[Bug tree-optimization/97053] [10/11 Regression] an O2, O3 codegen bug

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97053

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Better testcase that won't cease to test the bug even if FRE or some other pass
gets smarter and optimizes the a = "XXXXXXXX"; __builtin_memcpy (&a, "ABCD",
4);
into a = "ABCDXXXX":

struct S { short a; char b[9]; int c; char d; int e; };

__attribute__((noipa)) void
foo (struct S *x)
{
  if (__builtin_strcmp (x->b, "ABCDXXXX") != 0)
    __builtin_abort ();
}

__attribute__((noipa)) void
bar (char *x)
{
  struct S b = {};
  b.a = 5;
  __builtin_memcpy (b.b, x, 8); 
  b.d = 'X';
  b.e = 1;
  foo (&b);
}

int
main ()
{
  bar ("ABCDXXXX");
  return 0;
}

(In reply to Eric Botcazou from comment #2)
> The statement generated by DSE
> 
> MEM <char[12]> [(struct Data *)&data + 8B] = {};
> 
> looks nonsensical and I guess store-merging is not prepared for it.

There is nothing non-sensical nor wrong on it, it is standard GIMPLE IL,
equivalent in behavior to __builtin_memset (&data + 8B, 0, 12);