[Bug gcov-profile/89673] New: [GCOV] A label followed with a blank(empty) statement will be wrongly marked as executed in gcov

[yangyibiao at nju dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89673

            Bug ID: 89673
           Summary: [GCOV] A label followed with a blank(empty) statement
                    will be wrongly marked as executed in gcov
           Product: gcc
           Version: 8.2.0
            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 -v
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='Ubuntu
8.2.0-1ubuntu2~18.04' --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 --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 --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-multilib --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 8.2.0 (Ubuntu 8.2.0-1ubuntu2~18.04)

$ cat small.c
struct decision
{
  char enforce_mode;
  struct decision *next;
};


static void clear_modes (p)  register struct decision *p;
{
  goto blah;

foo:
    ;//  p->enforce_mode = 0;
blah:
  if (p)
    goto foo;
}

main()
{
  struct decision *p = 0;
  clear_modes (p);
  exit (0);
}


$ gcc -O0 --coverage small.c -w; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:90.91% of 11
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:struct decision
        -:    2:{
        -:    3:  char enforce_mode;
        -:    4:  struct decision *next;
        -:    5:};
        -:    6:
        -:    7:
        1:    8:static void clear_modes (p)  register struct decision *p;
        -:    9:{
        1:   10:  goto blah;
        -:   11:
        1:   12:foo:
        -:   13:    ;//  p->enforce_mode = 0;
        1:   14:blah:
        1:   15:  if (p)
    #####:   16:    goto foo;
        1:   17:}
        -:   18:
        1:   19:main()
        -:   20:{
        1:   21:  struct decision *p = 0;
        1:   22:  clear_modes (p);
        1:   23:  exit (0);
        -:   24:}

Line #12 is wrongly marked as executed. While Line 13 is not removed, the
result is correct as follows:

$ gcc -O0 --coverage small.c -w; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:75.00% of 12
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:struct decision
        -:    2:{
        -:    3:  char enforce_mode;
        -:    4:  struct decision *next;
        -:    5:};
        -:    6:
        -:    7:
        1:    8:static void clear_modes (p)  register struct decision *p;
        -:    9:{
        1:   10:  goto blah;
        -:   11:
    #####:   12:foo:
    #####:   13:  p->enforce_mode = 0;
        1:   14:blah:
        1:   15:  if (p)
    #####:   16:    goto foo;
        1:   17:}
        -:   18:
        1:   19:main()
        -:   20:{
        1:   21:  struct decision *p = 0;
        1:   22:  clear_modes (p);
        1:   23:  exit (0);
        -:   24:}