• simonpj's avatar
    [project @ 2000-08-01 09:08:25 by simonpj] · fe69f3c1
    simonpj authored
    Simon's Marktoberdorf Commits
    
    1.  Tidy up the renaming story for "system binders", such as
    dictionary functions, default methods, constructor workers etc.  These
    are now documented in HsDecls.  The main effect of the change, apart
    from tidying up, is to make the *type-checker* (instead of the
    renamer) generate names for dict-funs and default-methods.  This is
    good because Sergei's generic-class stuff generates new classes at
    typecheck time.
    
    
    2.  Fix the CSE pass so it does not require the no-shadowing invariant.
    Keith discovered that the simplifier occasionally returns a result
    with shadowing.  After much fiddling around (which has improved the
    code in the simplifier a bit) I found that it is nearly impossible to
    arrange that it really does do no-shadowing.  So I gave up and fixed
    the CSE pass (which is the only one to rely on it) instead.
    
    
    3. Fix a performance bug in the simplifier.  The change is in
    SimplUtils.interestingArg.  It computes whether an argment should 
    be considered "interesting"; if a function is applied to an interesting
    argument, we are more likely to inline that function.
    Consider this case
    	let x = 3 in f x
    The 'x' argument was considered "uninteresting" for a silly reason.
    Since x only occurs once, it was unconditionally substituted, but
    interestingArg didn't take account of that case.  Now it does.
    
    I also made interestingArg a bit more liberal.  Let's see if we
    get too much inlining now.
    
    
    4.  In the occurrence analyser, we were choosing a bad loop breaker.
    Here's the comment that's now in OccurAnal.reOrderRec
    
        score ((bndr, rhs), _, _)
    	| exprIsTrivial rhs 	   = 3	-- Practically certain to be inlined
    		-- Used to have also: && not (isExportedId bndr)
    		-- But I found this sometimes cost an extra iteration when we have
    		--	rec { d = (a,b); a = ...df...; b = ...df...; df = d }
    		-- where df is the exported dictionary. Then df makes a really
    		-- bad choice for loop breaker
    
    I also increased the score for bindings with a non-functional type, so that
    dictionaries have a better chance of getting inlined early
    
    
    5. Add a hash code to the InScopeSet (and make it properly abstract)
    This should make uniqAway a lot more robust.  Simple experiments suggest
    that uniqAway no longer gets into the long iteration chains that it used
    to.
    
    
    6.  Fix a bug in the inliner that made the simplifier tend to get into
    a loop where it would keep iterating ("4 iterations, bailing out" message).
    In SimplUtils.mkRhsTyLam we float bindings out past a big lambda, thus:
    	x = /\ b -> let g = \x -> f x x
    		    in E
    becomes
    	g* = /\a -> \x -> f x x
    	x = /\ b -> let g = g* b in E
    	
    It's essential that we don't simply inling g* back into the RHS of g,
    else we will be back to square 1.  The inliner is meant not to do this
    because there's no benefit to the inlining, but the size calculation
    was a little off in CoreUnfold.
    
    
    7.  In SetLevels we were bogus-ly building a Subst with an empty in-scope
    set, so a WARNING popped up when compiling some modules.  (knights/ChessSetList
    was the example that tickled it.)  Now in fact the warning wasn't an error,
    but the Right Thing to do is to carry down a proper Subst in SetLevels, so
    that is what I have now done.  It is very little more expensive.
    fe69f3c1
MkIface.lhs 21.9 KB