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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_list_safe(node
, instructions
) {
120 ir_instruction
*ir
= (ir_instruction
*) node
;
122 if (ir
->ir_type
== ir_type_assignment
) {
123 ir_assignment
*assign
= (ir_assignment
*)ir
;
125 if (hash_table_find(ht
, assign
) == NULL
) {
126 hash_table_insert(ht
, assign
, assign
);
128 /* If the LHS of the assignment is a condition variable that was
129 * previously added, insert an additional assignment of false to
132 const bool assign_to_cv
=
133 hash_table_find(ht
, assign
->lhs
->variable_referenced()) != NULL
;
135 if (!assign
->condition
) {
138 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
139 glsl_type::bool_type
,
140 cond_expr
->clone(mem_ctx
, NULL
),
143 assign
->condition
= cond_expr
->clone(mem_ctx
, NULL
);
147 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
148 glsl_type::bool_type
,
149 cond_expr
->clone(mem_ctx
, NULL
),
155 /* Now, move from the if block to the block surrounding it. */
157 if_ir
->insert_before(ir
);
162 ir_if_to_cond_assign_visitor::visit_enter(ir_if
*ir
)
167 return visit_continue
;
171 ir_if_to_cond_assign_visitor::visit_leave(ir_if
*ir
)
173 /* Only flatten when beyond the GPU's maximum supported nesting depth. */
174 if (this->depth
-- <= this->max_depth
)
175 return visit_continue
;
177 bool found_control_flow
= false;
178 ir_assignment
*assign
;
180 /* Check that both blocks don't contain anything we can't support. */
181 foreach_list(n
, &ir
->then_instructions
) {
182 ir_instruction
*then_ir
= (ir_instruction
*) n
;
183 visit_tree(then_ir
, check_control_flow
, &found_control_flow
);
185 foreach_list(n
, &ir
->else_instructions
) {
186 ir_instruction
*else_ir
= (ir_instruction
*) n
;
187 visit_tree(else_ir
, check_control_flow
, &found_control_flow
);
189 if (found_control_flow
)
190 return visit_continue
;
192 void *mem_ctx
= ralloc_parent(ir
);
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.
198 ir_variable
*const then_var
=
199 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
200 "if_to_cond_assign_then",
202 ir
->insert_before(then_var
);
204 ir_dereference_variable
*then_cond
=
205 new(mem_ctx
) ir_dereference_variable(then_var
);
207 assign
= new(mem_ctx
) ir_assignment(then_cond
, ir
->condition
);
208 ir
->insert_before(assign
);
210 move_block_to_cond_assign(mem_ctx
, ir
, then_cond
,
211 &ir
->then_instructions
,
212 this->condition_variables
);
214 /* Add the new condition variable to the hash table. This allows us to
215 * find this variable when lowering other (enclosing) if-statements.
217 hash_table_insert(this->condition_variables
, then_var
, then_var
);
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.
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",
229 ir
->insert_before(else_var
);
231 ir_dereference_variable
*else_cond
=
232 new(mem_ctx
) ir_dereference_variable(else_var
);
235 new(mem_ctx
) ir_expression(ir_unop_logic_not
,
236 then_cond
->clone(mem_ctx
, NULL
));
238 assign
= new(mem_ctx
) ir_assignment(else_cond
, inverse
);
239 ir
->insert_before(assign
);
241 move_block_to_cond_assign(mem_ctx
, ir
, else_cond
,
242 &ir
->else_instructions
,
243 this->condition_variables
);
245 /* Add the new condition variable to the hash table. This allows us to
246 * find this variable when lowering other (enclosing) if-statements.
248 hash_table_insert(this->condition_variables
, else_var
, else_var
);
253 this->progress
= true;
255 return visit_continue
;