llvm dev - Nov 2016 - Using ConstantDataVector instead of ConstantVector

Hello.
     I'm curious why can't I convert a Value like
       <16 x i16> <i16 2, i16 2, i16 2, i16 2, i16 2, i16 2, i16 2...
i16 2>
      to ConstantVector - using llvm::dyn_cast<llvm::ConstantVector>()
returns NULL.

     However, converting it with dyn_cast to ConstantDataVector fortunately
works.

     Note that at
http://llvm.org/docs/doxygen/html/classllvm_1_1ConstantDataVector.html
it is written "A vector constant whose element type is a simple
1/2/4/8-byte integer or
float/double", etc. This is a bit misleading, since vectors of bigger sizes
can be used.

   Thank you,
     Alex

On 11/9/2016 1:30 AM, Alex Susu via llvm-dev wrote:
>   Hello.
>     I'm curious why can't I convert a Value like
>       <16 x i16> <i16 2, i16 2, i16 2, i16 2, i16 2, i16 2, i16
2...
> i16 2>
>      to ConstantVector - using llvm::dyn_cast<llvm::ConstantVector>()
> returns NULL.
>
>     However, converting it with dyn_cast to ConstantDataVector 
> fortunately works.
>
>     Note that at 
> http://llvm.org/docs/doxygen/html/classllvm_1_1ConstantDataVector.html 
> it is written "A vector constant whose element type is a simple 
> 1/2/4/8-byte integer or float/double", etc. This is a bit misleading, 
> since vectors of bigger sizes can be used.
I think you somehow found some old doxygen pages? 
http://llvm.org/doxygen/classllvm_1_1Constant.html is what it looks like 
on trunk.

The class hierarchy is set up the way it is because it's convenient for 
the implementation; essentially, ConstantAggregate subclasses are 
constants which use other constants, and ConstantData subclasses don't 
use other constants.

You can use Constant::getAggregateElement() if you need to iterate over 
the elements of a constant of vector type.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project

> On Nov 9, 2016, at 1:30 AM, Alex Susu via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
>  Hello.
>    I'm curious why can't I convert a Value like
>      <16 x i16> <i16 2, i16 2, i16 2, i16 2, i16 2, i16 2, i16
2... i16 2>
>     to ConstantVector - using llvm::dyn_cast<llvm::ConstantVector>()
returns NULL.
> 
>    However, converting it with dyn_cast to ConstantDataVector fortunately
works.
> 
>    Note that at
http://llvm.org/docs/doxygen/html/classllvm_1_1ConstantDataVector.html it is
written "A vector constant whose element type is a simple 1/2/4/8-byte
integer or float/double", etc. This is a bit misleading, since vectors of
bigger sizes can be used.

This is the *individual element* type, did you misread and thought it was the
number of elements in the vector? Or to total byte size of the vector?

The implementation is clear limiting to these elements AFAICT.

— 
Mehdi