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glsl: don't let an 'if' then-branch kill copy propagation (elements) for else-branch

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When handling 'if' in copy propagation elements, 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.

One example in shader-db part of shaders/unity/8.shader_test:

    (assign  (xyz) (var_ref col_1)  (var_ref tmpvar_8) )
    (if (expression bool < (swiz y (var_ref xlv_TEXCOORD0) )(constant float (0.000000)) ) (
      (assign  (xyz) (var_ref col_1)  (expression vec3 + (var_ref tmpvar_8) ... ) ... )
    )
    (
      (assign  (xyz) (var_ref col_1)  (expression vec3 lrp (var_ref col_1) ... ) ... )
    ))

The variable col_1 was replaced by tmpvar_8 in the then-part but not
in the else-part.

NIR deals well with copy propagation, so it already covered for the
missing ones that this patch fixes.

Reviewed-by: Eric Anholt <eric@anholt.net>
This commit is contained in:
Caio Marcelo de Oliveira Filho 2018-06-26 16:26:46 -07:00
parent e4f32dec23
commit 507a8037a7
1 changed files with 21 additions and 19 deletions
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40
src/compiler/glsl/opt_copy_propagation_elements.cpp
View file

@ -257,7 +257,7 @@ public:
void add_copy(ir_assignment *ir);
void kill(kill_entry *k);
void handle_if_block(exec_list *instructions);
void handle_if_block(exec_list *instructions, exec_list *kills, bool *killed_all);
copy_propagation_state *state;
@ -468,12 +468,12 @@ ir_copy_propagation_elements_visitor::visit_enter(ir_call *ir)
}
void
ir_copy_propagation_elements_visitor::handle_if_block(exec_list *instructions)
ir_copy_propagation_elements_visitor::handle_if_block(exec_list *instructions, exec_list *kills, bool *killed_all)
{
exec_list *orig_kills = this->kills;
bool orig_killed_all = this->killed_all;
this->kills = new(mem_ctx) exec_list;
this->kills = kills;
this->killed_all = false;
/* Populate the initial acp with a copy of the original */
@ -485,21 +485,9 @@ ir_copy_propagation_elements_visitor::handle_if_block(exec_list *instructions)
delete this->state;
this->state = orig_state;
if (this->killed_all)
this->state->erase_all();
exec_list *new_kills = this->kills;
*killed_all = this->killed_all;
this->kills = orig_kills;
this->killed_all = this->killed_all || orig_killed_all;
/* Move the new kills into the parent block's list, removing them
* from the parent's ACP list in the process.
*/
foreach_in_list_safe(kill_entry, k, new_kills) {
kill(k);
}
ralloc_free(new_kills);
this->killed_all = orig_killed_all;
}
ir_visitor_status
@ -507,8 +495,22 @@ ir_copy_propagation_elements_visitor::visit_enter(ir_if *ir)
{
ir->condition->accept(this);
handle_if_block(&ir->then_instructions);
handle_if_block(&ir->else_instructions);
exec_list *new_kills = new(mem_ctx) exec_list;
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) {
state->erase_all();
killed_all = true;
} else {
foreach_in_list_safe(kill_entry, k, new_kills)
kill(k);
}
ralloc_free(new_kills);
/* handle_if_block() already descended into the children. */
return visit_continue_with_parent;