From cd3964ebd3e94ed0df4ecaadb7fd34e991cec753 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Tue, 19 Apr 2022 10:20:04 -0400 Subject: [PATCH] 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. --- 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 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 // . -// Activate __glibcxx_assert within this file to shake out any bugs. -#define _GLIBCXX_ASSERTIONS 1 - #include #include @@ -1114,6 +1111,7 @@ template } __glibcxx_assert(false); + __builtin_unreachable(); } template @@ -1202,6 +1200,8 @@ template 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 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 } __glibcxx_assert(false); + __builtin_unreachable(); } // Define the overloads for float. -- 2.7.4