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Date: Fri, 16 Jan 2015 08:56:59 +0100
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Subject: [PHP-DEV] Generating more efficient code for while-loop
From: ben.coutu@zeyos.com (Benjamin Coutu)

Hello,=0A=0APlease consider the following PHP code:

while ( <CONDITION> ) {
  <STATEMENT>=0A}

It currently compiles to something like this for the Zend Engine:

0: <CONDITION>=0A1: JMPZ -> 4
2: <STATEMENT>=0A3: JMP -> 0
4: ...=0A
This can easily be rewritten in an equivalent but much more efficient form:

0: JMP -> 2
1: <STATEMENT>
2: <CONDITION>
3: JMPNZ -> 1

The trick is to jump to the conditional expression before the first iterati=
on and then only having to continue with just on conditional jump on every =
subsequent cycle.=0A=0AThis would result in only 1 jump per loop iteration =
compared to effectively 2 jumps needed per iteration with the current imple=
mentation.
=0AIt would also make the loop tighter as upon entering the loop (after fir=
st conditional evaluation), one less opcode remains relevant to the loop.=
=0A=0AAn analogous approach can be taken for the for-loop.=0A=0AThanks,=0A=
=0ABen=0A=0APS: This is my first post on a PHP mailinglist - I am very exci=
ted! :)=0A=0A-- =0A=0ABenjamin Coutu=0AZeyon Technologies Inc.=0Ahttp://www=
.zeyos.com