c_delta.pl

#!/usr/bin/perl -w

# This Delta debugger specifically targets C code. Its design point --
# in two different senses -- is to be complementary to a line-based
# Delta like this one:
#
#   http://delta.tigris.org/
#
# First, c_delta aims for maximum reduction and specifically targets
# transformations not available to a language-independent Delta
# debugger, such as reordering function calls.
#
# Second, c_delta is stupid in the sense that it generates a lot of
# invalid code and also most of its changes do not reduce program size
# by a large amount. Thus, it is best used as a second pass with a
# faster Delta like the Berkeley one trimming the obviously irrelevant
# code.

use strict;
use Regexp::Common;
use re 'eval';

# TODO:

# print stats for individual regexes

# watch for unexpected abnormal compiler outputs

# add passes to 
#   remove digits from numbers to make them smaller
#   turn checksum calls into regular printfs

# write code to adapatively run multiple instances of a 
#   transformation when this has good expected value
#   measure cost of success vs. failure, take into account
#   proabability of success
# eventually back off to linear scan

# harder
#   transform a function to return void
#   inline a function call
#   un-nest nested calls in expressions
#   move arguments and locals to global scope
#   remove level of pointer indirection
#   remove array dimension
#   remove argument from function, including all calls

# long term todo: rewrite this tool to operate on ASTs

my $DEBUG = 0;

my $barevar = "\\-?[0-9a-zA-Z\_]+";
my $field = "\\.($barevar)";
my $index = "\\\[($barevar)\\\]";
my $var = "([\\&\\*]*)($barevar)(($field)|($index))*";
my $arith = "\\+|\\-|\\%|\\/|\\*";
my $comp = "\\<\\=|\\>\\=|\\<|\\>|\\=\\=|\\!\\=|\\=";
my $logic = "\\&\\&|\\|\\|";
my $bit = "\\||\\&|\\^|\\<\\<|\\>\\>";
my $binop = "($arith)|($comp)|($logic)|($bit)";
my $border = "[\\*\\{\\(\\[\\:\\,\\}\\)\\]\\;\\,]";
my $borderorspc = "(($border)|(\\s))";
my $rettype = "int|void|short|long|char|signed|unsigned|const|static|(union\\s+U[0-9]+)|(struct\\s+S[0-9+])";
my $functype = "(($rettype)\\s*|\\*\\s*)+";
my $fname = "(?<fname>$barevar)";
my $funcstart_orig = "$functype\\s+(?<fname>$barevar)\\s*$RE{balanced}{-parens=>'()'}";
my $funcstart = "$functype\\s+XXX\\s*$RE{balanced}{-parens=>'()'}";
my $proto = "$funcstart;";
my $func = "$funcstart\\s*$RE{balanced}{-parens=>'{}'}";

#print "$field\n";
#print "$index\n";
#print "$border\n";
#print "$var1\n";
#print "$var2\n";

# these match without additional qualification
my @regexes_to_replace = (
    ["$RE{balanced}{-parens=>'()'}", ""],
    ["$RE{balanced}{-parens=>'{}'}", ""],
    ["=\\s*$RE{balanced}{-parens=>'{}'}", ""],
    ["\\:\\s*[0-9]+\\s*;", ";"],
    ["\\;", ""],
    ["\\^\\=", "="],
    ["\\|\\=", "="],
    ["\\&\\=", "="],
    ["\\+\\=", "="],
    ["\\-\\=", "="],
    ["\\*\\=", "="],
    ["\\/\\=", "="],
    ["\\%\\=", "="],
    ["\\<\\<\\=", "="],
    ["\\>\\>\\=", "="],
    ["\\+", ""],
    ["\\-", ""],
    ["\\!", ""],
    ["\\~", ""],
    ['"(.*?)"', ""],
    ['"(.*?)",', ""],
    );

# these match when preceded and followed by $borderorspc
my @delimited_regexes_to_replace = (
    ["($barevar)\\s*:", ""],
    ["goto\\s+($barevar);", ""],
    ["char", "int"],
    ["short", "int"],
    ["long", "int"],
    ["signed", "int"],
    ["unsigned", "int"],
    ["int argc, char \\*argv\\[\\]", "void"],
    ["int.*?;", ""],
    ["for", ""],
    ["if\\s+\\(.*?\\)", ""],
    ["struct.*?;", ""],
    ["union.*?;", ""],
    ["($rettype)\\s+($var)\\s+$RE{balanced}{-parens=>'()'}\\s+$RE{balanced}{-parens=>'{}'}", ""],
    ["($rettype)\\s+($barevar)\\s+$RE{balanced}{-parens=>'()'}\\s+$RE{balanced}{-parens=>'{}'}", ""],
    ["$barevar\\s*$RE{balanced}{-parens=>'()'},", "0"],
    ["$barevar\\s*$RE{balanced}{-parens=>'()'},", ""],
    ["$barevar\\s*$RE{balanced}{-parens=>'()'}", "0"],
    ["$barevar\\s*$RE{balanced}{-parens=>'()'}", ""],
    );

my @subexprs = (
    "($var)(\\s*)($binop)(\\s*)($var)",
    "($var)(\\s*)($binop)",
    "($binop)(\\s*)($var)",
    "($var)",
    "($var)(\\s*\\?\\s*)($var)(\\s*\\:\\s*)($var)",
    );

foreach my $x (@subexprs) {
    push @delimited_regexes_to_replace, ["$x", "0"];
    push @delimited_regexes_to_replace, ["$x", "1"];
    push @delimited_regexes_to_replace, ["$x", ""];
    push @delimited_regexes_to_replace, ["$x,", "0,"];
    push @delimited_regexes_to_replace, ["$x,", "1,"];
    push @delimited_regexes_to_replace, ["$x,", ""];
}

#######################################################################

my $prog;

sub find_match ($$$) {
    (my $p2, my $s1, my $s2) = @_;
    my $count = 1;
    die if (!(defined($p2) && defined($s1) && defined($s2)));
    while ($count > 0) {
	return -1 if ($p2 >= (length ($prog)-1));
	my $s = substr($prog, $p2, 1);
	if (!defined($s)) {
	    my $l = length ($prog);
	    print "$p2 $l\n";
	    die;
	}
	$count++ if ($s eq $s1);
	$count-- if ($s eq $s2);
	$p2++;
    }
    return $p2-1;
}

# these are set at startup time and never change
my $cfile;
my $test;
my $trial_num = 0;   

sub read_file () {
    open INF, "<$cfile" or die;
    $prog = "";
    while (my $line = <INF>) {
	$prog .= $line;
    }
    if (substr($prog, 0, 1) ne " ") {
	$prog = " $prog";
    }
    if (substr ($prog, -1, 1) ne " ") {
	$prog = "$prog ";
    }
    close INF;
}

sub save_copy ($) {
    (my $fn) = @_;
    open OUTF, ">$fn" or die;
    print OUTF $prog;
    close OUTF;
}

sub write_file () {
    if (defined($DEBUG) && $DEBUG) {
	save_copy ("delta_tmp_${trial_num}.c");
    }
    $trial_num++;
    open OUTF, ">$cfile" or die;
    print OUTF $prog;
    close OUTF;
}

sub runit ($) {
    (my $cmd) = @_;
    if ((system "$cmd") != 0) {
	return -1;
    }   
    return ($? >> 8);
}

sub run_test () {
    my $res = runit "./$test";
    return ($res == 0);
}

my %cache = ();
my $cache_hits = 0;
my $good_cnt;
my $bad_cnt;
my $pass_num = 0;
my $pos;
my %method_worked = ();
my %method_failed = ();
my $old_size = 1000000000;
 
sub delta_test ($$) {
    (my $method, my $ok_to_enlarge) = @_;
    my $len = length ($prog);
    print "[$pass_num $method ($pos / $len) s:$good_cnt f:$bad_cnt] ";

    my $result = $cache{$prog};

    if (defined($result)) {
	$cache_hits++;
	print "(hit) ";
	print "failure\n";
	read_file ();    
	$bad_cnt++;
	$method_failed{$method}++;
	return 0;
    }
    
    write_file ();
    $result = run_test ();
    $cache{$prog} = $result;
    
    if ($result) {
	print "success\n";
	system "cp $cfile $cfile.bak";
	$good_cnt++;
	$method_worked{$method}++;
	my $size = length ($prog);
	die if (($size > $old_size) && !$ok_to_enlarge);
	if ($size < $old_size) {
	    %cache = ();
	}
	$old_size = $size;
	return 1;
    } else {
	print "failure\n";
	system "cp $cfile.bak $cfile";
	read_file ();    
	$bad_cnt++;
	$method_failed{$method}++;
	return 0;
    }
}

sub sanity_check () {
    print "sanity check... ";
    my $res = run_test ();
    if (!$res) {
	die "test (and sanity check) fails";
    }
}

sub delta_pass ($) {
    (my $method) = @_;
    
    $pos = 0;
    $good_cnt = 0;
    $bad_cnt = 0;

    sanity_check();

    print "========== starting pass <$method> ==========\n";

    while (1) {
	return ($good_cnt > 0) if ($pos >= length ($prog));
	my $worked = 0;

	if ($method eq "replace_regex") {
	    my $n=-1;
	    foreach my $l (@regexes_to_replace) {	       
		$n++;
		my $str = @{$l}[0];
		my $repl = @{$l}[1];
		my $first = substr($prog, 0, $pos);
		my $rest = substr($prog, $pos);
		if ($rest =~ s/(^$str)/$repl/) {
		    print "num $n replacing '$1' with '$repl' : ";
		    $prog = $first.$rest;
		    $worked |= delta_test ($method, 0);
		}
	    }
	    $n=-1;
	    foreach my $l (@delimited_regexes_to_replace) {
		$n++;
		my $str = @{$l}[0];
		my $repl = @{$l}[1];
		my $first = substr($prog, 0, $pos);
		my $rest = substr($prog, $pos);
		
		# avoid infinite loops!
		next if ($repl eq "0" && $rest =~ /^($borderorspc)0$borderorspc/);
		next if ($repl eq "1" && $rest =~ /^($borderorspc)0$borderorspc/);
		next if ($repl eq "0," && $rest =~ /^($borderorspc)0,$borderorspc/);
		next if ($repl eq "1," && $rest =~ /^($borderorspc)0,$borderorspc/);

		if ($rest =~ s/^(?<delim1>$borderorspc)(?<str>$str)(?<delim2>$borderorspc)/$+{delim1}$repl$+{delim2}/) {
		    print "num $n delimited replacing '$+{str}' with '$repl' : ";
		    $prog = $first.$rest;
		    $worked |= delta_test ($method, 0);
		}
	    }
	} elsif ($method eq "del_blanks_all") {
	    if ($prog =~ s/\s{2,}/ /g) {
		$worked |= delta_test ($method, 0);
	    }
	    return 0;
	} elsif ($method eq "indent") {	    
	    write_file();
	    system "indent $cfile";
	    read_file();
	    $worked |= delta_test ($method, 1);
	    return 0;
	} elsif ($method eq "del_blanks") {
	    my $rest = substr($prog, $pos);
	    if ($rest =~ /^(\s{2,})/) {
		my $len = length ($1);
		substr ($prog, $pos, $len) =  " ";
		$worked |= delta_test ($method, 0);
	    }
	} elsif ($method eq "parens_exclusive") {
	    if (substr($prog, $pos, 1) eq "(") {
		my $p2 = find_match ($pos+1,"(",")");
		if ($p2 != -1) {
		    die if (substr($prog, $pos, 1) ne "(");
		    die if (substr($prog, $p2, 1) ne ")");
		    substr ($prog, $p2, 1) = "";
		    substr ($prog, $pos, 1) = "";
		    print "deleting at $pos--$p2 : ";
		    $worked |= delta_test ($method, 0);
		}
	    }
	} elsif ($method eq "move_func") {
	    my $first = substr($prog, 0, $pos);
	    my $rest = substr($prog, $pos);
	    my $proto2 = $proto;
	    die if (!($proto2 =~ s/XXX/$fname/));
	    if ($rest =~ /^($proto2)/) {
		my $realproto = $1;
		my $fname = $+{fname};
		print "found prototype for '$fname'\n";
		my $func2 = $func;
		die if (!($func2 =~ s/XXX/$fname/));
		if ($rest =~ s/($func2)//) {
		    my $body = $1;
		    print "got body!\n";
		    print "replacing < $realproto > with < $body >\n";
		    substr ($rest, 0, length($realproto)) = $body;
		    $prog = $first.$rest;
		    $worked |= delta_test ($method, 0);
		}
	    } 
	} elsif ($method eq "brackets_exclusive") {
	    if (substr($prog, $pos, 1) eq "{") {
		my $p2 = find_match ($pos+1,"{","}");
		if ($p2 != -1) {
		    die if (substr($prog, $pos, 1) ne "{");
		    die if (substr($prog, $p2, 1) ne "}");
		    substr ($prog, $p2, 1) = "";
		    substr ($prog, $pos, 1) = "";
		    print "deleting at $pos--$p2 : ";
		    $worked |= delta_test ($method, 0);
		}
	    }
	} else {
	    die "unknown reduction method";
	}

	if (!$worked) {
	    $pos++;
	}
    }
}

# invariant: test always succeeds for $cfile.bak

my %all_methods = (

    "del_blanks_all" => 0,
    "del_blanks" => 1,
    "move_func" => 2,
    "brackets_exclusive" => 2,
    "parens_exclusive" => 3,
    "replace_regex" => 4,
    "indent" => 5,

    );
 
#################### main #####################

sub usage() {
    print "usage: c_delta.pl test_script.sh file.c [method [method ...]]\n";
    print "available methods are --all or:\n";
    foreach my $method (keys %all_methods) {
	print "  --$method\n";
    }
    die;
}

$test = shift @ARGV;
usage if (!defined($test));
if (!(-x $test)) {
    print "test script '$test' not found, or not executable\n";
    usage();
}

$cfile = shift @ARGV;
usage if (!defined($cfile));
if (!(-e $cfile)) {
    print "'$cfile' not found\n";
    usage();
}

my %methods = ();
usage if (!defined(@ARGV));
foreach my $arg (@ARGV) {
    if ($arg eq "--all") {
	foreach my $method (keys %all_methods) {
	    $methods{$method} = 1;
	}
    } else {
	my $found = 0;
	foreach my $method (keys %all_methods) {
	    if ($arg eq "--$method") {
		$methods{$method} = 1;
		$found = 1;
		last;
	    }
	}
	if (!$found) {
	    print "unknown method '$arg'\n";
	    usage();
	}
    }
}

system "cp $cfile $cfile.orig";
system "cp $cfile $cfile.bak";

sub bymethod {
    return $all_methods{$a} <=> $all_methods{$b};
}

# iterate to global fixpoint

read_file ();    

while (1) {
    my $success = 0;
    save_copy ("delta_backup_${pass_num}.c");
    foreach my $method (sort bymethod keys %methods) {
	$success |= delta_pass ($method);
    }
    $pass_num++;
    last if (!$success);
}

print "\n";
print "statistics:\n";
foreach my $method (sort keys %methods) {
    my $w = $method_worked{$method};
    $w=0 unless defined($w);
    my $f = $method_failed{$method};
    $f=0 unless defined($f);
    print "  method $method worked $w times and failed $f times\n";
}
print "there were $cache_hits cache hits\n";