[LLVMdev] Removing function params.

[John Criswell]

On 10/22/13 10:17 AM, James Courtier-Dutton wrote:
> Hi,
>
> I am writing my own passes in LLVM.
> I start with a function with various uses of a LLVM IR function
> parameter: e.g. paramB.
>
> After running one of my passes, all the uses of the paramB vanish.
> How do I do the last step, and remove the paramB from the function
> parameters in the LLVM IR?

In order to add or remove parameters from a function, you will need to 
create a new function and clone the contents of the old function into 
the new function.  You will then need to replace uses of the old 
function with the new function.

There's a utility function called (I think) cloneFunctionInto which 
makes this whole process much simpler.  Look for a source file with the 
word "Clone" in it in llvm/lib/Transforms; the function will be located 
there.

As an FYI, if you want to remove an argument because it is unused, LLVM 
already has a transform pass that does that.  I think it's 
DeadArgumentElimination.

-- John T.

>
> I want to go from:
> function test( int paramA, int paramB)
> { ... }
>
> to:
> function test( int paramA)
> { ... }
>
> Is there an LLVM IR API method that does this, or do I have to create
> a whole new function and add all the basic blocks and instructions
> from the old one to it?
>
> Also, how do I do the opposite:
> I want to go from:
> function test( int paramA)
> { ... }
>
> to:
> function test( int paramA, int paramB)
> { ... }
>
>
> Kind Regards
>
> James.
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