transforms.artiq_ir_generator: split out finally→reraise control flow.

This makes it accessible to introspect by local access validator,
making some previously rejected code valid.

Fixes #331.

artiq/compiler/transforms/artiq_ir_generator.py

@@ -690,6 +690,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
             handlers.append((handler, post_handler))
 
         if any(node.finalbody):
+            # Finalize and continue after try statement.
             self.final_branch = old_final_branch
 
             finalizer = self.add_block("finally")
@@ -698,13 +699,17 @@ class ARTIQIRGenerator(algorithm.Visitor):
             self.visit(node.finalbody)
             post_finalizer = self.current_block
 
-            reraise = self.add_block('try.reraise')
+            # Finalize and reraise. Separate from previous case to expose flow
-            reraise.append(ir.Reraise(self.unwind_target))
+            # to LocalAccessValidator.
+            finalizer_reraise = self.add_block("finally.reraise")
+            self.current_block = finalizer_reraise
+
+            self.visit(node.finalbody)
+            self.terminate(ir.Reraise(self.unwind_target))
 
         self.current_block = tail = self.add_block("try.tail")
         if any(node.finalbody):
             final_targets.append(tail)
-            final_targets.append(reraise)
 
             for block in final_paths:
                 block.append(ir.Branch(finalizer))
@@ -713,8 +718,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 body.append(ir.SetLocal(final_state, "$cont", tail))
                 body.append(ir.Branch(finalizer))
 
-            cleanup.append(ir.SetLocal(final_state, "$cont", reraise))
+            cleanup.append(ir.Branch(finalizer_reraise))
-            cleanup.append(ir.Branch(finalizer))
 
             for handler, post_handler in handlers:
                 if not post_handler.is_terminated():

artiq/test/lit/exceptions/finally_reraise.py

@@ -0,0 +1,22 @@
+# RUN: %python -m artiq.compiler.testbench.jit %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+# REQUIRES: exceptions
+
+x = 1
+
+def doit():
+    try:
+        if x > 0:
+            raise ZeroDivisionError
+        r = 0
+    finally:
+        print('final')
+    return r
+
+try:
+    doit()
+except ZeroDivisionError:
+    print('caught')
+
+# CHECK-L: final
+# CHECK-L: caught