#8832: Constant-folding regression wrt `clearBit (bit 0) 0 ` -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: high | Milestone: 7.12.1 Component: Compiler | Version: 7.8.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | simplCore/should_compile/T8832 Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by bgamari): The problem here is that the `Bits` instance for `Integer` overrides `bit`, using it's own `bitInteger` function in place of the usual `bitDefault`. `bitDefault` is constant folded by `PrelRules` by virtue of being implemented in terms of `shiftL`. This is presumably done to optimize the case of construction of a `BigNat` for large arguments, but `bitBigNat#`, which is what handles this case, is currently just the naive implementation with a TODO. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8832#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler