llvm dev - Aug 2011 - [LLVMdev] Trouble using the MCJIT: "Target does not support MC emission" error

I'm trying to wire up some code to use the MC-based JIT; my understanding is
that it should be able to JIT AVX code (and that the regular JIT cannot). 
However, I'm getting the error "Target does not support MC
emission!" when I call EngineBuilder::create().  I assume that I'm just
not doing something necessary for initialization, but I'm not sure what it
would be--I am calling all of:

    llvm::InitializeNativeTarget();
    llvm::InitializeAllTargetMCs();
    LLVMLinkInMCJIT();
    LLVMLinkInJIT();

and the module I'm trying to load does have a reasonable target:

target triple = "x86_64-apple-darwin11.0.0"

I've attached a short test case that has the sequence of calls that I'm
making and one of the bitcode files I'm trying to use.  I'd be happy for
any guidance or suggestions.

Thanks,
-matt

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Hi Matt,

You may want to have a look at lli in the llvm codebase. It can use the MCJIT
for x86_64, so will have examples of all the setup required.

Do note, however, that the MCJIT is relatively feature limited at this point.
It's not (yet) a drop-in replacement for the old JIT.

-Jim

On Aug 25, 2011, at 4:16 AM, Matt Pharr wrote:
> I'm trying to wire up some code to use the MC-based JIT; my
understanding is that it should be able to JIT AVX code (and that the regular
JIT cannot).  However, I'm getting the error "Target does not support
MC emission!" when I call EngineBuilder::create().  I assume that I'm
just not doing something necessary for initialization, but I'm not sure what
it would be--I am calling all of:
> 
>    llvm::InitializeNativeTarget();
>    llvm::InitializeAllTargetMCs();
>    LLVMLinkInMCJIT();
>    LLVMLinkInJIT();
> 
> and the module I'm trying to load does have a reasonable target:
> 
> target triple = "x86_64-apple-darwin11.0.0"
> 
> I've attached a short test case that has the sequence of calls that
I'm making and one of the bitcode files I'm trying to use.  I'd be
happy for any guidance or suggestions.
> 
> Thanks,
> -matt
> 
> <a.bc><bug.cpp>_______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Hi Matt,

I am unsure about MCJIT, but I guess the problem is the same.
Just like when invoking llc, you need to pass the information to use AVX 
(llc -mattr=+avx).
I guess the corresponding code should look like this:

     llvm::EngineBuilder engineBuilder(module);
     engineBuilder.setErrorStr(&eeError);
     engineBuilder.setEngineKind(llvm::EngineKind::JIT);
     engineBuilder.setUseMCJIT(true);
     engineBuilder.setMCPU("corei7-avx");
     std::vector<std::string> attrs;
     attrs.push_back("avx");
     engineBuilder.setMAttrs(attrs);
     llvm::ExecutionEngine *ee = engineBuilder.create();

Note that I have just today filed a bug report also related to jitted 
AVX: http://llvm.org/bugs/show_bug.cgi?id=10742
Thus, it might very well be the case that I am also mistaken and need to 
do something different.

Best,
Ralf

Am 25.08.2011 13:16, schrieb Matt Pharr:
> I'm trying to wire up some code to use the MC-based JIT; my
understanding is that it should be able to JIT AVX code (and that the regular
JIT cannot).  However, I'm getting the error "Target does not support
MC emission!" when I call EngineBuilder::create().  I assume that I'm
just not doing something necessary for initialization, but I'm not sure what
it would be--I am calling all of:
>
>      llvm::InitializeNativeTarget();
>      llvm::InitializeAllTargetMCs();
>      LLVMLinkInMCJIT();
>      LLVMLinkInJIT();
>
> and the module I'm trying to load does have a reasonable target:
>
> target triple = "x86_64-apple-darwin11.0.0"
>
> I've attached a short test case that has the sequence of calls that
I'm making and one of the bitcode files I'm trying to use.  I'd be
happy for any guidance or suggestions.
>
> Thanks,
> -matt
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Hi Ralf,

FYI, old JIT doesn't support AVX at all, no encoding info, etc... The
only way to use AVX+JIT is using MCJIT, which contains the correct
encoding, but unfortunately the framework isn't good yet as the old
one is.

On Thu, Aug 25, 2011 at 10:12 AM, Ralf Karrenberg <Chareos at gmx.de>
wrote:
> Hi Matt,
>
> I am unsure about MCJIT, but I guess the problem is the same.
> Just like when invoking llc, you need to pass the information to use AVX
> (llc -mattr=+avx).
> I guess the corresponding code should look like this:
>
>     llvm::EngineBuilder engineBuilder(module);
>     engineBuilder.setErrorStr(&eeError);
>     engineBuilder.setEngineKind(llvm::EngineKind::JIT);
>     engineBuilder.setUseMCJIT(true);
>     engineBuilder.setMCPU("corei7-avx");
>     std::vector<std::string> attrs;
>     attrs.push_back("avx");
>     engineBuilder.setMAttrs(attrs);
>     llvm::ExecutionEngine *ee = engineBuilder.create();
>
> Note that I have just today filed a bug report also related to jitted
> AVX: http://llvm.org/bugs/show_bug.cgi?id=10742
> Thus, it might very well be the case that I am also mistaken and need to
> do something different.
>
> Best,
> Ralf
>
> Am 25.08.2011 13:16, schrieb Matt Pharr:
>> I'm trying to wire up some code to use the MC-based JIT; my
understanding is that it should be able to JIT AVX code (and that the regular
JIT cannot).  However, I'm getting the error "Target does not support
MC emission!" when I call EngineBuilder::create().  I assume that I'm
just not doing something necessary for initialization, but I'm not sure what
it would be--I am calling all of:
>>
>>      llvm::InitializeNativeTarget();
>>      llvm::InitializeAllTargetMCs();
>>      LLVMLinkInMCJIT();
>>      LLVMLinkInJIT();
>>
>> and the module I'm trying to load does have a reasonable target:
>>
>> target triple = "x86_64-apple-darwin11.0.0"
>>
>> I've attached a short test case that has the sequence of calls that
I'm making and one of the bitcode files I'm trying to use.  I'd be
happy for any guidance or suggestions.
>>
>> Thanks,
>> -matt
>>
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>


-- 
Bruno Cardoso Lopes
http://www.brunocardoso.cc