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, 7 insertions, 0 deletions

diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index d878bd8fd03..d63dac100c7 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -1118,6 +1118,13 @@ enum ir_expression_operation {
     */
    ir_last_binop = ir_binop_ubo_load,
 
+   ir_triop_lrp,
+
+   /**
+    * A sentinel marking the last of the ternary operations.
+    */
+   ir_last_triop = ir_triop_lrp,
+
    ir_quadop_vector,
 
    /**