[Bug tree-optimization/107372] New: Loop distribution create memcpy between structs with different storage order

[Bug tree-optimization/107372] New: Loop distribution create memcpy between structs with different storage order

[krebbel at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107372

            Bug ID: 107372
           Summary: Loop distribution create memcpy between structs with
                    different storage order
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: krebbel at gcc dot gnu.org
  Target Milestone: ---

For t.c with "gcc -O3 t.c":

struct L
{
  unsigned int val[256];
} __attribute__((scalar_storage_order ("little-endian")));

struct B
{
  unsigned int val[256];
} __attribute__((scalar_storage_order ("big-endian")));

void
foo (struct L *restrict l, struct B *restrict b)
{
  int i;
  for (i = 0; i < 256; i++)
    l->val[i] = b->val[i];
}


The loop distribution pass currently generates a memcpy although it recognizes
correctly that both sides of the assignment have different storage order:

Analyzing # of iterations of loop 1
  exit condition [255, + , 4294967295] != 0
  bounds on difference of bases: -255 ... -255
  result:
    # of iterations 255, bounded by 255
Creating dr for *b_5(D).val[i_11]
analyze_innermost: t.c:16:23: missed: failed: reverse storage order.

...

void foo (struct L * restrict l, struct B * restrict b)
{
  int i;

  <bb 2> [local count: 10737416]:
  __builtin_memcpy (l_6(D), b_5(D), 1024);
  return;

}

[Bug tree-optimization/107372] Loop distribution create memcpy between structs with different storage order

[krebbel at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107372

--- Comment #1 from Andreas Krebbel <krebbel at gcc dot gnu.org> ---
Created attachment 53764
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53764&action=edit
Experimental Fix

Looks like the error while analyzing the data ref is not propagated to the
upper layers to actually prevent the optimization. This patch fixes this for
me.

[Bug tree-optimization/107372] Loop distribution creates memcpy between structs with different storage order

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107372

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andreas Krebbel from comment #1)
> Created attachment 53764 [details]
> Experimental Fix
> 
> Looks like the error while analyzing the data ref is not propagated to the
> upper layers to actually prevent the optimization. This patch fixes this for
> me.

But that's on purpose I think.  create_data_ref does never "fail", the caller
has to check for proper analysis of the DR though.  For loop distribution
we should FAIL looking at DR_STEP?  Ah, for example compute_access_range
performs its own analysis so it needs to check for the storage order itself
I think or the callers need to match up storage order of source and
destination.

Your patch leaks memory.

[Bug tree-optimization/107372] Loop distribution creates memcpy between structs with different storage order

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107372

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

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

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed correctly by r13-4244-g55cb8c5c9abfe8 .

[Bug tree-optimization/107372] Loop distribution creates memcpy between structs with different storage order

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107372

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.4