fold-const: do not fold NaN result from non-NaN operands (was: Re: [PATCH] fold-const: do not fold 'inf/inf' with -ftrapping-math [PR95115])
Commit Message
Bootstrapped and tested on x86_64-linux-gnu. Ok for trunk, gcc-11, and
gcc-10? (I'd consider PR 95115 a 10/11/12 regression because GCC
10/11/12 miscompiles glibc acos/asin function, but not GCC 9.)
These operations should raise an invalid operation exception at runtime.
So they should not be folded during compilation unless -fno-trapping-math
is used.
gcc/
PR middle-end/95115
* fold-const.cc (const_binop): Do not fold NaN result from
non-NaN operands.
gcc/testsuite
* gcc.dg/pr95115.c: New test.
---
gcc/fold-const.cc | 11 +++++++++++
gcc/testsuite/gcc.dg/pr95115.c | 25 +++++++++++++++++++++++++
2 files changed, 36 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr95115.c
Comments
On Tue, Feb 1, 2022 at 6:10 AM Xi Ruoyao <xry111@mengyan1223.wang> wrote:
>
> Bootstrapped and tested on x86_64-linux-gnu. Ok for trunk, gcc-11, and
> gcc-10? (I'd consider PR 95115 a 10/11/12 regression because GCC
> 10/11/12 miscompiles glibc acos/asin function, but not GCC 9.)
>
> These operations should raise an invalid operation exception at runtime.
> So they should not be folded during compilation unless -fno-trapping-math
> is used.
OK for trunk and branches after a while.
Thanks,
Richard.
> gcc/
> PR middle-end/95115
> * fold-const.cc (const_binop): Do not fold NaN result from
> non-NaN operands.
>
> gcc/testsuite
> * gcc.dg/pr95115.c: New test.
> ---
> gcc/fold-const.cc | 11 +++++++++++
> gcc/testsuite/gcc.dg/pr95115.c | 25 +++++++++++++++++++++++++
> 2 files changed, 36 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/pr95115.c
>
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index b155611578d..8fc01cdfb77 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -1305,6 +1305,17 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
> inexact = real_arithmetic (&value, code, &d1, &d2);
> real_convert (&result, mode, &value);
>
> + /* Don't constant fold this floating point operation if
> + both operands are not NaN but the result is NaN, and
> + flag_trapping_math. Such operations should raise an
> + invalid operation exception. */
> + if (flag_trapping_math
> + && MODE_HAS_NANS (mode)
> + && REAL_VALUE_ISNAN (result)
> + && !REAL_VALUE_ISNAN (d1)
> + && !REAL_VALUE_ISNAN (d2))
> + return NULL_TREE;
> +
> /* Don't constant fold this floating point operation if
> the result has overflowed and flag_trapping_math. */
> if (flag_trapping_math
> 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
>
>
@@ -1305,6 +1305,17 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
inexact = real_arithmetic (&value, code, &d1, &d2);
real_convert (&result, mode, &value);
+ /* Don't constant fold this floating point operation if
+ both operands are not NaN but the result is NaN, and
+ flag_trapping_math. Such operations should raise an
+ invalid operation exception. */
+ if (flag_trapping_math
+ && MODE_HAS_NANS (mode)
+ && REAL_VALUE_ISNAN (result)
+ && !REAL_VALUE_ISNAN (d1)
+ && !REAL_VALUE_ISNAN (d2))
+ return NULL_TREE;
+
/* Don't constant fold this floating point operation if
the result has overflowed and flag_trapping_math. */
if (flag_trapping_math
new file mode 100644
@@ -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);
+}