Hey:
On Sat, Jan 17, 2015 at 2:14 AM, Benjamin Coutu <ben.co...@zeyos.com> wrote:
> Hi Dimitry,
>
> Thank you for the acknowledgment. I am a big fan of your work.
>
> I think adding the suggested changes to foreach will be a good improvement.
> With foreach one cold actually merge the jump-into-opcode (line 0 in the
> while-loop example) with FE_RESET.
>
> On another note, I think there are many simple compiler optimizations
> (without the need for real code analysis) that should now be possible,
> especially in light of AST. The following samples of common patterns come to
> mind:
>
> if/while (! ...)
> BOOL_NOT+JMPZ -> JMPNZ
>
> if/while ( ... &&/|| ... )
> BOOL+JMPZ -> JMPZ (BOOL is obsolete)
>
> case (...)
> CASE+JMPZ -> CASE (add JMPZ functionality to CASE operation)
>
> I understand that these aren't huge improvements per se, but they are very
> common and could at least help reduce the generated bytecode size (thinking
> OpCache).
I believe some of these works already be done in
opcache/Optimizer/block_pass.c based on CFG
thanks
>
> Cheers,
>
> Ben
>
> ========== Original ==========
> From: Dmitry Stogov <dmi...@zend.com>
> To: Benjamin Coutu <ben.co...@zeyos.com>
> Date: Fri, 16 Jan 2015 17:12:34 +0100
> Subject: Re: [PHP-DEV] Generating more efficient code for while-loop
>
> Hi Benjamin,
>
> Thanks for idea.
> With PHP7 AST compiler, it's quite easy to implement this (it took us 15
> minutes to try :)
> However, it doesn't make big improvement on our benchmarks.
> We will take a look into possibilities to apply your idea to other patterns
> (e.g. for and foreach loops).
>
> Anyway, it makes full sense to include this optimization into PHP7.
> I just like to try other opportunities first.
>
> Thanks. Dmitry.
>
> On Fri, Jan 16, 2015 at 10:56 AM, Benjamin Coutu <ben.co...@zeyos.com>
> wrote:
>
>> Hello,
>>
>> Please consider the following PHP code:
>>
>> while ( <CONDITION> ) {
>> <STATEMENT>
>> }
>>
>> It currently compiles to something like this for the Zend Engine:
>>
>> 0: <CONDITION>
>> 1: JMPZ -> 4
>> 2: <STATEMENT>
>> 3: JMP -> 0
>> 4: ...
>>
>> 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
>> iteration and then only having to continue with just on conditional jump on
>> every subsequent cycle.
>>
>> This would result in only 1 jump per loop iteration compared to
>> effectively 2 jumps needed per iteration with the current implementation.
>>
>> It would also make the loop tighter as upon entering the loop (after first
>> conditional evaluation), one less opcode remains relevant to the loop.
>>
>> An analogous approach can be taken for the for-loop.
>>
>> Thanks,
>>
>> Ben
>>
>> PS: This is my first post on a PHP mailinglist - I am very excited! :)
>>
>> --
>>
>> Benjamin Coutu
>> Zeyon Technologies Inc.
>> http://www.zeyos.com
>>
>>
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>> PHP Internals - PHP Runtime Development Mailing List
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>>
>>
>
--
Xinchen Hui
@Laruence
http://www.laruence.com/
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