wasm-opt doesn't drop some stack shuffling instructions before unreachable

[osa1]

When I optimize the attached .wasm with the current main branch (9792f2c) using this invocation:

wasm-opt \
      -g \
      --all-features \
      --closed-world \
      --traps-never-happen \
      --type-unfinalizing \
      -Os \
      --type-ssa \
      --gufa \
      -Os \
      --type-merging \
      -Os \
      --type-finalizing \
      test.wasm -o test.opt.wasm

The generated .wasm has 34 instruction sequences of drop; unreachable.

In those cases the drop instruction could be dropped.

test.wasm.zip

[kripken]

Thanks @osa1 , that was indeed a missed optimization. I opened #6719 to add it.