[GHC] #10730: Spectral norm allocations increased 17% between 7.6 and 7.8

[GHC]

#10730: Spectral norm allocations increased 17% between 7.6 and 7.8
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        Reporter:  bgamari           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  low               |               Milestone:
       Component:  Compiler          |                 Version:  7.8.3
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Description changed by bgamari:

Old description:

> It appears that `spectral-norm` regressed rather severely from 7.6 to 7.8
> in total allocations. Meanwhile the binary size also increased by 7% or
> so. However, it also appears that runtime was unaffected by this change.
>
> The rule firings are very similar between 7.6 and 7.8. Three rules fire
> in 786 that do not fire in 7.6,
> {{{
>   1 Class op formatArg
>   1 Class op parseFormat
>   1 tagToEnum#
> }}}
>
> The difference in allocation persists even if one reverts the
> `Text.Printf` rewrite that gives rise to the `formatArg` and
> `parseFormat` rules, so these can be safely ignored.

New description:

 It appears that `spectral-norm` regressed rather severely from 7.6 to 7.8
 in total allocations. Meanwhile the binary size also increased by 7% or
 so. However, it also appears that runtime was unaffected by this change.

 The rule firings are very similar between 7.6 and 7.8. Three rules fire in
 7.8 that do not fire in 7.6,
 {{{
   1 Class op formatArg
   1 Class op parseFormat
   1 tagToEnum#
 }}}

 The difference in allocation persists even if one reverts the
 `Text.Printf` rewrite that gives rise to the `formatArg` and `parseFormat`
 rules, so these can be safely ignored.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10730#comment:1>
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