#!/bin/sh
#! -*-perl-*-

# Detect instances of "if (p) free (p);".
# Likewise "if (p != 0)", "if (0 != p)", or with NULL; and with braces.

# Copyright (C) 2008-2021 Free Software Foundation, Inc.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
#
# Written by Jim Meyering

# This is a prologue that allows to run a perl script as an executable
# on systems that are compliant to a POSIX version before POSIX:2017.
# On such systems, the usual invocation of an executable through execlp()
# or execvp() fails with ENOEXEC if it is a script that does not start
# with a #! line.  The script interpreter mentioned in the #! line has
# to be /bin/sh, because on GuixSD systems that is the only program that
# has a fixed file name.  The second line is essential for perl and is
# also useful for editing this file in Emacs.  The next two lines below
# are valid code in both sh and perl.  When executed by sh, they re-execute
# the script through the perl program found in $PATH.  The '-x' option
# is essential as well; without it, perl would re-execute the script
# through /bin/sh.  When executed by perl, the next two lines are a no-op.
eval 'exec perl -wSx "$0" "$@"'
     if 0;

my $VERSION = '2020-04-04 15:07'; # UTC
# The definition above must lie within the first 8 lines in order
# for the Emacs time-stamp write hook (at end) to update it.
# If you change this file with Emacs, please let the write hook
# do its job.  Otherwise, update this string manually.

use strict;
use warnings;
use Getopt::Long;

(my $ME = $0) =~ s|.*/||;

# use File::Coda; # https://meyering.net/code/Coda/
END {
  defined fileno STDOUT or return;
  close STDOUT and return;
  warn "$ME: failed to close standard output: $!\n";
  $? ||= 1;
}

sub usage ($)
{
  my ($exit_code) = @_;
  my $STREAM = ($exit_code == 0 ? *STDOUT : *STDERR);
  if ($exit_code != 0)
    {
      print $STREAM "Try '$ME --help' for more information.\n";
    }
  else
    {
      print $STREAM <<EOF;
Usage: $ME [OPTIONS] FILE...

Detect any instance in FILE of a useless "if" test before a free call, e.g.,
"if (p) free (p);".  Any such test may be safely removed without affecting
the semantics of the C code in FILE.  Use --name=FOO --name=BAR to also
detect free-like functions named FOO and BAR.

OPTIONS:

   --list       print only the name of each matching FILE (\\0-terminated)
   --name=N     add name N to the list of \'free\'-like functions to detect;
                  may be repeated

   --help       display this help and exit
   --version    output version information and exit

Exit status:

  0   one or more matches
  1   no match
  2   an error

EXAMPLE:

For example, this command prints all removable "if" tests before "free"
and "kfree" calls in the linux kernel sources:

    git ls-files -z |xargs -0 $ME --name=kfree

EOF
    }
  exit $exit_code;
}

sub is_NULL ($)
{
  my ($expr) = @_;
  return ($expr eq 'NULL' || $expr eq '0');
}

{
  sub EXIT_MATCH {0}
  sub EXIT_NO_MATCH {1}
  sub EXIT_ERROR {2}
  my $err = EXIT_NO_MATCH;

  my $list;
  my @name = qw(free);
  GetOptions
    (
     help => sub { usage 0 },
     version => sub { print "$ME version $VERSION\n"; exit },
     list => \$list,
     'name=s@' => \@name,
    ) or usage 1;

  # Make sure we have the right number of non-option arguments.
  # Always tell the user why we fail.
  @ARGV < 1
    and (warn "$ME: missing FILE argument\n"), usage EXIT_ERROR;

  my $or = join '|', @name;
  my $regexp = qr/(?:$or)/;

  # Set the input record separator.
  # Note: this makes it impractical to print line numbers.
  $/ = '"';

  my $found_match = 0;
 FILE:
  foreach my $file (@ARGV)
    {
      open FH, '<', $file
        or (warn "$ME: can't open '$file' for reading: $!\n"),
          $err = EXIT_ERROR, next;
      while (defined (my $line = <FH>))
        {
          # Skip non-matching lines early to save time
          $line =~ /\bif\b/
            or next;
          while ($line =~
              /\b(if\s*\(\s*([^)]+?)(?:\s*!=\s*([^)]+?))?\s*\)
              #  1          2                  3
               (?:   \s*$regexp\s*\((?:\s*\([^)]+\))?\s*([^)]+)\)\s*;|
                \s*\{\s*$regexp\s*\((?:\s*\([^)]+\))?\s*([^)]+)\)\s*;\s*\}))/sxg)
            {
              my $all = $1;
              my ($lhs, $rhs) = ($2, $3);
              my ($free_opnd, $braced_free_opnd) = ($4, $5);
              my $non_NULL;
              if (!defined $rhs) { $non_NULL = $lhs }
              elsif (is_NULL $rhs) { $non_NULL = $lhs }
              elsif (is_NULL $lhs) { $non_NULL = $rhs }
              else { next }

              # Compare the non-NULL part of the "if" expression and the
              # free'd expression, without regard to white space.
              $non_NULL =~ tr/ \t//d;
              my $e2 = defined $free_opnd ? $free_opnd : $braced_free_opnd;
              $e2 =~ tr/ \t//d;
              if ($non_NULL eq $e2)
                {
                  $found_match = 1;
                  $list
                    and (print "$file\0"), next FILE;
                  print "$file: $all\n";
                }
            }
        }
    }
  continue
    {
      close FH;
    }

  $found_match && $err == EXIT_NO_MATCH
    and $err = EXIT_MATCH;

  exit $err;
}

my $foo = <<'EOF';
# The above is to *find* them.
# This adjusts them, removing the unnecessary "if (p)" part.

# FIXME: do something like this as an option (doesn't do braces):
free=xfree
git grep -l -z "$free *(" \
  | xargs -0 useless-if-before-free -l --name="$free" \
  | xargs -0 perl -0x3b -pi -e \
   's/\bif\s*\(\s*(\S+?)(?:\s*!=\s*(?:0|NULL))?\s*\)\s+('"$free"'\s*\((?:\s*\([^)]+\))?\s*\1\s*\)\s*;)/$2/s'

# Use the following to remove redundant uses of kfree inside braces.
# Note that -0777 puts perl in slurp-whole-file mode;
# but we have plenty of memory, these days...
free=kfree
git grep -l -z "$free *(" \
  | xargs -0 useless-if-before-free -l --name="$free" \
  | xargs -0 perl -0777 -pi -e \
     's/\bif\s*\(\s*(\S+?)(?:\s*!=\s*(?:0|NULL))?\s*\)\s*\{\s*('"$free"'\s*\((?:\s*\([^)]+\))?\s*\1\s*\);)\s*\}[^\n]*$/$2/gms'

Be careful that the result of the above transformation is valid.
If the matched string is followed by "else", then obviously, it won't be.

When modifying files, refuse to process anything other than a regular file.
EOF

## Local Variables:
## mode: perl
## indent-tabs-mode: nil
## eval: (add-hook 'before-save-hook 'time-stamp)
## time-stamp-line-limit: 50
## time-stamp-start: "my $VERSION = '"
## time-stamp-format: "%:y-%02m-%02d %02H:%02M"
## time-stamp-time-zone: "UTC0"
## time-stamp-end: "'; # UTC"
## End: