Exclusive branches in diamond call graphs

[tilk]

Suppose we have a code like this:

@def_method(m, method1):
def _():
    method3(m)

@def_method(m, method2):
def _():
    method3(m)

with Transaction().body(m):
    with m.If(foo):
        method1(m)
    with m.Else():
        method2(m)

Currently, an exception "Method 'method3' can't be called twice from the same transaction" will be raised. But these calls are on syntactically different branches, so they could technically be allowed.