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Diffstat (limited to 'docs/users_guide/using-optimisation.rst')
| -rw-r--r-- | docs/users_guide/using-optimisation.rst | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/docs/users_guide/using-optimisation.rst b/docs/users_guide/using-optimisation.rst index b368544696..390b179f33 100644 --- a/docs/users_guide/using-optimisation.rst +++ b/docs/users_guide/using-optimisation.rst @@ -1611,6 +1611,32 @@ by saying ``-fno-wombat``. while demand analysis is disabled (by :ghc-flag:`-fno-strictness`) has no effect. +.. ghc-flag:: -fworker-wrapper-cbv + :shortdesc: Enable w/w splits for wrappers whos sole purpose is evaluating arguments. + :type: dynamic + :category: optimization + + Disabling this flag prevents a W/W split if the only benefit would be call-by-value + for some arguments. + + Otherwise this exploits strictness information by passing strict value arguments + call-by-value to the functions worker. Even for functions who would + otherwise not get a worker. + + This avoids (potentially repeated) checks for evaluatedness of arguments in + the rhs of the worker by pushing this check to the call site. + If the argument is statically visible to be a value at the call site the + overhead for the check disappears completely. + + This can cause slight codesize increases. It will also cause many more functions + to get a worker/wrapper split which can play badly with rules (see Ticket #20364) + which is why it's currently disabled by default. + In particular if you depend on rules firing on functions marked as NOINLINE without + marking use sites of these functions as INLINE or INLINEABLE then things will break + unless this flag is disabled. + + While WorkerWrapper is disabled this has no effect. + .. ghc-flag:: -fbinary-blob-threshold=⟨n⟩ :shortdesc: *default: 500K.* Tweak assembly generator for binary blobs. :type: dynamic |