[LLVMdev] Jit singleton
jyasskin at google.com
Wed Feb 10 09:22:23 PST 2010
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
> 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 !
> 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
>> 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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