llvm dev - Oct 2016 - Adding assembly instructions to LLVM

Hi,

As part of a project I need to compile C code for a new architecture that
is based on x86 with some new instructions. In my C code I'm going to use
inline assembly, so the only thing I need from LLVM is to recognize the
instruction and put it in the binary in the right place with correct input
values/register addresses.

I tried to add a simple ADD instruction, following the instructions in
http://llvm.org/docs/ExtendingLLVM.html#adding-a-new-instruction and just
duplicating everything I saw for the ADD instruction for my instruction.
The problem is that this page doesn't explain where I should add the opcode
for my instruction.

I've been reading the documents and the source code for several days now
and I feel kind of lost right now. I was hoping someone here could point me
to the right direction.

Thank you
Soroosh
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On Sun, Oct 30, 2016 at 04:33:08PM -0500, soroosh khoram via llvm-dev
wrote:
> I've been reading the documents and the source code for several days
now
> and I feel kind of lost right now. I was hoping someone here could point me
> to the right direction.
The expansion for add on x86 starts in
lib/Targets/X86/X86InstrArithmethic.td, line 1197 (defm ADD) and
involves somewhat complicated multiclassing to deal with various operand
combinations. A better starting point is likely the "test" family,
line
1223ff.

Joerg

On 10/30/16 5:33 PM, soroosh khoram via llvm-dev wrote:
> Hi,
>
> As part of a project I need to compile C code for a new architecture 
> that is based on x86 with some new instructions. In my C code I'm 
> going to use inline assembly, so the only thing I need from LLVM is to 
> recognize the instruction and put it in the binary in the right place 
> with correct input values/register addresses.
If you already have an assembler that recognizes your new instruction, 
it may be easier to use the -no-integrated-as argument on the clang 
command line and have it use the assembler that supports the instruction.

If there is no assembler that understands your new instructions, then 
enhancing LLVM's code generator/internal assembler/internal disassembler 
is probably a good way to go.

Regards,

John Criswell
>
> I tried to add a simple ADD instruction, following the instructions in 
> http://llvm.org/docs/ExtendingLLVM.html#adding-a-new-instruction and 
> just duplicating everything I saw for the ADD instruction for my 
> instruction. The problem is that this page doesn't explain where I 
> should add the opcode for my instruction.
>
> I've been reading the documents and the source code for several days 
> now and I feel kind of lost right now. I was hoping someone here could 
> point me to the right direction.
>
> Thank you
> Soroosh
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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