[clang] [compiler-rt] [libc] [flang] [clang-tools-extra] [mlir] [llvm] [libcxx] [mlir][Linalg] Support dynamic tiles in `lower_pack` transform (PR #76003)

[Han-Chung Wang via cfe-commits]

hanhanW wrote:

I'm -1 on using `tensor.reshape` op. IMO, we should only use tensor.expand/collapse_shape; they work much better with existing transformations.

Out of curiosity, what use case do you have in mind? Why do we lower fully dynamic pack op? If it is at high level graph level, we can just use `tensor.pack` which carries more meaningful information. If it is at low level stage (e.g., around vectorization), I think the inner tile sizes should already be resolved to static values? In this context, we can still use `tensor.expand_shape`. It supports the case where one dynamic extent can be expanded into a single dynamic extent and other static extents (e.g., `? -> ?x4`).

https://github.com/llvm/llvm-project/pull/76003