Using -g causes differences in generated core.

For nofib/shootout/fannkuch-redux:

Normal results

> /e/ghc-8.6.1/bin/ghc.exe Main.hs -O2 -XBangPatterns -fforce-recomp -ddump-simpl -dsuppress-all -dsuppress-uniques | less
...
Result size of Tidy Core
  = {terms: 2,747, types: 2,736, coercions: 100, joins: 50/73}
...

> /e/ghc-8.6.1/bin/ghc.exe Main.hs -O2 -XBangPatterns -fforce-recomp -ddump-simpl -dsuppress-all -dsuppress-uniques -g | less
...
Result size of Tidy Core
  = {terms: 2,654, types: 2,557, coercions: 100, joins: 38/71}
...

There are also structural differences in the generated code.

I've hit the issue with a tree based on head as well so likely happening there as well.

Trac metadata

Trac field	Value
Version	8.6.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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