[Bug middle-end/100672] wrong code with vector shift and unary minus

[zsojka at seznam dot cz via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100672

--- Comment #7 from Zdenek Sojka <zsojka at seznam dot cz> ---
(In reply to Richard Biener from comment #2)
> Maybe sth is wrong with the testcase?  clang also results in an abort.  Isn't
> right-shift of negative values undefined?
> 

Thank you for having a look.

I believe the behavior is fully defined. The vectors are unsigned, and the
conversion to unsigned is done by adding 2**64; this behaves the same:

$ cat testcase.c
typedef unsigned long long __attribute__((__vector_size__ (32))) V;

V
foo (V v)
{
  return -(v >> 1);
}

int
main (void)
{
  V v = foo ((V) { 0xfffffffffffffffe, 0xfffffffffffffffc,
                   0xfffffffffffffffa, 0xfffffffffffffff8 });
  if (v[0] != 1 || v[1] != 2 || v[2] != 3 || v[3] != 4)
    __builtin_abort ();
  return 0;
}

Maybe clang behaves the same since the behavior was the same in the moment when
clang was forked.