[Bug gcov-profile/99441] New: [GCOV] Wrong coverage with complex "if" condition

[Bug gcov-profile/99441] New: [GCOV] Wrong coverage with complex "if" condition

[njuwy at smail dot nju.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99441

            Bug ID: 99441
           Summary: [GCOV] Wrong coverage with complex "if" condition
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: gcov-profile
          Assignee: unassigned at gcc dot gnu.org
          Reporter: njuwy at smail dot nju.edu.cn
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure -enable-checking=release -enable-languages=c,c++
-disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.0 (GCC) 

$ cat test.c
typedef __SIZE_TYPE__ size_t;
typedef __UINTPTR_TYPE__ uintptr_t;

struct S {
  int a;
  unsigned short b;
  int c, d, e;
  long f, g, h;
  int i, j;
};
static struct S *k;
static size_t l = 1;
int m;

static int bar(void) {
  unsigned i;
  int j;
  if (k[0].c == 0) {
    ++m;
    size_t n = l * 2;
    struct S *o;
    k = (struct S *)__builtin_realloc(k, sizeof(struct S) * n);
    for (i = l; i < n; i++) {
      void *p = (void *)&k[i];
      int q = 0;
      size_t r = sizeof(struct S);
      if ((((uintptr_t)p) % __alignof__(long)) == 0 && r % sizeof(long) == 0) {
        long __attribute__((may_alias)) *s = (long *)p;
        long *t = (long *)((char *)s + r);
        while (s < t)
          *s++ = 0;
      } else
        __builtin_memset(p, q, r);
    }
  }
  return 1;
}

int main() {
  k = (struct S *)__builtin_malloc(sizeof(struct S));
  __builtin_memset(k, '\0', sizeof(struct S));
  k->a = -1;
  for (int i = 0; i < 15; ++i)
    bar();
}

$ gcc -O0 --coverage test.c;./a.out;gcov test;cat test.c.gcov
libgcov profiling error:/home/wangyang/coverage/found
bug/gcc/test.gcda:overwriting an existing profile data with a different
timestamp
File 'test.c'
Lines executed:95.45% of 22
Creating 'test.c.gcov'

        -:    0:Source:test.c
        -:    0:Graph:test.gcno
        -:    0:Data:test.gcda
        -:    0:Runs:1
        -:    1:typedef __SIZE_TYPE__ size_t;
        -:    2:typedef __UINTPTR_TYPE__ uintptr_t;
        -:    3:
        -:    4:struct S {
        -:    5:  int a;
        -:    6:  unsigned short b;
        -:    7:  int c, d, e;
        -:    8:  long f, g, h;
        -:    9:  int i, j;
        -:   10:};
        -:   11:static struct S *k;
        -:   12:static size_t l = 1;
        -:   13:int m;
        -:   14:
       15:   15:static int bar(void) {
        -:   16:  unsigned i;
        -:   17:  int j;
       15:   18:  if (k[0].c == 0) {
       15:   19:    ++m;
       15:   20:    size_t n = l * 2;
        -:   21:    struct S *o;
       15:   22:    k = (struct S *)__builtin_realloc(k, sizeof(struct S) * n);
       30:   23:    for (i = l; i < n; i++) {
       15:   24:      void *p = (void *)&k[i];
       15:   25:      int q = 0;
       15:   26:      size_t r = sizeof(struct S);
       30:   27:      if ((((uintptr_t)p) % __alignof__(long)) == 0 && r %
sizeof(long) == 0) {
       15:   28:        long __attribute__((may_alias)) *s = (long *)p;
       15:   29:        long *t = (long *)((char *)s + r);
      120:   30:        while (s < t)
      105:   31:          *s++ = 0;
        -:   32:      } else
    #####:   33:        __builtin_memset(p, q, r);
        -:   34:    }
        -:   35:  }
       15:   36:  return 1;
        -:   37:}
        -:   38:
        1:   39:int main() {
        1:   40:  k = (struct S *)__builtin_malloc(sizeof(struct S));
        1:   41:  __builtin_memset(k, '\0', sizeof(struct S));
        1:   42:  k->a = -1;
       16:   43:  for (int i = 0; i < 15; ++i)
       15:   44:    bar();
        -:   45:}

Line #27 should only be executed 15 times

[Bug gcov-profile/99441] [GCOV] Wrong coverage with complex "if" condition

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99441

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So line 27 has a short cutting conditional included, so technically it is
executed 30 times, one for each side of the &&.

[Bug gcov-profile/99441] [GCOV] Wrong coverage with complex "if" condition

[njuwy at smail dot nju.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99441

--- Comment #2 from Yang Wang <njuwy at smail dot nju.edu.cn> ---
(In reply to Andrew Pinski from comment #1)
> So line 27 has a short cutting conditional included, so technically it is
> executed 30 times, one for each side of the &&.


$ gcc -O0 --coverage test.c;./a.out;gcov test;cat test.c.gcov
libgcov profiling error:/home/wangyang/coverage/found
bug/gcc/test.gcda:overwriting an existing profile data with a different
timestamp
File 'test.c'
Lines executed:95.83% of 24
Creating 'test.c.gcov'

        -:    0:Source:test.c
        -:    0:Graph:test.gcno
        -:    0:Data:test.gcda
        -:    0:Runs:1
        -:    1:typedef __SIZE_TYPE__ size_t;
        -:    2:typedef __UINTPTR_TYPE__ uintptr_t;
        -:    3:
        -:    4:struct S {
        -:    5:  int a;
        -:    6:  unsigned short b;
        -:    7:  int c, d, e;
        -:    8:  long f, g, h;
        -:    9:  int i, j;
        -:   10:};
        -:   11:static struct S *k;
        -:   12:static size_t l = 1;
        -:   13:int m;
        -:   14:
       15:   15:static int bar(void) {
        -:   16:  unsigned i;
        -:   17:  int j;
       15:   18:  if (k[0].c == 0) {
       15:   19:    ++m;
       15:   20:    size_t n = l * 2;
        -:   21:    struct S *o;
       15:   22:    k = (struct S *)__builtin_realloc(k, sizeof(struct S) * n);
       30:   23:    for (i = l; i < n; i++) {
       15:   24:      void *p = (void *)&k[i];
       15:   25:      int q = 0;
       15:   26:      size_t r = sizeof(struct S);
       15:   27:      if ((((uintptr_t)p) % __alignof__(long)) == 0 
       15:   28:        && 
       30:   29:        r % sizeof(long) == 0) {
       15:   30:        long __attribute__((may_alias)) *s = (long *)p;
       15:   31:        long *t = (long *)((char *)s + r);
      120:   32:        while (s < t)
      105:   33:          *s++ = 0;
        -:   34:      } else
    #####:   35:        __builtin_memset(p, q, r);
        -:   36:    }
        -:   37:  }
       15:   38:  return 1;
        -:   39:}
        -:   40:
        1:   41:int main() {
        1:   42:  k = (struct S *)__builtin_malloc(sizeof(struct S));
        1:   43:  __builtin_memset(k, '\0', sizeof(struct S));
        1:   44:  k->a = -1;
       16:   45:  for (int i = 0; i < 15; ++i)
       15:   46:    bar();
        -:   47:}


Thanks for your reply!
I tried to separate line 27 and put it in a different lines. The coverage of
right side(line 29) is 30, and the left side(line 27) is 15, which is a bit
different from  the execution logic about "&&", where the left side of "&&"
should not be less than the right side. Is it a bug?

[Bug gcov-profile/99441] [GCOV] Wrong coverage with complex "if" condition

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99441

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-03-08
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1