Add a checker to detected unmodified variables

[Quuxplusone]

Bugzilla Link	PR16890
Status	NEW
Importance	P enhancement
Reported by	michael.morrell@intel.com
Reported on	2013-08-14 17:16:28 -0700
Last modified on	2013-08-15 19:23:52 -0700
Version	unspecified
Hardware	Macintosh MacOS X
CC	jrose@belkadan.com, llvm-bugs@lists.llvm.org, michael.morrell@intel.com
Fixed by commit(s)
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I think if it would be nice if the following reported some kind of error:

  int foo()
  {
     int i = 0;

     return i;
  }

where a variable is never modified (to me, this indicates that some code that
modified the variable is missing).   If the variable is really not supposed to
change, the user can declare it as "const" (or use a #define).

[Quuxplusone]

This is /definitely/ a style checker, since in LLVM at least we often use temporary variables just to break up large expressions. Marking local variable const could certainly be considered good practice, but it's not something people do often, especially not for pointers.

[Quuxplusone]

I'm not sure what you mean by a "style checker".

This is a check that many people might not want and so should be disabled by default, but I think it would be valuable to have as an option.

[Quuxplusone]

That's mostly what I meant. It's a checker whose usefulness is strongly dependent on the conventions and style guidelines of a particular codebase. I'll add it to the potential checkers list.