[LLVMdev] Should LLVM JIT default to lazy or non-lazy?

[Jeffrey Yasskin]

On Wed, Oct 28, 2009 at 9:57 AM, Jeffrey Yasskin <jyasskin at google.com> wrote:
> On Wed, Oct 28, 2009 at 9:50 AM, Chris Lattner <clattner at apple.com> wrote:
>>
>> On Oct 28, 2009, at 9:41 AM, Jeffrey Yasskin wrote:
>>
>>> In r85295, in response to the discussion at http://llvm.org/PR5184
>>> (Lazy JIT ain't thread-safe), I changed the default JIT from lazy to
>>> non-lazy. It has since come to my attention that this may have been
>>> the wrong change, so I wanted to ask you guys.
>>>
>>> A couple reasons to make the default non-lazy compilation:
>>> * The lack of thread-safety surprises new users
>>> * Crashes due to this will be rare and so hard to track down
>>> * The current lazy scheme is almost never the right answer for performance
>>> * It's only one line of code to turn on lazy compilation when it is
>>> the right answer for you.
>>>
>>> And a couple to default to lazy compilation:
>>> * It's safe for single-threaded code.
>>> * There are existing users who have assumed this default.
>>> * PPC and ARM don't support non-lazy compilation yet (the tests
>>> currently run the lazy jit).
>>> * Gratuitous changes are bad.
>>
>> If the objection was about changing the sense of a magic bool, why not
>> change the argument to be an enum instead?  That should make it extremely
>> clear in the source what behavior is desired.
>
> No, the magic bools all keep the same sense. The change affects the
> behavior of programs without a call to
> JIT->DisableLazyCompilation(bool). Anyone who's already calling it
> with any parameter keeps their current behavior.

... but I'd be perfectly happy to rename that function and have it
take an enum instead.