llvm dev - Mar 2015 - [LLVMdev] casting Constant * to value *?

Hi all,

extracting datafields of globals, the API code ends up in a Constant * 


Constant* const_ptr_103 = ConstantExpr::getGetElementPtr(gvar_struct_foo, 
const_ptr_103_indices);

it can be used to initialize e.g. a new instruction like:

StoreInst* void_119 = new StoreInst(const_float_102, const_ptr_103, false, 
label_entry_113);


But how about replacing the operand of an already existing instruction using 
a Constant *?

Instruction->setOperand(1,__needs_a_value*_here__);


Thx
Alex

On 3/17/15 8:40 PM, Alexander Poddey wrote:
> Hi all,
>
> extracting datafields of globals, the API code ends up in a Constant *
>
>
> Constant* const_ptr_103 = ConstantExpr::getGetElementPtr(gvar_struct_foo,
> const_ptr_103_indices);
>
> it can be used to initialize e.g. a new instruction like:
>
> StoreInst* void_119 = new StoreInst(const_float_102, const_ptr_103, false,
> label_entry_113);
>
>
> But how about replacing the operand of an already existing instruction
using
> a Constant *?
>
> Instruction->setOperand(1,__needs_a_value*_here__);
If you look at the inheritance tree, you'll see that an llvm::Constant 
is a subclass of llvm::Value.  Therefore, you can use an llvm::Constant 
anywhere in which an llvm::Value is needed.

To look at the inheritance tree, look at the LLVM doxygen documentation.

Regards,

John Criswell
>
>
> Thx
> Alex
>
>
>
>
>   
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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

John, you are right.
I 'browsed' the doxygen's inheritance diagram.
Shouldn't I then be able to cast Constant * to Value*?

Plugging the retrieved Constant* (from ConstantExpr::getGetElementPtr)
into Instruction->setOperand compiles, but gives me an assertion failure at 
runtime.
I have no access to the code at the moment. I will gather more information 
possibly tomorrow.

Thanks 
Alex  




John Criswell wrote:
> On 3/17/15 8:40 PM, Alexander Poddey wrote:
>> Hi all,
>>
>> extracting datafields of globals, the API code ends up in a Constant *
>>
>>
>> Constant* const_ptr_103 =
ConstantExpr::getGetElementPtr(gvar_struct_foo,
>> const_ptr_103_indices);
>>
>> it can be used to initialize e.g. a new instruction like:
>>
>> StoreInst* void_119 = new StoreInst(const_float_102, const_ptr_103,
>> false, label_entry_113);
>>
>>
>> But how about replacing the operand of an already existing instruction
>> using a Constant *?
>>
>> Instruction->setOperand(1,__needs_a_value*_here__);
> 
> If you look at the inheritance tree, you'll see that an llvm::Constant
> is a subclass of llvm::Value.  Therefore, you can use an llvm::Constant
> anywhere in which an llvm::Value is needed.
> 
> To look at the inheritance tree, look at the LLVM doxygen documentation.
> 
> Regards,
> 
> John Criswell
>>
>>
>> Thx
>> Alex
>>
>>
>>
>>
>>   
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
>