When handling 'if' in copy propagation, if a certain variable was
killed when processing the first branch of the 'if', then the second
would get any propagation from previous nodes.
x = y;
if (...) {
z = x; // This would turn into z = y.
x = 22; // x gets killed.
} else {
w = x; // This would NOT turn into w = y.
}
With the change, we let copy propagation happen independently in the
two branches and only then apply the killed values for the subsequent
code.
Results for Skylake:
total instructions in shared programs: 15238463 -> 15238503 (<.01%)
instructions in affected programs: 10317 -> 10357 (0.39%)
helped: 0
HURT: 20
total cycles in shared programs: 571868000 -> 571868028 (<.01%)
cycles in affected programs: 43507 -> 43535 (0.06%)
helped: 14
HURT: 6
The hurt instruction count is caused because the extra propagation
causes an input variable to be read from two branches of an
if (load_input intrinsic in NIR). Depending on the complexity of each
branch this might be a win or not in terms of cycles.
---
src/compiler/glsl/opt_copy_propagation.cpp | 44 ++++++++++++----------
1 file changed, 25 insertions(+), 19 deletions(-)
diff --git a/src/compiler/glsl/opt_copy_propagation.cpp
b/src/compiler/glsl/opt_copy_propagation.cpp
index 206dffe4f1c..4ba5eedb2b1 100644
--- a/src/compiler/glsl/opt_copy_propagation.cpp
+++ b/src/compiler/glsl/opt_copy_propagation.cpp
@@ -71,7 +71,7 @@ public:
void add_copy(ir_assignment *ir);
void kill(ir_variable *ir);
- void handle_if_block(exec_list *instructions);
+ void handle_if_block(exec_list *instructions, set *kills, bool *killed_all);
/** Hash of lhs->rhs: The available copies to propagate */
hash_table *acp;
@@ -207,14 +207,13 @@ ir_copy_propagation_visitor::visit_enter(ir_call *ir)
}
void
-ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
+ir_copy_propagation_visitor::handle_if_block(exec_list *instructions, set
*kills, bool *killed_all)
{
hash_table *orig_acp = this->acp;
set *orig_kills = this->kills;
bool orig_killed_all = this->killed_all;
- kills = _mesa_set_create(NULL, _mesa_hash_pointer,
- _mesa_key_pointer_equal);
+ this->kills = kills;
this->killed_all = false;
/* Populate the initial acp with a copy of the original */
@@ -222,22 +221,12 @@ ir_copy_propagation_visitor::handle_if_block(exec_list
*instructions)
visit_list_elements(this, instructions);
- if (this->killed_all) {
- _mesa_hash_table_clear(orig_acp, NULL);
- }
+ _mesa_hash_table_destroy(acp, NULL);
+ *killed_all = this->killed_all;
- set *new_kills = this->kills;
this->kills = orig_kills;
- _mesa_hash_table_destroy(acp, NULL);
this->acp = orig_acp;
- this->killed_all = this->killed_all || orig_killed_all;
-
- struct set_entry *s_entry;
- set_foreach(new_kills, s_entry) {
- kill((ir_variable *) s_entry->key);
- }
-
- _mesa_set_destroy(new_kills, NULL);
+ this->killed_all = orig_killed_all;
}
ir_visitor_status
@@ -245,8 +234,25 @@ ir_copy_propagation_visitor::visit_enter(ir_if *ir)
{
ir->condition->accept(this);
- handle_if_block(&ir->then_instructions);
- handle_if_block(&ir->else_instructions);
+ set *new_kills = _mesa_set_create(NULL, _mesa_hash_pointer,
+ _mesa_key_pointer_equal);
+ bool then_killed_all = false;
+ bool else_killed_all = false;
+
+ handle_if_block(&ir->then_instructions, new_kills, &then_killed_all);
+ handle_if_block(&ir->else_instructions, new_kills, &else_killed_all);
+
+ if (then_killed_all || else_killed_all) {
+ _mesa_hash_table_clear(acp, NULL);
+ killed_all = true;
+ } else {
+ struct set_entry *s_entry;
+ set_foreach(new_kills, s_entry) {
+ kill((ir_variable *) s_entry->key);
+ }
+ }
+
+ _mesa_set_destroy(new_kills, NULL);
/* handle_if_block() already descended into the children. */
return visit_continue_with_parent;
--
2.17.1
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