[Mesa-dev] [PATCH v2] i965/fs: half exec_size when dealing with 64 bits attributes

[Alejandro Piñeiro]

The HW has a restriction that only vertical stride may cross register
boundaries. Until now this was only handled on VGRFs at
rw_reg_from_fs_reg, but it is also needed for attributes.

v2:
 * Remove reference to commit id on commit message (Juan Suarez)
 * Simplify code that compute final exec_size (Ian Romanick)
 * Use REG_SIZE on that same code (Kenneth Graunke)

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
---

Even although Kenneth granted the RB, as the changes proposed modifies the patch
significantly, sending the v2 just in case.

 src/mesa/drivers/dri/i965/brw_fs.cpp | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 80803a6..e9ac35a 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1844,11 +1844,28 @@ fs_visitor::convert_attr_sources_to_hw_regs(fs_inst *inst)
                    inst->src[i].nr +
                    inst->src[i].reg_offset;
 
-         unsigned width = inst->src[i].stride == 0 ? 1 : inst->exec_size;
+         /* As explained at brw_reg_from_fs_reg, From the Haswell PRM:
+          *
+          * VertStride must be used to cross GRF register boundaries. This
+          * rule implies that elements within a 'Width' cannot cross GRF
+          * boundaries.
+          *
+          * So, for registers that are large enough, we have to split the exec
+          * size in two and trust the compression state to sort it out.
+          */
+         unsigned total_size = inst->exec_size *
+                               inst->src[i].stride *
+                               type_sz(inst->src[i].type);
+
+         assert(total_size <= 2 * REG_SIZE);
+         const unsigned exec_size =
+            (total_size <= REG_SIZE) ? inst->exec_size : inst->exec_size / 2;
+
+         unsigned width = inst->src[i].stride == 0 ? 1 : exec_size;
          struct brw_reg reg =
             stride(byte_offset(retype(brw_vec8_grf(grf, 0), inst->src[i].type),
                                inst->src[i].subreg_offset),
-                   inst->exec_size * inst->src[i].stride,
+                   exec_size * inst->src[i].stride,
                    width, inst->src[i].stride);
          reg.abs = inst->src[i].abs;
          reg.negate = inst->src[i].negate;
-- 
2.7.4