[Bug tree-optimization/107972] backward propagation of finite property not performed
jakub at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Dec 6 09:57:45 GMT 2022
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?
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