| Message ID | 20220414194716.334032-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | libstdc++: Stop defining _GLIBCXX_ASSERTIONS in floating_to_chars.cc | expand |
On Thu, 14 Apr 2022 at 20:48, Patrick Palka via Libstdc++ <libstdc++@gcc.gnu.org> wrote: > > Assertions were originally enabled in the compiled-in floating-point > std::to_chars implementation to help shake out any bugs, but they > apparently impose a significant performance penalty, in particular for > the hex formatting which is around 25% slower with assertions enabled. > This seems too high of a cost for unconditionally enabling them. > > The newly added calls to __builtin_unreachable work around the compiler > no longer knowing that the set of valid values of 'fmt' is limited (which > was previously upheld by an assert). > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? OK, thanks. > > libstdc++-v3/ChangeLog: > > * src/c++17/floating_to_chars.cc: Don't define > _GLIBCXX_ASSERTIONS. > (__floating_to_chars_shortest): Add __builtin_unreachable calls to > squelch false-positive -Wmaybe-uninitialized and -Wreturn-type > warnings. > (__floating_to_chars_precision): Likewise. > --- > libstdc++-v3/src/c++17/floating_to_chars.cc | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc > index 66bd457cbe2..4599d68a39c 100644 > --- a/libstdc++-v3/src/c++17/floating_to_chars.cc > +++ b/libstdc++-v3/src/c++17/floating_to_chars.cc > @@ -22,9 +22,6 @@ > // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see > // <http://www.gnu.org/licenses/>. > > -// Activate __glibcxx_assert within this file to shake out any bugs. > -#define _GLIBCXX_ASSERTIONS 1 > - > #include <charconv> > > #include <bit> > @@ -1114,6 +1111,7 @@ template<typename T> > } > > __glibcxx_assert(false); > + __builtin_unreachable(); > } > > template<typename T> > @@ -1202,6 +1200,8 @@ template<typename T> > effective_precision = min(precision, max_eff_scientific_precision); > output_specifier = "%.*Lg"; > } > + else > + __builtin_unreachable(); > const int excess_precision = (fmt != chars_format::general > ? precision - effective_precision : 0); > > @@ -1234,6 +1234,8 @@ template<typename T> > output_length_upper_bound = sign + strlen("0"); > output_length_upper_bound += sizeof(radix) + effective_precision; > } > + else > + __builtin_unreachable(); > > // Do the sprintf into the local buffer. > char buffer[output_length_upper_bound+1]; > @@ -1570,6 +1572,7 @@ template<typename T> > } > > __glibcxx_assert(false); > + __builtin_unreachable(); > } > > // Define the overloads for float. > -- > 2.36.0.rc2.10.g1ac7422e39 >
diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc index 66bd457cbe2..4599d68a39c 100644 --- a/libstdc++-v3/src/c++17/floating_to_chars.cc +++ b/libstdc++-v3/src/c++17/floating_to_chars.cc @@ -22,9 +22,6 @@ // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // <http://www.gnu.org/licenses/>. -// Activate __glibcxx_assert within this file to shake out any bugs. -#define _GLIBCXX_ASSERTIONS 1 - #include <charconv> #include <bit> @@ -1114,6 +1111,7 @@ template<typename T> } __glibcxx_assert(false); + __builtin_unreachable(); } template<typename T> @@ -1202,6 +1200,8 @@ template<typename T> effective_precision = min(precision, max_eff_scientific_precision); output_specifier = "%.*Lg"; } + else + __builtin_unreachable(); const int excess_precision = (fmt != chars_format::general ? precision - effective_precision : 0); @@ -1234,6 +1234,8 @@ template<typename T> output_length_upper_bound = sign + strlen("0"); output_length_upper_bound += sizeof(radix) + effective_precision; } + else + __builtin_unreachable(); // Do the sprintf into the local buffer. char buffer[output_length_upper_bound+1]; @@ -1570,6 +1572,7 @@ template<typename T> } __glibcxx_assert(false); + __builtin_unreachable(); } // Define the overloads for float.