[Bug tree-optimization/107972] backward propagation of finite property not performed

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107972

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The backwards propagation fixed, but neither:
double
foo (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a + b;
  if (!__builtin_isfinite (res))
    __builtin_unreachable ();
  return res;
}

double
bar (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a - b;
  if (!__builtin_isfinite (res))
    __builtin_unreachable ();
  return res;
}

double
baz (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a * b;
  if (!__builtin_isfinite (res))
    __builtin_unreachable ();
  return res;
}

double
qux (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  double res = a / b;
  if (!__builtin_isfinite (res))
    __builtin_unreachable ();
  return res;
}

double
quux (double a, double b)
{
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a / b;
  if (__builtin_isnan (res) || res == 0.0)
    __builtin_unreachable ();
  return res;
}
nor
double
foo (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a + b;
  __attribute__((assume (__builtin_isfinite (res))));
  return res;
}

double
bar (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a - b;
  __attribute__((assume (__builtin_isfinite (res))));
  return res;
}

double
baz (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a * b;
  __attribute__((assume (__builtin_isfinite (res))));
  return res;
}

double
qux (double a, double b)
{
  if (!__builtin_isfinite (a))
    return 42.0;
  double res = a / b;
  __attribute__((assume (__builtin_isfinite (res))));
  return res;
}

double
quux (double a, double b)
{
  if (!__builtin_isfinite (b))
    return 42.0;
  double res = a / b;
  __attribute__((assume (!__builtin_isnan (res) && res != 0.0)));
  return res;
}
avoids the 4.2e+1 cases in the output, because in neither case we properly
determine the ranges of res (that it is in foo/bar/baz/qux [-DBL_MAX,DBL_MAX]).
For quux I think we don't have a way to represent that right now, we'd need a
union of 2 ranges and after all, we also flush denormals to zero, so I think
we'd need if (!(res < 1.0)) __builtin_unreachable (); or __attribute__((assume
(res < 1.0))); so that we get [1.0, +INF] non-NAN range.
Aldy/Andrew, any ideas what's going on?