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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 "compiler/glsl_types.h"
51 #include "util/hash_table.h" /* Needed for the hashing functions */
55 class ir_if_to_cond_assign_visitor
: public ir_hierarchical_visitor
{
57 ir_if_to_cond_assign_visitor(unsigned max_depth
)
59 this->progress
= false;
60 this->max_depth
= max_depth
;
63 this->condition_variables
=
64 _mesa_set_create(NULL
, _mesa_hash_pointer
,
65 _mesa_key_pointer_equal
);
68 ~ir_if_to_cond_assign_visitor()
70 _mesa_set_destroy(this->condition_variables
, NULL
);
73 ir_visitor_status
visit_enter(ir_if
*);
74 ir_visitor_status
visit_leave(ir_if
*);
76 bool found_unsupported_op
;
81 struct set
*condition_variables
;
84 } /* anonymous namespace */
87 lower_if_to_cond_assign(exec_list
*instructions
, unsigned max_depth
)
89 if (max_depth
== UINT_MAX
)
92 ir_if_to_cond_assign_visitor
v(max_depth
);
94 visit_list_elements(&v
, instructions
);
100 check_control_flow(ir_instruction
*ir
, void *data
)
102 ir_if_to_cond_assign_visitor
*v
= (ir_if_to_cond_assign_visitor
*)data
;
104 switch (ir
->ir_type
) {
106 case ir_type_discard
:
108 case ir_type_loop_jump
:
110 v
->found_unsupported_op
= true;
118 move_block_to_cond_assign(void *mem_ctx
,
119 ir_if
*if_ir
, ir_rvalue
*cond_expr
,
120 exec_list
*instructions
,
123 foreach_in_list_safe(ir_instruction
, ir
, instructions
) {
124 if (ir
->ir_type
== ir_type_assignment
) {
125 ir_assignment
*assign
= (ir_assignment
*)ir
;
127 if (_mesa_set_search(set
, assign
) == NULL
) {
128 _mesa_set_add(set
, assign
);
130 /* If the LHS of the assignment is a condition variable that was
131 * previously added, insert an additional assignment of false to
134 const bool assign_to_cv
=
136 set
, assign
->lhs
->variable_referenced()) != NULL
;
138 if (!assign
->condition
) {
141 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
142 glsl_type::bool_type
,
143 cond_expr
->clone(mem_ctx
, NULL
),
146 assign
->condition
= cond_expr
->clone(mem_ctx
, NULL
);
150 new(mem_ctx
) ir_expression(ir_binop_logic_and
,
151 glsl_type::bool_type
,
152 cond_expr
->clone(mem_ctx
, NULL
),
158 /* Now, move from the if block to the block surrounding it. */
160 if_ir
->insert_before(ir
);
165 ir_if_to_cond_assign_visitor::visit_enter(ir_if
*ir
)
170 return visit_continue
;
174 ir_if_to_cond_assign_visitor::visit_leave(ir_if
*ir
)
176 /* Only flatten when beyond the GPU's maximum supported nesting depth. */
177 if (this->depth
-- <= this->max_depth
)
178 return visit_continue
;
180 this->found_unsupported_op
= false;
182 ir_assignment
*assign
;
184 /* Check that both blocks don't contain anything we can't support. */
185 foreach_in_list(ir_instruction
, then_ir
, &ir
->then_instructions
) {
186 visit_tree(then_ir
, check_control_flow
, this);
188 foreach_in_list(ir_instruction
, else_ir
, &ir
->else_instructions
) {
189 visit_tree(else_ir
, check_control_flow
, this);
191 if (this->found_unsupported_op
)
192 return visit_continue
; /* can't handle inner unsupported opcodes */
194 void *mem_ctx
= ralloc_parent(ir
);
196 /* Store the condition to a variable. Move all of the instructions from
197 * the then-clause of the if-statement. Use the condition variable as a
198 * condition for all assignments.
200 ir_variable
*const then_var
=
201 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
202 "if_to_cond_assign_then",
204 ir
->insert_before(then_var
);
206 ir_dereference_variable
*then_cond
=
207 new(mem_ctx
) ir_dereference_variable(then_var
);
209 assign
= new(mem_ctx
) ir_assignment(then_cond
, ir
->condition
);
210 ir
->insert_before(assign
);
212 move_block_to_cond_assign(mem_ctx
, ir
, then_cond
,
213 &ir
->then_instructions
,
214 this->condition_variables
);
216 /* Add the new condition variable to the hash table. This allows us to
217 * find this variable when lowering other (enclosing) if-statements.
219 _mesa_set_add(this->condition_variables
, then_var
);
221 /* If there are instructions in the else-clause, store the inverse of the
222 * condition to a variable. Move all of the instructions from the
223 * else-clause if the if-statement. Use the (inverse) condition variable
224 * as a condition for all assignments.
226 if (!ir
->else_instructions
.is_empty()) {
227 ir_variable
*const else_var
=
228 new(mem_ctx
) ir_variable(glsl_type::bool_type
,
229 "if_to_cond_assign_else",
231 ir
->insert_before(else_var
);
233 ir_dereference_variable
*else_cond
=
234 new(mem_ctx
) ir_dereference_variable(else_var
);
237 new(mem_ctx
) ir_expression(ir_unop_logic_not
,
238 then_cond
->clone(mem_ctx
, NULL
));
240 assign
= new(mem_ctx
) ir_assignment(else_cond
, inverse
);
241 ir
->insert_before(assign
);
243 move_block_to_cond_assign(mem_ctx
, ir
, else_cond
,
244 &ir
->else_instructions
,
245 this->condition_variables
);
247 /* Add the new condition variable to the hash table. This allows us to
248 * find this variable when lowering other (enclosing) if-statements.
250 _mesa_set_add(this->condition_variables
, else_var
);
255 this->progress
= true;
257 return visit_continue
;