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Date: Thu, 10 Jan 2008 15:36:18 -0800
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Thread-Topic: php-5.2.3: zend_opcode.c: pass_two() question
Thread-Index: AchT4ZmYy5CpBNS3T8GcO9WScZ6tFA==
To: <internals@lists.php.net>
Subject: php-5.2.3: zend_opcode.c: pass_two() question
From: Kannan@facebook.com ("Kannan Muthukkaruppan")

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An example assignment such as:=20
        $x =3D 10;
doesn't seem to get handled as a simple ref-count incrementing
assignment (in zend_assign_to_variable()). Instead, $x ends up getting a
new "zval" into which a=20
copy of the RHS (10) is made.
=20
This seems to be because the zval/znode corresponding to the literal 10
is an  IS_CONST operand of the assignment opcode. And, during the end of
compilation of a function, the IS_CONST operands in the function's
op_array are patched up as "references" (is_ref is set to 1).
=20
zend_opcode.c:pass_two()=20
  ...
 while (opline < end) {
  if (opline->op1.op_type =3D=3D IS_CONST) {
   opline->op1.u.constant.is_ref =3D 1;
   opline->op1.u.constant.refcount =3D 2; /* Make sure is_ref won't be
reset */
  }
  if (opline->op2.op_type =3D=3D IS_CONST) {
   opline->op2.u.constant.is_ref =3D 1;
   opline->op2.u.constant.refcount =3D 2;
  }
   ...=20
=20
And zend_assign_to_variable(), when it sees the RHS to be a reference
("is_ref =3D=3D 1") ends up doing a copy rather than a ref-count
incrementing assignment.=20
=20
It seems like performance would be better if we didn't mark constant
operands as "references" in pass_two(). But presumably it is required to
handle some cases that'll otherwise break? I am trying to understand
what those cases are.  If someone can shed further light on this issue,
it is much appreciated...
=20
regards,
Kannan Muthukkaruppan

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