On Sun, Jan 30, 2022 at 7:39 PM Xi Ruoyao via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> 'inf/inf' should raise an invalid operation exception at runtime. So it
> should not be folded during compilation unless -fno-trapping-math is
> used.
I wonder if it would make sense to handle it similar to
inexact = real_arithmetic (&value, code, &d1, &d2);
real_convert (&result, mode, &value);
/* Don't constant fold this floating point operation if
the result has overflowed and flag_trapping_math. */
if (flag_trapping_math
&& MODE_HAS_INFINITIES (mode)
&& REAL_VALUE_ISINF (result)
&& !REAL_VALUE_ISINF (d1)
&& !REAL_VALUE_ISINF (d2))
return NULL_TREE;
thus whenever we fold to NaN but flag_trapping_math is set,
do not fold? We already exclude NaN operands earlier
(but unconditionally return NaN even for NaN + 1. though
that should raise invalid as well, no?)
I suppose Joseph should know best what the correct semantics
are here.
Thanks,
Richard.
> gcc/
> PR middle-end/95115
> * fold-const.cc (const_binop): Do not fold "inf/inf".
>
> gcc/testsuite
> * gcc.dg/pr95115.c: New test.
> ---
> gcc/fold-const.cc | 8 ++++++++
> gcc/testsuite/gcc.dg/pr95115.c | 25 +++++++++++++++++++++++++
> 2 files changed, 33 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/pr95115.c
>
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index fd9c6352d4f..0e99d5a2e3d 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -1283,6 +1283,14 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
> && (flag_trapping_math || ! MODE_HAS_INFINITIES (mode)))
> return NULL_TREE;
>
> + /* Don't perform "inf/inf", because it would raise an invalid
> + operation exception (IEEE 754 section 7.2 clause d). */
> + if (code == RDIV_EXPR
> + && flag_trapping_math
> + && REAL_VALUE_ISINF (d1)
> + && REAL_VALUE_ISINF (d2))
> + return NULL_TREE;
> +
> /* If either operand is a NaN, just return it. Otherwise, set up
> for floating-point trap; we return an overflow. */
> if (REAL_VALUE_ISNAN (d1))
> diff --git a/gcc/testsuite/gcc.dg/pr95115.c b/gcc/testsuite/gcc.dg/pr95115.c
> new file mode 100644
> index 00000000000..46a95dfb698
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr95115.c
> @@ -0,0 +1,25 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -ftrapping-math" } */
> +/* { dg-add-options ieee } */
> +/* { dg-require-effective-target fenv_exceptions } */
> +
> +#include <fenv.h>
> +#include <stdlib.h>
> +
> +double
> +x (void)
> +{
> + double d = __builtin_inf ();
> + return d / d;
> +}
> +
> +int
> +main (void)
> +{
> + double r = x ();
> + if (!__builtin_isnan (r))
> + abort ();
> + if (!fetestexcept (FE_INVALID))
> + abort ();
> + exit (0);
> +}
> --
> 2.35.1
>
>
