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Date: Wed, 10 Jun 2015 07:42:30 -0700
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To: Matt Wilmas <php_lists@realplain.com>
Cc: Dmitry Stogov <dmitry@php.net>, Stanislav Malyshev <smalyshev@gmail.com>, 
	PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Undefined variables undefined order
From: pollita@php.net (Sara Golemon)

On Tue, Jun 9, 2015 at 6:05 AM, Matt Wilmas <php_lists@realplain.com> wrote:
> Hah, looks like this just changed last week after barely 3 weeks. :-P  I
> didn't verify, just noticed the code change:
> http://git.php.net/?p=php-src.git;a=commitdiff;h=c09698753e7d1d95299dca54c8ca888c885fd45b
>
Dmitry, what's the reasoning behind this diff in the first place?
Doesn't the compiler fold (<const-string> . <const-string>) already
anyhow?  How would we wind up with CONCAT_CONST_CONST at runtime?

> Now CONCAT is consistent, but not others.  Which places need changing
> anyway?  Just binary ops in VM?
>
> A couple/few extra instructions are unavoidable, I guess on any
> architecture, for the intermediate save of op1, but can anyone show that it
> makes ANY measurable difference (other than instruction count)?
>
I'm 90% certain that fixing the ordering (by saving to a temp var)
doesn't *actually* result in extra instructions.  GCC's optimizer is
pretty clever.  It'll notice you're only writing to the temp var once,
and reading from it once (immediately), so it'll end up organizing the
instructions in a way which satisfies the explicit order, but as an
inline call.

-Sara