| Message ID | 582B3331.30402@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
Hi, > There seems to be a separate api for checking trapping support: > ieee_support_halting, but it only checked if the exception status > flags are available, so check trapping support too by enabling > and disabling traps. Thanks for the patch. I am worried about the unnecessary operations that we’re doing here: doesn’t glibc have a way to tell you what it supports without having to do it (twice, enabling then disabling)? Also, the glibc doc states that: "Each of the macros FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW is defined when the implementation supports handling of the corresponding exception”. It evens says: > Each constant is defined if and only if the FPU you are compiling for supports that exception, so you can test for FPU support with ‘#ifdef’. So it seems rather clear that compile-time tests are the recommended way to go. FX
On 15/11/16 16:22, FX wrote: >> There seems to be a separate api for checking trapping support: >> ieee_support_halting, but it only checked if the exception status >> flags are available, so check trapping support too by enabling >> and disabling traps. > > Thanks for the patch. > > I am worried about the unnecessary operations that we’re doing here: doesn’t glibc have a way to tell you what it supports without having to do it (twice, enabling then disabling)? > > Also, the glibc doc states that: "Each of the macros FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW is defined when the implementation supports handling of the corresponding exception”. It evens says: > >> Each constant is defined if and only if the FPU you are compiling for supports that exception, so you can test for FPU support with ‘#ifdef’. > > So it seems rather clear that compile-time tests are the recommended way to go. i think that's a documentation bug then, it should say that the macros imply the support of fpu exception status flags, but not trapping. (otherwise glibc could not provide iso c annex f conforming fenv on aarch64 and arm, where FE_* must be defined, but only status flag support is required.) disabling/enabling makes this api a lot heavier than before, but trapping cannot be decided at compile-time, although the result may be cached, i think this should not be a frequent operation. otoh rereading my patch i think i fail to restore the original exception state correctly.
> disabling/enabling makes this api a lot heavier > than before, but trapping cannot be decided at > compile-time, although the result may be cached, > i think this should not be a frequent operation. > > otoh rereading my patch i think i fail to restore > the original exception state correctly. Well, if we have no choice, then let’s do it. (With an updated patch) FX
diff --git a/gcc/testsuite/gfortran.dg/ieee/ieee_6.f90 b/gcc/testsuite/gfortran.dg/ieee/ieee_6.f90 index 8fb4f6f..43aa3bf 100644 --- a/gcc/testsuite/gfortran.dg/ieee/ieee_6.f90 +++ b/gcc/testsuite/gfortran.dg/ieee/ieee_6.f90 @@ -9,7 +9,7 @@ implicit none type(ieee_status_type) :: s1, s2 - logical :: flags(5), halt(5) + logical :: flags(5), halt(5), haltworks type(ieee_round_type) :: mode real :: x @@ -18,6 +18,7 @@ call ieee_set_flag(ieee_all, .false.) call ieee_set_rounding_mode(ieee_down) call ieee_set_halting_mode(ieee_all, .false.) + haltworks = ieee_support_halting(ieee_overflow) call ieee_get_status(s1) call ieee_set_status(s1) @@ -46,7 +47,7 @@ call ieee_get_rounding_mode(mode) if (mode /= ieee_to_zero) call abort call ieee_get_halting_mode(ieee_all, halt) - if ((.not. halt(1)) .or. any(halt(2:))) call abort + if ((haltworks .and. .not. halt(1)) .or. any(halt(2:))) call abort call ieee_set_status(s2) @@ -58,7 +59,7 @@ call ieee_get_rounding_mode(mode) if (mode /= ieee_to_zero) call abort call ieee_get_halting_mode(ieee_all, halt) - if ((.not. halt(1)) .or. any(halt(2:))) call abort + if ((haltworks .and. .not. halt(1)) .or. any(halt(2:))) call abort call ieee_set_status(s1) @@ -79,6 +80,6 @@ call ieee_get_rounding_mode(mode) if (mode /= ieee_to_zero) call abort call ieee_get_halting_mode(ieee_all, halt) - if ((.not. halt(1)) .or. any(halt(2:))) call abort + if ((haltworks .and. .not. halt(1)) .or. any(halt(2:))) call abort end diff --git a/libgfortran/config/fpu-glibc.h b/libgfortran/config/fpu-glibc.h index 6e505da..e254fb1 100644 --- a/libgfortran/config/fpu-glibc.h +++ b/libgfortran/config/fpu-glibc.h @@ -121,7 +121,43 @@ get_fpu_trap_exceptions (void) int support_fpu_trap (int flag) { - return support_fpu_flag (flag); + int exceptions = 0; + int old, ret; + + if (!support_fpu_flag (flag)) + return 0; + +#ifdef FE_INVALID + if (flag & GFC_FPE_INVALID) exceptions |= FE_INVALID; +#endif + +#ifdef FE_DIVBYZERO + if (flag & GFC_FPE_ZERO) exceptions |= FE_DIVBYZERO; +#endif + +#ifdef FE_OVERFLOW + if (flag & GFC_FPE_OVERFLOW) exceptions |= FE_OVERFLOW; +#endif + +#ifdef FE_UNDERFLOW + if (flag & GFC_FPE_UNDERFLOW) exceptions |= FE_UNDERFLOW; +#endif + +#ifdef FE_DENORMAL + if (flag & GFC_FPE_DENORMAL) exceptions |= FE_DENORMAL; +#endif + +#ifdef FE_INEXACT + if (flag & GFC_FPE_INEXACT) exceptions |= FE_INEXACT; +#endif + + old = fedisableexcept (exceptions); + if (old == -1) + return 0; + + ret = feenableexcept (exceptions) != -1; + feenableexcept (old); + return ret; }