Defer CallStack computations by representing them as data constructors.
#1202
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…ors. This avoids expensive calls to `combineCallStacks` in the common case; the actual call stack values are only computed in the case where they need to be printed out.
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On a particular large example computation I have, which divides some degree-14,000 integer polynomials, here are the runtime numbers (when running without profiling):
So we're still paying a significant penalty for call stacks, but a significantly smaller one. |
| @@ -92,7 +113,13 @@ combineCallStacks :: | |||
| CallStack {- ^ call stack of the application context -} -> | |||
| CallStack {- ^ call stack of the function being applied -} -> | |||
| CallStack | |||
| combineCallStacks appstk fnstk = appstk <> dropCommonPrefix appstk fnstk | |||
| combineCallStacks appstk fnstk = CombineCallStacks appstk fnstk | |||
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I'm not sure how common this is, but is it worth checking for the special cases where one of the arguments is the EmptyCallStack?
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Good idea. That would cost very little to check for, and it would strictly reduce the memory consumption whenever that rule matches.
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I added special cases for EmptyCallStack. Looking at +RTS -s, any performance differences (on my use case at least) are lost in the noise. But we might as well keep it in; it only reduces total allocation by 0.01% but it might be more on other examples.
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I don't know if we should do anything about it now, but I've noticed in the past that the call stack combination algorithm doesn't always produce the results I expect. My hypothesis is that this is because the algorithm I lifted from GHC assumes that lambda-lifting has been done, whereas Cryptol does not do this pass. As a result, functions nested with |
This avoids expensive calls to
combineCallStacksin the common case; the actual call stack values are only computed in the case where they need to be printed out.This helps with #1201.