Discussion on Removal of Garbage Collector and other GCC Multi threaded Work

[Nicholas Krause]

On 2/27/20 3:02 PM, David Malcolm wrote:
> On Thu, 2020-02-27 at 14:07 -0500, Nicholas Krause wrote:
>> Greetings All,
>>
>> After doing some more research it seems that it may be time to
>> remove
>> the garbage collector. I'm
>> aware of the linkage to precompiled headers but even them I think
>> its
>> time due to two reasons:
>>
>> 1. The work related to multithreading gcc is working around the
>> global
>> state of the collector which
>> makes scaling less likely in terms of threads. In addition it is
>> causing   unnecessary compilations
>> in terms of workarounds in this project.
>>
>> 2. Memory usage may be decreased in certain passes due to being able
>> to
>> implement memory allocation
>> at a pass or per pass type level with more knowledge than a generic
>> garbage collector. I'm aware this
>> is done for a lot of passes. However it  could be done for the other
>> passes that are linked currently to the
>> garbage collector.
>>
>> I'm not sure what memory allocation strategies we want to implement
>> in
>> terms of replacing the garbage
>> collector but I think its time.
> Nick, you've sent various emails to this list suggesting big changes to
> GCC's codebase (updating from C++98 to C++11 is another one that
> springs to mind), but I believe you've yet to send the project an
> actual patch for anything.
 Â I did awhile but most of them were bug fixes on bugzilla. Not
sure if any got merged. Most of these days I doing research so
sorry about that. If your not familiar with it my work is here:
https://docs.google.com/document/d/1po_RRgSCtRyYgMHjV0itW8iOzJXpTdHYIpC9gUMjOxk/edit 

>
> It's great that you want to help, and that you have ideas about the
> high-level architecture of the project, but may I respectfully suggest
> you start with something *much* smaller and more concrete?   There are
> plenty of bugs in BZ that could use attention.
Of course this was to be long term :). Like the C++11 its more to
get others involved in planning for it. The change patch was
small for C++11. The problem really was testing and figuring out
language support which I helped out with.

Very sorry if your misunderstanding me or my work,
Nick
>
> Hope this is constructive
> David
>
>> On another I'm looking into the issues with PHI nodes and operators
>> as
>> to how to lock or decrease global
>> state there as this seems to be the biggest complication when I've
>> time.
>> In addition as Jeff stated we
>> will also want to encapsulate SSA operands and other SSA related
>> things
>> in a series of classes as part of
>> this.
>>
>>
>> Regards,
>> Nick
>>