Coccinelle: flag conditions with no effect

///Find conditions where if and else branch are functionally

// identical.

//

// There can be false positives in cases where the positional

// information is used (as with lockdep) or where the identity

// is a placeholder for not yet handled cases.

// Unfortunately there also seems to be a tendency to use

// the last if else/else as a "default behavior" - which some

// might consider a legitimate coding pattern. From discussion

// on kernelnewbies though it seems that this is not really an

// accepted pattern and if at all it would need to be commented

//

// In the Linux kernel it does not seem to actually report

// false positives except for those that were documented as

// being intentional.

// the two known cases are:

//   arch/sh/kernel/traps_64.c:read_opcode()

//        } else if ((pc & 1) == 0) {

//              /* SHcompact */

//              /* TODO : provide handling for this.  We don't really support

//                 user-mode SHcompact yet, and for a kernel fault, this would

//                 have to come from a module built for SHcompact.  */

//              return -EFAULT;

//      } else {

//              /* misaligned */

//              return -EFAULT;

//      }

//   fs/kernfs/file.c:kernfs_fop_open()

//       * Both paths of the branch look the same.  They're supposed to

//       * look that way and give @of->mutex different static lockdep keys.

//       */

//      if (has_mmap)

//              mutex_init(&of->mutex);

//      else

//              mutex_init(&of->mutex);

//

// All other cases look like bugs or at least lack of documentation

//

// Confidence: Moderate

// Copyright: (C) 2016 Nicholas Mc Guire, OSADL.  GPLv2.

// Comments:

// Options: --no-includes --include-headers

virtual org

virtual report

@cond@

statement S1;

position p;

@@

* if@p (...) S1 else S1

@script:python depends on org@

p << cond.p;

@@

cocci.print_main("WARNING: possible condition with no effect (if == else)",p)

@script:python depends on report@

p << cond.p;

@@

coccilib.report.print_report(p[0],"WARNING: possible condition with no effect (if == else)")