[LLVMdev] Operand, instruction

[Nipun Arora]

Hi,

How can one extract the operand of an instruction in an LLVM pass?

Like I can get the opcode bt I'd like to get the operands as well

Thanks

Nipun

[Devang Patel]

getOperand(i). See Instruction.h and User.h

-
Devang
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[John Criswell]

Use the getOperand() method of class Instruction (which I think is
inherited from Value or User or some other LLVM class). It takes a
single parameter that is an index specifying which operand to return.
The return value is a llvm::Value *, IIRC.

If you haven't used it yet, I'd recommend using the LLVM doxygen
documentation (http://llvm.org/doxygen/hierarchy.html). I've found it
to be an invaluable resource for answering these sorts of questions. In
this case, just look up the llvm::Instruction class and see if it has a
method that does what you want. If it doesn't, check its parent class,
the grandparent class, etc. until you find the method you want.

-- John T.

> Thanks
> Nipun

[help__me_please]

Can anyone tell how to get the result name or instruction name of all
instruction? For example if the instruction is "x=add y,z", here i need "x".
Using getName(), i am getting some instructions result name, but llvm
produces some instruction like "%0=add i32 tmp, 1", here getName() shows
empty string as result name.
So please help.

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[Duncan Sands]

Hi,

> Can anyone tell how to get the result name or instruction name of all
> instruction? For example if the instruction is "x=add y,z", here i need "x".
> Using getName(), i am getting some instructions result name, but llvm
> produces some instruction like "%0=add i32 tmp, 1", here getName() shows
> empty string as result name.
> So please help.

as you have noticed, names are optional: instructions may not have names.
That said, you can give names to all instructions by running the instnamer
pass.

Ciao,

Duncan.

[Devang Patel]

On Fri, Mar 26, 2010 at 6:53 AM, help__me_please
<krish...@cse.iitb.ac.in> wrote:
>
> Can anyone tell how to get the result name or instruction name of all
> instruction? For example if the instruction is "x=add y,z", here i need "x".
> Using getName(), i am getting some instructions result name, but llvm
> produces some instruction like "%0=add i32 tmp, 1", here getName() shows
> empty string as result name.
> So please help.
>

Instruction names are optional and not reliable. Why do you need a
name ? You can use use_iterator to find instruction's uses.
-
Devang

[help__me_please]

Actually i have to implement strength reduction, for that i have to first
detect induction variables using ALLEN-COCKE-KENNEDY algorithm. To find out
induction variables, i need the name of the instruction.
Thanks for the reply.

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[help__me_please]

Thanks for the reply.
My problem is solved.
Thanks once again.

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[Duncan Sands]

Hi,

> Actually i have to implement strength reduction, for that i have to first
> detect induction variables using ALLEN-COCKE-KENNEDY algorithm. To find out
> induction variables, i need the name of the instruction.

I suspect you are confused. Surely you only need a way of referring to each
instruction. For this you can use a pointer to the instruction.

Ciao,

Duncan.

[help__me_please]

Can you tell how to use vector globally? I mean, i am able to add entries to
a vector in a basicblock, but whenever a basicblock function call is
returned, the vector becomes empty. So how to use data structures globally?
And one thing, where is main ( or same kind of) function in llvm?
Thanks for you reply.

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[Arvind Sudarsanam]

Hi,

Instead of a basic block function call....You might want to use a module
function call...then iterate through functions and then iterate through
basic blocks...
Hope this helped.

Best Regards
Arvind
------------------------------------------------------------------------
------------
Arvind Sudarsanam Phone: (435) 512-7769
CPU Technology, Inc Fax: (866) 848-5599
1500 Kansas Ave, Suite 3E
Longmont, CO 80501

[help__me_please]

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.

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[John Criswell]

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.

[help__me_please]

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.

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[John Criswell]

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"
>

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

[Nick Lewycky]

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.

Nick

[help__me_please]

Thanks for the reply.
You are correct, sometimes ago i found myself this functions. I was
searching for just this functions. Still one problem is there, adding a
instruction in another basic block, error shows that basic block has no
terminator inst, but that's not true.
Thanks again for help.

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[help__me_please]

Thanks for the reply.

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[Ben Perry]

if (ConstantInt *c = (ConstantInt *) dyn_cast<ConstantInt>(index)){
errs() << "And it's a constant!!!!!!1111oneone!! (" <<c->getZExtValue()
<< ")\n";
}

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-----Original Message-----
From: llvmdev...@cs.uiuc.edu [mailto:llvmdev...@cs.uiuc.edu] On
Behalf Of help__me_please
Sent: Thursday, April 22, 2010 8:38 AM
To: llv...@cs.uiuc.edu
Subject: Re: [LLVMdev] Operand, instruction

Hello, how to get the numerical value of an constant operand? For ex. %tmp =
mul i32 %indvar, 6 , in this instruction second operand is a numerical
constant with value 6. But i am only able to print it by using
getOperand(1), not able to store it in any integer variable. Using getName()
returns a empty string. Is there any way to solve this problem?
Thank you.

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[help__me_please]

Hello, how to get the numerical value of an constant operand? For ex. %tmp =
mul i32 %indvar, 6 , in this instruction second operand is a numerical
constant with value 6. But i am only able to print it by using
getOperand(1), not able to store it in any integer variable. Using getName()
returns a empty string. Is there any way to solve this problem?
Thank you.

John Criswell-2 wrote:
>

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[Duncan Sands]

Hi Ben,

> if (ConstantInt *c = (ConstantInt *) dyn_cast<ConstantInt>(index)){
> errs()<< "And it's a constant!!!!!!1111oneone!! ("<<c->getZExtValue()
> << ")\n";
> }

I don't think you need the "(ConstantInt *)" cast. The getZExtValue will fail
if the constant doesn't fit in 64 bits.

Ciao,

Duncan.

[help__me_please]

Thanks for the quick reply.
I am able to get the numerical value. But i also need the numerical value to
be in value type, so that it can be used as operand of other instruction.
For that i am trying to create a new ConstantInt, but i am unable to find
create() function for ConstantInt.

Thanks again for the quick and helpful reply.

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[John Criswell]

help__me_please wrote:
> Thanks for the quick reply.
> I am able to get the numerical value. But i also need the numerical value to
> be in value type, so that it can be used as operand of other instruction.
> For that i am trying to create a new ConstantInt, but i am unable to find
> create() function for ConstantInt.
>

There is no need to do that. If you look at the inheritance hierarchy
in doxygen, ConstantInt inherits (indirectly) from Value. You can use a
ConstantInt in any place where a Value can be used.

-- John T.

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[help__me_please]

Thanks again for your reply.

You are right. But i am looking to change the value of that constant value
and use that as operand in other instruction. For example there is one
constant operand with value 6, i will multiply it with 2, and then use 12 as
operand in other instruction. So i need to convert 12 to value class and
then i will be able to set it as operand.
Hope i am clear now.
Thanks.

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[Eli Friedman]

On Thu, Apr 22, 2010 at 11:39 AM, help__me_please
<krish...@cse.iitb.ac.in> wrote:
>
> Thanks again for your reply.
> You are right. But i am looking to change the value of that constant value
> and use that as operand in other instruction. For example there is one
> constant operand with value 6, i will multiply it with 2, and then use 12 as
> operand in other instruction. So i need to convert 12 to value class and
> then i will be able to set it as operand.
> Hope i am clear now.
> Thanks.

I think you're looking for ConstantInt::get; the naming is a bit
different from instructions because constants values are reused.

-Eli