[GHC] #14219: Include source location information in -ddump-rule-rewrites

[GHC]

#14219: Include source location information in -ddump-rule-rewrites
-------------------------------------+-------------------------------------
           Reporter:  harendra       |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
  (Debugging)                        |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Debugging
  Unknown/Multiple                   |  information is incorrect
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Inlining is one of the most common and powerful optimizations and it
 interacts with rewrite-rules which is also common the libraries including
 base. When debugging a performance problem we are interacting with the
 rewrite-rules written by others hidden somewhere in some library that we
 are using. When I use the `-ddump-rule-rewrites` option I get an output
 like this:

 {{{
 Rule fired
     Rule: Class op >>=
     Module: (BUILTIN)
     Before: GHC.Base.>>= TyArg GHC.Types.IO ValArg GHC.Base.$fMonadIO
     After:  GHC.Base.$fMonadIO1
 }}}

 This does not say where exactly this rule is defined in the source. It is
 sort of ok if this is my code I would perhaps know where this rule is. But
 when it is in some dependency that I am using it is hard to find.

 It will be really helpful if the source location information can be
 provided in this dump information, so that one can go and examine the
 source.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14219>
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