#13360: Add a flag to enable inferring HasCallStack constraints -------------------------------------+------------------------------------- Reporter: gridaphobe | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by saurabhnanda): **UPDATE** It seems that GHC is optimising away all callstack related code if `callStack` is not actually being used (which was the case with `postgresql-simple`). Here are the same benchmarks as [https://ghc.haskell.org/trac/ghc/ticket/13360#comment:20: earlier], but with `callStack` [https://github.com/vacationlabs/postgresql- simple/commit/355f0bcefacfaa6dfb808b5bbbb4fa89956650ae: actually being used.] There seems to be a **1.6x perf penalty** in real-world IO-centric code. It seems to be quite a big perf penalty. How do I dig deeper? **HasCallStack, where the callStack is actually being used** {{{ benchmarking complicatedQuery/without error time 289.7 μs (250.6 μs .. 330.3 μs) 0.905 R² (0.850 R² .. 0.961 R²) mean 276.8 μs (263.2 μs .. 293.6 μs) std dev 49.36 μs (34.39 μs .. 70.50 μs) variance introduced by outliers: 92% (severely inflated) benchmarking complicatedQuery/with error time 269.1 μs (242.8 μs .. 294.2 μs) 0.947 R² (0.919 R² .. 0.979 R²) mean 274.3 μs (262.3 μs .. 286.1 μs) std dev 43.09 μs (33.99 μs .. 54.33 μs) variance introduced by outliers: 90% (severely inflated) }}} **Without HasCallStack** {{{ benchmarking complicatedQuery/without error time 183.9 μs (179.6 μs .. 189.9 μs) 0.992 R² (0.987 R² .. 0.997 R²) mean 186.6 μs (183.1 μs .. 193.1 μs) std dev 15.60 μs (11.45 μs .. 20.83 μs) variance introduced by outliers: 74% (severely inflated) benchmarking complicatedQuery/with error time 180.7 μs (176.3 μs .. 187.1 μs) 0.992 R² (0.984 R² .. 0.999 R²) mean 181.9 μs (179.4 μs .. 186.7 μs) std dev 11.55 μs (7.139 μs .. 19.47 μs) variance introduced by outliers: 61% (severely inflated) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13360#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler