Jason Ekstrand <ja...@jlekstrand.net> writes:
> On Fri, Jan 18, 2019 at 6:09 PM Francisco Jerez <curroje...@riseup.net>
> wrote:
>
>> 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) {
>>
>
> It would be nice to throw in a quick comment as to why we're adding a
> temporary when stride >= 4.
>
There seemed to be no pre-existing comment about any of the other
conditions to allocate a temporary, so I've added the following:
+ /* Get a new VGRF for the "low" 32x16-bit multiplication result if
+ * reusing the original destination is impossible due to hardware
+ * restrictions, source/destination overlap, or it being the null
+ * register.
+ */
>
>> 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
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
signature.asc
Description: PGP signature
_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
