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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On Mon, Mar 28, 2011 at 12:48 PM, George Baah <georgebaah at gmail.com> wrote:> 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.p->getOperand(3) will return %N as an llvm::Value(). Then you can use dyn_cast<llvm::ConstantInt> to see if it's a ConstantInt as opposed to a run-time variable (or some other flavor of constant like a ConstantExpr), and then you can pull the value out using getValue() or get{Z,S}ExtValue().> 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 >>> >>> >> > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > >
Thanks Guys for the information. I now understand! On Mon, Mar 28, 2011 at 4:16 PM, Jeffrey Yasskin <jyasskin at google.com>wrote:> On Mon, Mar 28, 2011 at 12:48 PM, George Baah <georgebaah at gmail.com> > wrote: > > 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. > > p->getOperand(3) will return %N as an llvm::Value(). Then you can use > dyn_cast<llvm::ConstantInt> to see if it's a ConstantInt as opposed to > a run-time variable (or some other flavor of constant like a > ConstantExpr), and then you can pull the value out using getValue() or > get{Z,S}ExtValue(). > > > 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 > >>> > >>> > >> > > > > > > _______________________________________________ > > 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/20110329/e23caf7e/attachment.html>