diff --git a/configure b/configure
index 798e8aff..dc558195 100755
--- a/configure
+++ b/configure
@@ -638,6 +638,7 @@ LTLIBOBJS
 LIBOBJS
 INDENT
 CLANG_FORMAT
+CLANG
 ASTYLE
 PERL_VERSION
 PERL
@@ -807,6 +808,7 @@ CXXCPP
 PERL
 ASTYLE
 CLANG_FORMAT
+CLANG
 INDENT'
 
 
@@ -1475,6 +1477,7 @@ Some influential environment variables:
   ASTYLE      `astyle' (Artistic Style) program
   CLANG_FORMAT
               `clang-format' (LLVM/Clang) program
+  CLANG       `clang` program
   INDENT      `indent' program
 
 Use these variables to override the choices made by `configure' or to help
@@ -16603,6 +16606,53 @@ if test "x$CLANG_FORMAT" = "xno"; then :
 fi
 #
 
+# Extract the first word of "clang", so it can be a program name with args.
+set dummy clang; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_CLANG+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $CLANG in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_CLANG="$CLANG" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+as_dummy="$LLVM_BINDIR:$PATH"
+for as_dir in $as_dummy
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_CLANG="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  test -z "$ac_cv_path_CLANG" && ac_cv_path_CLANG="no"
+  ;;
+esac
+fi
+CLANG=$ac_cv_path_CLANG
+if test -n "$CLANG"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $CLANG" >&5
+$as_echo "$CLANG" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+if test "x$CLANG" = "xno"; then :
+  missing_required_runtime_prereq=yes
+fi
+#
+
 for ac_prog in gindent indent
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
@@ -19206,6 +19256,13 @@ if test "x$CLANG_FORMAT" = "xno"; then :
 $as_echo "$as_me: WARNING: You must install \`clang-format' before running C-Reduce." >&2;}
     CLANG_FORMAT=clang-format
 
+fi
+if test "x$CLANG" = "xno"; then :
+
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: You must install \`clang' before running C-Reduce." >&5
+$as_echo "$as_me: WARNING: You must install \`clang' before running C-Reduce." >&2;}
+    CLANG=clang
+
 fi
 
 if test "$missing_required_runtime_prereq" = "yes"; then :
diff --git a/configure.ac b/configure.ac
index cb7b4dd7..5aa5ae97 100644
--- a/configure.ac
+++ b/configure.ac
@@ -127,6 +127,10 @@ AC_ARG_VAR([CLANG_FORMAT], [`clang-format' (LLVM/Clang) program])
 AC_PATH_PROG([CLANG_FORMAT], [clang-format], [no], [$LLVM_BINDIR:$PATH])
 AS_IF([test "x$CLANG_FORMAT" = "xno"], [missing_required_runtime_prereq=yes])
 #
+AC_ARG_VAR([CLANG], [`clang' (LLVM/Clang) program])
+AC_PATH_PROG([CLANG], [clang], [no], [$LLVM_BINDIR:$PATH])
+AS_IF([test "x$CLANG" = "xno"], [missing_required_runtime_prereq=yes])
+#
 AC_ARG_VAR([INDENT], [`indent' program])
 AC_PATH_PROGS([INDENT], [gindent indent], [no])
 AS_IF([test "x$INDENT" = "xno"], [missing_optional_runtime_prereq=yes])
@@ -163,6 +167,11 @@ AS_IF([test "x$CLANG_FORMAT" = "xno"],
     AC_MSG_WARN([You must install `clang-format' before running C-Reduce.])
     CLANG_FORMAT=clang-format
   ])
+AS_IF([test "x$CLANG" = "xno"],
+  [
+    AC_MSG_WARN([You must install `clang' before running C-Reduce.])
+    CLANG=clang
+  ])
 
 AS_IF([test "$missing_required_runtime_prereq" = "yes"],
   AC_MSG_WARN([Read the INSTALL file for info about C-Reduce dependencies.]))
diff --git a/creduce/CMakeLists.txt b/creduce/CMakeLists.txt
index 7ada4459..c1fb3585 100644
--- a/creduce/CMakeLists.txt
+++ b/creduce/CMakeLists.txt
@@ -51,6 +51,15 @@ if(NOT CLANG_FORMAT)
   set(missing_required_runtime_prereq "yes")
 endif()
 
+find_program(CLANG
+  "clang${CMAKE_EXECUTABLE_SUFFIX}"
+  PATHS "${LLVM_TOOLS_BINARY_DIR}"
+  )
+if(NOT CLANG)
+  message(STATUS "`clang${CMAKE_EXECUTABLE_SUFFIX}' was not found")
+  set(missing_required_runtime_prereq "yes")
+endif()
+
 find_program(INDENT
   NAMES
     "gindent${CMAKE_EXECUTABLE_SUFFIX}"
@@ -143,6 +152,11 @@ if(NOT CLANG_FORMAT)
   set(CLANG_FORMAT "clang-format")
 endif()
 
+if(NOT CLANG)
+  message("You must install `clang' before running C-Reduce.")
+  set(CLANG "clang")
+endif()
+
 if(missing_required_runtime_prereq STREQUAL "yes")
   message("Read the INSTALL file for info about C-Reduce dependencies.")
 endif()
@@ -224,6 +238,8 @@ string(REPLACE "\@ASTYLE@" "${ASTYLE}"
   CREDUCE_CONTENT "${CREDUCE_CONTENT}")
 string(REPLACE "\@CLANG_FORMAT@" "${CLANG_FORMAT}"
   CREDUCE_CONTENT "${CREDUCE_CONTENT}")
+string(REPLACE "\@CLANG@" "${CLANG}"
+  CREDUCE_CONTENT "${CREDUCE_CONTENT}")
 string(REPLACE "\@INDENT@" "${INDENT}"
   CREDUCE_CONTENT "${CREDUCE_CONTENT}")
 file(WRITE
@@ -263,6 +279,9 @@ add_custom_target(Modules ALL
   COMMAND ${CMAKE_COMMAND} -E copy_if_different
     ${PROJECT_SOURCE_DIR}/pass_comments.pm
     ${PROJECT_BINARY_DIR}
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    ${PROJECT_SOURCE_DIR}/pass_defines.pm
+    ${PROJECT_BINARY_DIR}
   COMMAND ${CMAKE_COMMAND} -E copy_if_different
     ${PROJECT_SOURCE_DIR}/pass_include_includes.pm
     ${PROJECT_BINARY_DIR}
diff --git a/creduce/Makefile.am b/creduce/Makefile.am
index d845bfa1..3e69d550 100644
--- a/creduce/Makefile.am
+++ b/creduce/Makefile.am
@@ -24,6 +24,7 @@ dist_perllib_DATA = \
 	pass_clang_binsrch.pm \
 	pass_clex.pm \
 	pass_comments.pm \
+	pass_defines.pm \
 	pass_include_includes.pm \
 	pass_includes.pm \
 	pass_indent.pm \
@@ -87,6 +88,7 @@ creduce_config_edit = sed \
 	-e 's|@GIT_HASH[@]|$(GIT_HASH)|g' \
 	-e 's|@ASTYLE[@]|$(ASTYLE)|g' \
 	-e 's|@CLANG_FORMAT[@]|$(CLANG_FORMAT)|g' \
+	-e 's|@CLANG[@]|$(CLANG)|g' \
 	-e 's|@INDENT[@]|$(INDENT)|g'
 
 creduce_config.pm: Makefile git_version.txt
diff --git a/creduce/Makefile.in b/creduce/Makefile.in
index a6002464..317f3e60 100644
--- a/creduce/Makefile.in
+++ b/creduce/Makefile.in
@@ -176,6 +176,7 @@ CC = @CC@
 CCDEPMODE = @CCDEPMODE@
 CFLAGS = @CFLAGS@
 CLANG_FORMAT = @CLANG_FORMAT@
+CLANG = @CLANG@
 CPP = @CPP@
 CPPFLAGS = @CPPFLAGS@
 CXX = @CXX@
@@ -315,6 +316,7 @@ dist_perllib_DATA = \
 	pass_clang_binsrch.pm \
 	pass_clex.pm \
 	pass_comments.pm \
+	pass_defines.pm \
 	pass_include_includes.pm \
 	pass_includes.pm \
 	pass_indent.pm \
@@ -369,6 +371,7 @@ creduce_config_edit = sed \
 	-e 's|@GIT_HASH[@]|$(GIT_HASH)|g' \
 	-e 's|@ASTYLE[@]|$(ASTYLE)|g' \
 	-e 's|@CLANG_FORMAT[@]|$(CLANG_FORMAT)|g' \
+	-e 's|@CLANG[@]|$(CLANG)|g' \
 	-e 's|@INDENT[@]|$(INDENT)|g'
 
 CLEANFILES = \
diff --git a/creduce/creduce.in b/creduce/creduce.in
index ee86f24d..3da3831a 100644
--- a/creduce/creduce.in
+++ b/creduce/creduce.in
@@ -755,8 +755,9 @@ my @all_methods = (
 
     { "name" => "pass_include_includes", "arg" => "0",               "pri" => 100, },
     { "name" => "pass_includes", "arg" => "0",                                      "first_pass_pri" =>  0, },
-    { "name" => "pass_unifdef",  "arg" => "0",                       "pri" => 450,  "first_pass_pri" =>  0, },
-    { "name" => "pass_comments", "arg" => "0",                       "pri" => 451,  "first_pass_pri" =>  0, },
+    { "name" => "pass_defines",  "arg" => "0",                       "pri" => 450,  "first_pass_pri" =>  0, },
+    { "name" => "pass_unifdef",  "arg" => "0",                       "pri" => 451,  "first_pass_pri" =>  0, },
+    { "name" => "pass_comments", "arg" => "0",                       "pri" => 452,  "first_pass_pri" =>  0, },
     { "name" => "pass_blank",    "arg" => "0",                                      "first_pass_pri" =>  1, },
     { "name" => "pass_clang_binsrch",    "arg" => "replace-function-def-with-decl", "first_pass_pri" =>  2, },
     { "name" => "pass_clang_binsrch",    "arg" => "remove-unused-function",         "first_pass_pri" =>  3, },
diff --git a/creduce/creduce_config.pm.in b/creduce/creduce_config.pm.in
index 07333cc6..150d3104 100644
--- a/creduce/creduce_config.pm.in
+++ b/creduce/creduce_config.pm.in
@@ -33,6 +33,7 @@ use constant {
     #
     ASTYLE		=> q{@ASTYLE@},
     CLANG_FORMAT	=> q{@CLANG_FORMAT@},
+    CLANG		=> q{@CLANG@},
     INDENT		=> q{@INDENT@},
 };
 
@@ -49,6 +50,7 @@ our @EXPORT_OK = qw(
     GIT_VERSION
     ASTYLE
     CLANG_FORMAT
+    CLANG
     INDENT
     );
 our %EXPORT_TAGS = qw();
diff --git a/creduce/pass_defines.pm b/creduce/pass_defines.pm
new file mode 100644
index 00000000..ea4d1f7f
--- /dev/null
+++ b/creduce/pass_defines.pm
@@ -0,0 +1,148 @@
+## -*- mode: Perl -*-
+##
+## Copyright (c) 2016 The University of Utah
+## Copyright (c) 2016 Ori Brostovski <ori@ceemple.com>, <oribrost@gmail.com>
+## Copyright (c) 2016 Ceemple Software Ltd
+##
+## All rights reserved.
+##
+## This file is distributed under the University of Illinois Open Source
+## License.  See the file COPYING for details.
+
+###############################################################################
+# test run with:  creduce --no-cache --n 1 --no-default-passes --add-pass pass_defines 0 0 `which true` bubu
+
+package pass_defines;
+
+use strict;
+use warnings;
+
+use File::Compare;
+use creduce_utils;
+
+my $clang;
+
+sub backslash_x ($) { 
+    return sprintf("\\x%X", ord($_[0])); 
+}
+
+sub check_prereqs () {
+    $clang =
+        find_external_program(creduce_config::CLANG, "clang");
+    return defined ($clang);
+}
+
+sub new ($$) {
+    my $flag = 0;
+    return \$flag;
+}
+
+sub advance ($$$) {
+    (my $cfile, my $arg, my $state) = @_;
+    my $flag = ${$state};
+    $flag = 1;
+    return \$flag;
+}
+
+sub advance_on_success ($$$) {
+    (my $cfile, my $arg, my $state) = @_;
+    return $state;    
+}
+sub addI ($) { 
+    return "-I" . $_[0]; 
+};
+
+sub do_transform ($) {
+    (my $cfile) = @_;
+    my $suffix = substr($cfile,rindex($cfile,"."));
+
+    open INF, "<$cfile" or die;
+    my $tmpfile1 = File::Temp::tmpnam() . $suffix;
+    open TF1, ">$tmpfile1" or die;
+    my $tmpfile2 = File::Temp::tmpnam() . $suffix;
+    my $tmpfile3 = File::Temp::tmpnam() . $suffix;
+    my $index = 0;
+    
+    while (my $line = <INF>) {
+        if ($line =~ m/^\s*#\s*include/) {
+            my $sline = $line;
+            $sline =~ s/([^a-zA-Z0-9])/backslash_x($1)/ge;
+            print TF1 "char *__creduce_before_include_" . $index . " = \"$sline\";\n";
+            print TF1 $line;
+            print TF1 "char *__creduce_after_include_" . $index . " = \"$sline\";\n";
+        } else {
+            print TF1 $line;
+        }
+    }
+    close TF1;
+    close INF;
+    
+    my $iargs = "";
+    if (exists $ENV{CREDUCE_INCLUDE_PATH}) {
+        my @args = split(/:/,$ENV{CREDUCE_INCLUDE_PATH});
+        $iargs = "";
+        foreach my $iarg (@args) {
+            $iargs = $iargs . " -I" . $iarg;
+        }
+    }
+    my $lang_arg = "";
+    if (exists $ENV{CREDUCE_LANG}) {
+        if ($ENV{CREDUCE_LANG} eq "CXX") {
+            $lang_arg = "-x c++";
+        } elsif ($ENV{CREDUCE_LANG} eq "C") {
+            $lang_arg = "-x c"
+        }
+    }
+    system("$clang -Wno-pragma-system-header-outside-header -E $lang_arg " .
+           "$iargs $tmpfile1 -o $tmpfile2");
+
+    unless (open TF2, "<$tmpfile2") {
+        return 0;
+    }
+    open OUTF, ">$tmpfile3" or die;
+    my $in_include = 0;
+    while (my $line = <TF2>) {
+        if ($in_include) {
+            if ($line =~ m/^char \*__creduce_after_include/) {
+                $in_include = 0;
+            }
+        } else {
+            if ($line =~ m/^char \*__creduce_before_include.*= \"(.*)\"/) {
+                my $value = $1;
+                $value =~ s/\\xA$/\n/;
+                $value =~ s/\\x(..)/chr(hex($1))/ge;
+                print OUTF $value;
+                $in_include = 1;
+            } elsif ($line !~ /^# /) {
+                print OUTF $line;
+            }
+        }
+    }
+    close OUTF;
+    close TF2;
+
+    unlink $tmpfile1;
+    unlink $tmpfile2;
+
+    if (compare($tmpfile3, $cfile)) {
+        File::Copy::move($tmpfile3, $cfile);
+        return 1;
+    } else {
+        unlink $tmpfile3;
+        return 0;
+    }
+}
+
+sub transform($$$) {
+    (my $cfile, my $arg, my $state) = @_;
+    my $flag = ${$state};
+
+    if ($flag) {
+        return ($STOP, \$flag);
+    }
+    
+    my $success = do_transform($cfile);
+    return ($success ? $OK : $STOP, \$flag);
+}
+
+1;