`IndexSwitchLowering` stored case values as `SmallVector<int32_t>`,
which silently truncated any `int64_t` case value larger than INT32_MAX
(e.g. `4294967296` became `0`). The `cf.switch` flag was also created
via `arith.index_cast index -> i32`, losing the upper 32 bits on 64-bit
platforms.
Fix: store case values as `SmallVector<APInt>` with 64-bit width, cast
the index argument to `i64`, and use the `ArrayRef<APInt>` overload of
`cf::SwitchOp::create` so the resulting switch correctly uses `i64` case
values and flag type.
Fixes#111589
Assisted-by: Claude Code
acbf3f3186