[LLVMdev] Operand, instruction

Nick Lewycky nicholas at mxc.ca
Tue Apr 13 22:48:08 PDT 2010

There's an entire tutorial at http://llvm.org/docs/tutorial which 
includes covers the IRBuilder to generate all sorts of IR, including the 
add instruction. You can skip ahead to chapter 3 if you just want to see 
LLVM API, but I suggest you read the whole tutorial if you have the time.


help__me_please wrote:
> 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"
> 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
>>> add
>>> 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.
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