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author | Patrick Palka <ppalka@redhat.com> | 2022-04-19 10:20:04 -0400 |
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committer | Patrick Palka <ppalka@redhat.com> | 2022-04-19 10:20:04 -0400 |
commit | cd3964ebd3e94ed0df4ecaadb7fd34e991cec753 (patch) | |
tree | 00c3cf8f67d2df5ea7a7d20968921cc85cbf5d4e | |
parent | fdb3f82fb324c3ddd7464d11c8ea60a98f486a0e (diff) | |
download | gcc-cd3964ebd3e94ed0df4ecaadb7fd34e991cec753.zip gcc-cd3964ebd3e94ed0df4ecaadb7fd34e991cec753.tar.gz gcc-cd3964ebd3e94ed0df4ecaadb7fd34e991cec753.tar.bz2 |
libstdc++: Stop defining _GLIBCXX_ASSERTIONS in floating_to_chars.cc
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, most notably for
the hex formatting which is around 25% slower with assertions enabled.
This seems too high 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).
libstdc++-v3/ChangeLog:
* src/c++17/floating_to_chars.cc (_GLIBCXX_ASSERTIONS): Don't
define.
(__floating_to_chars_shortest): Add __builtin_unreachable calls to
squelch false-positive -Wmaybe-uninitialized and -Wreturn-type
warnings.
(__floating_to_chars_precision): Likewise.
-rw-r--r-- | libstdc++-v3/src/c++17/floating_to_chars.cc | 9 |
1 files 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 66bd457..4599d68 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. |