From: simonpj@microsoft.com <unknown>
Date: Fri, 21 Aug 2009 09:52:51 +0000 (+0000)
Subject: Fix Trac #3437: strictness of specialised functions
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=ef5376d5fa26d37c828a9c88dde3cf6f92f273ab;hp=ef5376d5fa26d37c828a9c88dde3cf6f92f273ab;p=ghc-hetmet.git

Fix Trac #3437: strictness of specialised functions

'lilac' helpful pin-pointed a space leak that was due to a specialised
function being insufficiently strict.  Here's the new comment in SpecConstr:

Note [Transfer strictness]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We must transfer strictness information from the original function to
the specialised one.  Suppose, for example

  f has strictness     SS
        and a RULE     f (a:as) b = f_spec a as b

Now we want f_spec to have strictess  LLS, otherwise we'll use call-by-need
when calling f_spec instead of call-by-value.  And that can result in
unbounded worsening in space (cf the classic foldl vs foldl')

See Trac #3437 for a good example.

The function calcSpecStrictness performs the calculation.
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