Given the attached test case, I get warnings from -Wconversion. I cannot find a way to quieten those warnings. I believe the bit-and operations should quieten the warnings.
Here is the command line I used: gcc -v -save-temps -O2 -std=gnu99 -W -Wall -Wconversion -pedantic -c test.c Here is the output: ==== Using built-in specs. Target: x86_64-redhat-linux Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-cpu=generic --build=x86_64-redhat-linux Thread model: posix gcc version 4.3.0 20080229 (Red Hat 4.3.0-0.13) (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-std=gnu99' '-W' '-Wall' '-Wconversion' '-pedantic' '-c' '-mtune=generic' /usr/libexec/gcc/x86_64-redhat-linux/4.3.0/cc1 -E -quiet -v test.c -mtune=generic -std=gnu99 -W -Wall -Wconversion -pedantic -O2 -fpch-preprocess -o test.i ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.3.0/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../../x86_64-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/gcc/x86_64-redhat-linux/4.3.0/include /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-std=gnu99' '-W' '-Wall' '-Wconversion' '-pedantic' '-c' '-mtune=generic' /usr/libexec/gcc/x86_64-redhat-linux/4.3.0/cc1 -fpreprocessed test.i -quiet -dumpbase test.c -mtune=generic -auxbase test -O2 -W -Wall -Wconversion -pedantic -std=gnu99 -version -o test.s GNU C (GCC) version 4.3.0 20080229 (Red Hat 4.3.0-0.13) (x86_64-redhat-linux) compiled by GNU C version 4.3.0 20080229 (Red Hat 4.3.0-0.13), GMP version 4.2.2, MPFR version 2.3.0-p2. GGC heuristics: --param ggc-min-expand=63 --param ggc-min-heapsize=61903 Compiler executable checksum: fdfb1d6ccb856fd413903980b80f9fc0 test.c: In function âmy_func1â: test.c:9: warning: conversion to âunsigned char:1â from âunsigned intâ may alter its value test.c:10: warning: conversion to âunsigned int:31â from âunsigned intâ may alter its value test.c: In function âmy_func2â: test.c:16: warning: conversion to âunsigned char:1â from âunsigned intâ may alter its value test.c:17: warning: conversion to âunsigned int:31â from âunsigned intâ may alter its value test.c: In function âmy_func3â: test.c:24: warning: conversion to âshort unsigned intâ from âunsigned intâ may alter its value COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-std=gnu99' '-W' '-Wall' '-Wconversion' '-pedantic' '-c' '-mtune=generic' as -V -Qy -o test.o test.s GNU assembler version 2.18.50.0.3 (x86_64-redhat-linux) using BFD version version 2.18.50.0.3-2 20071102 COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/4.3.0/:/usr/libexec/gcc/x86_64-redhat-linux/4.3.0/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/4.3.0/:/usr/lib/gcc/x86_64-redhat-linux/:/usr/libexec/gcc/x86_64-redhat-linux/4.3.0/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/4.3.0/:/usr/lib/gcc/x86_64-redhat-linux/ LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/4.3.0/:/usr/lib/gcc/x86_64-redhat-linux/4.3.0/:/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-std=gnu99' '-W' '-Wall' '-Wconversion' '-pedantic' '-c' '-mtune=generic' ==== Here is the test.c file: ==== typedef struct _my_struct_t { unsigned int small:1; unsigned int big:31; } my_struct_t, *my_struct_p_t; void my_func1(unsigned int sm, unsigned int bi, my_struct_p_t msp) { msp->small = sm; msp->big = bi; } void my_func2(unsigned int sm, unsigned int bi, my_struct_p_t msp) { msp->small = sm & 1U; msp->big = bi & 0x7fffffffU; } unsigned short my_func3(unsigned int sm) { unsigned short res; res = sm & 0xffffU; return res; } ==== Here is the test.i preprocessed file: ==== # 1 "test.c" # 1 "<built-in>" # 1 "<command-line>" # 1 "test.c" typedef struct _my_struct_t { unsigned int small:1; unsigned int big:31; } my_struct_t, *my_struct_p_t; void my_func1(unsigned int sm, unsigned int bi, my_struct_p_t msp) { msp->small = sm; msp->big = bi; } void my_func2(unsigned int sm, unsigned int bi, my_struct_p_t msp) { msp->small = sm & 1U; msp->big = bi & 0x7fffffffU; } unsigned short my_func3(unsigned int sm) { unsigned short res; res = sm & 0xffffU; return res; } ==== Kind regards, Christian -- Summary: Quieten -Wconversion warnings Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: christian dot iseli at licr dot org GCC build triplet: x86_64-redhat-linux GCC host triplet: x86_64-redhat-linux GCC target triplet: x86_64-redhat-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35701
