llvm dev - Dec 2016 - How to get the value for casting in a bitcast instruction more efficiently?

Hi everyone,

This is a simple question but is there an efficient way to get the
*value for casting* directly from a bitcast instruction?

bitcast format :<result> = bitcast <ty> <*value*> to
<ty2>

For example, if i have

MemAddr
...
0x3d61238   %key = alloca [16 x i8], align 16
0x3d612a8   %plain_text = alloca [64 x i8], align 16
0x3d61318   %key1 = bitcast [16 x i8]* %key to i8*
...

The way i am using is processing all opcodes in %key1, and go back to
find %key along the def-use chain. But is there a better way for doing
this?

Thanks very much!

Best
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This might help:

http://llvm.org/docs/ProgrammersManual.html#the-value-class

Or maybe I'm misunderstanding what you mean by "efficient way to get
the
value". When you say 'value', I'm assuming you mean the class.
In your
case, AllocaInst inherits from value.

-Ryan

On Thu, Dec 15, 2016 at 10:24 AM, Shen Liu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi everyone,
>
> This is a simple question but is there an efficient way to get the *value
for casting* directly from a bitcast instruction?
>
> bitcast format :<result> = bitcast <ty> <*value*> to
<ty2>
>
> For example, if i have
>
> MemAddr
> ...
> 0x3d61238   %key = alloca [16 x i8], align 16
> 0x3d612a8   %plain_text = alloca [64 x i8], align 16
> 0x3d61318   %key1 = bitcast [16 x i8]* %key to i8*
> ...
>
> The way i am using is processing all opcodes in %key1, and go back to find
%key along the def-use chain. But is there a better way for doing this?
>
> Thanks very much!
>
> Best
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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Hi Ryan,

Thanks for your reply!  Yes i can use llvm::Use.get() API to do this, i
just want to know whether there's a better way(e.g. an existed API like
getValue()) to make my code look more professional.

On Thu, Dec 15, 2016 at 2:58 PM, Ryan Taylor via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> This might help:
>
> http://llvm.org/docs/ProgrammersManual.html#the-value-class
>
> Or maybe I'm misunderstanding what you mean by "efficient way to
get the
> value". When you say 'value', I'm assuming you mean the
class. In your
> case, AllocaInst inherits from value.
>
> -Ryan
>
> On Thu, Dec 15, 2016 at 10:24 AM, Shen Liu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi everyone,
>>
>> This is a simple question but is there an efficient way to get the
*value for casting* directly from a bitcast instruction?
>>
>> bitcast format :<result> = bitcast <ty> <*value*> to
<ty2>
>>
>> For example, if i have
>>
>> MemAddr
>> ...
>> 0x3d61238   %key = alloca [16 x i8], align 16
>> 0x3d612a8   %plain_text = alloca [64 x i8], align 16
>> 0x3d61318   %key1 = bitcast [16 x i8]* %key to i8*
>> ...
>>
>> The way i am using is processing all opcodes in %key1, and go back to
find %key along the def-use chain. But is there a better way for doing this?
>>
>> Thanks very much!
>>
>> Best
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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