glsl: Convert mix() to use a new ir_triop_lrp opcode.

Many GPUs have an instruction to do linear interpolation which is more
efficient than simply performing the algebra necessary (two multiplies,
an add, and a subtract).

Pattern matching or peepholing this is more desirable, but can be
tricky.  By using an opcode, we can at least make shaders which use the
mix() built-in get the more efficient behavior.

Currently, all consumers lower ir_triop_lrp.  Subsequent patches will
actually generate different code.

v2 [mattst88]:
   - Add LRP_TO_ARITH flag to ir_to_mesa.cpp. Will be removed in a
     subsequent patch and ir_triop_lrp translated directly.
v3 [mattst88]:
   - Move changes from the next patch to opt_algebraic.cpp to accept
     3-src operations.

Reviewed-by: Matt Turner <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>
Signed-off-by: Kenneth Graunke <[email protected]>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 75948db16fa..44a21b6c335 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -186,12 +186,12 @@ ir_algebraic_visitor::swizzle_if_required(ir_expression *expr,
 ir_rvalue *
 ir_algebraic_visitor::handle_expression(ir_expression *ir)
 {
-   ir_constant *op_const[2] = {NULL, NULL};
-   ir_expression *op_expr[2] = {NULL, NULL};
+   ir_constant *op_const[3] = {NULL, NULL, NULL};
+   ir_expression *op_expr[3] = {NULL, NULL, NULL};
    ir_expression *temp;
    unsigned int i;
 
-   assert(ir->get_num_operands() <= 2);
+   assert(ir->get_num_operands() <= 3);
    for (i = 0; i < ir->get_num_operands(); i++) {
       if (ir->operands[i]->type->is_matrix())
 	 return ir;