[llvm-dev] type information about instruction

[Tim Northover via llvm-dev]

On 21 July 2017 at 04:49, Anastasiya Ruzhanskaya via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I would like to keep info about size and type info of all instructions ( and
> Values at the same time). I can do this by extracting type of the Values,
> but if I have still some unused instructions , I can't keep track on them. I
> try to convert them to Value and get the type or simply get the type of
> instruction, but have the following error:
>
> Assertion `Ty->isSized() && "Cannot getTypeInfo() on a type that is
> unsized!"' failed.

You've got two issues you need to take account of here.

First is that the Type of an instruction is the type of the Value it
produces, which isn't necessarily what you want. Some instructions
("ret" in your case, but also other branches, and "store") produce no
actual value that can be used later so their type is "void" which has
no size. What you probably want is the type of one of the operands
(RetI->getOperand(0)->getType() for example would be "i32" in your
example).

The other thing you're likely to hit is that aggregate types can have
sizes that depend on the DataLayout. For example {i32, i64} might have
size 96 or 128 depending on the ABI. So you should be using
DataLayout::getTypeSizeInBits if you need to cover these cases instead
of Type's own accessor.

Cheers.

Tim.