[Bug c/89126] New: missing -Wtype-limits for int variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89126

            Bug ID: 89126
           Summary: missing -Wtype-limits for int variables
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC issues -Wtype-limits warnings for relational expressions that either cannot
be true or cannot be false due to the limits of the type of one of their
operands.  This seems to work except for operands of type int where GCC fails
to issue any warnings.

$ cat u.c && gcc -S -Wall -Wextra -Wpedantic u.c
int fchar (signed char x)
{ 
  if (x <= __SCHAR_MAX__)   // -Wtype-limits (good)
    return 1;

  if (x > __SCHAR_MAX__)    // -Wtype-limits (good)
    return 1;

  return 0;
}

int fshrt (short x)
{ 
  if (x <= __SHRT_MAX__)    // -Wtype-limits (good)
    return 1;

  if (x > __SHRT_MAX__)     // -Wtype-limits (good)
    return 1;

  return 0;
}

int fint (int x)
{
  if (x <= __INT_MAX__)     // missing -Wtype-limits
    return 1;

  if (x > __INT_MAX__)     // missing -Wtype-limits
    return 1;

  return 0;
}


int flong (int x)
{
  if (x <= __LONG_MAX__)    // -Wtype-limits (good)
    return 1;

  if (x > __LONG_MAX__)     // -Wtype-limits (good)
    return 1;

  return 0;
}

u.c: In function ‘fchar’:
u.c:3:9: warning: comparison is always true due to limited range of data type
[-Wtype-limits]
    3 |   if (x <= __SCHAR_MAX__)   // -Wtype-limits (good)
      |         ^~
u.c:6:9: warning: comparison is always false due to limited range of data type
[-Wtype-limits]
    6 |   if (x > __SCHAR_MAX__)    // -Wtype-limits (good)
      |         ^
u.c: In function ‘fshrt’:
u.c:14:9: warning: comparison is always true due to limited range of data type
[-Wtype-limits]
   14 |   if (x <= __SHRT_MAX__)    // -Wtype-limits (good)
      |         ^~
u.c:17:9: warning: comparison is always false due to limited range of data type
[-Wtype-limits]
   17 |   if (x > __SHRT_MAX__)     // -Wtype-limits (good)
      |         ^
u.c: In function ‘flong’:
u.c:37:9: warning: comparison is always true due to limited range of data type
[-Wtype-limits]
   37 |   if (x <= __LONG_MAX__)    // -Wtype-limits (good)
      |         ^~
u.c:40:9: warning: comparison is always false due to limited range of data type
[-Wtype-limits]
   40 |   if (x > __LONG_MAX__)     // -Wtype-limits (good)
      |         ^