[PATCH] D25152: [RFC/WIP] CodeGen: Initial support for references to absolute symbols in immediate operands.

[Chandler Carruth via llvm-commits]

chandlerc added a comment.

I'm *really* excited to see this fixed. Our handling of these references has been a source of a lot of frustration.

A small comment on the overall design:

> This patch implements part of this change. Rather than introducing the
>  "absolute" flag, it just checks for !range metadata on GlobalObjects
>  (switching to the correct representation is a TODO).

So you're still planning on adding the `absolute` bit here? What will that gain us over the range metadata?

> At the SDAG level,
>  if a global reference has !range metadata and the target/object format
>  supports the required relocations (ELF only for now), we combine it into a
>  special ConstantSDNode which holds a reference to the symbol. Like any other
>  ConstantSDNode, this ConstantSDNode can appear as an immediate operand. This
>  means that we now have ConstantSDNodes which are not in fact constant integers,
>  but to a certain extent this seems like the least worst approach.

Oof. I see your explanation of why, but this does seem painful. We have both "target" and "opaque" constants already though (although i have *no* idea what "opaque" constants really are), so this doesn't really seem to make things much worse.

In some ways, modeling relocation constants as "target constants" makes a lot of sense...


https://reviews.llvm.org/D25152