Commit e66106a5 authored by simonmar's avatar simonmar
Browse files

[project @ 2003-07-30 10:01:46 by simonmar]

Throw away an SCC on a single variable.  This seems to be justified:
there can be no work to attribute to the current cost centre when
evaluating a lone variable, other than the act of entering the
closure, and possibly returning immediately if it is a variable.

This also fixes a bug in profiling, which showed up as incorrect
transformations made by the simplifier resulting in extra strictness.
The simplifier assumes (in Simplify.simplLazyBind) that (let x = e in
x) will have been turned into x, but this isn't true if there's an SCC
around the x.
parent 31d1bcbe
......@@ -214,7 +214,12 @@ mkCoerce2 to_ty from_ty expr
mkSCC :: CostCentre -> Expr b -> Expr b
-- Note: Nested SCC's *are* preserved for the benefit of
-- cost centre stack profiling
-- Note2: We throw away an SCC on a single variable. If the
-- variable is a value, then there is no work to do in
-- evaluating it, and if it is a thunk, then it will be
-- attributed to its own CCS anyhow.
mkSCC cc (Lit lit) = Lit lit
mkSCC cc (Var v) = Var v
mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
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