GCC 4.8.5 fails the test case submitted in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78084.  A slightly reduced test case is below.  The unused hv variable, the unaligned test, and the vec_vsx_ld call in the call to f are all necessary in order to cause the micompilation.

Code generated by GCC 7 runs successfully to completion.

$ cat t.c && gcc -O1 -Wall -mvsx t.c && ./a.out 
#include <altivec.h>

#define vec_u8_t vector unsigned char

void __attribute__ ((noclone, noinline))
f (vec_u8_t v) { }

static void __attribute__ ((noclone, noinline))
testcase (const unsigned char *dest)
{
  vec_u8_t hv = vec_ld (0, dest);
  (void)&hv;

  vec_u8_t compare = vec_vsx_ld (0, dest);

  if ((unsigned long)dest & 15)
    __builtin_printf ("unaligned address %p\n", dest);

  f (vec_vsx_ld (0, dest));

  if (!vec_all_eq (compare, vec_vsx_ld (0, dest)))
    __builtin_abort ();
}

const unsigned char __attribute__((aligned(16))) buf[] = {
   0,  1,  2,  3,  4,  5,  6,  7,
  10, 11, 12, 13, 14, 15, 16, 17,
  20, 21, 22, 23, 24, 25, 26, 27,
  30, 31, 32, 33, 34, 35, 36, 37,
  40, 41, 42, 43, 44, 45, 46, 47
};

int main (void)
{
  testcase (buf);
  testcase (buf + 8);

  return 0;
}
unaligned address 0x10000928
Aborted