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glsl: Optimize 1/exp(x) into exp(-x).

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Lots of shaders divide by exp2(...) which we turn into a multiplication
by the reciprocal. We can avoid the reciprocal by simply negating exp2's
argument.

total instructions in shared programs: 5947154 -> 5946695 (-0.01%)
instructions in affected programs:     118661 -> 118202 (-0.39%)
helped:                                380

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
This commit is contained in:
Matt Turner
2015-02-10 12:31:37 -08:00
parent a9065cef48
commit ea0f0eb6c0
1 changed files with 6 additions and 0 deletions
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6
src/glsl/opt_algebraic.cpp
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@@ -747,6 +747,12 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
if (op_expr[0] && op_expr[0]->operation == ir_unop_rcp)
return op_expr[0]->operands[0];
if (op_expr[0] && (op_expr[0]->operation == ir_unop_exp2 ||
op_expr[0]->operation == ir_unop_exp)) {
return new(mem_ctx) ir_expression(op_expr[0]->operation, ir->type,
neg(op_expr[0]->operands[0]));
}
/* While ir_to_mesa.cpp will lower sqrt(x) to rcp(rsq(x)), it does so at
* its IR level, so we can always apply this transformation.
*/