Performance regression vs. 7.2.1

nofib/spectral/mandel is showing a regression since 7.2.1.

Create a larger test input:

$ cat >mandel.in
-2.0
-2.0
2.0
2.0
512
512
256

With today's 7.3:

$ ./mandel <mandel.in +RTS -s >/dev/null
Enter min x  = Enter min y  = Enter max x  = Enter max y  = Screen width = Screen height= Screen depth =    3,517,780,112 bytes allocated in the heap
      21,178,480 bytes copied during GC
          98,960 bytes maximum residency (19 sample(s))
          42,640 bytes maximum slop
               2 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0      6736 colls,     0 par    0.11s    0.11s     0.0000s    0.0002s
  Gen  1        19 colls,     0 par    0.00s    0.00s     0.0001s    0.0003s

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    2.92s  (  2.92s elapsed)
  GC      time    0.11s  (  0.11s elapsed)
  EXIT    time    0.00s  (  0.00s elapsed)
  Total   time    3.03s  (  3.03s elapsed)

With 7.2.1:

$ ./mandel <mandel.in +RTS -s >/dev/null
Enter min x  = Enter min y  = Enter max x  = Enter max y  = Screen width = Screen height= Screen depth =    2,554,096,496 bytes allocated in the heap
      16,583,464 bytes copied during GC
          98,928 bytes maximum residency (16 sample(s))
          44,216 bytes maximum slop
               2 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0      4919 colls,     0 par    0.08s    0.08s     0.0000s    0.0002s
  Gen  1        16 colls,     0 par    0.00s    0.00s     0.0001s    0.0003s

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    2.29s  (  2.29s elapsed)
  GC      time    0.08s  (  0.08s elapsed)
  EXIT    time    0.00s  (  0.00s elapsed)
  Total   time    2.37s  (  2.37s elapsed)

Both were standard builds (GhcLibOpts contains -O2), and the programs themselves were compiled with -O2.

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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CC
Operating system
Architecture