From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 733683858D39; Fri, 31 Dec 2021 16:46:46 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 733683858D39 From: "thomas at habets dot se" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/103881] New: Wconversion false positive when using |= and &= with two rvalues in binary op Date: Fri, 31 Dec 2021 16:46:46 +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: 11.2.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: thomas at habets dot se 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 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: Fri, 31 Dec 2021 16:46:46 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103881 Bug ID: 103881 Summary: Wconversion false positive when using |=3D and &=3D with two rvalues in binary op Product: gcc Version: 11.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: thomas at habets dot se Target Milestone: --- Got: Warnings of conversion from int when doing "x |=3D f() | f()", with all typ= es set to uint8_t. No warning when using "=3D" instead of "|=3D". Per https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D40752, this makes me won= der if "|=3D" creates as implicit cast to int (but why?). But if that's the case then why does "x |=3D f()" and "x |=3D a & a" not wa= rn? And if "|=3D" implicitly casts to int, that should mean there's no way at a= ll to not trigger this warning for |=3D into an uint8_t? Or does binary "&" implicitly cast to int (again, why?), then why does "x |= =3D a & a" and "x =3D f() & f()" not warn? Reproduce program: #include uint8_t f(); void foo() { uint8_t t =3D 0; t |=3D f(); // one rvalue: no warning t |=3D f() & f(); // two rvalues: warn t &=3D f() & f(); // same with &=3D t =3D f() & f(); // no warning with assign uint8_t a =3D f(); // no warning t |=3D a & a; // no warning with variables. t |=3D f() & a; // warning with one rvalue t |=3D a & f(); // no matter position. } Output $ gcc -v -save-temps -Wconversion -c bug2.c Using built-in specs. COLLECT_GCC=3Dgcc OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Debian 11.2.0-10' --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-R0liEm/gcc-11-11.2.0/= debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-11-R0liEm/gcc-11-11.2.0/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=3D8 Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 11.2.0 (Debian 11.2.0-10)=20 COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-Wconversion' '-c' '-mtune=3Dgene= ric' '-march=3Dx86-64' /usr/lib/gcc/x86_64-linux-gnu/11/cc1 -E -quiet -v -imultiarch x86_64-linux= -gnu bug2.c -mtune=3Dgeneric -march=3Dx86-64 -Wconversion -fpch-preprocess -fasynchronous-unwind-tables -o bug2.i ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/11/include-fi= xed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/11/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-linux-gnu/11/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-Wconversion' '-c' '-mtune=3Dgene= ric' '-march=3Dx86-64' /usr/lib/gcc/x86_64-linux-gnu/11/cc1 -fpreprocessed bug2.i -quiet -dumpbase bug2.c -dumpbase-ext .c -mtune=3Dgeneric -march=3Dx86-64 -Wconversion -vers= ion -fasynchronous-unwind-tables -o bug2.s GNU C17 (Debian 11.2.0-10) version 11.2.0 (x86_64-linux-gnu) compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 GNU C17 (Debian 11.2.0-10) version 11.2.0 (x86_64-linux-gnu) compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP GGC heuristics: --param ggc-min-expand=3D100 --param ggc-min-heapsize=3D131= 072 Compiler executable checksum: 010de8893e7b0de1cd6903c6a1890e7a bug2.c: In function =E2=80=98foo=E2=80=99: bug2.c:7:8: warning: conversion from =E2=80=98int=E2=80=99 to =E2=80=98uint= 8_t=E2=80=99 {aka =E2=80=98unsigned char=E2=80=99} may change value [-Wconversion] 7 | t |=3D f() & f(); // two rvalues: warn | ^ bug2.c:8:8: warning: conversion from =E2=80=98int=E2=80=99 to =E2=80=98uint= 8_t=E2=80=99 {aka =E2=80=98unsigned char=E2=80=99} may change value [-Wconversion] 8 | t &=3D f() & f(); // same with &=3D | ^ bug2.c:13:8: warning: conversion from =E2=80=98int=E2=80=99 to =E2=80=98uin= t8_t=E2=80=99 {aka =E2=80=98unsigned char=E2=80=99} may change value [-Wconversion] 13 | t |=3D f() & a; // warning with one rvalue | ^ bug2.c:14:8: warning: conversion from =E2=80=98int=E2=80=99 to =E2=80=98uin= t8_t=E2=80=99 {aka =E2=80=98unsigned char=E2=80=99} may change value [-Wconversion] 14 | t |=3D a & f(); // no matter position. | ^ COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-Wconversion' '-c' '-mtune=3Dgene= ric' '-march=3Dx86-64' as -v --64 -o bug2.o bug2.s GNU assembler version 2.37 (x86_64-linux-gnu) using BFD version (GNU Binuti= ls for Debian) 2.37 COMPILER_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/11/:/usr/lib/gcc/x86_64-linux= -gnu/11/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/11/:/= usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=3D/usr/lib/gcc/x86_64-linux-gnu/11/:/usr/lib/gcc/x86_64-linux-= gnu/11/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/11/../../..= /../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/11/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS=3D'-v' '-save-temps' '-Wconversion' '-c' '-mtune=3Dgene= ric' '-march=3Dx86-64'=