Re: [PATCH GCC][11/13]Annotate partition by its parallelism execution type

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Jun 12, 2017 at 7:03 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> Hi,
> This patch checks and records if partition can be executed in parallel by
> looking if there exists data dependence cycles.  The information is needed
> for distribution because the idea is to distribute parallel type partitions
> away from sequential ones.  I believe current distribution doesn't work
> very well because it does blind distribution/fusion.
> Bootstrap and test on x86_64 and AArch64.  Is it OK?

+  /* In case of no data dependence.  */
+  if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
+    return false;
+  /* Or the data dependence can be resolved by compilation time alias
+     check.  */
+  else if (!alias_sets_conflict_p (get_alias_set (DR_REF (dr1)),
+                                  get_alias_set (DR_REF (dr2))))
+    return false;

dependence analysis should use TBAA already, in which cases do you need this?
It seems to fall foul of the easy mistake of not honoring GCCs memory model
as well ... see dr_may_alias_p.

+  /* Further check if any data dependence prevents us from executing the
+     partition parallelly.  */
+  EXECUTE_IF_SET_IN_BITMAP (partition->reads, 0, i, bi)
+    {
+      dr1 = (*datarefs_vec)[i];
+      EXECUTE_IF_SET_IN_BITMAP (partition->writes, 0, j, bj)
+       {

what about write-write dependences?

+  EXECUTE_IF_SET_IN_BITMAP (partition->reads, 0, i, bi)
+    {
+      dr1 = (*datarefs_vec)[i];
+      EXECUTE_IF_SET_IN_BITMAP (partition->writes, i + 1, j, bj)
+       {
+         dr2 = (*datarefs_vec)[j];
+         /* Partition can only be executed sequentially if there is any
+            data dependence cycle.  */

exact copy of the loop nest follows?!  Maybe you meant to iterate
over writes in the first loop.

Richard.


> Thanks,
> bin
> 2017-06-07  Bin Cheng  <bin.cheng@arm.com>
>
>         * tree-loop-distribution.c (alias.h): Include header file.
>         (enum partition_type): New.
>         (struct partition): New field type.
>         (partition_merge_into): Update partition type.
>         (data_dep_in_cycle_p): New function.
>         (build_rdg_partition_for_vertex): Compute partition type.
>         (rdg_build_partitions): Dump partition type.