llvm: unify lowering via Resolver and Cursor; remove non-sealed PHI wiring; apply Resolver to extern/call/boxcall/arrays/maps/mem; add llvmlite harness docs; add LLVM layer overview; add LoopForm preheader

src/llvm_py/instructions/ret.py

@@ -0,0 +1,49 @@
+"""
+Return instruction lowering
+Handles void and value returns
+"""
+
+import llvmlite.ir as ir
+from typing import Dict, Optional
+
+def lower_return(
+    builder: ir.IRBuilder,
+    value_id: Optional[int],
+    vmap: Dict[int, ir.Value],
+    return_type: ir.Type
+) -> None:
+    """
+    Lower MIR Return instruction
+    
+    Args:
+        builder: Current LLVM IR builder
+        value_id: Optional return value ID
+        vmap: Value map
+        return_type: Expected return type
+    """
+    if value_id is None:
+        # Void return
+        builder.ret_void()
+    else:
+        # Get return value
+        ret_val = vmap.get(value_id)
+        if not ret_val:
+            # Default based on return type
+            if isinstance(return_type, ir.IntType):
+                ret_val = ir.Constant(return_type, 0)
+            elif isinstance(return_type, ir.DoubleType):
+                ret_val = ir.Constant(return_type, 0.0)
+            else:
+                # Pointer type - null
+                ret_val = ir.Constant(return_type, None)
+        
+        # Type adjustment if needed
+        if hasattr(ret_val, 'type') and ret_val.type != return_type:
+            if isinstance(return_type, ir.IntType) and ret_val.type.is_pointer:
+                # ptr to int
+                ret_val = builder.ptrtoint(ret_val, return_type)
+            elif isinstance(return_type, ir.PointerType) and isinstance(ret_val.type, ir.IntType):
+                # int to ptr
+                ret_val = builder.inttoptr(ret_val, return_type)
+        
+        builder.ret(ret_val)