Exponential inlining code blowup

(Transferring a new thread from #5539 (closed) to a new ticket, since it's really a separate problem.) kosmikus helpfully provided this program

module TestCase where

import Control.Applicative

data X = X
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)
  (Maybe String)

mb :: (String -> Maybe a) -> String -> Maybe (Maybe a)
mb _ ""  = Just Nothing
mb _ "-" = Just Nothing
mb p xs  = Just <$> p xs

run :: [String] -> Maybe X
run
  [ x1
  , x2
  , x3
  , x4
  , x5
  , x6
  , x7
  , x8
  , x9
  ] = X
  <$> mb pure x1
  <*> mb pure x2
  <*> mb pure x3
  <*> mb pure x4
  <*> mb pure x5
  <*> mb pure x6
  <*> mb pure x7
  <*> mb pure x8
  <*> mb pure x9

Unless mb is marked as NOINLINE, it gets expanded in the body of run a number of times that seems to grow exponentially with the size of the list (9 in the example).

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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