* \file opt_if_simplification.cpp
*
* Moves constant branches of if statements out to the surrounding
- * instruction stream.
+ * instruction stream, and inverts if conditionals to avoid empty
+ * "then" blocks.
*/
#include "ir.h"
+namespace {
+
class ir_if_simplification_visitor : public ir_hierarchical_visitor {
public:
ir_if_simplification_visitor()
bool made_progress;
};
+} /* unnamed namespace */
+
/* We only care about the top level "if" instructions, so don't
* descend into expressions.
*/
ir_visitor_status
ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
{
+ (void) ir;
return visit_continue_with_parent;
}
ir_visitor_status
ir_if_simplification_visitor::visit_leave(ir_if *ir)
{
+ /* If the if statement has nothing on either side, remove it. */
+ if (ir->then_instructions.is_empty() &&
+ ir->else_instructions.is_empty()) {
+ ir->remove();
+ this->made_progress = true;
+ return visit_continue;
+ }
+
/* FINISHME: Ideally there would be a way to note that the condition results
* FINISHME: in a constant before processing both of the other subtrees.
* FINISHME: This can probably be done with some flags, but it would take
* that matters out.
*/
if (condition_constant->value.b[0]) {
- foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
- ir_instruction *then_ir = (ir_instruction *)then_iter.get();
- ir->insert_before(then_ir);
- }
+ ir->insert_before(&ir->then_instructions);
} else {
- foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
- ir_instruction *else_ir = (ir_instruction *)else_iter.get();
- ir->insert_before(else_ir);
- }
+ ir->insert_before(&ir->else_instructions);
}
ir->remove();
this->made_progress = true;
+ return visit_continue;
+ }
+
+ /* Turn:
+ *
+ * if (cond) {
+ * } else {
+ * do_work();
+ * }
+ *
+ * into :
+ *
+ * if (!cond)
+ * do_work();
+ *
+ * which avoids control flow for "else" (which is usually more
+ * expensive than normal operations), and the "not" can usually be
+ * folded into the generation of "cond" anyway.
+ */
+ if (ir->then_instructions.is_empty()) {
+ ir->condition = new(ralloc_parent(ir->condition))
+ ir_expression(ir_unop_logic_not, ir->condition);
+ ir->else_instructions.move_nodes_to(&ir->then_instructions);
+ this->made_progress = true;
}
return visit_continue;