`mlir::affine::simplifyConstrainedMinMaxOp` called
`canonicalizeMapAndOperands` with `newOperands` that could contain null
`Value()`s. These nulls came from
`unpackOptionalValues(constraints.getMaybeValues(), newOperands)` where
internal constraint variables added by `appendDimVar` (for `dimOp`,
`dimOpBound`, and `resultDimStart*`) have no associated SSA values.
Passing null Values to `canonicalizeMapAndOperands` risks undefined
behavior:
- `seenDims.find(null_value)` in the DenseMap causes all null operands
to collide at the same key, producing incorrect dim remapping.
- Any null operand that remains referenced in the result map would
propagate as a null Value into `AffineValueMap`, crashing callers that
try to use those operands to create ops.
Fix: Before calling `canonicalizeMapAndOperands`, filter null operands
from `newOperands` by replacing their dim/symbol positions in `newMap`
with constant 0 (safe because internal constraint dims should not appear
in the bound map expression) and compacting `newOperands` to contain
only non-null Values.
Fixes#127436
Assisted-by: Claude Code
d725513e7d