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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"
54 class ir_if_to_cond_assign_visitor
: public ir_hierarchical_visitor
{
56 ir_if_to_cond_assign_visitor(unsigned max_depth
)
58 this->progress
= false;
59 this->max_depth
= max_depth
;
62 this->condition_variables
= hash_table_ctor(0, hash_table_pointer_hash
,
63 hash_table_pointer_compare
);
66 ~ir_if_to_cond_assign_visitor()
68 hash_table_dtor(this->condition_variables
);
71 ir_visitor_status
visit_enter(ir_if
*);
72 ir_visitor_status
visit_leave(ir_if
*);
78 struct hash_table
*condition_variables
;
81 } /* anonymous namespace */
84 lower_if_to_cond_assign(exec_list
*instructions
, unsigned max_depth
)
86 if (max_depth
== UINT_MAX
)
89 ir_if_to_cond_assign_visitor
v(max_depth
);
91 visit_list_elements(&v
, instructions
);
97 check_control_flow(ir_instruction
*ir
, void *data
)
99 bool *found_control_flow
= (bool *)data
;
100 switch (ir
->ir_type
) {
102 case ir_type_discard
:
104 case ir_type_loop_jump
:
106 *found_control_flow
= true;
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
)
119 foreach_in_list_safe(ir_instruction
, ir
, instructions
) {
120 if (ir
->ir_type
== ir_type_assignment
) {
121 ir_assignment
*assign
= (ir_assignment
*)ir
;
123 if (hash_table_find(ht
, assign
) == NULL
) {
124 hash_table_insert(ht
, assign
, assign
);
126 /* If the LHS of the assignment is a condition variable that was
127 * previously added, insert an additional assignment of false to
130 const bool assign_to_cv
=
131 hash_table_find(ht
, assign
->lhs
->variable_referenced()) != NULL
;
133 if (!assign
->condition
) {
136 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
137 glsl_type::bool_type
,
138 cond_expr
->clone(mem_ctx
, NULL
),
141 assign
->condition
= cond_expr
->clone(mem_ctx
, NULL
);
145 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
146 glsl_type::bool_type
,
147 cond_expr
->clone(mem_ctx
, NULL
),
153 /* Now, move from the if block to the block surrounding it. */
155 if_ir
->insert_before(ir
);
160 ir_if_to_cond_assign_visitor::visit_enter(ir_if
*ir
)
165 return visit_continue
;
169 ir_if_to_cond_assign_visitor::visit_leave(ir_if
*ir
)
171 /* Only flatten when beyond the GPU's maximum supported nesting depth. */
172 if (this->depth
-- <= this->max_depth
)
173 return visit_continue
;
175 bool found_control_flow
= false;
176 ir_assignment
*assign
;
178 /* Check that both blocks don't contain anything we can't support. */
179 foreach_in_list(ir_instruction
, then_ir
, &ir
->then_instructions
) {
180 visit_tree(then_ir
, check_control_flow
, &found_control_flow
);
182 foreach_in_list(ir_instruction
, else_ir
, &ir
->else_instructions
) {
183 visit_tree(else_ir
, check_control_flow
, &found_control_flow
);
185 if (found_control_flow
)
186 return visit_continue
;
188 void *mem_ctx
= ralloc_parent(ir
);
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.
194 ir_variable
*const then_var
=
195 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
196 "if_to_cond_assign_then",
198 ir
->insert_before(then_var
);
200 ir_dereference_variable
*then_cond
=
201 new(mem_ctx
) ir_dereference_variable(then_var
);
203 assign
= new(mem_ctx
) ir_assignment(then_cond
, ir
->condition
);
204 ir
->insert_before(assign
);
206 move_block_to_cond_assign(mem_ctx
, ir
, then_cond
,
207 &ir
->then_instructions
,
208 this->condition_variables
);
210 /* Add the new condition variable to the hash table. This allows us to
211 * find this variable when lowering other (enclosing) if-statements.
213 hash_table_insert(this->condition_variables
, then_var
, then_var
);
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.
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",
225 ir
->insert_before(else_var
);
227 ir_dereference_variable
*else_cond
=
228 new(mem_ctx
) ir_dereference_variable(else_var
);
231 new(mem_ctx
) ir_expression(ir_unop_logic_not
,
232 then_cond
->clone(mem_ctx
, NULL
));
234 assign
= new(mem_ctx
) ir_assignment(else_cond
, inverse
);
235 ir
->insert_before(assign
);
237 move_block_to_cond_assign(mem_ctx
, ir
, else_cond
,
238 &ir
->else_instructions
,
239 this->condition_variables
);
241 /* Add the new condition variable to the hash table. This allows us to
242 * find this variable when lowering other (enclosing) if-statements.
244 hash_table_insert(this->condition_variables
, else_var
, else_var
);
249 this->progress
= true;
251 return visit_continue
;