Object getter method optimization

9 years ago by Lin Yo-An — view source

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Hello Everyone,

I am recently trying to write an optimizer that could optimize the getter
method call into just one object fetch opcode.

I'd like to know thoughts from you guys, here is the note:
https://c9s.hackpad.com/INLINE-OP-TVGo9WcshbZ

--
Best Regards,

Yo-An Lin
https://github.com/c9s

9 years ago by Dmitry Stogov — view source

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Hi Yo-An Lin,

Unfortunately, this approach won't work.
At first, at compile time we don't know the body of called getter.
At second, the called method might be changed even at run-time, because of polymorphism.

Tricks like this might be implemented using JIT and polymorphic inline caches.

Thanks. Dmitry.

9 years ago by Lin Yo-An — view source

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Hi Dmitry,

Thanks for your reply! You're correct. let me try to explain your points:

If I have a main.php and worker.php

And I defined work($worker) { $status = $worker->getStatus(); } inside
main.php

when main.php is compiled, we don't know what the class entry of $worker
is. What we only know is invoking a method "getStatus" on $worker CV unless
we know we have to compile worker.php before main.php and add a type hint
on $worker.

Is it correct?

Since the original approach doesn't work, here comes another new idea:

When executing method call on an object, if we found the method body are
just 2 op codes (FETCH_OBJ_R and RETURN), we then denote the method is a
"getter method"

And the next time, when we execute the same method, we found the "getter
method" flag, we simply execute FETCH_OBJ_R on that object and return the
value to avoid extra op code execution time.

Do you think if this could work?

Best Regards and Thanks for your work on PHP VM
Yo-An Lin

Hi Yo-An Lin,

Unfortunately, this approach won't work.
At first, at compile time we don't know the body of called getter.
At second, the called method might be changed even at run-time, because of
polymorphism.

Tricks like this might be implemented using JIT and polymorphic inline
caches.

Thanks. Dmitry.

From: Lin Yo-An cornelius.howl@gmail.com
Sent: Friday, March 18, 2016 05:23
To: internals
Subject: [PHP-DEV] Object getter method optimization

Hello Everyone,

I am recently trying to write an optimizer that could optimize the getter
method call into just one object fetch opcode.

I'd like to know thoughts from you guys, here is the note:
https://c9s.hackpad.com/INLINE-OP-TVGo9WcshbZ

--
Best Regards,

Yo-An Lin
https://github.com/c9s

--
Best Regards,

Yo-An Lin

9 years ago by Andrea Faulds — view source

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Hi Lin,

Lin Yo-An wrote:

Since the original approach doesn't work, here comes another new idea:

When executing method call on an object, if we found the method body are
just 2 op codes (FETCH_OBJ_R and RETURN), we then denote the method is a
"getter method"

And the next time, when we execute the same method, we found the "getter
method" flag, we simply execute FETCH_OBJ_R on that object and return the
value to avoid extra op code execution time.

Do you think if this could work?

For a while I'd also been wondering if we could implement some
implementation along these lines. Another approach could be possibly
replacing such methods with an C implementation (though I don't know if
non-internal classes can have internal methods).

I don't know how successful it will be, but I'm interested to hear how
much improvement it gives if you get it working.

Thanks!

--
Andrea Faulds
https://ajf.me/

9 years ago by Nikita Nefedov — view source

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Hi Lin,

Lin Yo-An wrote:

Since the original approach doesn't work, here comes another new idea:

When executing method call on an object, if we found the method body are
just 2 op codes (FETCH_OBJ_R and RETURN), we then denote the method is a
"getter method"

And the next time, when we execute the same method, we found the "getter
method" flag, we simply execute FETCH_OBJ_R on that object and return
the
value to avoid extra op code execution time.

Do you think if this could work?

For a while I'd also been wondering if we could implement some
implementation along these lines. Another approach could be possibly
replacing such methods with an C implementation (though I don't know if
non-internal classes can have internal methods).

I don't know how successful it will be, but I'm interested to hear how
much improvement it gives if you get it working.

Thanks!

I was playing with this idea sometime ago, it gives good performance boost
for code like for ($i = 0; $i < 100000; $i++) $a->getFoo(); but in the
end of the day it's a very limited optimization.
If you abstract away from getters and say you want to optimize more and
more small functions like this one, you end up realizing that what you're
actually doing is what JIT compilation would do in a more generic way.

9 years ago by Lin Yo-An — view source

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I was playing with this idea sometime ago, it gives good performance
boost for code like for ($i = 0; $i < 100000; $i++) $a->getFoo(); but in
the end of the day it's a very limited optimization.
If you abstract away from getters and say you want to optimize more and
more small functions like this one, you end up realizing that what you're
actually doing is what JIT compilation would do in a more generic way.

I agree with you that JIT could achieve this.

Although this could be done by JIT, however the JIT approach would require
good code generation to produce efficient getter code to return the
property value, and there will be a JIT threshold and extra compilation
time for caller to reach.

--

--
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9 years ago by Dmitry Stogov — view source

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Hi Yo-An Lin,

This "run-time inlining" approach may work.

PHP compiler (or optimizer) may mark functions and methods suitable for "run-time" inlining (e.g. methods without arguments and FETCH_OBJ_R UNUSED, CONST -> TMP; RETURN TMP).

Then INIT_METHOD_CALL may check this flag and execute "optimized code sequence" instead of pushing stack frame and real call.

However, I'm not sure what kind of performance impact this may make, because we will have to make additional check on each INIT_METHOD_CALL execution.

Thanks. Dmitry.