validators.escape: cache_get result lives forever.

artiq/compiler/types.py

@@ -610,8 +610,13 @@ def is_function(typ):
 def is_rpc_function(typ):
     return isinstance(typ.find(), TRPCFunction)
 
-def is_c_function(typ):
-    return isinstance(typ.find(), TCFunction)
+def is_c_function(typ, name=None):
+    typ = typ.find()
+    if name is None:
+        return isinstance(typ, TCFunction)
+    else:
+        return isinstance(typ, TCFunction) and \
+            typ.name == name
 
 def is_builtin(typ, name=None):
     typ = typ.find()

artiq/compiler/validators/escape.py

@@ -87,7 +87,13 @@ class RegionOf(algorithm.Visitor):
             return None
 
     visit_BinOpT = visit_sometimes_allocating
-    visit_CallT = visit_sometimes_allocating
+
+    def visit_CallT(self, node):
+        if types.is_c_function(node.func.type, "cache_get"):
+            # The cache is borrow checked dynamically
+            return None
+        else:
+            self.visit_sometimes_allocating(node)
 
     # Value lives as long as the object/container, if it's mutable,
     # or else forever