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

["krebbel at gcc dot gnu.org" <gcc-bugzilla@gcc.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;

}