[llvm-dev] When I got a Operator by iterating a Value's User, how can I got the relevant Instruction?

[周书林 via llvm-dev]

Sure!

The following snippet is the main function I implemented to visit the Users
of GlobalVariables.

for(Value::user_iterator i=gv->user_begin(), e=gv->user_end(); i!=e; i++)
{
    User* cur_user = *i;
    cur_user->print(llvm::outs());
    llvm::outs()<<"\n";

    if(Instruction* inst = dyn_cast<Instruction>(cur_user))
    {
        // record source location info
    }
    else if(GEPOperator* gepo = dyn_cast<GEPOperator>(cur_user))
    {
        llvm::outs()<<"It is a GEPOperator.\n";

        for(aute it=gepo->user_begin(); it!=gepo->uesr_end(); ++it)
        {
            User* user = *it;
            llvm::outs()<<"One of the User:";
            user->print(llvm::outs());
            llvm::outs()<<"\n";
        }
    }
}


And the source file of test case is, the "ttt.field_b" in the main() is
presented as a GEPOperator in the generated IR file.

struct TTT{
    int field_a;
    int field_b;
    int field_c;
};
struct TTT ttt;

int main()
{
    ...
    int b = a - ttt.field_b;
    ...
}




Craig Topper <craig.topper at gmail.com> 于2021年6月18日周五 下午12:55写道：

> Can you share your code?
>
> On Thu, Jun 17, 2021 at 9:44 PM 周书林 <zhoushulin1992 at gmail.com> wrote:
>
>> Hi Craig,
>>
>> I have tried to visit the Users of current GEPOperator, but the results
>> are not what I am looking for.
>> In detail, when I tried to get the Users of GEPOperator of the LoadInst,
>> i.e. * getelementptr inbounds (%struct.TTT, %struct.TTT* @ttt, i32 0,
>> i32 2) *,
>> the results are turned out to be Users of GlobalVariable *@ttt, *i.e.
>> something like
>> *i8* bitcast (%struct.TTT* @ttt to i8*)*, or *i32* getelementptr
>> inbounds (%struct.TTT, %struct.TTT* @ttt, i32 0, i32 1)*.
>>
>> I am not sure what happened here. Is that the def-use chain of structural
>> global variables always contains the whole information related to the
>> global variable?
>>
>> Sincerely,
>> Shulin
>>
>> Craig Topper <craig.topper at gmail.com> 于2021年6月18日周五 上午10:14写道：
>>
>>> I see so you want to see where the GlobalVariable is accesssed. You
>>> should be able to get the Users of the ConstantExpr as well, those will
>>> either be another ConstantExpr or an Instruction. In your example, one of
>>> the Users of the GEPOperator should be the LoadInst.
>>>
>>> ~Craig
>>>
>>>
>>> On Thu, Jun 17, 2021 at 7:06 PM 周书林 <zhoushulin1992 at gmail.com> wrote:
>>>
>>>> Hi Craig,
>>>>
>>>> I started from GlobalVaribles, so there are situations that I met the
>>>> ConstantExprs, i.e. some Operators.
>>>>
>>>> Craig Topper <craig.topper at gmail.com> 于2021年6月18日周五 上午8:37写道：
>>>>
>>>>> How did you choose where you started from? An Instruction can only be
>>>>> used by another Instruction, but it seems you've started from a Constant
>>>>> which can be used by ConstantExprs.
>>>>>
>>>>> ~Craig
>>>>>
>>>>>
>>>>> On Thu, Jun 17, 2021 at 5:25 PM 周书林 via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> Hi Michael,
>>>>>>
>>>>>> Thank you very much!
>>>>>> I have a further question: if I want to get the dataflow of a target
>>>>>> Value, is there any way to handle these situations when iterate the
>>>>>> Users?Or only by iterator all the instructions and their operands?
>>>>>>
>>>>>> Sincerely,
>>>>>> Shulin
>>>>>>
>>>>>> Michael Kruse <llvmdev at meinersbur.de> 于2021年6月18日周五 上午5:11写道：
>>>>>>
>>>>>>> Am Do., 17. Juni 2021 um 10:24 Uhr schrieb 周书林 via llvm-dev
>>>>>>> <llvm-dev at lists.llvm.org>:
>>>>>>> > %39 = load i32, i32* getelementptr inbounds (%struct.TTT,
>>>>>>> %struct.TTT* @ttt, i32 0, i32 2), align 8, !dbg !971
>>>>>>>
>>>>>>> %39 is the LoadInst, while getelementptr is its second operand. It is
>>>>>>> inlined because it is an llvm::Constant, not an instruction.
>>>>>>> Constants
>>>>>>> do not participate in use/user-chains and hence there is no link from
>>>>>>> GEP to the LoadInst that is using it. The constant GEP object may be
>>>>>>> used by an arbitrary number of other instructions, other constants in
>>>>>>> the same or other functions.
>>>>>>>
>>>>>>> Node that there "GEPOperator" can represent either a
>>>>>>> GetElementPtrInst
>>>>>>> (i.e. an instruction) or a GEP constant expression (derived from
>>>>>>> ConstantExpr)
>>>>>>>
>>>>>>> Michael
>>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>> --
> ~Craig
>
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