Rodrigo Mesquita authored Dec 18, 2025 and Marge Bot committed Apr 14, 2026

This commit adds support for static constructors when compiling and
linking ByteCode objects.

Top-level StgRhsCon get lowered to ProtoStaticCons rather than to
ProtoBCOs. A ProtoStaticCon gets allocated directly as a data con
application on the heap (using the new primop newConApp#).

Previously, we would allocate a ProtoBCO which, when evaluated, would
PACK and return the constructor.
A few more details are given in Note [Static constructors in Bytecode].

Secondly, this commit also fixes issue #25636 which was caused by
linking *unlifted* constructors in BCO instructions as
    - (1) a thunk indexing the array of BCOs in a module
    - (2) which evaluated to a BCO which still had to be evaluated to
      return the unlifted constructor proper.

The (2) issue has been resolved by allocating the static constructors
directly. The (1) issue can be resolved by ensuring that we allocate all
unlifted top-level constructors eagerly, and leave the knot-tying for
the lifted BCOs and top-level constructors only.

The top-level unlifted constructors are never mutually recursive, so we
can allocate them all in one go as long as we do it in topological
order. Lifted fields of unlifted constructors can still be filled by the
knot-tied lifted variables since in those fields it is fine to keep
those thunks. See Note [Tying the knot in createBCOs] for more details.

Fixes #25636

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Metric Decrease:
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