On Fri, May 3, 2013 at 3:05 PM, Eric Anholt <e...@anholt.net> wrote:
> 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%)
> ---
> src/glsl/opt_if_simplification.cpp | 27 ++++++++++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
>
> 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;
> --
Reviewed-by: Matt Turner <matts...@gmail.com>
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