From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 0D539386195B; Tue, 14 Jul 2020 14:41:25 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 0D539386195B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1594737685; bh=E2Cw8rfZoS/Yup/KUvGQE+Y13201qHp7hcnr2noOryM=; h=From:To:Subject:Date:From; b=dkyrCahi0JFMXoMR3TkoVtap0btoEAvOS8+cMRgS3GF6OoGheyRKKm4UwzRjVTX4B Q+IugRdw3JW0paaOqzMaRbxx8XHfLfuV5LNItQYqdftaVf+d/eC2MvMgtuofLnnEvN TGPrNB9tWNVN1pllwI17MEL1RbR2HVIrrCB2fvqE= From: "ingo at hannover dot ccc.de" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/96196] New: infinite loop removed by optimizer Date: Tue, 14 Jul 2020 14:41:24 +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: 10.1.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: ingo at hannover dot ccc.de 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 attachments.created 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 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 14 Jul 2020 14:41:25 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96196 Bug ID: 96196 Summary: infinite loop removed by optimizer Product: gcc Version: 10.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: ingo at hannover dot ccc.de Target Milestone: --- Created attachment 48875 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D48875&action=3Dedit Preprocessed file If compiled with any of -Ofast -Os -O3 or -O2, g++ will optimize the while = loop away and exit immediately, when it should run forever. #include #include int main() { const std::vector a{1}; std::vector b; std::cout << "before loop: " << b.size() << " < " << a.size() << "\= n"; while(b.size() < a.size()) { // uncommenting this fixes the loop with -O2 //std::cout << "."; } std::cout << "after loop: " << b.size() << " < " << a.size() << "\n= "; } This bug occurs at least with g++ from the following debian packages: * g++-10 (version 1:10.1.0-4) * g++-10 (version 1:10.1.0-5) * gcc-snapshot (version 1:20200616-1) gcc version 9 seems fine, also clang-9 and clang-10. Output from g++-10 version 1:10.1.0-5: $ g++-10 -v -save-temps -O2 infloop.cc -o infloop Using built-in specs. COLLECT_GCC=3Dg++-10 COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa:hsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Debian 10.1.0-5' --with-bugurl=3Dfile:///usr/share/doc/gcc-10/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-10 --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-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=3Drelea= se --with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch --disable-werror --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-10-pmMab1/gcc-10-10.1.0/= debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-10-pmMab1/gcc-10-10.1.0/deb= ian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=3Drelease --build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.1.1 20200713 (Debian 10.1.0-5)=20 COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-O2' '-o' 'infloop' '-shared-libg= cc' '-mtune=3Dgeneric' '-march=3Dx86-64' /usr/lib/gcc/x86_64-linux-gnu/10/cc1plus -E -quiet -v -imultiarch x86_64-linux-gnu -D_GNU_SOURCE infloop.cc -mtune=3Dgeneric -march=3Dx86-64 = -O2 -fpch-preprocess -fasynchronous-unwind-tables -o infloop.ii ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/10" ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/include-fi= xed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/include/c++/10 /usr/include/x86_64-linux-gnu/c++/10 /usr/include/c++/10/backward /usr/lib/gcc/x86_64-linux-gnu/10/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-O2' '-o' 'infloop' '-shared-libg= cc' '-mtune=3Dgeneric' '-march=3Dx86-64' /usr/lib/gcc/x86_64-linux-gnu/10/cc1plus -fpreprocessed infloop.ii -quiet -dumpbase infloop.cc -mtune=3Dgeneric -march=3Dx86-64 -auxbase infloop -O2 = -version -fasynchronous-unwind-tables -o infloop.s GNU C++14 (Debian 10.1.0-5) version 10.1.1 20200713 (x86_64-linux-gnu) compiled by GNU C version 10.1.1 20200713, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP warning: MPFR header version 4.0.2 differs from library version 4.1.0. GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 GNU C++14 (Debian 10.1.0-5) version 10.1.1 20200713 (x86_64-linux-gnu) compiled by GNU C version 10.1.1 20200713, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP warning: MPFR header version 4.0.2 differs from library version 4.1.0. GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 Compiler executable checksum: 6cd36725701c85e62ce50f8955bd2a9a COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-O2' '-o' 'infloop' '-shared-libg= cc' '-mtune=3Dgeneric' '-march=3Dx86-64' as -v --64 -o infloop.o infloop.s GNU assembler version 2.34.90 (x86_64-linux-gnu) using BFD version (GNU Binutils for Debian) 2.34.90.20200706 COMPILER_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux= -gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/= usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-= gnu/10/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/../../..= /../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/us= r/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-O2' '-o' 'infloop' '-shared-libg= cc' '-mtune=3Dgeneric' '-march=3Dx86-64' /usr/lib/gcc/x86_64-linux-gnu/10/collect2 -plugin /usr/lib/gcc/x86_64-linux-gnu/10/liblto_plugin.so -plugin-opt=3D/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper -plugin-opt=3D-fresolution=3Dinfloop.res -plugin-opt=3D-pass-through=3D-lgc= c_s -plugin-opt=3D-pass-through=3D-lgcc -plugin-opt=3D-pass-through=3D-lc -plugin-opt=3D-pass-through=3D-lgcc_s -plugin-opt=3D-pass-through=3D-lgcc -= -build-id --eh-frame-hdr -m elf_x86_64 --hash-style=3Dgnu --as-needed -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -o infloop /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/Scrt1.o /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/10/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gn= u/10 -L/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib -L/lib/x86_64-linux-gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/10/../../.. infloop.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/10/crtendS.o /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crtn.o COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-O2' '-o' 'infloop' '-shared-libg= cc' '-mtune=3Dgeneric' '-march=3Dx86-64'=