llvm dev - Sep 2014 - [LLVMdev] Is it necessary to implement the whole backend in order to add a new "pass" to the backend ?

Hello all,

I am new to llvm. I need to make some changes to the LR. The backend should
modify the LR, but only after all the normal work and all the optimizations
are done.
Just before outputting the native code, LR is modified. I was wondering if
I should implement the whole backend in order to achieve this or is it
possible to implement a new pass and use that. Thanks !

Regards,
Sachin
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140912/3825c7a3/attachment.html>

Dear Sachin,

First, it's not clear to me what you mean by "LR."  Do you mean
that you
want to modify the LLVM Intermediate Representation (the LLVM IR)?

Assuming you're wanting to transform code with LLVM, then answer is no.  
You can implement a pass that performs the transformation/optimization 
you want and add it to the compiler. If you need to modify the code 
generation portions of LLVM, you can write a MachineFunctionPass that 
modifies the native code generated by LLVM after LLVM has done 
instruction selection, instruction scheduling, and register allocation 
but before emitting the final assembly/object file.

Regards,

John Criswell

On 9/12/14, 6:45 PM, sachin arora wrote:
> Hello all,
>
> I am new to llvm. I need to make some changes to the LR. The backend 
> should modify the LR, but only after all the normal work and all the 
> optimizations are done.
> Just before outputting the native code, LR is modified. I was 
> wondering if I should implement the whole backend in order to achieve 
> this or is it possible to implement a new pass and use that. Thanks !
>
> Regards,
> Sachin
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140913/be5d77ae/attachment.html>

Respected Sir,

Thank you for your response. By LR I mean LLVM IR with all the
optimizations done. For instance I call Register Transfer Language of GCC
an LR because it is produced after some optimizations are performed on the
IR. For my project I need to make some changes to this LR so that the
outputted native code has certain additional features. In your reply you
say that I need to implement only a MachineFunctionPass to achieve this;
that's all I needed to know. Thanks again.

Regards,
Sachin

On Sat, Sep 13, 2014 at 11:55 AM, John Criswell <criswell at illinois.edu>
wrote:
>  Dear Sachin,
>
> First, it's not clear to me what you mean by "LR."  Do you
mean that you
> want to modify the LLVM Intermediate Representation (the LLVM IR)?
>
> Assuming you're wanting to transform code with LLVM, then answer is no.
> You can implement a pass that performs the transformation/optimization you
> want and add it to the compiler.  If you need to modify the code generation
> portions of LLVM, you can write a MachineFunctionPass that modifies the
> native code generated by LLVM after LLVM has done instruction selection,
> instruction scheduling, and register allocation but before emitting the
> final assembly/object file.
>
> Regards,
>
> John Criswell
>
>
> On 9/12/14, 6:45 PM, sachin arora wrote:
>
> Hello all,
>
>  I am new to llvm. I need to make some changes to the LR. The backend
> should modify the LR, but only after all the normal work and all the
> optimizations are done.
> Just before outputting the native code, LR is modified. I was wondering if
> I should implement the whole backend in order to achieve this or is it
> possible to implement a new pass and use that. Thanks !
>
>  Regards,
> Sachin
>
>
> _______________________________________________
> LLVM Developers mailing listLLVMdev at cs.uiuc.edu        
http://llvm.cs.uiuc.eduhttp://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140913/58693211/attachment.html>