exponential blowup in inlining (without INLINE pragmas)

The test case for #10397 (closed) also demonstrates an exponential blowup by the inliner, without any INLINE pragmas.

I added another four fields to the Register type, and I get these final Core program sizes. (The variation in sizes between versions is not really important, the point is just that they are very large for all versions.)

ghc-7.6.3:
*** CorePrep:
Result size of CorePrep
  = {terms: 1,702,684, types: 1,950,647, coercions: 103}

ghc-7.8.4:
*** CorePrep:
Result size of CorePrep
  = {terms: 1,964,183, types: 1,950,620, coercions: 97}

ghc-7.10.1:
*** CorePrep:
Result size of CorePrep
  = {terms: 1,964,212, types: 1,950,764, coercions: 97}

ghc-7.11:
*** CorePrep:
Result size of CorePrep
  = {terms: 1,964,212, types: 1,950,764, coercions: 97}

Ideally GHC should not produce enormous Core programs on its own like this.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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