[Bug gcov-profile/83813] New: [GCOV] unsigned char in a union lead to incorrect coverage in gcov

[yangyibiao at nju dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83813

            Bug ID: 83813
           Summary: [GCOV] unsigned char in a union lead to incorrect
                    coverage in gcov
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: gcov-profile
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yangyibiao at nju dot edu.cn
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

# gcc-8 -v
Using built-in specs.
COLLECT_GCC=gcc-8
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='Ubuntu
8-20170923-1ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,c++,go,brig,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 --enable-nls --with-sysroot=/ --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-plugin --enable-default-pie
--with-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.0.0 20170923 (experimental) [trunk revision 253118] (Ubuntu
8-20170923-1ubuntu2)

# cat small.c
union U
{
    int f0;
    unsigned char f1;
};

int main()
{
    int i = 0;
    union U u = {0};
    for (u.f1 = 0; u.f1 != -2; ++u.f1) {
        i ^= u.f1;
        if (i < 1)
            return 0;
    }

    return 1;
}

# gcc-8 small.c -fprofile-arcs -ftest-coverage; ./a.out; gcov-8 small.c; cat
small.c.gcov
File 'small.c'
Lines executed:85.71% of 7
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:union U
        -:    2:{
        -:    3:    int f0;
        -:    4:    unsigned char f1;
        -:    5:};
        -:    6:
        1:    7:int main()
        -:    8:{
        1:    9:    int i = 0;
        1:   10:    union U u = {0};
        1:   11:    for (u.f1 = 0; u.f1 != -2; ++u.f1) {
    #####:   12:        i ^= u.f1;
        1:   13:        if (i < 1)
        1:   14:            return 0;
        -:   15:    }
        -:   16:
        -:   17:    return 1;
        -:   18:}


Line #12 is wrongly marked as not executed. While change f1's type as int or
unsigned int, the coverage is correct.