[LLVMdev] How to get more details from storeInst ?

[Cheng Liu]

Dear Duancan Ciao,

Your suggestion is really helpful.
Thank you very much.

Best regards,

On 1/18/2013 5:04 PM, Duncan Sands [via LLVM] wrote:
> Hi Cheng,
>
> On 18/01/13 03:00, Cheng Liu wrote:
> > I have a loop fully unrolled and got the following store instruction.
> >
> > store i32 %add.3, i32* getelementptr inbounds ([20 x [20 x i32]]* 
> @c, i32 0,
> > i32 0, i32 0), align 4
> >
> > I want to know exactly which element of the array that is going to be
> > stored, which help me to transform the high level language to 
> hardware. Take
> > the instruction above as an example, I know the data is stored into 
> c[0][0].
> > It is just that I don't how to get c, 0, 0 from the instruction.
>
> this bit
>    i32* getelementptr inbounds ([20 x [20 x i32]]* @c, i32 0, i32 0, 
> i32 0)
> is a constant expression (ConstantExpr class), not an instruction (you 
> can
> tell because it is printed inline).
>
> If SI is your store instruction (with type StoreInst*) then using
>    SI->getPointerOperand()
> you get the stored to pointer.  Call the result Ptr.
>
> You can cast that to a ConstantExpr* using
>    cast<ConstantExpr>(Ptr)
> This will assert if Ptr isn't a constant expression.  You can use 
> dyn_cast
> instead which will return null if it isn't a constant expression.  At 
> this
> point you can rummage around inside the constant expression.  It is 
> probably
> simpler though to #include the Operator.h header, and cast Ptr to the
> GEPOperator class instead.
>
> Ciao, Duncan.
>
> >
> > At the moment, I use the method getNumOperands() and getOperand( int 
> i) to
> > check all the operands of the instruction. However, I can only get two
> > operands. One of them is the data %add.s, and the other is the 
> pointer. The
> > pointer has no name and it is not a constant.
>
> Yes, it is a constant (Constant class).
>
>   I couldn't move further into
>
> > the pointer to get the index of the element.
> >
> > Anyone could give me some suggestions on this?
> >
> >
> >
> > --
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> http://llvm.1065342.n5.nabble.com/How-to-get-more-details-from-storeInst-tp53841.html
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-- 
Cheng Liu
PhD Candidate
Electrical and Electronic Engineering
The University of Hong Kong





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