[Mesa-dev] [PATCH] i965/fs: Fix projector==1.0 optimization pre-gen6.

[Eric Anholt]

The optimization was supposed to turn an attribute component that was
always 1.0 into a mov of 1.0.  But by leaving loop this patch removes
out of that test, we applied the projection correction to the 1.0 and
got some other value, breaking openarena once it was converted to
using the new compiler backend.

Originally this hunk was separate from the former loop to make the
generated instructions slightly better pipelined.  We now have
automatic instruction scheduling to handle that, and the generated
instruction sequence looked the same to me after this change (except
for the bugfix).
---

idr, are you set up to test this patch with your code?  It's a
retyping of what I did on Ken's machine, so I'm paranoid that I've
mangled it.

 src/mesa/drivers/dri/i965/brw_fs.cpp |   10 +++-------
 1 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index b6aa60e..40327ac 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -491,17 +491,13 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
                   emit(FS_OPCODE_LINTERP, attr,
                        this->delta_x[barycoord_mode],
                        this->delta_y[barycoord_mode], fs_reg(interp));
+		  if (intel->gen < 6) {
+		     emit(BRW_OPCODE_MUL, attr, attr, this->pixel_w);
+		  }
 	       }
 	       attr.reg_offset++;
 	    }
 
-	    if (intel->gen < 6) {
-	       attr.reg_offset -= type->vector_elements;
-	       for (unsigned int k = 0; k < type->vector_elements; k++) {
-		  emit(BRW_OPCODE_MUL, attr, attr, this->pixel_w);
-		  attr.reg_offset++;
-	       }
-	    }
 	 }
 	 location++;
       }
-- 
1.7.7.3