[GHC] #3693: Show stack traces

[GHC]

#3693: Show stack traces
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        Reporter:  jpet              |            Owner:  Tarrasch
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.10.1
       Component:  Runtime System    |          Version:  6.10.4
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by scpmw):

 Status update: I have now finished polishing up the initial source-note
 patches for tracking source code relations throughout the Core and Stg
 stages:

 https://github.com/scpmw/ghc/commits/profiling-review2

 This is in many ways the most tricky part of the whole endeavour, as it
 touches pretty much every single pass that does something interesting with
 Core. It also extends the whole tickish framework a bit, which means cost-
 centres, HPC ticks and breakpoints have had some of their code rebuilt.

 On the other hand, it now passes the whole testsuite (minus T4891 and
 T5435_dyn_asm, which fail on master for me), and I tested that '-g' causes
 no extra allocations across nofib. I *think* it should be merge-ready for
 7.9.

 Notes for review (Simon?):

 - I tried to be chatty with the comments and spell out exactly how I
 understand the properties of tickishs. Some new tickish flags and lots of
 documentation in `CoreSyn.lhs`.

 - Given that we now support multiple ticks in the tree at the same time, I
 had to give `mkTick` a rewrite.

 - The change to `cheapEqExpr` is a bit awkward, but it was the only cheap
 way I could think of for making it look through ticks.

 - Small changes with their own commit are optional changes or refactoring.

 Next up will the Cmm support, which so far still needs work on the
 CmmContext replacement.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3693#comment:58>
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