llvm dev - Jan 2016 - Get arguments of a function (bitcast)

Hi All,

I need to get the list of arguments of a function which is bitcasted.

Here is the C code excerpt:

main()
{
 .....

  /* Get input samples */
  input_dsp(input, N, 1);

.....
}

and here is llvm ir for the code section:

%call = call i32 (i32*, i32, i32, ...)* bitcast (i32 (...)* @input_dsp to
i32 (i32*, i32, i32, ...)*)(i32* getelementptr inbounds ([256 x i32]*
@input, i32 0, i32 0), i32 256, i32 1)


When I use the ordinary method for getting arguments,

for (Function::ArgumentListType::iterator it f->getArgumentList().begin(); it
!= f->getArgumentList().end(); it++) {...}

i get a segmentation fault which i think i valid. But how can i get
arguments of *input_dsp* which are *input*, *N* and *1* in this case.

Best,
Mo
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Hi Mo,

Have a look at the Value::stripPointerCasts() method [1] to strip all 
bitcasts from the function pointer.

-Manuel

[1] 
http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html#a38ea12c04523d63adda732b9c5d6da0a

On 2016-01-12 16:43, Mohammad Norouzi via llvm-dev
wrote:
> Hi All,
> 
> I need to get the list of arguments of a function which is bitcasted.
> 
> Here is the C code excerpt:
> 
> main()
> {
>  .....
> 
>   /* Get input samples */
>   input_dsp(input, N, 1);
> 
> .....
> }
> 
> and here is llvm ir for the code section:
> 
> %call = call i32 (i32*, i32, i32, ...)* bitcast (i32 (...)* @input_dsp 
> to
> i32 (i32*, i32, i32, ...)*)(i32* getelementptr inbounds ([256 x i32]*
> @input, i32 0, i32 0), i32 256, i32 1)
> 
> 
> When I use the ordinary method for getting arguments,
> 
> for (Function::ArgumentListType::iterator it >
f->getArgumentList().begin(); it != f->getArgumentList().end(); it++)
> {...}
> 
> i get a segmentation fault which i think i valid. But how can i get
> arguments of *input_dsp* which are *input*, *N* and *1* in this case.
> 
> Best,
> Mo
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Dear Mohammad,

Are you trying to get the formal arguments or the actual arguments?

If you're trying to get the actual arguments, you can use the CallSite 
class (http://llvm.org/doxygen/classllvm_1_1CallSite.html).  Create a 
local CallSite variable constructed from the Instruction * (in this 
case, a CallInst).  You can then use the getArgument() method to get the 
various operands to the call site.  The CallSite class is nice because 
it abstracts away details of the CallInst and InvokeInst instructions.

If you want the formal arguments, you need to find the function that the 
CallInst calls.  You can do that as Manual suggests. However, keep in 
mind that the CallInst may be an indirect call and, therefore, you may 
not see a Function constant.  In that case, you'll need to use a call 
graph analysis pass (like DSA) to determine which set of functions the 
CallInst can call.

Regards,

John Criswell


On 1/12/16 10:43 AM, Mohammad Norouzi via llvm-dev
wrote:
> Hi All,
>
> I need to get the list of arguments of a function which is bitcasted.
>
> Here is the C code excerpt:
>
> main()
> {
>  .....
>
>   /* Get input samples */
>   input_dsp(input, N, 1);
>
> .....
> }
>
> and here is llvm ir for the code section:
>
> %call = call i32 (i32*, i32, i32, ...)* bitcast (i32 (...)* @input_dsp 
> to i32 (i32*, i32, i32, ...)*)(i32* getelementptr inbounds ([256 x 
> i32]* @input, i32 0, i32 0), i32 256, i32 1)
>
>
> When I use the ordinary method for getting arguments,
>
> for (Function::ArgumentListType::iterator it = 
> f->getArgumentList().begin(); it != f->getArgumentList().end(); it++)
> {...}
>
> i get a segmentation fault which i think i valid. But how can i get 
> arguments of /input_dsp/ which are /input/, /N/ and /1/ in this case.
>
> Best,
> Mo
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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