[LLVMdev] Operand, instruction
criswell at uiuc.edu
Tue Apr 13 23:38:19 PDT 2010
> Thanks for reply.
> I have used AllocaInst, it's working but i think it's only for allocating
> some memory for new variable. And CallInst creates a call instruction. I am
> looking for creating a add or sub instruction.
> I used function instruction(), which gives me error "error: cannot allocate
> an object of abstract type ‘llvm::Instruction’" and also "Instruction.h:28:
> note: because the following virtual functions are pure within
> ‘llvm::Instruction’:", "Instruction.h:50: note: virtual llvm::Instruction*
> llvm::Instruction::clone(llvm::LLVMContext&) const"
An add or sub should be a BinaryOperator, if memory serves me
correctly. Looking at mainline doxygen, there's a whole bunch of
CreateNSWAdd, CreateNSWMul, etc. methods. It's one of those that you want.
-- John T.
> Also i have used BinaryOperator::create(), but it gives error that there is
> no function called create().
> Thanks again for your reply.
> John Criswell-2 wrote:
>> help__me_please wrote:
>>> Can you please give an example of creating an instruction (for example
>>> instructions with two operand a and b)? I am trying instruction() for a
>>> while, but no success yet.
>> You need to look for the appropriate subclass of llvm::Instruction and
>> find the method for creating a new instruction. The method is usually a
>> static method and takes arguments pointing to the values to use as
>> operands. Doxygen is your best resource for finding these methods.
>> For example, if you look at
>> http://llvm.org/doxygen/classllvm_1_1AllocaInst.html, you can see that
>> the AllocaInst class (which represents an alloca instruction) has a
>> standard constructor method that takes the type of object to allocate,
>> the name of the new alloca instruction, an instruction before which to
>> insert the alloca instruction, etc.
>> As another example, the CallInst class
>> (http://llvm.org/doxygen/classllvm_1_1CallInst.html) represents a call
>> instruction and has a static Create() method that you can use to create
>> a new call instruction.
>> -- John T.
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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