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Diffstat (limited to 'docs/users_guide/using-optimisation.rst')
| -rw-r--r-- | docs/users_guide/using-optimisation.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/docs/users_guide/using-optimisation.rst b/docs/users_guide/using-optimisation.rst index a57225da25..6d33c5b5bc 100644 --- a/docs/users_guide/using-optimisation.rst +++ b/docs/users_guide/using-optimisation.rst @@ -816,6 +816,20 @@ by saying ``-fno-wombat``. more detailed list. Usually that identifies the loop quite accurately, because some numbers are very large. +.. ghc-flag:: -fdmd-unbox-width=⟨n⟩ + :shortdesc: *default: 3.* Boxity analysis pretends that returned records + with this many fields can be unboxed. + :type: dynamic + :category: + + :default: 3 + + Boxity analysis optimistically pretends that a function returning a record + with at most ``-fdmd-unbox-width`` fields has only call sites that don't + need the box of the returned record. That may in turn allow more argument + unboxing to happen. Set to 0 to be completely conservative (which guarantees + that no reboxing will happen due to this mechanism). + .. ghc-flag:: -fspec-constr :shortdesc: Turn on the SpecConstr transformation. Implied by :ghc-flag:`-O2`. :type: dynamic |