[GHC] #14974: 2-fold memory usage regression GHC 8.2.2 -> GHC 8.4.1 compiling `mmark` package

[GHC]

#14974: 2-fold memory usage regression GHC 8.2.2 -> GHC 8.4.1 compiling `mmark`
package
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        Reporter:  hvr               |                Owner:  davide
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.4.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by davide):

 The 2 peaks of the terms_per_pass.png​ plot are the core size after 3
 consecutive 3 passes (for both the GHC 8.2.2 and GHC 8.4.1 peak):
 SpecConstr, SpecConstr, Simplifier. Note there are no other SpecConstr
 passes. The core size between GHC 8.2.2 and GHC 8.4.1 track very closely
 until immediately before the SpecConstr pass. Perhaps a small change in
 core (before SpecConstr) is allowing for more specialization to happen, or
 SpecConstr is needlessly creating more core.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14974#comment:7>
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