[LLVMdev] GetElementPtrConstantExpr

[Alessio Giovanni Baroni]

Thanks to all! It's all ok now.

Alessio.



2012/12/19 Duncan Sands <baldrick at free.fr>

> On 19/12/12 10:25, Alessio Giovanni Baroni wrote:
>
>> Ok, now it's arising another problem. IR code that I obtain is the
>> following:
>>
>> i8* bitcast ([5 x i8] c"hello\00" to i8*)
>>
>
> You need to put your "hello" in a (constant) global variable.  You can then
> bitcast the address of the global to i8*.  I suggest you compile some C
> code
> that makes use of the address of a string using "clang -emit-llvm" to see
> how
> this can be done.
>
> Ciao, Duncan.
>
> PS: Unlike in C, in LLVM IR an array is not the same thing as a pointer to
> the
> first element.
>
>
>> generated from instructions:
>>
>> ConstantExpr::getBitCast (ConstantDataArray::getString (getGlobalContext
>> (),
>> "hello"), PointerType::get (Type::getInt8Ty (getGlobalContext ()), 0))
>>
>> but the LLC tool says: invalid cast opcode for cast from '[5 x i8]' to
>> 'i8*'.
>>
>> Any help?
>>
>>
>> 2012/12/18 Óscar Fuentes <ofv at wanadoo.es <mailto:ofv at wanadoo.es>>
>>
>>     Alessio Giovanni Baroni <alessiogiovanni.baroni at gmail.**com<alessiogiovanni.baroni at gmail.com>
>>
>>     <mailto:alessiogiovanni.**baroni at gmail.com<alessiogiovanni.baroni at gmail.com>>>
>> writes:
>>
>>      > Because I need to convert an [4 x i8] type to i8* in the
>> instantiation of a
>>      > GlobalVariable.
>>      > I have the follow declaration: %xxx = type { i8* } and I must emit
>> the
>>      > following variable:
>>      > @yyy = linkonce_odr constant %xxx { [4 x i8] c"hello\00" }, but
>> it's wrong.
>>      >
>>      > How do I do?
>>
>>     You can use the ConstantExpr::getBitCast static member function:
>>
>>     http://llvm.org/doxygen/**classllvm_1_1ConstantExpr.**html#**
>> aba93ec4079f8d709a1d5b47453107**82e<http://llvm.org/doxygen/classllvm_1_1ConstantExpr.html#aba93ec4079f8d709a1d5b4745310782e>
>>
>>     This is a common idiom on LLVM: a base class has static methods for
>>     creating instances of derived classes.
>>
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>>
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