Add stack-to-local promotion, verify all optimizations end-to-end
Stack-to-local promotion (Phase 1):
- is_promotable() identifies straight-line words (no control flow/calls/I/O)
- StackSim maps stack slots to WASM locals
- Stack manipulation (Swap, Rot, Nip, Tuck, Dup, Drop) emits ZERO instructions
- Prologue loads items from memory, epilogue writes back
- ~7x instruction reduction for DUP * and similar patterns
End-to-end verification (16 tests proving each optimization is active):
- verify_peephole_active: 0+ elimination
- verify_constant_folding_active: 3 4 + folded to 7
- verify_strength_reduction_active: 4* becomes shift
- verify_dce_active: code after EXIT eliminated
- verify_tail_call_active: recursive RECURSE works
- verify_inlining_active: small word inlined and folded
- verify_compound_ops_active: 2DUP works
- verify_dsp_caching_active: factorial via RECURSE
- verify_consolidation_active: CONSOLIDATE word
- verify_stack_promotion_*: 7 tests for promoted codegen
22 additional codegen promotion tests (wasmtime execution).
Fix F~ stack overflow panic (checked_sub instead of unchecked).
380 unit tests + 11 compliance tests, all passing.
ok
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