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When storing a globalized variable whose expression is a Wasm constant expression (only refs to immutable globals, inline constants, array/struct allocations), emit it as an immutable global with the expression as its initializer instead of a mutable global with a default value and GlobalSet. Skip this optimisation when always is true (multiple stores from different code paths).
After the distance-based globalization pass, propagate to fixpoint: a block whose fields are all global/constant becomes global, and a closure whose free variables are all global/constant becomes global (cascading to its free variables via globalize_closure).
Allow blocks with up to 2 non-available fields to be globalized in the propagation pass. In code generation, use partial constant initialization: the ArrayNewFixed is emitted as an immutable global initializer with placeholder values, and only the non-available fields are patched via ArraySet in the function body. This enables cascading for nested blocks (e.g. linked lists) where globalizing an inner block makes it available for outer blocks.
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Put constant expressions at toplevel into global variables, in order to reduce the size of the toplevel function.