[clang] [lld] [llvm] [mlir] [IR] Introduce `T<address space>` to `DataLayout` to represent flat address space if a target supports it (PR #108786)

[Shilei Tian via llvm-commits]

shiltian wrote:

> I would like to avoid adding additional special properties to AS0, or defining the flat concept.

How can we add a new specification w/o defining it?

> The simple solution is just have a switch over the target architecture in Attributor.

That means in the future when a new (GPU/accelerator) target is added, someone has to know that is one place to add a new case. FWIW, it is not just Attributor. The situation applies to all passes that potentially don't have access to TTI/TM.

I don't really like the solution, but that is what I'm doing to move other PRs forward w/o being blocked by this one.

https://github.com/llvm/llvm-project/pull/108786