[Bug gcov-profile/90439] New: [GCOV] multiple expression across different lines in if statement is inconsistent when the body is empty

[yangyibiao at nju dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90439

            Bug ID: 90439
           Summary: [GCOV] multiple expression across different lines in
                    if statement is inconsistent when the body is empty
           Product: gcc
           Version: 9.0
            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: ---

$ gcov -v
gcov (GCC) 9.0.1 20190414 (experimental)
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or 
FITNESS FOR A PARTICULAR PURPOSE.


$ cat small.c
void test1 (int x, unsigned u)
{
  if ((1U << x) != 64
      || (2 << x) != u
      || (1 << x) == 14
      || (3 << 2) != 12)
    ; // __builtin_abort ();
}

int main (void)
{
  test1 (6, 128U);
}


$ gcc -O0 -g --coverage small.c; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:100.00% of 6
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        1:    1:void test1 (int x, unsigned u)
        -:    2:{
        1:    3:  if ((1U << x) != 64
        1:    4:      || (2 << x) != u
        -:    5:      || (1 << x) == 14
        -:    6:      || (3 << 2) != 12)
        -:    7:    ; // __builtin_abort ();
        1:    8:}
        -:    9:
        1:   10:int main (void)
        -:   11:{
        1:   12:  test1 (6, 128U);
        -:   13:}

Line #6 is marked as "-" which means that it is not an instrumentation site.
When Line #7 is not removed, it is marked as executed as follows. In other
words, it is now an instrumentation site. 

I know that when Line #7 is removed, empty body in if statement will lead to
compiler optimizations. But I am still confused by this inconsistency as Line
#4 and Line #3 are both marked as executed in both situations. 

$ gcc -O0 -g --coverage small.c; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:87.50% of 8
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        1:    1:void test1 (int x, unsigned u)
        -:    2:{
        1:    3:  if ((1U << x) != 64
        1:    4:      || (2 << x) != u
        -:    5:      || (1 << x) == 14
        1:    6:      || (3 << 2) != 12)
    #####:    7:    __builtin_abort ();
        1:    8:}
        -:    9:
        1:   10:int main (void)
        -:   11:{
        1:   12:  test1 (6, 128U);
        -:   13:}