[GHC] #13360: Add a flag to enable inferring HasCallStack constraints

[GHC]

#13360: Add a flag to enable inferring HasCallStack constraints
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        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:                    |
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Comment (by gridaphobe):

 Interesting! So it appears that the overhead is coming from the contents
 of each entry in the call stack.

 I'm a bit surprised by this, the `String` and `SrcLoc` should both be
 floated out and shared between calls (like you did manually with
 `spuriousSrcLoc`). I wouldn't expect that to cause such an overhead.

 It would be good to isolate which part of the stack entries is causing the
 overhead, e.g. Is it the `String`s? (we could use `Addr#` like GHC does
 for compiler-generated errors) Is the number of fields in a `SrcLoc`
 causing one of GHC's size heuristics to act strangely? etc.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13360#comment:25>
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