llvm dev - May 2009 - [LLVMdev] A problem creating operands for a new IR instruction to the mailing list

I have a question about inserting instructions into the LLVM IR.  I can insert
instructions, but my operands do not have the right type, so it fails an
assertion at runtime.

I am trying to insert an immediate load instructions, as a means of claiming a
new register.

Here is what I do:
    Builder.SetInsertPoint(LLVMBB, I);

// The following line looks to me like it would have a chance of loading either
// address 5, or else immediate value 5. Unfortunately, it does neither. It
compiles
// but crashes at runtime, that the type of the operand is incompatible
        Instruction *newI=Builder.CreateLoad(5,"");

// I also tested this, just to do a little sanity check. It also compiles then
// crashes, for the obvious reason that the operand is a register, but an
address
// or an immediate value is expected.
        //Instruction
*newI=Builder.CreateLoad(I->getOperand(1),""); // also wrong

So to say it simply, my question is, "How can I create a new Value*, which
indicates
an immediate value, such as immediate value 5?"

Thank you for your assistance,
Kao Chang
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On 2009-05-05 17:00, seventh moon wrote:
> I have a question about inserting instructions into the LLVM IR. I can
> insert instructions, but my operands do not have the right type, so it
> fails an assertion at runtime.
>
> I am trying to insert an immediate load instructions, as a means of
> claiming a new register.
>
> Here is what I do:
> Builder.SetInsertPoint(LLVMBB, I);
>
> // The following line looks to me like it would have a chance o! f
> loading either
> // address 5, or else immediate value 5. Unfortunately, it does
> neither. It compiles
> // but crashes at runtime, that the type of the operand is incompatible
> Instruction *newI=Builder.CreateLoad(5,"");
>
> // I also tested this, just to do a little sanity check. It also
> compiles then
> // crashes, for the obvious reason that the operand is a register, but
> an address
> // or an immediate value is expected.
> //Instruction *newI=Builder.CreateLoad(I->getOperand(1),"");
// also
> wrong
>
> So to say it simply, my question is, "How can I create a new Value*,
> which indicates
> an immediate value, such as immediate value 5?"
You should use a constant instead of a load:

Constant *C = ConstantInt::get(Type::Int32Ty, 5);

Note that the constant is not an instruction, but it can be used like
any other Value*.

Best regards,
--Edwin

If you want an immediate constant value, ConstantInt::get(APInt(32, 5,
false)) will perhaps help you ?

Olivier.

2009/5/5 seventh moon <suigintou_ at hotmail.com>
>  I have a question about inserting instructions into the LLVM IR.  I can
> insert instructions, but my operands do not have the right type, so it
fails
> an assertion at runtime.
>
> I am trying to insert an immediate load instructions, as a means of
> claiming a new register.
>
> Here is what I do:
>     Builder.SetInsertPoint(LLVMBB, I);
>
> // The following line looks to me like it would have a chance o! f loading
> either
> // address 5, or else immediate value 5. Unfortunately, it does neither. It
> compiles
> // but crashes at runtime, that the type of the operand is incompatible
>         Instruction *newI=Builder.CreateLoad(5,"");
>
> // I also tested this, just to do a little sanity check. It also compiles
> then
> // crashes, for the obvious reason that the operand is a register, but an
> address
> // or an immediate value is expected.
>         //Instruction
*newI=Builder.CreateLoad(I->getOperand(1),""); //
> also wrong
>
> So to say it simply, my question is, "How can I create a new Value*,
which
> indicates
> an immediate value, such as immediate value 5?"
>
> Thank you for your assistance,
> Kao Chang
> ------------------------------
> 用部落格分享照片、影音、趣味小工具和最愛清單，盡情秀出! 你自己 — Windows Live
Spaces<http://home.spaces.live.com/?showUnauth=1&lc=1028>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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seventh moon wrote:
> [snip]
>
> So to say it simply, my question is, "How can I create a new Value*,
which indicates
> an immediate value, such as immediate value 5?"
>   
I don't know much about LLVM's code generators, but if all you need is
to create a Value * for an immediate constant, you might try using the
ConstantInt::get() method
(http://llvm.org/doxygen/classllvm_1_1ConstantInt.html#77cd822480bc78732c84a9619e49e14a).
A ConstantInt is a subclass of Value, and you can use it to create
constant integer values in the LLVM IR.

-- John T.

Thank you for your answer.  But there is still a problem.

You seem correct about how to define a constant operand.  So I added it into my
code, like so:
       Builder.SetInsertPoint(LLVMBB, I);
       Constant *C = ConstantInt::get(APInt(32, 5, false));
        Instruction *newI=Builder.CreateLoad(C,"");


It compiles. But it still aborts at runtime with a complaint that the type is
not right.
This leads me to think that immediate loads are not generated with the
CreateLoad
instruction?

Another person's reply to my question indicated that a way to avoid
inserting the
immediate load entirely; but that is also not what I want, because my explicit
purpose
in inserting this load is to claim a register.

Thank you,
Kao Chang

Date: Tue, 5 May 2009 16:07:33 +0200
From: meurant.olivier at gmail.com
To: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] A problem creating operands for a new IR instruction	to
the mailing list

If you want an immediate constant value, ConstantInt::get(APInt(32, 5, false))
will perhaps help you ?

Olivier.

2009/5/5 seventh moon <suigintou_ at hotmail.com>






I have a question about inserting instructions into the LLVM IR.  I can insert
instructions, but my operands do not have the right type, so it fails an
assertion at runtime.


I am trying to insert an immediate load instructions, as a means of claiming a
new register.


Here is what I do:
    Builder.SetInsertPoint(LLVMBB, I);


// The following line looks to me like it would have a chance o!
 f loading either
// address 5, or else immediate value 5. Unfortunately, it does neither. It
compiles

// but crashes at runtime, that the type of the operand is incompatible
        Instruction *newI=Builder.CreateLoad(5,"");


// I also tested this, just to do a little sanity check. It also compiles then

// crashes, for the obvious reason that the operand is a register, but an
address
// or an immediate value is expected.

        //Instruction
*newI=Builder.CreateLoad(I->getOperand(1),""); // also wrong


So to say it simply, my question is, "How can I create a new Value*, which
indicates
an immediate value, such as immediate value 5?"


Thank you for your assistance,
Kao Chang

用部落格分享照片、影音、趣味小工具和最愛清單，盡情秀出!
 你自己 — Windows Live Spaces

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