[mlir][linalg] Fix UBSan division-by-zero in PackOp folding (#186271) When tensor-cast folding propagates a zero constant into a dynamic tile size, `FoldTensorCastPackOp` would proceed to fold the pack into an `expand_shape` using that zero tile — causing undefined behaviour (integer division/modulo by zero, caught by UBSan as SIGFPE). 1. Guard `FoldTensorCastPackOp`: bail out early if any of the resolved tile sizes is zero, preventing the invalid fold entirely. 2. Restrict the `hasZeros` check in `commonVerifierPackAndUnPackOp` to only inspect `Attribute` operands (statically-known zeros), not dynamic `Value` operands. The verifier can only meaningfully reject zero tiles that are statically visible; dynamic zeros are an inherently runtime condition. 3. Add `assert(*constantTile \!= 0)` guards in `requirePaddingValue` and `requirePaddingValueStrict` to document and enforce the precondition that static tile sizes passed to those helpers are non-zero. Also rename existing negative test cases from `no_fold_*`/`nofold_*` to `negative_*` for consistency with MLIR testing conventions, and add a regression test that ensures a pack with a zero tile size is not folded into `tensor.expand_shape`. Fixes #185352 Assisted-by: Claude Code
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