Compiling the XP framework

Lately I was experimenting with the PHP extension bcompiler, which offers an API to write the opcodes generated from zend_compile() to files. For a general understanding of this you must know that PHP is a compiled language (but does compilation into memory and then executes that instead of compiling to disk and then running that). The compilation step is not exposed to the user in any way, and there is no defined serialization format for compiled PHP. This is where bcompiler comes in.

Note: Compiling PHP sourcecode does not improve runtime performance, it simply saves the (small) overhead generated by the compile step. My main focus in this experiment was not performance, though, but to test the ability to generate PHP bytecode, and if that would work transparently alongside PHP sourcecode.

<?php 
  $a= 'Hello'; 
  echo $a;
?>

1. Tokenize the sourcecode
   Basically what is exposed by the token_get_all() function the above is parsed into: T_VARIABLE[$a] '=' T_CONSTANT_ENCAPSED_STRING['Hello'] ';' T_ECHO T_VARIABLE[$a] ';'.
   
2. Give these tokens to the parser
   The (yacc-generated) parser will match these tokens to the grammar and generate bytecodes while doing so. The first statement is matched to the following rule: variable '=' expr { zend_check_writable_variable(&$1); zend_do_end_variable_parse(BP_VAR_W, 0 TSRMLS_CC); zend_do_assign(&$$, &$1, &$3 TSRMLS_CC); }
   
3. Populate the opcode array
   The above zend_*() function calls produce opcodes and add them to an opcode array.
   

   
       # line name                 operands
      -- ---- ----------------     --------------------------------------
       0@  1: assign               CV[#1 $a] := C[string:"Hello"] (*V[#0])
       1@  2: echo                 CV[#1 $a]
       2@  3: return               C[null]
       3@  3: handle_exception
   

4. Execute this
   For each opcode, the zend engine has an opcode handler that will execute the opcode. The first opcode will be taken care of by the ZEND_ASSIGN handler and will basically do something like $locals['a']= 'Hello';, the second by ZEND_ECHO ($print_function($locals['a'])), and so on.

<?php 
  $f= fopen('compiled.phb', 'wb');
  bcompiler_write_header($f);
  bcompiler_write_file($f, 'source.php');
  bcompiler_write_footer($f);
  fclose($f);
?>

<?php 
  include('compiled.phb');
  include('source.php');
?>

<?php 
  $archive= new Archive(new File('xp-compiled.xar'));
  $archive->open(ARCHIVE_CREATE);
  
  $filter= new NegationOfFilter(new AnyOfFilter(array(
    new CollectionFilter(),
    new RegexFilter('/.svn/')
  )));
  
  foreach (new FilteredIOCollectionIterator($origin, $filter, TRUE) as $e) {
    if (xp::CLASS_FILE_EXT === substr($e->getUri(), -10)) {
      // Compile and add to XAR
    } else {
      // Add to XAR as-is
  }
  
  $archive->create();
?>

<?php 
  // Before the loop
  $compiler= new Process(
    Runtime::getInstance()->getExecutable()->getFilename(), 
    array('compiler.php', $build)
  );
  
  // Inside the loop
  $compiler->in->write($filename);
  sscanf($compiler->out->readLine(), "%c %[^\n]", $status, $data);
  if ('+' !== $status) {
    // Compile error
  }
  
  // compiler.php
  while ($l= fgets(STDIN, 1024)) {
    $name= rtrim($l);
    $temp= tempnam($argv[1], 'comp');
    
    // ... Compile it, handling errors ...
    
    echo '+ ', $temp, "\n";
  }
?>

  $ xar tvf rel/xp-compiled.xar
    33.869 lang/archive/Archive.class.php
    29.443 lang/archive/ArchiveClassLoader.class.php
    21.031 lang/archive/ArchiveReader.class.php
       525 lang/archive/package-info.xp
    10.011 lang/ChainedException.class.php
  [...]

<?php 
  /**
   * Customer service handler
   *
   */
  class CustomerHandler extends Object {
  
    /**
     * Gets a customer by customer ID
     *
     * @param   int id
     * @return  com.example.vo.Customer
     * @throws  util.NoSuchElementException in case nothing is found
     */
    #[@webmethod]
    public function getCustomer($id) {
      // ...
    }
  }
?>

{
  fields  => []
  methods => [
    getCustomer => [
      ARGUMENTS    => [ "int" ],
      RETURNS      => "com.example.vo.Customer"
      THROWS       => [ "util.NoSuchElementException" ]
      COMMENT      => "Gets a customer by customer ID"
      ANNOTATIONS  => [ webmethod => null ]
      NAME         => "getCustomer"
    ]
  ]
  class   => [
    COMMENT        => "Customer service handler"
    ANNOTATIONS    => []
  ]
}

<?php 
  function implode($delim, array $input) {
    // ...
  }
?>

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