[Bug c/80872] New: There is no warning on accidental infinite loops

["david at westcontrol dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80872

            Bug ID: 80872
           Summary: There is no warning on accidental infinite loops
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david at westcontrol dot com
  Target Milestone: ---

Would it be possible to add warnings on accidental infinite loops, such as:

void foo(void) {
  for (int i = 0; i <= 0x7fffffff; i++) {
     // ...
  }
}

The compiler (correctly) translates this to an infinite loop, in all versions
of gcc that I tested, and in both C and C++, with optimisation enabled.  But no
warning is given, even with -Wall -Wextra.  That includes the -Wtype-limits
warning, which I thought should trigger here.  Perhaps the order of passes is
such that the code is simplified to an infinite loop before the type limits
checking is done?

Replacing " <= 0x7fffffff" with "< 0x80000000" gives triggers -Wsign-compare
but not -Wtype-limits, which is relevant because in C -Wsign-compare is in
-Wextra but not -Wall.  Exceeding the limits of unsigned int in the literal
here correctly triggers -Wtype-limits.