[LLVMdev] how to change one operand of an LLVM instruction

[Tanya Lattner]

On Sep 8, 2009, at 2:46 PM, Susan Horwitz wrote:

> I am trying to implement node splitting to transform irreducible  
> CFGS to
> reducible ones.  This means making copies of some basic blocks,  
> which in
> turn means making copies of individual instructions.  I can use the
> "clone" function to make an exact copy, but then I need to change some
> operands. For example, when I copy
> 	%1 = ...
> 	%2 = add %1, 5
>
> I get
> 	%3 = ...
> 	%4 = add %1, 5
>
> and I need to change the %1 operand in the copy to be %3.
>
> The only way I see to do this is to create a new instruction instead  
> of a
> clone, using a big switch on the opcode (since different instructions'
> constructors have different parameters).
>
> Anyone know of an easier way to do this?
>

Are you using CloneBasicBlock? If so, you should pass it a ValueMap.  
You can then iterate over the instructions in the new basicblock and  
update the instruction operand references.

Check out CloneFunction.cpp for some examples.

-Tanya





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