[LLVMdev] Accessing Return Variable Names

[Igor Merkulow]

Hi John,

%4 is not returned, because it's a temp register value and not a named
variable.
But you can implement something like the code below to get this value.
(Not the most elegant, but more or less working solution).

static std::string getName(Instruction* i)
{
            if(i->getOpcode() == Instruction::Store)
            {
                return
getName((dyn_cast<StoreInst>(&*i))->getPointerOperand());
            }
            else if(i->getOpcode() == Instruction::Ret)
            {
                return "Return";
            }

            std::string name;
            raw_string_ostream s(name);

            s << *i; // string representation of an instruction

            size_t var_start = name.find('%'); // var starts with a %
            size_t var_end = name.find(" ", var_start+1); // till space
            size_t var_comma = name.find(",", var_start+1); // or comma

            return var_comma<var_end?
                        name.substr(var_start,var_comma-var_start) :
                        name.substr(var_start, var_end-var_start);
}

Have fun
Igor

On Thu, Jul 5, 2012 at 11:15 PM, John Backes <back0145 at umn.edu> wrote:

> Hello,
>
> I'm new to llvm development and I have a question which I think should
> be straight forward, but I am having trouble figuring it out.  I want to
> be able to access the return variable name for an instruction.  For some
> instructions I can get this value through the "getName" method.  For
> example, with the instruction:
>
>  > %arg11 = bitcast i32* %arg1 to i8*, !dbg !42, !id !43
>
> calling the "getName" method returns:
>
>  > arg11
>
> However, for the instruction:
>
>  > %4 = load i32* %arg1, align 4, !dbg !57, !id !59
>
> the "getName" method returns the empty string.  How would I find the
> value "4" for this load instruction?  Thanks in advance.
>
> - John
>
>
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