[Git][ghc/ghc][master] Doc: Fix out-of-sync using-optimisation page
Marge Bot (@marge-bot)
gitlab at gitlab.haskell.org
Fri May 12 03:09:25 UTC 2023
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
a856d98e by Pierre Le Marre at 2023-05-11T23:09:08-04:00
Doc: Fix out-of-sync using-optimisation page
- Make explicit that default flag values correspond to their -O0 value.
- Fix -fignore-interface-pragmas, -fstg-cse, -fdo-eta-reduction,
-fcross-module-specialise, -fsolve-constant-dicts, -fworker-wrapper.
- - - - -
1 changed file:
- docs/users_guide/using-optimisation.rst
Changes:
=====================================
docs/users_guide/using-optimisation.rst
=====================================
@@ -117,9 +117,9 @@ The easiest way to see what ``-O`` (etc.) “really mean” is to run with
single: -fno-\* options (GHC)
These flags turn on and off individual optimisations. Flags marked as
-on by default are enabled by ``-O``, and as such you shouldn't
-need to set any of them explicitly. A flag ``-fwombat`` can be negated
-by saying ``-fno-wombat``.
+*on* by default are enabled at all optimisation levels by default, and
+as such you shouldn't need to set any of them explicitly. A flag
+``-fwombat`` can be negated by saying ``-fno-wombat``.
.. ghc-flag:: -fcore-constant-folding
:shortdesc: Enable constant folding in Core. Implied by :ghc-flag:`-O`.
@@ -127,7 +127,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-core-constant-folding
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables Core-level constant folding, i.e. propagation of values
that can be computed at compile time.
@@ -138,7 +138,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-case-merge
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Merge immediately-nested case expressions that scrutinise the same variable.
For example, ::
@@ -162,7 +162,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-case-folding
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Allow constant folding in case expressions that scrutinise some primops:
For example, ::
@@ -185,7 +185,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-call-arity
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enable call-arity analysis.
@@ -195,7 +195,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-exitification
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables the floating of exit paths out of recursive functions.
@@ -205,7 +205,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cmm-elim-common-blocks
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables the common block elimination optimisation
in the code generator. This optimisation attempts to find identical
@@ -217,7 +217,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cmm-sink
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables the sinking pass in the code generator.
This optimisation attempts to find identical Cmm blocks and
@@ -231,7 +231,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cmm-static-pred
:category:
- :default: off but enabled with :ghc-flag:`-O`.
+ :default: off but enabled by :ghc-flag:`-O`.
This enables static control flow prediction on the final Cmm
code. If enabled GHC will apply certain heuristics to identify
@@ -244,7 +244,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cmm-control-flow
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables some control flow optimisations in the Cmm code
generator, merging basic blocks and avoiding jumps right after jumps.
@@ -255,7 +255,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-asm-shortcutting
:category:
- :default: off
+ :default: off but enabled by :ghc-flag:`-O2`.
This enables shortcutting at the assembly stage of the code generator.
In simpler terms shortcutting means if a block of instructions A only consists
@@ -268,12 +268,12 @@ by saying ``-fno-wombat``.
does nothing on macOS.
.. ghc-flag:: -fblock-layout-cfg
- :shortdesc: Use the new cfg based block layout algorithm.
+ :shortdesc: Use the new cfg based block layout algorithm. Implied by :ghc-flag:`-O`.
:type: dynamic
:reverse: -fno-block-layout-cfg
:category:
- :default: off but enabled with :ghc-flag:`-O`.
+ :default: off but enabled by :ghc-flag:`-O`.
The new algorithm considers all outgoing edges of a basic blocks for
code layout instead of only the last jump instruction.
@@ -326,7 +326,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cpr-anal
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Turn on CPR analysis, which enables the worker/wrapper transformation (cf.
:ghc-flag:`-fworker-wrapper`) to unbox the result of a function, such as ::
@@ -386,7 +386,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-cse
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables the common-sub-expression elimination
optimisation. Switching this off can be useful if you have some
@@ -394,12 +394,12 @@ by saying ``-fno-wombat``.
.. ghc-flag:: -fstg-cse
:shortdesc: Enable common sub-expression elimination on the STG
- intermediate language
+ intermediate language. Implied by :ghc-flag:`-O`.
:type: dynamic
:reverse: -fno-stg-cse
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Enables the common-sub-expression elimination optimisation on the STG
intermediate language, where it is able to common up some subexpressions
@@ -422,7 +422,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-dicts-strict
:category:
- :default: off
+ :default: off but enabled by :ghc-flag:`-O2`.
Make dictionaries strict.
@@ -447,7 +447,7 @@ by saying ``-fno-wombat``.
Behaviour is unconditionally enabled starting with 9.2
.. ghc-flag:: -fdo-eta-reduction
- :shortdesc: Enable eta-reduction. Implied by :ghc-flag:`-O`.
+ :shortdesc: Enable eta-reduction. Always enabled by default.
:type: dynamic
:reverse: -fno-do-eta-reduction
:category:
@@ -518,7 +518,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-float-in
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Float let-bindings inwards, nearer their binding
site. See `Let-floating: moving bindings to give faster programs
@@ -544,7 +544,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-full-laziness
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Run the full laziness optimisation (also known as
let-floating), which floats let-bindings outside enclosing lambdas,
@@ -591,7 +591,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-ignore-asserts
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Causes GHC to ignore uses of the function ``Exception.assert`` in source
code (in other words, rewriting ``Exception.assert p e`` to ``e`` (see
@@ -603,7 +603,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-ignore-interface-pragmas
:category:
- :default: off
+ :default: Implied by :ghc-flag:`-O0`, otherwise off.
Tells GHC to ignore all inessential information when reading
interface files. That is, even if :file:`M.hi` contains unfolding or
@@ -632,7 +632,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-liberate-case
:category:
- :default: off but enabled with :ghc-flag:`-O2`.
+ :default: off but enabled by :ghc-flag:`-O2`.
Turn on the liberate-case transformation. This unrolls recursive function
once in its own RHS, to avoid repeated case analysis of free variables. It's
@@ -657,7 +657,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-loopification
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
When this optimisation is enabled the code generator will turn all
self-recursive saturated tail calls into local jumps rather than
@@ -1074,7 +1074,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-specialise
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Specialise each type-class-overloaded function
defined in this module for the types at which it is called in this
@@ -1101,12 +1101,12 @@ by saying ``-fno-wombat``.
.. ghc-flag:: -fcross-module-specialise
:shortdesc: Turn on specialisation of overloaded functions imported from
- other modules.
+ other modules. Implied by :ghc-flag:`-O`.
:type: dynamic
:reverse: -fno-cross-module-specialise
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Specialise ``INLINABLE`` (:ref:`inlinable-pragma`)
type-class-overloaded functions imported from other modules for the types at
@@ -1136,7 +1136,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-inline-generics
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
:since: 9.2.1
.. index::
@@ -1175,12 +1175,12 @@ by saying ``-fno-wombat``.
.. ghc-flag:: -fsolve-constant-dicts
:shortdesc: When solving constraints, try to eagerly solve
- super classes using available dictionaries.
+ super classes using available dictionaries. Implied by :ghc-flag:`-O`.
:type: dynamic
:reverse: -fno-solve-constant-dicts
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
When solving constraints, try to eagerly solve
super classes using available dictionaries.
@@ -1229,7 +1229,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-stg-lift-lams
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O2`.
Enables the late lambda lifting optimisation on the STG
intermediate language. This selectively lifts local functions to
@@ -1281,7 +1281,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-strictness
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
Turn on demand analysis.
@@ -1441,7 +1441,7 @@ by saying ``-fno-wombat``.
:reverse: -fno-unbox-small-strict-fields
:category:
- :default: on
+ :default: off but enabled by :ghc-flag:`-O`.
.. index::
single: strict constructor fields
@@ -1654,10 +1654,13 @@ by saying ``-fno-wombat``.
.. ghc-flag:: -fworker-wrapper
- :shortdesc: Enable the worker/wrapper transformation.
+ :shortdesc: Enable the worker/wrapper transformation. Implied by :ghc-flag:`-O`
+ and by :ghc-flag:`-fstrictness`.
:type: dynamic
:category:
+ :default: off but enabled by :ghc-flag:`-O`.
+
Enable the worker/wrapper transformation after a demand analysis pass.
Exploits strictness and absence information by unboxing strict arguments
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a856d98eb13401b78fa7eba9a54ea4c501ebb0a2
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a856d98eb13401b78fa7eba9a54ea4c501ebb0a2
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