[LLVMdev] Jit singleton

[Jeffrey Yasskin]

I've committed this as
http://llvm.org/viewvc/llvm-project?view=rev&revision=95837. Thanks
again!

On Wed, Feb 10, 2010 at 10:11 AM, Olivier Meurant
<meurant.olivier at gmail.com> wrote:
> Thanks Jeffrey !
>
> If possible, keep me inform (on revision number), I'm interested to see how
> you will do the unit test. (For my future patch... :) ).
>
> Thanks again.
> Olivier.
>
>
> On Wed, Feb 10, 2010 at 6:22 PM, Jeffrey Yasskin <jyasskin at google.com>
> wrote:
>>
>> Thanks for the patch! I'll clean this up, convert your sample to a
>> unit test, and commit it for 2.7.
>>
>> On Sun, Feb 7, 2010 at 6:09 AM, Olivier Meurant
>> <meurant.olivier at gmail.com> wrote:
>> > Hi Jeffrey,
>> >
>> > Thanks for pointing me in the right direction !
>> > I'm not using the JIT in lazy mode, but it was fun to understand the
>> > lazy-stub code.
>> >
>> > Attached you will find a patch which follow your 1st option : a map
>> > Stub_address -> JITResolver instance, except that the used map is a
>> > "std::map" to apply the same upper_bound trick as in the map
>> > CallSiteToFunctionMap of the ResolverState. (If it is necessary for
>> > call_site -> function, this should be necessary for call_site ->
>> > resolver...
>> > Event if I'm not sure to master all subtle reasons - code
>> > alignment/prologue
>> > ?)
>> > A mutex on the StubToResolverMap should prevent any possible race
>> > conditions.
>> >
>> > Every object (Emitter, Resolver, ResolverState) have now a private
>> > member
>> > instance of JIT (JIT *Jit).
>> >
>> > The bugpoint tool is using a extern 'C' function :
>> > "getPointerToNamedFunction" to get native pointer on function. This
>> > function
>> > used the TheJit static pointer. To keep alive this functionality, I have
>> > added a static SmallVector<JIT*> JitPool (with its mutex JitPoolLock),
>> > which
>> > keep pointers of available JIT instance. A new static method on JIT
>> > object
>> > "getPointerToNamedFunctionOnJitPool" fills the need (iterate over
>> > available
>> > JIT to find the function).
>> >
>> > Attached you will find a test, based on "HowToUseJit" example, which
>> > instantiate 2 JIT, in eager/lazy mode and retrieve native pointer via
>> > getPointerToNamedFunction function. Where does it belong ? Should I add
>> > something to llvm test suite ? To the test directory ?
>> >
>> > Let me know what you think !
>> > Thanks.
>> >
>> > Olivier.
>> >
>> > On Thu, Feb 4, 2010 at 9:03 PM, Jeffrey Yasskin <jyasskin at google.com>
>> > wrote:
>> >>
>> >> In eager compilation mode, I don't know of anything that would go
>> >> wrong with having multiple JITs in the process. However, in lazy
>> >> compilation mode, we need to map stub addresses to the JIT that knows
>> >> how to compile them. Right now, that's done by looking up the static
>> >> "TheJITResolver" variable and assuming it's the only JIT, but we could
>> >> 1) use a static DenseMap<stub_address, JITResolver*> instead, or 2)
>> >> include the JITResolver* inside the stub as an argument to the
>> >> compilation callback. Nobody's needed this enough to get it working
>> >> though.
>> >>
>> >> I think it'd make some sense to fix it for eager compilation even
>> >> before getting lazy compilation working. Would you like to write a
>> >> patch? You'll have to remove all uses of TheJIT and TheJITResolver
>> >> except for the one in JITResolver::JITCompilerFn, and change the "only
>> >> one JIT" check to say something about "only one JIT compiling lazily".
>> >>
>> >> I don't think this change will require passing an LLVMContext to the
>> >> JIT--it should just use the Context of the function it's jitting.
>> >>
>> >> The code freeze for llvm-2.7 is on Feb 21 (this probably isn't a
>> >> "major" change), so if you want it in the 2.7 release, please try to
>> >> mail the patch well ahead of that.
>> >>
>> >> On Thu, Feb 4, 2010 at 5:47 AM, Olivier Meurant
>> >> <meurant.olivier at gmail.com> wrote:
>> >> > Hi everyone !
>> >> >
>> >> > If I call ExecutionEngine::createJIT (or EngineBuilder::create) more
>> >> > than
>> >> > one time, the second time fails on a assertion "Multiple JIT
>> >> > resolvers?".
>> >> > It seems that the JIT is designed to be a singleton in the process,
>> >> > and
>> >> > I
>> >> > was wondering if it was something mandatory.
>> >> > How hard will it be to make it a non-singleton object ? Is this a
>> >> > JIT-only
>> >> > problem (work needed on JIT classes only) ? Is it a much wider design
>> >> > constraint (on codegen ?) ?
>> >> >
>> >> > In case, if you ask why I want to create more than one JIT, here is a
>> >> > reason
>> >> > :
>> >> > I have a JIT application which works fine, a thread is responsible to
>> >> > prepare code execution (work on module, add functions, optimize, call
>> >> > JIT...) and a another thread is responsible for executing the code
>> >> > produced
>> >> > in the first thread.
>> >> > It works great, but the preparation thread is heavily loaded. I
>> >> > decide
>> >> > to
>> >> > look at what happens, if I spawns 2 threads for preparation of the
>> >> > code.
>> >> > I have a working prototype, which have one module and one context by
>> >> > thread,
>> >> > and it works. But the JIT is still shared between 2 threads and the
>> >> > time
>> >> > needed to emit a function is not negligible. It will be a great boost
>> >> > of
>> >> > performances, if I can create one execution engine by thread.
>> >> >
>> >> > What do you think ? Do you have any comments on it ?
>> >> > Thanks for reading !
>> >> >
>> >> > Olivier.
>> >> >
>> >> > _______________________________________________
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>> >> >
>> >> >
>> >
>> >
>
>