#3073: Avoid reconstructing dictionaries in recursive instance methods
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Reporter: simonpj | Owner:
Type: run-time performance bug | Status: new
Priority: normal| Milestone:
Component: Compiler |Version: 6.10.1
Severity: normal| Keywords:
Difficulty: Unknown | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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Ganesh writes: I have a problem in GHC 6.10 with functions in a class
instance calling
other functions in the same class instance. It seems that the dictionary
is freshly constructed for this call, despite being already available.
The reason I care is that I want to memoise some expensive computations
inside the dictionary for each instance. [Obviously I also have to make
sure that the dictionary isn't constructed multiple times by external
callers, but I can make other arrangements to ensure that.]
To see the problem in action, run main from the attached code. In GHC 6.8
and before, this only executes the trace statement once. In GHC 6.10, the
trace statement executes twice, at all optimisation levels.
This seems related to #2902, but I'm a little unclear on whether it's the
same problem or not.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3073
GHC http://www.haskell.org/ghc/
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