[Bug middle-end/70593] New: [6 Regression] Miscompilation of xen starting with r226901

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70593

            Bug ID: 70593
           Summary: [6 Regression] Miscompilation of xen starting with
                    r226901
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

__attribute__((noinline, noclone)) unsigned long
foo (unsigned long x, unsigned long y, unsigned z)
{
  unsigned long a, b, c, d = z;
  asm volatile ("xorl\t%k1, %k1\n\txorl\t%k2, %k2\n\txorl\t%k3,
%k3\n\tmovl\t$7, %k0"
                : "=&c" (d), "=&D" (a), "=&S" (b), "=&r" (c) : "0" (d), "1"
(x), "2" (y), "3" (d) : "memory");
  return d;
}

int
main ()
{
  if (foo (1, 2, 3) != 7)
    __builtin_abort ();
  return 0;
}

is miscompiled on x86_64-linux at -O2 starting with r226901, -O2
-fno-tree-coalesce-vars works.  The return value d is in %rcx at the end of the
inline asm, but with -O2 the copy of %rcx to %rax is lost.