[LLVMdev] pragmas

[Luke Dalessandro]

You could encode this information as simple library function calls and 
then find them again in the generated LLVM IR. The client then just 
needs a header declaring the functions and information on what they 
mean. Since there are never any definitions of them they won't end up 
going anywhere.

A more ambitious plan would be to modify llvm-gcc with new __builtins 
and create intrinsics in LLVM to map them to. There's really no 
advantage to this other than not needing the header file while 
compiling. There's a big disadvantage in that you end up mucking with 
both the front end and the llvm intrinsics.

Finally, you can modify llvm-gcc pragma handling to insert things that 
you want, but this is more work. You have to deal with the c-parser and 
c++ parser, and understand more of the front end internals. I would 
avoid this unless you feel like you want pragmas that have some sort of 
lexical semantics, and don't want to force people to use BEGIN and END 
macros.

Hope this is helpful,
Luke

Anthony Danalis wrote:
> Hello
> 
> Is there a "generic" pragma that is supported by LLVM and is visible  
> by optimization passes?  or any other way for a programmer to pass  
> meta-data information to the compiler?
> I am writing an analysis pass that could benefit from user provided  
> information.  At this stage, I could like to keep the kind of  
> information that the user can provide as general as possible.   
> Examples would be "x, y are (not) aliased", "loop trip count =  
> x" (where x is either a static constant, or an expression", "branch  
> cond. is true most of the time" (or x% of the time), and other  
> information that might be statically undecidable, but the developer  
> knows the answer to.
> 
> thanks,
> Anthony
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev