[mlir] [llvm] [mlir][mesh] Add spmdization pass (PR #80518)

[Chengji Yao via llvm-commits]

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+// RUN: mlir-opt --mesh-spmdization --test-constant-fold %s | FileCheck %s
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yaochengji wrote:

Could you also add spmdiazation/reshard of a partial tensor?

E.g. a partial tensor resharded to a sharded tensor, then a reduce-scatter would be inserted.

https://github.com/llvm/llvm-project/pull/80518