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From: "yadongh at vt dot edu" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/95141] New: Incorrect integer overflow warning message for bitand expression Date: Thu, 14 May 2020 19:51:10 +0000 [thread overview] Message-ID: <bug-95141-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141 Bug ID: 95141 Summary: Incorrect integer overflow warning message for bitand expression Product: gcc Version: 8.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: yadongh at vt dot edu Target Milestone: --- C code: #include <stdint.h> uint64_t test(uint8_t IA1) { return (uint8_t)(IA1 & 158) & 1UL; } Command: gcc -c test.c Warning message: test.c: In function ‘test’: test.c:5:31: warning: integer overflow in expression ‘(long unsigned int)IA1 & 158 & 1’ of type ‘long unsigned int’ results in ‘0’ [-Woverflow] return (uint8_t)(IA1 & 158) & 1UL; ~~~~~~~~~~~~~~~~~~~~~^~~~~ gcc -v output: Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc- major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enab le-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-pl ugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-mult ilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 8.3.0 (Debian 8.3.0-6) Note that I find this reproducible starting from GCC 7.1 to 10.1 (on GodBolt). Platform: Debian 10 Linux Problem statement: There are a lot of explicit/implicit integer type casts here, but in no way I think integer overflow can happen. Note that essentially we are returning zero here as 158 & 1 is just zero. Some other interesting observations: (uint8_t)(IA1 & 159) & 1UL; --- No Warning (uint8_t)(IA1 & 158U) & 1UL; --- No Warning (uint8_t)(IA1 & 254) & 1UL; --- Warning (uint8_t)(IA1 & 2) & 1UL; --- No Warning
next reply other threads:[~2020-05-14 19:51 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-14 19:51 yadongh at vt dot edu [this message] 2020-05-15 7:30 ` [Bug c/95141] [8/9/10/11 Regression] " jakub at gcc dot gnu.org 2020-05-15 9:02 ` rguenth at gcc dot gnu.org 2020-05-18 13:28 ` rguenth at gcc dot gnu.org 2020-05-20 7:40 ` cvs-commit at gcc dot gnu.org 2020-05-20 7:42 ` [Bug c/95141] [8/9/10 " rguenth at gcc dot gnu.org 2020-06-23 11:06 ` cvs-commit at gcc dot gnu.org 2020-06-23 11:08 ` [Bug c/95141] [8/9 " rguenth at gcc dot gnu.org 2021-05-14 9:53 ` [Bug c/95141] [9 " jakub at gcc dot gnu.org 2021-06-01 8:17 ` rguenth at gcc dot gnu.org 2022-05-27 8:52 ` rguenth at gcc dot gnu.org
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