Class-pair init constructor now registers a single hidden ivar
on each sx-defined class:
class_addIvar(cls, "__sx_state", 8, 3, "^v")
before objc_registerClassPair. After the class is registered,
the constructor calls class_getInstanceVariable to fetch the
runtime Ivar handle and stores it in a per-class global
'__<ClassName>_state_ivar : *void'. Trampolines (A.4b.ii) will
read this global to 'object_getIvar' the state struct pointer.
lower.zig declares the per-class global at scan time
(declareObjcDefinedStateIvarGlobal) so emit_llvm finds it by
name when populating. Encoding '^v' = void* (a generic pointer
— the runtime treats it as opaque storage). log2 alignment = 3
for 8-byte pointer alignment on 64-bit.
144-objc-class-ivar-registration.sx exercises the round-trip:
after main starts, class_getInstanceVariable(SxFoo, "__sx_state")
returns non-null. Runs against the real Obj-C runtime on macOS.
142's IR snapshot refreshed to include the new constructor body
(class_addIvar + class_getInstanceVariable + ivar-global store).
173 example tests pass (+1 from 144). zig build test green.
c2178c062b