Mesa (master): glsl: Flip around "if" statements with empty "then" blocks.
Eric Anholt
anholt at kemper.freedesktop.org
Sun May 5 20:56:26 UTC 2013
Module: Mesa
Branch: master
Commit: 739b88330c26457834c5e7e1b2e16cc3655d3fac
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=739b88330c26457834c5e7e1b2e16cc3655d3fac
Author: Eric Anholt <eric at anholt.net>
Date: Fri May 3 13:17:56 2013 -0700
glsl: Flip around "if" statements with empty "then" blocks.
This cleans up some funny-looking code in some unigine shaders I was
looking at. Also slightly helps on planeshift and a few shaders in an
upcoming Valve release.
total instructions in shared programs: 1653715 -> 1653587 (-0.01%)
instructions in affected programs: 16550 -> 16422 (-0.77%)
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Matt Turner <mattst88 at gmail.com>
---
src/glsl/opt_if_simplification.cpp | 27 ++++++++++++++++++++++++++-
1 files changed, 26 insertions(+), 1 deletions(-)
diff --git a/src/glsl/opt_if_simplification.cpp b/src/glsl/opt_if_simplification.cpp
index e1a23d9..db59b13 100644
--- a/src/glsl/opt_if_simplification.cpp
+++ b/src/glsl/opt_if_simplification.cpp
@@ -25,7 +25,8 @@
* \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"
@@ -101,6 +102,30 @@ ir_if_simplification_visitor::visit_leave(ir_if *ir)
}
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;
More information about the mesa-commit
mailing list