[Mesa-dev] [PATCH 2/5] intel/fs: Lower integer multiply correctly when destination stride equals 4.

[Francisco Jerez]

Because the "low" temporary needs to be accessed with word type and
twice the original stride, attempting to preserve the alignment of the
original destination can potentially lead to instructions with illegal
destination stride greater than four.  Because the CHV/BXT alignment
restrictions are now being enforced by the regioning lowering pass run
after lower_integer_multiplication(), there is no real need to
preserve the original strides anymore.

Note that this bug can be reproduced on stable branches, but
back-porting would be non-trivial, because the fix relies on the
regioning lowering pass recently introduced.
---
 src/intel/compiler/brw_fs.cpp | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index f475b617df2..5768e0d6542 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -3962,13 +3962,11 @@ fs_visitor::lower_integer_multiplication()
                 regions_overlap(inst->dst, inst->size_written,
                                 inst->src[0], inst->size_read(0)) ||
                 regions_overlap(inst->dst, inst->size_written,
-                                inst->src[1], inst->size_read(1))) {
+                                inst->src[1], inst->size_read(1)) ||
+                inst->dst.stride >= 4) {
                needs_mov = true;
-               /* Get a new VGRF but keep the same stride as inst->dst */
                low = fs_reg(VGRF, alloc.allocate(regs_written(inst)),
                             inst->dst.type);
-               low.stride = inst->dst.stride;
-               low.offset = inst->dst.offset % REG_SIZE;
             }
 
             /* Get a new VGRF but keep the same stride as inst->dst */
-- 
2.19.2