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, 1 insertions, 0 deletions

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 63b74285aa3..757bd71aaba 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -5189,6 +5189,7 @@ st_link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
                          DIV_TO_MUL_RCP |
                          EXP_TO_EXP2 |
                          LOG_TO_LOG2 |
+                         LRP_TO_ARITH |
                          (options->EmitNoPow ? POW_TO_EXP2 : 0) |
                          (!ctx->Const.NativeIntegers ? INT_DIV_TO_MUL_RCP : 0));