[Mesa-dev] [PATCH v2 10/20] i965/fs: lower all non-force_writemask_all DF instructions to SIMD4 on IVB/BYT

[Samuel Iglesias Gonsálvez]

The hardware applies the same channel enable signals to both halves of
the compressed instruction which will be just wrong under non-uniform
control flow. Fix this by splitting those instructions to SIMD4.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
---
 src/mesa/drivers/dri/i965/brw_fs.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index c9b6c995dc9..a622b7a640b 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -4577,6 +4577,15 @@ get_fpu_lowered_simd_width(const struct gen_device_info *devinfo,
        */
       if (channels_per_grf != (exec_type_size == 8 ? 4 : 8))
          max_width = MIN2(max_width, channels_per_grf);
+
+      /* Lower all non-force_writemask_all DF instructions to SIMD4 on IVB/BYT
+       * because HW applies the same channel enable signals to both halves of
+       * the compressed instruction which will be just wrong under
+       * non-uniform control flow.
+       */
+      if (devinfo->gen == 7 && !devinfo->is_haswell &&
+          (exec_type_size == 8 || type_sz(inst->dst.type) == 8))
+         max_width = MIN2(max_width, 4);
    }
 
    /* Only power-of-two execution sizes are representable in the instruction
-- 
2.11.0