perf regression in @pure changes

[JeffBezanson]

Running @timholy 's test case from #13350:

commit 7dcc01b:

Without parentheses:
  0.567878 seconds (16.01 M allocations: 488.552 MB, 5.03% gc time)
With parentheses:
  0.421889 seconds (11 allocations: 480 bytes)

commit 8ce7a02

Without parentheses:
  2.149215 seconds (70.01 M allocations: 1.654 GB, 5.22% gc time)
With parentheses:
  2.251477 seconds (74.00 M allocations: 1.773 GB, 5.45% gc time)

cc @vtjnash

[vtjnash]

duplicate of #14294