[project @ 1999-05-11 16:44:02 by keithw]
(this is number 7 of 9 commits to be applied together) The code generator now incorporates the update avoidance optimisation: a thunk of __o type is now made SingleEntry rather than Updatable. We want to verify that SingleEntry thunks are indeed entered at most once. In order to do this, -ticky turns on eager blackholing. Ordinary thunks will be dealt with by the RTS, but CAFs are blackholed by the code generator. We blackhole with new blackholes: SE_CAF_BLACKHOLE. We will enter one of these if we attempt to enter a SingleEntry thunk twice.