Commit 13a428ca authored by simonpj's avatar simonpj
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[project @ 2002-01-04 11:35:47 by simonpj]

Comments only
parent 6346938c
......@@ -578,6 +578,11 @@ callSiteInline dflags active_inline inline_call occ id arg_infos interesting_con
-- then if the context is totally uninteresting (not applied, not scrutinised)
-- there is no point in substituting because it might just increase allocation,
-- by allocating the function itself many times
-- Note [Jan 2002]: this comment looks out of date. The actual code
-- doesn't inline *ever* in an uninteresting context. Why not? I
-- think it's just because we don't want to inline top-level constants
-- into uninteresting contexts, lest we (for example) re-nest top-level
-- literal lists.
--
-- Note: there used to be a '&& not top_level' in the guard above,
-- but that stopped us inlining top-level functions used only once,
......
......@@ -756,7 +756,16 @@ big the RHS might be. If this is the case we don't simplify the RHS
first, but just inline it un-simplified.
This is much better than first simplifying a perhaps-huge RHS and then
inlining and re-simplifying it.
inlining and re-simplifying it. Indeed, it can be at least quadratically
better. Consider
x1 = e1
x2 = e2[x1]
x3 = e3[x2]
...etc...
xN = eN[xN-1]
We may end up simplifying e1 N times, e2 N-1 times, e3 N-3 times etc.
NB: we don't even look at the RHS to see if it's trivial
We might have
......@@ -785,6 +794,9 @@ seems to be to do a callSiteInline based on the fact that there is
something interesting about the call site (it's strict). Hmm. That
seems a bit fragile.
Conclusion: inline top level things gaily until Phase 0 (the last
phase), at which point don't.
\begin{code}
preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> Bool
preInlineUnconditionally env top_lvl bndr
......@@ -795,7 +807,7 @@ preInlineUnconditionally env top_lvl bndr
-- top level, and preInlineUnconditionally floats them all back in.
-- Result is (a) static allocation replaced by dynamic allocation
-- (b) many simplifier iterations because this tickles
-- a related problem
-- a related problem; only one inlining per pass
--
-- On the other hand, I have seen cases where top-level fusion is
-- lost if we don't inline top level thing (e.g. string constants)
......
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