Hi Duncan, For this example, getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N I am trying to retrieve %N and instrument the program to see if the value pointed to by %N exceeds the array bound (10). I assume that %N will be associated with a load instruction. I have searched through all the tutorials etc. and still have no clue as to how to do this, that is, get the value and then instrument the code. George On Mon, Mar 28, 2011 at 4:32 AM, Duncan Sands <baldrick at free.fr> wrote:> Hi George, > > > I am trying to get the first index into this two-dimensional array, > that is *5.* > > not sure what you mean, but if you think of your array as being a 10 x 20 > matrix > then to get a pointer to element M,N you would do: > getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N > > > > > %4 = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 *5* > > * > > * > > I can iterate over the GEP and get the types of the operands but not the > values. > > > > How do I get the value (5)? > > getelementptr only does pointer arithmetic, i.e. using it you can get a > pointer > to an array element. But to get the element itself you need to use a load > instruction to load the value pointed to by the pointer. > > Ciao, Duncan. > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110328/98125c13/attachment.html>
Hi George,> For this example, > getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N > I am trying to retrieve %N and instrument the program to see if the value > pointed to by %N exceeds the array bound (10). I assume that > %N will be associated with a load instruction. I have searched through > all the tutorials etc. and still have no clue as to how to do this, that is, > get the value and then instrument the code.if %p = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N then you need an instruction %v = load %p to get the value %v pointed to by %p. Ciao, Duncan.> > George > > On Mon, Mar 28, 2011 at 4:32 AM, Duncan Sands <baldrick at free.fr > <mailto:baldrick at free.fr>> wrote: > > Hi George, > > > I am trying to get the first index into this two-dimensional array, > that is *5.* > > not sure what you mean, but if you think of your array as being a 10 x 20 matrix > then to get a pointer to element M,N you would do: > getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N > > > > > %4 = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 *5* > > * > > * > > I can iterate over the GEP and get the types of the operands but not the > values. > > > > How do I get the value (5)? > > getelementptr only does pointer arithmetic, i.e. using it you can get a pointer > to an array element. But to get the element itself you need to use a load > instruction to load the value pointed to by the pointer. > > Ciao, Duncan. > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu> http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > >
Oh I see what you mean but I don't think that is the value that I want.
In the code, I know that
%N = load i32* %k, align 4
%p = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N
So I analyze the GEP and know that %N is a pointer to an int32, which is the
array index.
I want to get that index so I can insert a check to see if it violates the
array bounds.
So the final code (in pseudocode) will look like,
%N = load i32* %k, align 4
if( 0 <= %N < array-size){
%p = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N
...
}else{
throw an exception.
}
On Mon, Mar 28, 2011 at 3:25 PM, Duncan Sands <baldrick at free.fr> wrote:
> Hi George,
>
>
> For this example,
>> getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N
>> I am trying to retrieve %N and instrument the program to see if the
value
>> pointed to by %N exceeds the array bound (10). I assume that
>> %N will be associated with a load instruction. I have searched through
>> all the tutorials etc. and still have no clue as to how to do this,
that
>> is,
>> get the value and then instrument the code.
>>
>
> if
> %p = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32 %N
> then you need an instruction
> %v = load %p
> to get the value %v pointed to by %p.
>
> Ciao, Duncan.
>
>
>> George
>>
>> On Mon, Mar 28, 2011 at 4:32 AM, Duncan Sands <baldrick at free.fr
>> <mailto:baldrick at free.fr>> wrote:
>>
>> Hi George,
>>
>> > I am trying to get the first index into this
two-dimensional
>> array,
>> that is *5.*
>>
>> not sure what you mean, but if you think of your array as being a 10
x
>> 20 matrix
>> then to get a pointer to element M,N you would do:
>> getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32 %M, i32
%N
>>
>> >
>> > %4 = getelementptr inbounds [10 x [20 x i32]]* %3, i32 0, i32
*5*
>> > *
>> > *
>> > I can iterate over the GEP and get the types of the operands
but not
>> the
>> values.
>> >
>> > How do I get the value (5)?
>>
>> getelementptr only does pointer arithmetic, i.e. using it you can
get a
>> pointer
>> to an array element. But to get the element itself you need to use
a
>> load
>> instruction to load the value pointed to by the pointer.
>>
>> Ciao, Duncan.
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
>> http://llvm.cs.uiuc.edu
>>
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>>
>
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