public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "claytongdavis at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/49510] New: bitshift warnings Date: Thu, 23 Jun 2011 00:39:00 -0000 [thread overview] Message-ID: <bug-49510-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49510 Summary: bitshift warnings Product: gcc Version: 4.5.2 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: c++ AssignedTo: unassigned@gcc.gnu.org ReportedBy: claytongdavis@gmail.com This is a request to improve the warnings for bitshifts where the right operand is negative or >= the size of the left operand. I am aware that this is undefined behavior, but a warning would be nice in a case like the one included below. GCC implements a cyclic bitshift instead. $ more gcc_bitshift.C #include <iostream> int main() { int shift = 32; std::cout<<"0xFFFFFFFF>>32 = "<<(0xFFFFFFFF>>shift)<<std::endl; std::cout<<"1<<32 = "<<(1<<shift)<<std::endl; shift = -1; std::cout<<"0xFFFFFFFF>>(-1) = "<<(0xFFFFFFFF>>shift)<<std::endl; std::cout<<"1<<(-1) = "<<(1<<shift)<<std::endl; } $ g++ -Wall -Wextra gcc_bitshift.C $ ./a.out 0xFFFFFFFF>>32 = 4294967295 1<<32 = 1 0xFFFFFFFF>>(-1) = 1 1<<(-1) = -2147483648 $ g++ -v Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.5.2-8ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.5 --enable-shared --enable-multiarch --with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib/x86_64-linux-gnu --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib/x86_64-linux-gnu --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin --enable-gold --enable-ld=default --with-plugin-ld=ld.gold --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4)
next reply other threads:[~2011-06-23 0:39 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-06-23 0:39 claytongdavis at gmail dot com [this message] 2011-06-23 11:43 ` [Bug c++/49510] " rguenth at gcc dot gnu.org 2021-09-28 9:23 ` pinskia at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-49510-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).