llvm dev - Nov 2006 - [LLVMdev] need help understanding getelementptr assembler instruction

Hi,

I must say I also was in need of this document but never knew it  
existed. It seems to be linked from the faq page only. I only read  
that the first day I came to LLVM. Maybe linking it from the  
GetElementPtr instruction in LangRef.html would make sense.

cheers
Eric

On Nov 12, 2006, at 8:47 PM, Reid Spencer wrote:
> Ram,
>
> Please read and understand the GetElementPtr FAQ available here:
>
> http://llvm.org/docs/GetElementPtr.html
>
> That will help you understand how it works. We wrote that document
> specifically because this question comes up all the time.
>
> Reid.
>
> On Sun, 2006-11-12 at 11:13 -0800, Ram Bhamidipaty wrote:
>> I am trying to understand the hello word assember example. This is
>> my version:
>>
>> %str1 = internal constant [13 x sbyte] c"Hello World\0a\00"
>>
>> declare int %printf(sbyte*, ...)
>>
>> implementation   ; Functions:
>>
>> int %main() {
>>   %str2 = getelementptr [13 x sbyte]* %str1, long 0, long 0
>>   call int(sbyte*, ...) *%printf(sbyte* %str2)
>>   ret int 0
>> }
>>
>> Why is getelementptr being given two "long 0" indices?
>>
>> Thanks for any help.
>> -Ram
>> _______________________________________________
>> LLVM Developers mailing list
>> 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

On Mon, 2006-11-13 at 01:10 -0800, Chris Lattner wrote:
> On Mon, 13 Nov 2006, Eric van Riet Paap wrote:
> > I must say I also was in need of this document but never knew it
> > existed. It seems to be linked from the faq page only. I only read
> > that the first day I came to LLVM. Maybe linking it from the
> > GetElementPtr instruction in LangRef.html would make sense.
> 
> That makes a tremendous amount of sense to me!
It's already there. Go to the bottom of the GEP instruction definition
in LangRef.html and you will find it.  I'm going to add it to the index
page too.

Reid.
> 
> -Chris
> 
> > On Nov 12, 2006, at 8:47 PM, Reid Spencer wrote:
> >
> >> Ram,
> >>
> >> Please read and understand the GetElementPtr FAQ available here:
> >>
> >> http://llvm.org/docs/GetElementPtr.html
> >>
> >> That will help you understand how it works. We wrote that document
> >> specifically because this question comes up all the time.
> >>
> >> Reid.
> >>
> >> On Sun, 2006-11-12 at 11:13 -0800, Ram Bhamidipaty wrote:
> >>> I am trying to understand the hello word assember example.
This is
> >>> my version:
> >>>
> >>> %str1 = internal constant [13 x sbyte] c"Hello
World\0a\00"
> >>>
> >>> declare int %printf(sbyte*, ...)
> >>>
> >>> implementation   ; Functions:
> >>>
> >>> int %main() {
> >>>   %str2 = getelementptr [13 x sbyte]* %str1, long 0, long 0
> >>>   call int(sbyte*, ...) *%printf(sbyte* %str2)
> >>>   ret int 0
> >>> }
> >>>
> >>> Why is getelementptr being given two "long 0"
indices?
> >>>
> >>> Thanks for any help.
> >>> -Ram
> >>> _______________________________________________
> >>> LLVM Developers mailing list
> >>> 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
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> 
> -Chris
>

On Mon, 13 Nov 2006, Eric van Riet Paap wrote:
> I must say I also was in need of this document but never knew it
> existed. It seems to be linked from the faq page only. I only read
> that the first day I came to LLVM. Maybe linking it from the
> GetElementPtr instruction in LangRef.html would make sense.
That makes a tremendous amount of sense to me!

-Chris
> On Nov 12, 2006, at 8:47 PM, Reid Spencer wrote:
>
>> Ram,
>>
>> Please read and understand the GetElementPtr FAQ available here:
>>
>> http://llvm.org/docs/GetElementPtr.html
>>
>> That will help you understand how it works. We wrote that document
>> specifically because this question comes up all the time.
>>
>> Reid.
>>
>> On Sun, 2006-11-12 at 11:13 -0800, Ram Bhamidipaty wrote:
>>> I am trying to understand the hello word assember example. This is
>>> my version:
>>>
>>> %str1 = internal constant [13 x sbyte] c"Hello
World\0a\00"
>>>
>>> declare int %printf(sbyte*, ...)
>>>
>>> implementation   ; Functions:
>>>
>>> int %main() {
>>>   %str2 = getelementptr [13 x sbyte]* %str1, long 0, long 0
>>>   call int(sbyte*, ...) *%printf(sbyte* %str2)
>>>   ret int 0
>>> }
>>>
>>> Why is getelementptr being given two "long 0" indices?
>>>
>>> Thanks for any help.
>>> -Ram
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> 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
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
-Chris

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