[Mesa-dev] [PATCH] i965/fs: Disable opt_sampler_eot for textureGather

[Neil Roberts]

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>
---

See here for some more discussion of this:

http://lists.freedesktop.org/archives/mesa-dev/2015-May/083640.html

As far as I can tell the Jenkins run mentioned in that email doesn't
seem to have any tests on Cherryview or Skylake so that probably
explains why it didn't pick up the regression.

 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 8dd680e..e9528e0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -2655,6 +2655,16 @@ 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.
     */
-- 
1.9.3