llvm dev - Dec 2010 - [LLVMdev] the optional function return attribute and the llvm-c bindings

everyone--

Is it my imagination, or is there no way in LLVM 2.8 (or current trunk) to use
the facilities defined in <llvm-c/Core.h> to get or set the optional
return parameter attribute on a function value?

All the functions in the "Operations on parameters" parameters section
actually seem to work only on the function arguments and not the return
parameter.  Is this intentional?  What should I do if I need to get or set the
return parameter attributes of a function from OCaml?


—
j h woodyatt <jhw at conjury.org>
http://jhw.dreamwidth.org/

Hi James,
> Is it my imagination, or is there no way in LLVM 2.8 (or current trunk) to
use the facilities defined in<llvm-c/Core.h>  to get or set the optional
return parameter attribute on a function value?
>
> All the functions in the "Operations on parameters" parameters
section actually seem to work only on the function arguments and not the return
parameter.  Is this intentional?  What should I do if I need to get or set the
return parameter attributes of a function from OCaml?
IIRC the function return value is considered to be the parameter with index 0.
The function itself is considered to be the parameter with index ~0U.

Ciao, Duncan.

On Dec 21, 2010, at 00:43, Duncan Sands wrote:
> 
> IIRC the function return value is considered to be the parameter with index
0.
> The function itself is considered to be the parameter with index ~0U.
Yes, that's what the documentation seems to say is the proper mode for
indexing the return parameter, but when I set an attribute on the parameter with
index zero, it gets applied to the first function argument and not the return
parameter.

I believe the reason for this to be that LLVMGetParams() [and its cognates] all
use Function::arg_iterator, which begins with the first function *argument*
parameter and not the return parameter.  The index argument to LLVMGetParams()
is actually incremented by one when it's mapped to the index used for the
Function::AttributeList member.  There are separate functions for the function
attributes, which are at index ~0UL, but no similar functions for handling the
function return parameter attribute at index zero.

Is this intentional?  What is the correct way to get and set a function return
parameter attribute with C-language binding to the LLVM core?


—
j h woodyatt <jhw at conjury.org>
http://jhw.dreamwidth.org/