[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.