[mlir][VectorOps] Fold extract on constant_mask (#183780)
Fold `vector.extract(vector.constant_mask)` to `vector.constant_mask` if
possible.
If the static position is outside of the masked area, the pattern will
fold to a constant all-false value instead.
Dynamic positions are only supported if the mask covers the entire
vector in that dimension.
Assisted-by: Claude Code
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Signed-off-by: Lukas Sommer <lukas.sommer@amd.com>
