Andrew Pimlott wrote:
On Wed, Feb 01, 2006 at 12:28:59AM -0800, Andrew Pimlott wrote:
The Haskell code looks like
predQuery pred = case lookup pred ctxIdx of Just f -> {-# SCC "pq.foo'" #-} f
Note that f is a function, which we expect to be expensive when it is
called. However, that should be charged to the definition of the
function, right?
We found a work-around: We replaced f to the right of the annotation
with
\z z2 z3 -> f z z2 z3
and suddenly the right SCCs showed up in the profile (which enabled us
to find the real leak, which was fixed by one strictness annotation).
Actually, f takes 4 arguments, and forcing only 2 of them was not
sufficient; in fact, forcing only 2 caused a different misleading SCC to
dominate the profile! I don't claim to understand why.
I don't understand why either, but I do know that cost-centre stacks
behave strangely in some corner cases. I have some examples stashed
away somewhere, and it's been a long term ToDo item to really pin down
the semantics of CCSs. If you could encapsulate your example as a bug
report (preferably make it as small as possible), that would be great.
Cheers,
Simon
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
