Mesa (master): i965/fs: Disable opt_sampler_eot for textureGather

[Neil Roberts]

Module: Mesa
Branch: master
Commit: bfdae9149e00bd5c2521db3e75669ae043eed5cc
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=bfdae9149e00bd5c2521db3e75669ae043eed5cc

Author: Neil Roberts <neil at linux.intel.com>
Date:   Fri May  8 17:35:18 2015 +0100

i965/fs: Disable opt_sampler_eot for textureGather

The opt_sampler_eot optimisation seems to break when the last
instruction is SHADER_OPCODE_TG4. A bunch of Piglit tests end up doing
this so it causes a lot of regressions. I can't find any documentation
or known workarounds to indicate that this is expected behaviour, but
considering that this is probably a pretty unlikely situation in a
real use case we might as well disable it in order to avoid the
regressions. In total this fixes 451 tests.

Reviewed-by: Ben Widawsky <ben at bwidawsk.net>
Reviewed-by: Chris Forbes <chrisf at ijw.co.nz>

---

 src/mesa/drivers/dri/i965/brw_fs.cpp |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index b2701b8..3414d92 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -2658,6 +2658,16 @@ fs_visitor::opt_sampler_eot()
    if (unlikely(tex_inst->is_head_sentinel()) || !tex_inst->is_tex())
       return false;
 
+   /* This optimisation doesn't seem to work for textureGather for some
+    * reason. I can't find any documentation or known workarounds to indicate
+    * that this is expected, but considering that it is probably pretty
+    * unlikely that a shader would directly write out the results from
+    * textureGather we might as well just disable it.
+    */
+   if (tex_inst->opcode == SHADER_OPCODE_TG4 ||
+       tex_inst->opcode == SHADER_OPCODE_TG4_OFFSET)
+      return false;
+
    /* If there's no header present, we need to munge the LOAD_PAYLOAD as well.
     * It's very likely to be the previous instruction.
     */