[LLVMdev] How to get the indices in an getelementptr Value?

[Qiuping Yi]

I find the root of my problem. I mistakenly invoking stripPointerCasts()
before casting. Now I can access these elements by casting the related
value to subclass llvm::constantExpr or GEPOperator. Thank you all.


--------------------------------------------
Qiuping Yi
Institute Of Software
Chinese Academy of Sciences

On Sun, Nov 23, 2014 at 3:17 PM, Qiuping Yi <yiqiuping at gmail.com> wrote:

> Hi David Majnemer,
>
> I found I can cast value "i32* getelementptr inbounds (%struct.Args*
> @globalArg, i64 0, i32 2)" to class GEPOperator, but failed on value "i32*
> getelementptr inbounds (%struct.Args* @globalArg, i64 0, i32 0)". As my
> previous email described, I found that the later value is a class
> llvm::Constant but not a subclass llvm::ConstantExpr. I find it is very
> strange.
>
>
> --------------------------------------------
> Qiuping Yi
> Institute Of Software
> Chinese Academy of Sciences
>
> On Sun, Nov 23, 2014 at 4:08 AM, David Majnemer <david.majnemer at gmail.com>
> wrote:
>
>> On Sat, Nov 22, 2014 at 11:09 AM, Sanjoy Das <
>> sanjoy at playingwithpointers.com> wrote:
>>
>>> Hi Qiuping,
>>>
>>> If I'm reading the IR correctly, what you have is a
>>> GetElementPtrConstantExpr [1].  It subclasses from llvm::Constant.
>>>
>>
>> If you want the same code to handle GetElementPtrConstantExpr *and*
>> GetElementPtrInst, you can use GEPOperator.
>>
>>
>>>
>>> Thanks,
>>> -- Sanjoy
>>>
>>> [1]:
>>> http://llvm.org/docs/doxygen/html/classllvm_1_1GetElementPtrConstantExpr.html
>>>
>>> On Sat, Nov 22, 2014 at 1:10 AM, Qiuping Yi <yiqiuping at gmail.com> wrote:
>>> > Hi Michael,
>>> >
>>> > Thank you very much.
>>> >
>>> > But idx_begin/idx_end iterators can only be used through a
>>> getelementptr
>>> > instruction, right? However, I think value "i32* getelementptr inbounds
>>> > (%struct.Args* @globalArg, i64 0, i32 2)" itself is not a getelementptr
>>> > instruction, so? Or could you tell me how can I get a getelementptr
>>> > instruction first from this value?
>>> >
>>> >
>>> > --------------------------------------------
>>> > Qiuping Yi
>>> > Institute Of Software
>>> > Chinese Academy of Sciences
>>> >
>>> > On Sat, Nov 22, 2014 at 4:49 PM, Michael Zolotukhin <
>>> mzolotukhin at apple.com>
>>> > wrote:
>>> >>
>>> >> Hi Qiuping,
>>> >>
>>> >> I guess you need to use getPointerOperand to access the pointer
>>> operand
>>> >> (@globalArg in your example) and idx_begin/idx_end iterators to access
>>> >> indexes. You can find a short description of these functions in
>>> >> documentation [1], or look at examples of their uses in the code,
>>> e.g. in
>>> >> lib/Transforms/InstCombine/*.cpp.
>>> >>
>>> >> [1] http://llvm.org/doxygen/classllvm_1_1GetElementPtrInst.html
>>> >>
>>> >> Best regards,
>>> >> Michael
>>> >>
>>> >> On Nov 22, 2014, at 12:32 AM, Qiuping Yi <yiqiuping at gmail.com> wrote:
>>> >>
>>> >> Hi, all
>>> >>
>>> >> I am a LLVM user. I want to get every element in the next instruction:
>>> >>
>>> >> %0 = load i32* getelementptr inbounds (%struct.Args* @globalArg, i64
>>> 0,
>>> >> i32 2), align 4, !dbg !85, !clap !86
>>> >>
>>> >> Now I can only get value "i32* getelementptr inbounds (%struct.Args*
>>> >> @globalArg, i64 0, i32 2)" through "getOperand(0)",
>>> >> but I can not get "%struct.Args* @globalArg", "i64 0", and "i32 2" in
>>> this
>>> >> instruction.
>>> >>
>>> >> I know I can get the indices of getelementptr instructions through
>>> >> "getOperand()", but now in the previous example,
>>> >> I want to get the indices from a getlementptr value. How should I do?
>>> >> Thank you in advance.
>>> >>
>>> >>
>>> >> Best Regards!
>>> >>
>>> >> --------------------------------------------
>>> >> Qiuping Yi
>>> >> Institute Of Software
>>> >> Chinese Academy of Sciences
>>> >> _______________________________________________
>>> >> 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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>>
>>
>
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