[llvm-dev] New to LLVM, need some help with JIT

[George Burgess IV via llvm-dev]

FWIW, invariant groups/invariant intrinsics may help with #2 (though, as
Lang noted, it's the job of your frontend to pass these on to LLVM):

 - http://llvm.org/docs/LangRef.html#invariant-group-metadata
 - http://llvm.org/docs/LangRef.html#llvm-invariant-start-intrinsic

On Fri, Jun 3, 2016 at 10:30 AM, Lang Hames via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Pooya,
>
> 1) What's the right way to add a class or an instance of it to a module? I
>> could only find ways to add structs to modules and I'm not sure how to deal
>> with classes. Any good references to check? Or any good
>> article/projects/code samples to look into?
>
>
> LLVM IR is a low level representation - it doesn't have any built-in
> representation of classes beyond the structs that you've seen. Your
> frontend has to map those concepts onto LLVM IR.
>
> 2) Is there a way to declare that certain parts of a structure won’t
>> change during execution?
>
>
> This is also a problem for the frontend.
>
> You could take a look at how clang maps these concepts from C++ to LLVM IR
> by writing some simple C++ examples and then running:
>
> clang++ -emit-llvm -S -o foo.ll foo.cpp
>
> If your input language is C/C++ you may want to use clang to build the IR
> that you want to JIT. There is an example of that in the
> clang/examples/clang-interpreter directory.
>
> Finally, if your ultimate goal is to experiment with optimizations in the
> JIT you may find the new tutorial series that I'm working on helpful:
> "Building A JIT in LLVM" at http://llvm.org/docs/tutorial/ . These
> tutorials are very new, and only the first chapter has a complete write-up,
> but all of the code is complete, and the code for Chapter 2, "Adding
> Optimizations", may be relevant to you.
>
> Cheers,
> Lang.
>
>
> On Thu, Jun 2, 2016 at 4:36 PM, Pooya SaadatPanah via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi,
>>
>> I'm a grad student working on a C++11 project and I have no compiler
>> background. I apologize for asking basic questions here.
>>
>> Currently I'm looking for ways to optimize my code and as a starting
>> point I wanted to experiment with loop unrolling and further I might
>> consider function in-lining . I have been introduced to JIT compiler of
>> LLVM and the possible application of it in my project.
>>
>> Currently I know the basics about creating a module and getting a JIT
>> compiler. I followed this:
>>
>> https://llvm.org/svn/llvm-project/llvm/trunk/examples/HowToUseJIT/HowToUseJIT.cpp
>>
>> I have two questions:
>>
>> 1) What's the right way to add a class or an instance of it to a module?
>> I could only find ways to add structs to modules and I'm not sure how to
>> deal with classes. Any good references to check? Or any good
>> article/projects/code samples to look into?
>>
>> 2) Is there a way to declare that certain parts of a structure won’t
>> change during execution? For instance, let’s say that I have a class 'foo'
>> and foo.x is 7 and doesn’t change over the life of the code, but foo.y
>> does. There is a function in class foo and the function uses foo.x as the
>> condition in the loop, thus I’d like to tell LLVM that foo.x is always 7,
>> so that it can unroll the loop "for(int i = 0;i < foo.x;i++)". But I’m a
>> little confused about how LLVM uses constants – they appear to be tied to
>> global variables only, and only an entire global variable, so I don’t see
>> how to make one component of it a constant.
>>
>> Thank you,
>>
>> -P.S.P
>>
>> --
>>
>>
>>
>>
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>> llvm-dev at lists.llvm.org
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>>
>>
>
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