1. not all opcode is catched by coverage at runtime
   a.php
   <?php

xdebug_start_code_coverage(XDEBUG_CC_UNUSED);
include("b.php");
?>

b.php
<?php

$a = "";
$a =
""
. "abc{$a}abc"
. "abc"
;
$cov = xdebug_get_code_coverage();
print_r($cov);

?>
result:
Array
(
[/home/xuefer/htdocs/skydotnet_php5/matrix/debug/test/a.php] => Array
(
[4] => 1
)

[/home/xuefer/htdocs/skydotnet_php5/matrix/debug/test/abc.php] => Array
    (
        [3] => 1
        [6] => 1
        [7] => -1
        [8] => -1
        [9] => 1
        [10] => -1
        [13] => -1
    )

)

at least
[7] => -1
[8] => -1
should be both 1

2. i'd suggest -1 to be 0
3. very slow with XDEBUG_CC_UNUSED, xdebug_prefil_code_coverage() is executed no matter if the op_array is done before.
   suggested fix:
   a. move it to xdebug_compile_file()
   b. add a hash (by pointer) that avoid re-fill the same op_array, but the file included before xdebug_start_code_coverage is will not be prefilled
   c. when xdebug_get_code_coverage(XDEBUG_CC_UNUSED), loop though all the op_array(file/function/class method) for xdebug_prefil_code_coverage(), it could be a bit hard to get the file op_array