Revert "transforms.artiq_ir_generator: treat builtins in 'with' syntactically."

This reverts commit ccc993071b.

artiq/compiler/transforms/artiq_ir_generator.py

@@ -695,11 +695,9 @@ class ARTIQIRGenerator(algorithm.Visitor):
         context_expr_node  = node.items[0].context_expr
         optional_vars_node = node.items[0].optional_vars
 
-        if isinstance(context_expr_node, asttyped.NameT) and \
-                context_expr_node.id == "sequential":
+        if types.is_builtin(context_expr_node.type, "sequential"):
             self.visit(node.body)
-        elif isinstance(context_expr_node, asttyped.NameT) and \
-                context_expr_node.id == "parallel":
+        elif types.is_builtin(context_expr_node.type, "parallel"):
             parallel = self.append(ir.Parallel([]))
 
             heads, tails = [], []
@@ -717,9 +715,6 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 if not tail.is_terminated():
                     tail.append(ir.Branch(self.current_block))
 
-        else:
-            assert False
-
     # Expression visitors
     # These visitors return a node in addition to mutating
     # the IR.

artiq/compiler/transforms/inferencer.py

@@ -762,11 +762,7 @@ class Inferencer(algorithm.Visitor):
             self._unify(node.type, typ.find().instance,
                         node.loc, None)
         else:
-            diag = diagnostic.Diagnostic("error",
-                "builtin function '{name}' cannot be used in this context",
-                {"name": typ.name},
-                node.loc)
-            self.engine.process(diag)
+            assert False
 
     def visit_CallT(self, node):
         self.generic_visit(node)

lit-test/test/inferencer/error_illegal_builtin.py

@@ -1,5 +0,0 @@
-# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
-# RUN: OutputCheck %s --file-to-check=%t
-
-# CHECK-L: ${LINE:+1}: error: builtin function 'sequential' cannot be used in this context
-sequential()