From 847bc36a38d42967ad6bf0492fe90a4892d9d799 Mon Sep 17 00:00:00 2001 From: Kenneth Graunke Date: Sun, 5 Jan 2014 22:57:01 -0800 Subject: [PATCH] glsl: Optimize pow(2, x) --> exp2(x). On Haswell, POW takes 24 cycles, while EXP2 only takes 14. Plus, using POW requires putting 2.0 in a register, while EXP2 doesn't. I believe that EXP2 will be faster than POW on basically all GPUs, so it makes sense to optimize it. Looking at the savage2 subset of shader-db: total instructions in shared programs: 113225 -> 113179 (-0.04%) instructions in affected programs: 2139 -> 2093 (-2.15%) instances of 'math pow': 795 -> 749 (-6.14%) instances of 'math exp': 389 -> 435 (11.8%) Signed-off-by: Kenneth Graunke Reviewed-by: Matt Turner --- src/glsl/opt_algebraic.cpp | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp index 5e885f78648..332f0b77b87 100644 --- a/src/glsl/opt_algebraic.cpp +++ b/src/glsl/opt_algebraic.cpp @@ -87,6 +87,12 @@ is_vec_one(ir_constant *ir) return (ir == NULL) ? false : ir->is_one(); } +static inline bool +is_vec_two(ir_constant *ir) +{ + return (ir == NULL) ? false : ir->is_value(2.0, 2); +} + static inline bool is_vec_negative_one(ir_constant *ir) { @@ -420,6 +426,11 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir) /* 1^x == 1 */ if (is_vec_one(op_const[0])) return op_const[0]; + + /* pow(2,x) == exp2(x) */ + if (is_vec_two(op_const[0])) + return expr(ir_unop_exp2, ir->operands[1]); + break; case ir_unop_rcp: -- 2.30.2