i965/fs: Avoid register coalescing away gen6 MATH workarounds.

The code that generates MATH instructions attempts to work around
the hardware ignoring source modifiers (abs and negate) by emitting
moves into temporaries.  Unfortunately, this pass coalesced those
registers, restoring the original problem.  Avoid doing that.

Fixes several OpenGL ES2 conformance failures on Sandybridge.

NOTE: This is a candidate for the 7.10 branch.

Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 66bbdbe80e..ed973f428f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3059,6 +3059,8 @@ fs_visitor::register_coalesce()
 	  inst->dst.type != inst->src[0].type)
 	 continue;
 
+      bool has_source_modifiers = inst->src[0].abs || inst->src[0].negate;
+
       /* Found a move of a GRF to a GRF.  Let's see if we can coalesce
        * them: check for no writes to either one until the exit of the
        * program.
@@ -3083,6 +3085,14 @@ fs_visitor::register_coalesce()
 	       break;
 	    }
 	 }
+
+	 /* The gen6 MATH instruction can't handle source modifiers, so avoid
+	  * coalescing those for now.  We should do something more specific.
+	  */
+	 if (intel->gen == 6 && scan_inst->is_math() && has_source_modifiers) {
+	    interfered = true;
+	    break;
+	 }
       }
       if (interfered) {
 	 continue;