From 84a40ce86b1010873b194eb9bf0b8744234b829c Mon Sep 17 00:00:00 2001 From: Kenneth Graunke Date: Fri, 12 Sep 2014 15:16:57 -0700 Subject: [PATCH] glsl: Speed up constant folding for swizzles. ir_rvalue::constant_expression_value() recursively walks down an IR tree, attempting to reduce it to a single constant value. This is useful when you want to know whether a variable has a constant expression value at all, and if so, what it is. The constant folding optimization pass attempts to replace rvalues with their constant expression value from the bottom up. That way, we can optimize subexpressions, and ideally stop as soon as we find a non-constant subexpression. In order to obtain the actual value of an expression, the optimization pass calls constant_expression_value(). But it should only do so if it knows the value can be combined into a constant. Otherwise, at each step of walking back up the tree, it will walk down the tree again, only to discover what it already knew: it isn't constant. We properly avoided this call for ir_expression nodes, but not for ir_swizzle nodes. This patch fixes that, drastically reducing compile times on certain shaders where tree grafting has given us huge expression trees. It also fixes SuperTuxKart. Thanks to Iago and Mike for help in tracking this down. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78468 Signed-off-by: Kenneth Graunke Reviewed-by: Jordan Justen Reviewed-by: Ian Romanick Cc: mesa-stable@lists.freedesktop.org --- src/glsl/opt_constant_folding.cpp | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/src/glsl/opt_constant_folding.cpp b/src/glsl/opt_constant_folding.cpp index d0e575460bd..74b855e5e94 100644 --- a/src/glsl/opt_constant_folding.cpp +++ b/src/glsl/opt_constant_folding.cpp @@ -79,6 +79,11 @@ ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue) } } + /* Ditto for swizzles. */ + ir_swizzle *swiz = (*rvalue)->as_swizzle(); + if (swiz && !swiz->val->as_constant()) + return; + ir_constant *constant = (*rvalue)->constant_expression_value(); if (constant) { *rvalue = constant; -- 2.11.0