From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 208753858D33; Wed, 28 Dec 2022 16:31:56 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 208753858D33 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1672245116; bh=EUBOrhof5Zo4zoKrRxHaQRsXE5S3bTemXX8qsfLpsAY=; h=From:To:Subject:Date:From; b=pRd3K7RNuKLL5ozIKD1pfpiwRJARTNo0GRJnwQxUZm84oN5+K2U/yXpFE8IMctq0I mEtD6APdPWF0vgg2qjZFVtWGWsMdVuwjgyTIJSqUp+b1GF3dbZDtWI9Cfqi/XUSW4b vGD3iaklVQylRECWb02EAsCEnTyY+OKHDM1+lRgs= From: "erosenberger at kinetica dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/108243] New: Missed optimization for static const std::string_view(const char*) Date: Wed, 28 Dec 2022 16:31:55 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 11.3.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: erosenberger at kinetica dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 List-Id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108243 Bug ID: 108243 Summary: Missed optimization for static const std::string_view(const char*) Product: gcc Version: 11.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: erosenberger at kinetica dot com Target Milestone: --- Given the following code: #include int main() { static const std::string_view foo("bar"); return foo.size(); } With gcc 7.3.1, using "g++ -std=3Dc++17 -O2", it treats foo as constexpr, a= nd compiles main to: mov $0x3,%eax retq With gcc 11.3.0, also using "g++ -std=3Dc++17 -O2", it does not treat foo as constexpr, using runtime initialization instead (with static guard, etc.) However, by using the string_view constructor that accepts a length: static const std::string_view foo("bar", 3); gcc 11.3.0 is then able to treat foo as constexpr and compiles to just a mov and ret as 7.3.1 does. Using Compiler Explorer it appears that gcc 9 is the first version where it lost the optimization; every subsequent version seems to behave as 11.3.0. --- Additional info: gcc 11.3.0: Using built-in specs. COLLECT_GCC=3D/usr/bin/g++ COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu 11.3.0-1ubuntu1~22.04' --with-bugurl=3Dfile:///usr/share/doc/gcc-11/README.= Bugs --enable-languages=3Dc,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix= =3D/usr --with-gcc-major-version-only --program-suffix=3D-11 --program-prefix=3Dx86_64-linux-gnu- --enable-shared --enable-linker-build-= id --libexecdir=3D/usr/lib --without-included-gettext --enable-threads=3Dposix --libdir=3D/usr/lib --enable-nls --enable-bootstrap --enable-clocale=3Dgnu --enable-libstdcxx-debug --enable-libstdcxx-time=3Dyes --with-default-libstdcxx-abi=3Dnew --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-= zlib --enable-libphobos-checking=3Drelease --with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch --disable-werror --enable-cet --with-arch-32=3Di686 --with-abi=3Dm64 --with-multilib-list=3Dm32,m64,mx32 --enable-multilib --with-tune=3Dgeneric --enable-offload-targets=3Dnvptx-none=3D/build/gcc-11-xKiWfi/gcc-11-11.3.0/= debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-11-xKiWfi/gcc-11-11.3.0/deb= ian/tmp-gcn/usr --without-cuda-driver --enable-checking=3Drelease --build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu --with-build-config=3Dbootstrap-lto-lean --enable-link-serialization=3D2 Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04)=20 gcc 7.3.1: Using built-in specs. COLLECT_GCC=3Dg++ COLLECT_LTO_WRAPPER=3D/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redh= at-linux/7/lto-wrapper Target: x86_64-redhat-linux Configured with: ../configure --enable-bootstrap --enable-languages=3Dc,c++,fortran,lto --prefix=3D/opt/rh/devtoolset-7/root= /usr --mandir=3D/opt/rh/devtoolset-7/root/usr/share/man --infodir=3D/opt/rh/devtoolset-7/root/usr/share/info --with-bugurl=3Dhttp://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=3Dposix --enable-checking=3Drelease --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-plugin --with-linker-hash-style=3Dgnu --enable-initfini-array --with-default-libstdcxx-abi=3Dgcc4-compatible --with-isl=3D/builddir/build/BUILD/gcc-7.3.1-20180303/obj-x86_64-redhat-lin= ux/isl-install --enable-libmpx --enable-gnu-indirect-function --with-tune=3Dgeneric --with-arch_32=3Di686 --build=3Dx86_64-redhat-linux Thread model: posix gcc version 7.3.1 20180303 (Red Hat 7.3.1-5) (GCC)=