[Bug gcov-profile/90054] New: [GCOV] A call statement to the __builtin_snprintf function is wrongly marked as not executed when it is in a for loop

[yangyibiao at nju dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90054

            Bug ID: 90054
           Summary: [GCOV] A call statement to the __builtin_snprintf
                    function is wrongly marked as not executed when it is
                    in a for loop
           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
int b = 1, d = 2;
char res[2];

void fn3 ()
{
  for (;;)
  {
    __builtin_snprintf (res, 2, "%d\n", d);
    if (d)
      break;
  }
  printf("%s\n", res);
}

int main ()
{
  fn3 ();
  return 0;
}

$ gcc -w -O0 --coverage small.c; ./a.out; gcov-8 small.c; cat small.c.gcov
2
File 'small.c'
Lines executed:88.89% of 9
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:int b = 1, d = 2;
        -:    2:char res[2];
        -:    3:
        1:    4:void fn3 ()
        -:    5:{
        -:    6:  for (;;)
        -:    7:  {
    #####:    8:    __builtin_snprintf (res, 2, "%d\n", d);
        1:    9:    if (d)
        1:   10:      break;
        -:   11:  }
        1:   12:  printf("%s\n", res);
        1:   13:}
        -:   14:
        1:   15:int main ()
        -:   16:{
        1:   17:  fn3 ();
        1:   18:  return 0;
        -:   19:}

Line #8 is wrongly marked as not executed. 

When the builtin_snprintf function is replaced with snprintf function, the
coverage report is correct as:

$ gcc -w -O0 --coverage small.c; ./a.out; gcov-8 small.c; cat small.c.gcov
2
File 'small.c'
Lines executed:90.00% of 10
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:int b = 1, d = 2;
        -:    2:char res[2];
        -:    3:
        1:    4:void fn3 ()
        -:    5:{
        -:    6:  for (;;)
    #####:    7:  {
        -:    8:    // __builtin_snprintf (res, 2, "%d\n", d);
        1:    9:    snprintf (res, 2, "%d\n", d);
        1:   10:    if (d)
        1:   11:      break;
        -:   12:  }
        1:   13:  printf("%s\n", res);
        1:   14:}
        -:   15:
        1:   16:int main ()
        -:   17:{
        1:   18:  fn3 ();
        1:   19:  return 0;
        -:   20:}