Adding instructions in pass directly from string containing IR

Hello,

I would like to add a pass which modifies IR by insertion set of IR instructions somewhere in the middle of the basicblock,

like example below:

%address = call i32* @llvm.target_intrinsic.getaddress()

%value = load i32, i32* %address

%addvalue = add nsw i32 %value, 10

store i32 %addvalue, i32* %address

Is there any function available which would allow for parsing the string (containing set of instructions) and generating instructions automatically instead of manually calling functions creating instructions from IRBuilder?

…at least for simple set of basic instructions

Regards,

Przemek

What arch btw?

wt., 1.06.2021, 19:16 użytkownik Przemyslaw Ossowski via llvm-dev <llvm-dev@lists.llvm.org> napisał:

Hi Przemek,

I doubt that such functionality exists right now. The main
problem I see is the name matching to embed it with other code.
If the new code is not connected, I'd recommend the pass to
read in an IR file with a function in it, link it into the module,
and insert a call wherever you want to "paste" the instructions.

Much cleaner than dealing with strings, IMHO.

~ Johannes

Thank you Johannes for your suggestion.

In case a call to the function which would contain the code I would like to paste is inserted into another function, then is it still possible to simply inline the code?
I would like to avoid calling the function with the “pasted” code. I assume there is a pass which inlines functions which should be executed later.

Thanks,
Przemek

If you insert a call prior to the inliner and mark it with the
`alwaysinline` attribute, it will be inlined for sure.

Reduces your problem to insert a call to a function :slight_smile:

~ Johannes

Thanks,
but when I went into details I’m wondering if using linker in a simple pass is possible.
Usually passes are executed per module.
Is it possible to use linker and later replace the original module with a newly linked module in simple pass?
Module is passed by reference to runOnModule, so probably it should be possible…

Przemek

This is an interesting approach, but in general I am trying to avoid function calls with additional code but paste the code into another function.
Or maybe I didn’t get the exact goal of ifunc.

And as I understood Johannes it should be possible to use LLVM IR Linker (in the LLVM IR pass???), then inline the code and optimize everything as one function. Then any dynamic resolving of shouldn’t be needed.

Thanks,
Przemek

I would link in the function with the code via clang early:
-Xclang -mlink-bitcode file.bc (not tested)
and then insert calls with the always inline attribute (or add
it on the function).

Hope this helps,
Johannes