i965: Don't copy propagate bitcasts with source modifiers.

Previously, copy propagation would cause bitcast_f2u(abs(float)) to
be performed in a single step, but the application of source modifiers
(abs, neg) happens after type conversion, leading to incorrect results.

That is, for bitcast_f2u(abs(float)) we would in fact generate code to
do abs(bitcast_f2u(float)).

For example, whereas bitcast_f2u(abs(float)) might result in a register
argument such as
   (abs)g2.2<0,1,0>UD

v2: Set interfered = true and break in register_coalesce instead of
    returning false.

Reviewed-by: Paul Berry <stereoytpe441@gmail.com>
(cherry picked from commit 9c48ae751ab28f35eb878551d24c071be0ce11b0)

1 files changed, 14 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index afd29deaede..3986bf5fe6e 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -2118,6 +2118,20 @@ fs_visitor::register_coalesce()
 	    }
 	 }
 
+         if (has_source_modifiers) {
+            for (int i = 0; i < 3; i++) {
+               if (scan_inst->src[i].file == GRF &&
+                   scan_inst->src[i].reg == inst->dst.reg &&
+                   scan_inst->src[i].reg_offset == inst->dst.reg_offset &&
+                   inst->dst.type != scan_inst->src[i].type)
+               {
+                 interfered = true;
+                 break;
+               }
+            }
+         }
+
+
 	 /* The gen6 MATH instruction can't handle source modifiers or
 	  * unusual register regions, so avoid coalescing those for
 	  * now.  We should do something more specific.