[Bug tree-optimization/58508] New: Redundant vector load of "actual" loop invariant in loop body.

[Bug tree-optimization/58508] New: Redundant vector load of "actual" loop invariant in loop body.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

            Bug ID: 58508
           Summary: Redundant vector load of "actual" loop invariant in
                    loop body.
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: congh at google dot com

When GCC vectorizes the loop below, it will firstly do loop versioning with
aliasing check on a and b. Since a and b have different strides (1 and 0), the
check guarantees that there is no aliasing between a and b across all
iterations. Then with this precondition *b becomes a loop invariant so that it
can be loaded outside the loop during vectorization (Note that this
precondition always holds when the loop is being vectorized). This can save us
a load and a shuffle instruction in each iteration.


void foo (int* a, int* b, int n)
{
  for (int i = 0; i < n; ++i)
    a[i] += *b;
}


I have a patch handling this case as an optimization. After loop versioning, I
detect all zero-strided data references and hoist the loads of them to the loop
header. The patch is shown below.


thanks,
Cong



Index: gcc/tree-vect-loop-manip.c
===================================================================
--- gcc/tree-vect-loop-manip.c    (revision 202662)
+++ gcc/tree-vect-loop-manip.c    (working copy)
@@ -2477,6 +2477,37 @@ vect_loop_versioning (loop_vec_info loop
       adjust_phi_and_debug_stmts (orig_phi, e, PHI_RESULT (new_phi));
     }

+  /* Extract load and store statements on pointers with zero-stride 
+     accesses.  */
+  if (LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo))
+    {
+
+      /* In the loop body, we iterate each statement to check if it is a load 
+     or store. Then we check the DR_STEP of the data reference.  If 
+     DR_STEP is zero, then we will hoist the load statement to the loop 
+     preheader, and move the store statement to the loop exit.  */
+
+      for (gimple_stmt_iterator si = gsi_start_bb (loop->header); 
+        !gsi_end_p (si); )
+    {
+      gimple stmt = gsi_stmt (si);
+      stmt_vec_info stmt_info = vinfo_for_stmt (stmt);
+      struct data_reference *dr = STMT_VINFO_DATA_REF (stmt_info);
+
+      if (dr && integer_zerop (DR_STEP (dr)))
+        {
+          if (DR_IS_READ (dr))
+        {
+          basic_block preheader = loop_preheader_edge (loop)->src;
+          gimple_stmt_iterator si_dst = gsi_last_bb (preheader);
+          gsi_move_after (&si, &si_dst);
+        }
+        }
+      else
+        gsi_next (&si);
+    }
+    } 
+
   /* End loop-exit-fixes after versioning.  */

   if (cond_expr_stmt_list)

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-09-24
             Blocks|                            |53947
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
While the observation is correct, the fix is not.  Please just emit the
load on the preheader edge, like we do for other dt_external vectors we
materialize.

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #2 from Cong Hou <congh at google dot com> ---
Thank you for the comment. I have modified the patch by using 

gsi_insert_on_edge_immediate (loop_preheader_edge (loop), stmt);

to move the statement. 


I have sent this patch again.


Thank you!


Cong

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[law at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #3 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Author: law
Date: Sat Oct 19 05:20:24 2013
New Revision: 203842

URL: http://gcc.gnu.org/viewcvs?rev=203842&root=gcc&view=rev
Log:
    PR tree-optimization/58508
    * tree-vect-loop-manip.c (vect_loop_versioning): Hoist loop invariant
    statement that contains data refs with zero-step.

    * gcc.dg/vect/pr58508.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr58508.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-loop-manip.c

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #5 from Cong Hou <congh at google dot com> ---
I guess I should add 

/* { dg-require-effective-target vect_int } */

to the test case. It is right?

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[bernd.edlinger at hotmail dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #6 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Cong Hou from comment #5)
> I guess I should add 
> 
> /* { dg-require-effective-target vect_int } */
> 
> to the test case. It is right?

Yes.

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #7 from Cong Hou <congh at google dot com> ---
OK. I made a new patch to fix this problem. Waiting to be approved.


thanks,
Cong



diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9d0f4a5..3d9916d 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2013-10-29  Cong Hou  <congh@google.com>
+
+       * gcc.dg/vect/pr58508.c: Update.
+
 2013-10-15  Cong Hou  <congh@google.com>

        * gcc.dg/vect/pr58508.c: New test.
diff --git a/gcc/testsuite/gcc.dg/vect/pr58508.c
b/gcc/testsuite/gcc.dg/vect/pr58508.c
index 6484a65..fff7a04 100644
--- a/gcc/testsuite/gcc.dg/vect/pr58508.c
+++ b/gcc/testsuite/gcc.dg/vect/pr58508.c
@@ -1,3 +1,4 @@
+/* { dg-require-effective-target vect_int } */
 /* { dg-do compile } */
 /* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-details" } */





On Tue, Oct 29, 2013 at 6:50 AM, bernd.edlinger at hotmail dot de
<gcc-bugzilla@gcc.gnu.org> wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508
>
> --- Comment #6 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
> (In reply to Cong Hou from comment #5)
>> I guess I should add
>>
>> /* { dg-require-effective-target vect_int } */
>>
>> to the test case. It is right?
>
> Yes.
>
> --
> You are receiving this mail because:
> You reported the bug.

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[congh at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

--- Comment #8 from congh at gcc dot gnu.org ---
Author: congh
Date: Fri Nov  8 18:44:46 2013
New Revision: 204590

URL: http://gcc.gnu.org/viewcvs?rev=204590&root=gcc&view=rev
Log:
2013-11-08  Cong Hou  <congh@google.com>

    PR tree-optimization/58508
    * gcc.dg/vect/pr58508.c: Update.


Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/vect/pr58508.c

[Bug tree-optimization/58508] [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508

Cong Hou <congh at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #9 from Cong Hou <congh at google dot com> ---
(In reply to congh from comment #8)
> Author: congh
> Date: Fri Nov  8 18:44:46 2013
> New Revision: 204590
> 
> URL: http://gcc.gnu.org/viewcvs?rev=204590&root=gcc&view=rev
> Log:
> 2013-11-08  Cong Hou  <congh@google.com>
> 
> 	PR tree-optimization/58508
> 	* gcc.dg/vect/pr58508.c: Update.
> 
> 
> Modified:
>     trunk/gcc/testsuite/ChangeLog
>     trunk/gcc/testsuite/gcc.dg/vect/pr58508.c
>From gcc-bugs-return-434303-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Nov 11 19:31:50 2013
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Subject: [Bug tree-optimization/53947] [meta-bug] vectorizer missed-optimizations
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idS947

Bug 53947 depends on bug 58508, which changed state.

Bug 58508 Summary: [Missed-Optimization] Redundant vector load of "actual" loop invariant in loop body.
http://gcc.gnu.org/bugzilla/show_bug.cgi?idX508

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED