition_variables
, then_var
, then_var
);
213 /* If there are instructions in the else-clause, store the inverse of the
214 * condition to a variable. Move all of the instructions from the
215 * else-clause if the if-statement. Use the (inverse) condition variable
216 * as a condition for all assignments.
218 if (!ir
->else_instructions
.is_empty()) {
219 ir_variable
*const else_var
=
220 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
221 "if_to_cond_assign_else",
223 ir
->insert_before(else_var
);
225 ir_dereference_variable
*else_cond
=
226 new(mem_ctx
) ir_dereference_variable(else_var
);
229 new(mem_ctx
) ir_expression(ir_unop_logic_not
,
230 then_cond
->clone(mem_ctx
, NULL
));
232 assign
= new(mem_ctx
) ir_assignment(else_cond
, inverse
);
233 ir
->insert_before(assign
);
235 move_block_to_cond_assign(mem_ctx
, ir
, else_cond
,
236 &ir
->else_instructions
,
237 this->condition_variables
);
239 /* Add the new condition variable to the hash table. This allows us to
240 * find this variable when lowering other (enclosing) if-statements.
242 hash_table_insert(this->condition_variables
, else_var
, else_var
);
247 this->progress
= true;
249 return visit_continue
;