[project @ 2001-11-23 11:57:59 by simonmar]
Fix a long-standing bug in the cost attribution of cost-center stacks. The problem case is this: let z = _scc_ "z" f x in ... z ... previously we were attributing the cost of allocating the closure 'z' to the enclosing cost center stack (CCCS), when it should really be attributed to "z":CCCS. The effects are particularly visible with retainer profiling, because the closure retaining 'f' and 'x' would show up with the wrong CCS attached. To fix this, we need a new form of CCS representation internally: 'PushCC CostCentre CostCentreStack' which subsumes (and therefore replaces) SingletonCCS. SingletonCCS is now represented by 'PushCC cc NoCCS'. The CCS argument to SET_HDR may now be an arbitrary expression, such as PushCostCentre(CCCS,foo_cc), as may be the argument to CCS_ALLOC(). So we combine SET_HDR and CCS_ALLOC into a single macro, SET_HDR_, to avoid repeated calls to PushCostCentre().