[llvm] [DirectX] Add support for Raw Buffer Loads and Stores for scalars and vectors of doubles and i64s in SM6.2 and earlier (PR #146627)

[Sarah Spall via llvm-commits]

spall wrote:

> We need a typedbuffer test cases that has two runlines. One where we specify in the target flag sm6.2 and one where we specify sm6.3. This way we have a case where we show the backport support and the difference of behaviors between the two shader models.

This PR is only meant to address RawBuffers; you want a test to show this doesn't regress the behavior for typedbuffers in SM6.3?

https://github.com/llvm/llvm-project/pull/146627