On Wed, 11 Apr 2012 23:46:03 -0700, Kenneth Graunke <kenn...@whitecape.org>
wrote:
> On 04/11/2012 08:49 PM, Matt Turner wrote:
> > On Wed, Apr 11, 2012 at 9:33 PM, Eric Anholt<e...@anholt.net> wrote:
> >> Cuts 8/1068 instructions from glyphy's fragment shaders on i965.
> >> ---
> >> src/glsl/opt_if_simplification.cpp | 8 ++++++++
> >> 1 file changed, 8 insertions(+)
> >>
> >> diff --git a/src/glsl/opt_if_simplification.cpp
> >> b/src/glsl/opt_if_simplification.cpp
> >> index 940dd08..7e88208 100644
> >> --- a/src/glsl/opt_if_simplification.cpp
> >> +++ b/src/glsl/opt_if_simplification.cpp
> >> @@ -66,6 +66,14 @@ do_if_simplification(exec_list *instructions)
> >> 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
> >> --
> >> 1.7.9.5
> >
> > Follow on: If then_instructions is empty, is there any benefit in
> > inverting the if conditional and moving the else_instructions into the
> > place of then_instructions?
> >
> > Matt
>
> Yeah. I think in that case, i965 would ultimately emit the assembly:
>
> if(8) ...
> else(8)
> ...actual code...
> endif(8)
>
> which is silly. This is a good place to patch that up.
>
> (I could've sworn we did that already, but I can't seem to find it.)Yeah, I thought we had as well, and there are instances of this structure in Unigine Tropics.
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