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