I would be surprised if the BURM is faster than a simple top-down walk.
The main advantage of using a BURM is that it allows for optimizations to be
easily coded as alternate reductions with lower cost. Typically there are many
difference sequences of bottom-up reductions that could be applied to reduce
the tree, and the BURM actually computes the *lowest-cost* sequence out of all
possible sequences. (It is solving a complicated optimization problem, although
in an efficient way.)
As a trivial example, in addition to writing a reduction for
expression + expression
that reduces
a + b
to instructions like
push a
push b
add
and
1 + 2
to (inefficient) instructions like
push 1
push 2
add
you can write a reduction for
constant + constant
and assign it a lower "cost" so that
1 + 2
reduces to
push 3
In the case of JavaScript, I'll bet that today's JavaScript engines are good at
doing various optimizations, so I don't see why an AS->JS cross-compiler needs
to do them in advance using a BURM.
- Gordon
-----Original Message-----
From: Alex Harui [mailto:aha...@adobe.com]
Sent: Friday, December 14, 2012 10:34 AM
To: flex-dev@incubator.apache.org
Subject: Re: [FalconJx] Prototype ActionScript -> JavaScript compiler code up
in svn
On 12/14/12 10:04 AM, "Michael Schmalle" <apa...@teotigraphix.com> wrote:
>
> Quoting Alex Harui <aha...@adobe.com>:
>
>>
>>
>>
>> On 12/14/12 4:24 AM, "Erik de Bruin" <e...@ixsoftware.nl> wrote:
>>
>>> Dude,
>>>
>>> "goog" it is.
>>>
>>> I just needed a little pep-talk, I guess ;-)
>> Right now, I'm trying to get FalconJS to compile an MXML file and
>> output the goog stuff. That work got delayed because there were more
>> distractions from the 4.9 release than I expected. Then I will try
>> to get the BURM/Reducer/Emitter to do the same. Mike sent me what he
>> tried to do in this area so I can reference it if needed.
>>
>> We are definitely in prototype/research mode and different angles
>> should be investigated. The key to the "Apache Way" is that if we
>> have to make choices in deciding what to ship, it should be done on
>> technical merit.
>
> What context are you speaking from? compiler, js framework?
In theory, everything in Apache is decided on technical merit. If your version
of AS to JS turns out to be faster and easier to maintain, it will win.
It will be interesting to figure out what to do if the BURM version is
significantly faster, but my gut says that won't be the case.
--
Alex Harui
Flex SDK Team
Adobe Systems, Inc.
http://blogs.adobe.com/aharui
