Mesa (master): i965/fs: Port texture projection avoidance optimization from the old backend.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: eb30820f268608cf451da32de69723036dddbc62
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=eb30820f268608cf451da32de69723036dddbc62

Author: Eric Anholt <eric at anholt.net>
Date:   Fri Jul 22 15:56:46 2011 -0700

i965/fs: Port texture projection avoidance optimization from the old backend.

This is part of fixing a ~1% performance regression in OpenArena when
changing the fixed function fragment shader to using the new backend.
Right now this just avoids the LINTERP of the projector, not the math
using it.

---

 src/mesa/drivers/dri/i965/brw_fs.cpp |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 15475fb..9c3180f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -463,9 +463,21 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
 	 } else {
 	    /* Perspective interpolation case. */
 	    for (unsigned int k = 0; k < type->vector_elements; k++) {
-	       struct brw_reg interp = interp_reg(location, k);
-	       emit(FS_OPCODE_LINTERP, attr,
-		    this->delta_x, this->delta_y, fs_reg(interp));
+	       /* FINISHME: At some point we probably want to push
+		* this farther by giving similar treatment to the
+		* other potentially constant components of the
+		* attribute, as well as making brw_vs_constval.c
+		* handle varyings other than gl_TexCoord.
+		*/
+	       if (location >= FRAG_ATTRIB_TEX0 &&
+		   location <= FRAG_ATTRIB_TEX7 &&
+		   k == 3 && !(c->key.proj_attrib_mask & (1 << location))) {
+		  emit(BRW_OPCODE_MOV, attr, fs_reg(1.0f));
+	       } else {
+		  struct brw_reg interp = interp_reg(location, k);
+		  emit(FS_OPCODE_LINTERP, attr,
+		       this->delta_x, this->delta_y, fs_reg(interp));
+	       }
 	       attr.reg_offset++;
 	    }