5.6. Flag reference

This section is a quick-reference for GHC’s command-line flags. For each flag, we also list its mode/dynamic status (see Dynamic and Mode options), and the flag’s opposite (if available).

5.6.1. Verbosity options

More details in Verbosity options

Flag Description Type Reverse
-fabstract-refinement-hole-fits default: off. Toggles whether refinements where one or more of the holes are abstract are reported. dynamic -fno-abstract-refinement-hole-fits
-fdefer-diagnostics Defer and group diagnostic messages by severity dynamic
-fdiagnostics-as-json Output diagnostics in Json format specified by JSON schema dynamic
-fdiagnostics-color=⟨always|auto|never⟩ Use colors in error messages dynamic
-fdiagnostics-show-caret Whether to show snippets of original source code dynamic -fno-diagnostics-show-caret
-ferror-spans Output full span in error messages dynamic
-fhide-source-paths hide module source and object paths dynamic
-fkeep-going Continue compilation as far as possible on errors dynamic
-fmax-refinement-hole-fits=⟨n⟩ default: 6. Set the maximum number of refinement hole fits for typed holes to display in type error messages. dynamic -fno-max-refinement-hole-fits
-fmax-relevant-binds=⟨n⟩ default: 6. Set the maximum number of bindings to display in type error messages. dynamic -fno-max-relevant-binds
-fmax-valid-hole-fits=⟨n⟩ default: 6. Set the maximum number of valid hole fits for typed holes to display in type error messages. dynamic -fno-max-valid-hole-fits
-fno-show-valid-hole-fits Disables showing a list of valid hole fits for typed holes in type error messages. dynamic
-fno-sort-valid-hole-fits Disables the sorting of the list of valid hole fits for typed holes in type error messages. dynamic -fsort-valid-hole-fits
-fprint-axiom-incomps Display equation incompatibilities in closed type families dynamic -fno-print-axiom-incomps
-fprint-equality-relations Distinguish between equality relations when printing dynamic -fno-print-equality-relations
-fprint-error-index-links=⟨always|auto|never⟩ Whether to emit diagnostic codes as ANSI hyperlinks to the Haskell Error Index. dynamic
-fprint-expanded-synonyms In type errors, also print type-synonym-expanded types. dynamic -fno-print-expanded-synonyms
-fprint-explicit-coercions Print coercions in types dynamic -fno-print-explicit-coercions
-fprint-explicit-foralls Print explicit forall quantification in types. See also ExplicitForAll dynamic -fno-print-explicit-foralls
-fprint-explicit-kinds Print explicit kind foralls and kind arguments in types. See also KindSignatures dynamic -fno-print-explicit-kinds
-fprint-explicit-runtime-reps Print RuntimeRep and Levity variables in types which are runtime-representation polymorphic. dynamic -fno-print-explicit-runtime-reps
-fprint-potential-instances display all available instances in type error messages dynamic -fno-print-potential-instances
-fprint-redundant-promotion-ticks Print redundant DataKinds promotion ticks dynamic -fno-print-redundant-promotion-ticks
-fprint-typechecker-elaboration Print extra information from typechecker. dynamic -fno-print-typechecker-elaboration
-fprint-unicode-syntax Use unicode syntax when printing expressions, types and kinds. See also UnicodeSyntax dynamic -fno-print-unicode-syntax
-frefinement-level-hole-fits=⟨n⟩ default: off. Sets the level of refinement of the refinement hole fits, where level n means that hole fits of up to n holes will be considered. dynamic -fno-refinement-level-hole-fits
-freverse-errors Output errors in reverse order dynamic -fno-reverse-errors
-fshow-docs-of-hole-fits Toggles whether to show the documentation of the valid hole fits in the output. dynamic -fno-show-docs-of-hole-fits
-fshow-error-context Whether to show textual information about error context dynamic -fno-show-error-context
-fshow-hole-constraints Show constraints when reporting typed holes. dynamic
-fshow-hole-matches-of-hole-fits Toggles whether to show the type of the additional holes in refinement hole fits. dynamic -fno-show-hole-matches-of-hole-fits
-fshow-provenance-of-hole-fits Toggles whether to show the provenance of the valid hole fits in the output. dynamic -fno-show-provenance-of-hole-fits
-fshow-type-app-of-hole-fits Toggles whether to show the type application of the valid hole fits in the output. dynamic -fno-show-type-app-of-hole-fits
-fshow-type-app-vars-of-hole-fits Toggles whether to show what type each quantified variable takes in a valid hole fit. dynamic -fno-show-type-app-vars-of-hole-fits
-fshow-type-of-hole-fits Toggles whether to show the type of the valid hole fits in the output. dynamic -fno-show-type-of-hole-fits
-fsort-by-size-hole-fits Sort valid hole fits by size. dynamic -fno-sort-by-size-hole-fits
-fsort-by-subsumption-hole-fits Sort valid hole fits by subsumption. dynamic -fno-sort-by-subsumption-hole-fits
-funclutter-valid-hole-fits Unclutter the list of valid hole fits by not showing provenance nor type applications of suggestions. dynamic
-Rghc-timing Summarise timing stats for GHC (same as +RTS -tstderr). dynamic
-v verbose mode (equivalent to -v3) dynamic
-v⟨n⟩ set verbosity level dynamic

5.6.2. Alternative modes of operation

More details in Modes of operation

Flag Description Type Reverse
--frontend ⟨module⟩ run GHC with the given frontend plugin; see Frontend plugins for details. mode
--help, -? Display help mode
--info display information about the compiler mode
--interactive Interactive mode - normally used by just running ghci; see Using GHCi for details. mode
--make Build a multi-module Haskell program, automatically figuring out dependencies. Likely to be much easier, and faster, than using make; see Using ghc --make for details. mode
--numeric-version display GHC version (numeric only) mode
--print-booter-version display bootstrap compiler version mode
--print-build-platform display platform on which GHC was built mode
--print-c-compiler-flags C compiler flags used to build GHC mode
--print-c-compiler-link-flags C linker flags used to build GHC mode
--print-debug-on print whether GHC was built with -DDEBUG mode
--print-global-package-db display GHC's global package database directory mode
--print-have-interpreter display whether GHC was built with interactive support mode
--print-have-native-code-generator display whether target platform has NCG support mode
--print-host-platform display host platform of GHC mode
--print-ld-flags display linker flags used to compile GHC mode
--print-leading-underscore display use of leading underscores on symbol names mode
--print-libdir display GHC library directory mode
--print-object-splitting-supported display whether GHC supports object splitting mode
--print-project-git-commit-id display Git commit id GHC is built from mode
--print-project-version display GHC version mode
--print-rts-ways display which way RTS was built mode
--print-stage display stage number of GHC mode
--print-support-smp display whether GHC was compiled with SMP support mode
--print-tables-next-to-code display whether GHC was compiled with --enable-tables-next-to-code mode
--print-target-platform display target platform of GHC mode
--print-unregisterised display whether this GHC was built in unregisterised mode mode
--run ⟨file⟩ Run a Haskell program. mode
--show-iface ⟨file⟩ display the contents of an interface file. mode
--show-options display the supported command line options mode
--supported-extensions, --supported-languages display the supported language extensions mode
--version, -V display GHC version mode
-e ⟨expr⟩ Evaluate expr; see Expression evaluation mode for details. mode
-M generate dependency information suitable for use in a Makefile; see Dependency generation for details. mode
-shared Create a shared object. mode

5.6.3. Which phases to run

More details in Batch compiler mode

Flag Description Type Reverse
--merge-objs Merge a set of objects into a GHCi library. mode
-C Stop after generating C (.hc file) mode
-c Stop after generating object (.o) file mode
-E Stop after preprocessing (.hspp file) mode
-F Enable the use of a pre-processor (set with -pgmF ⟨cmd⟩) dynamic
-S Stop after generating assembly (.s file) mode
-x ⟨suffix⟩ Override default behaviour for source files dynamic

5.6.4. Redirecting output

More details in Redirecting the compilation output(s)

Flag Description Type Reverse
-dep-makefile ⟨file⟩ Use ⟨file⟩ as the makefile dynamic
-dep-suffix ⟨suffix⟩ Make dependencies that declare that files with suffix .⟨suf⟩⟨osuf⟩ depend on interface files with suffix .⟨suf⟩hi dynamic
-dumpdir ⟨dir⟩ redirect dump files dynamic
-dynhisuf ⟨suffix⟩ set the suffix to use for dynamic interface files dynamic
-dyno ⟨file⟩ set dynamic output filename dynamic
-dynohi ⟨file⟩ set the filename in which to put the dynamic interface dynamic
-dynosuf ⟨suffix⟩ set the dynamic output file suffix dynamic
-hcsuf ⟨suffix⟩ set the suffix to use for intermediate C files dynamic
-hidir ⟨dir⟩ set directory for interface files dynamic
-hiedir ⟨dir⟩ set directory for extended interface files dynamic
-hiesuf ⟨suffix⟩ set the suffix to use for extended interface files dynamic
-hisuf ⟨suffix⟩ set the suffix to use for interface files dynamic
-o ⟨file⟩ set output filename dynamic
-odir ⟨dir⟩ set directory for object files dynamic
-ohi ⟨file⟩ set the filename in which to put the interface dynamic
-osuf ⟨suffix⟩ set the output file suffix dynamic
-outputdir ⟨dir⟩ set output directory dynamic
-stubdir ⟨dir⟩ redirect FFI stub files dynamic

5.6.5. Keeping intermediate files

More details in Keeping Intermediate Files

Flag Description Type Reverse
-keep-hc-file, -keep-hc-files Retain intermediate .hc files. dynamic
-keep-hi-files Retain intermediate .hi files (the default). dynamic -no-keep-hi-files
-keep-hscpp-file, -keep-hscpp-files Retain intermediate .hscpp files. dynamic
-keep-llvm-file, -keep-llvm-files Retain intermediate LLVM .ll files. Implies -fllvm. dynamic
-keep-o-files Retain intermediate .o files (the default). dynamic -no-keep-o-files
-keep-s-file, -keep-s-files Retain intermediate .s files. dynamic
-keep-tmp-files Retain all intermediate temporary files. dynamic

5.6.6. Temporary files

More details in Redirecting temporary files

Flag Description Type Reverse
-tmpdir ⟨dir⟩ set the directory for temporary files dynamic

5.6.7. Finding imports

More details in The search path

Flag Description Type Reverse
-i Empty the import directory list dynamic
-i⟨dir⟩[:⟨dir⟩]* add ⟨dir⟩, ⟨dir2⟩, etc. to import path dynamic

5.6.8. Interface file options

More details in Other options related to interface files

Flag Description Type Reverse
--show-iface ⟨file⟩ See Modes of operation. mode
-ddump-hi Dump the new interface to stdout dynamic
-ddump-hi-diffs Show the differences vs. the old interface dynamic
-ddump-minimal-imports Dump a minimal set of imports dynamic

5.6.9. Extended interface file options

More details in Options related to extended interface files

Flag Description Type Reverse
-fvalidate-ide-info Perform some sanity checks on the extended interface files dynamic
-fwrite-ide-info Write out extended interface files dynamic

5.6.10. Recompilation checking

More details in The recompilation checker

Flag Description Type Reverse
-exclude-module=⟨file⟩ Regard ⟨file⟩ as "stable"; i.e., exclude it from having dependencies on it. dynamic
-fforce-recomp Turn off recompilation checking. This is implied by any -ddump-X option when compiling a single file (i.e. when using -c). dynamic -fno-force-recomp
-fignore-hpc-changes Do not recompile modules just to match changes to HPC flags. This is especially useful for avoiding recompilation when using GHCi, and is enabled by default for GHCi. dynamic -fno-ignore-hpc-changes
-fignore-optim-changes Do not recompile modules just to match changes to optimisation flags. This is especially useful for avoiding recompilation when using GHCi, and is enabled by default for GHCi. dynamic -fno-ignore-optim-changes
-include-cpp-deps Include preprocessor dependencies dynamic
-include-pkg-deps Regard modules imported from packages as unstable dynamic

5.6.11. Interactive-mode options

More details in The .ghci and .haskeline files

Flag Description Type Reverse
-fbreak-on-error Break on uncaught exceptions and errors dynamic -fno-break-on-error
-fbreak-on-exception Break on any exception thrown dynamic -fno-break-on-exception
-fbreak-points Insert breakpoints in the GHCi debugger dynamic -fno-break-points
-fghci-hist-size=⟨n⟩ Set the number of entries GHCi keeps for :history. See The GHCi Debugger. dynamic
-fghci-leak-check (Debugging only) check for space leaks when loading new modules in GHCi. dynamic -fno-ghci-leak-check
-fimplicit-import-qualified Put in scope qualified identifiers for every loaded module dynamic -fno-implicit-import-qualified
-flocal-ghci-history Use current directory for the GHCi command history file .ghci-history. dynamic -fno-local-ghci-history
-fno-it No longer set the special variable it. dynamic -fno-no-it
-fprint-bind-result Turn on printing of binding results in GHCi dynamic -fno-print-bind-result
-fprint-evld-with-show Instruct :print to use Show instances where possible. dynamic
-fshow-loaded-modules Show the names of modules that GHCi loaded after a :load command. dynamic
-ghci-script Read additional .ghci files dynamic
-ignore-dot-ghci Disable reading of .ghci files dynamic -no-ignore-dot-ghci
-interactive-print ⟨name⟩ Select the function to use for printing evaluated expressions in GHCi dynamic

5.6.12. Packages

More details in Packages

Flag Description Type Reverse
-clear-package-db Clear the package db stack. dynamic
-distrust ⟨pkg⟩ Expose package ⟨pkg⟩ and set it to be distrusted. See Safe Haskell. dynamic
-distrust-all-packages Distrust all packages by default. See Safe Haskell. dynamic
-fpackage-trust Enable Safe Haskell trusted package requirement for trustworthy modules. dynamic
-global-package-db Add the global package db to the stack. dynamic
-hide-all-packages Hide all packages by default dynamic
-hide-package ⟨pkg⟩ Hide package ⟨pkg⟩ dynamic
-ignore-package ⟨pkg⟩ Ignore package ⟨pkg⟩ dynamic
-no-auto-link-packages Don't automatically link in the base and rts packages. dynamic
-no-global-package-db Remove the global package db from the stack. dynamic
-no-user-package-db Remove the user's package db from the stack. dynamic
-package ⟨pkg⟩ Expose package ⟨pkg⟩ dynamic
-package-db ⟨file⟩ Add ⟨file⟩ to the package db stack. dynamic
-package-env ⟨file⟩|⟨name⟩ Use the specified package environment. dynamic
-package-id ⟨unit-id⟩ Expose package by id ⟨unit-id⟩ dynamic
-this-unit-id ⟨unit-id⟩ Compile to be part of unit (i.e. package) ⟨unit-id⟩ dynamic
-trust ⟨pkg⟩ Expose package ⟨pkg⟩ and set it to be trusted. See Safe Haskell. dynamic
-user-package-db Add the user's package db to the stack. dynamic

5.6.13. Language options

Language options can be enabled either by a command-line option -Xblah, or by a {-# LANGUAGE blah #-} pragma in the file itself. See Controlling editions and extensions.

5.6.14. Warnings

More details in Warnings and sanity-checking

Flag Description Type Reverse
-fenable-th-splice-warnings Generate warnings for Template Haskell splices dynamic -fno-enable-th-splice-warnings
-fhelpful-errors Make suggestions for mis-spelled names. dynamic -fno-helpful-errors
-fmax-pmcheck-models=⟨n⟩ soft limit on the number of parallel models the pattern match checker should check a pattern match clause against dynamic
-fshow-warning-groups show which group an emitted warning belongs to. dynamic -fno-show-warning-groups
-fvia-C use the C code generator dynamic
-W enable normal warnings dynamic -Wno-extra
-w disable all warnings dynamic
-Wall enable almost all warnings (details in Warnings and sanity-checking) dynamic -Wno-all
-Wall-missed-specialisations warn when specialisation of any overloaded function fails. dynamic -Wno-all-missed-specialisations
-Wall-missed-specializations alias for -Wall-missed-specialisations dynamic -Wno-all-missed-specializations
-Wambiguous-fields warn about ambiguous field selectors or updates dynamic
-Wauto-orphans (deprecated) Does nothing dynamic
-Wbadly-staged-types warn when type binding is used at the wrong TH stage. dynamic -Wno-badly-staged-types
-Wcompat enable future compatibility warnings (details in Warnings and sanity-checking) dynamic -Wno-compat
-Wcompat-unqualified-imports Report unqualified imports of core libraries which are expected to cause compatibility problems in future releases. dynamic -Wno-compat-unqualified-imports
-Wcpp-undef warn on uses of the #if directive on undefined identifiers dynamic
-Wdata-kinds-tc warn when an illegal use of a type or kind without DataKinds is caught by the typechecker dynamic -Wno-data-kinds-tc
-Wdefault enable default flags dynamic -Wno-default
-Wdefaulted-exception-context warn when an Control.Exception.Context.ExceptionContext implicit parameter is defaulted to Control.Exception.Context.emptyExceptionContext. dynamic -Wnop-defaulted-exception-context
-Wdeferred-out-of-scope-variables Report warnings when variable out-of-scope errors are deferred until runtime. See -fdefer-out-of-scope-variables. dynamic -Wno-deferred-out-of-scope-variables
-Wdeferred-type-errors Report warnings when deferred type errors are enabled. This option is enabled by default. See -fdefer-type-errors. dynamic -Wno-deferred-type-errors
-Wdeprecated-flags warn about uses of commandline flags that are deprecated dynamic -Wno-deprecated-flags
-Wdeprecated-type-abstractions warn when type abstractions in constructor patterns are used without enabling TypeApplications dynamic -Wno-deprecated-type-abstractions
-Wdeprecations warn about uses of functions & types that have DEPRECATED pragmas, or WARNING pragmas with the deprecated category. dynamic -Wno-deprecations
-Wderiving-defaults warn about default deriving when using both DeriveAnyClass and GeneralizedNewtypeDeriving dynamic -Wno-deriving-defaults
-Wderiving-typeable warn when Typeable is derived dynamic -Wno-deriving-typeable
-Wdodgy-exports warn about dodgy exports dynamic -Wno-dodgy-exports
-Wdodgy-foreign-imports warn about dodgy foreign imports dynamic -Wno-dodgy-foreign-imports
-Wdodgy-imports warn about dodgy imports dynamic -Wno-dodgy-imports
-Wduplicate-constraints warn when a constraint appears duplicated in a type signature dynamic -Wno-duplicate-constraints
-Wduplicate-exports warn when an entity is exported multiple times dynamic -Wno-duplicate-exports
-Wempty-enumerations warn about enumerations that are empty dynamic -Wno-empty-enumerations
-Werror make warnings fatal dynamic -Wwarn
-Weverything enable all warnings supported by GHC dynamic -w
-Wextended-warnings warn about uses of functions & types that have WARNING or DEPRECATED pragmas, across all categories dynamic -Wno-extended-warnings
-Wextra alias for -W dynamic -Wno-extra
-Wforall-identifier (deprecated) Does nothing dynamic
-Wgadt-mono-local-binds warn when pattern matching on a GADT without MonoLocalBinds dynamic -Wno-gadt-mono-local-binds
-Whi-shadowing (deprecated) warn when a .hi file in the current directory shadows a library dynamic -Wno-hi-shadowing
-Widentities warn about uses of Prelude numeric conversions that are probably the identity (and hence could be omitted) dynamic -Wno-identities
-Wimplicit-kind-vars (deprecated) warn when kind variables are implicitly quantified over. dynamic -Wno-implicit-kind-vars
-Wimplicit-lift warn about implicit lift in Template Haskell quotes dynamic -Wno-implicit-lift
-Wimplicit-prelude warn when the Prelude is implicitly imported dynamic -Wno-implicit-prelude
-Wimplicit-rhs-quantification warn when type variables on the RHS of a type synonym are implicitly quantified dynamic -Wno-implicit-rhs-quantification
-Winaccessible-code warn about inaccessible code dynamic -Wno-inaccessible-code
-Wincomplete-export-warnings warn when some but not all of exports for a name are warned about dynamic -Wno-incomplete-export-warnings
-Wincomplete-patterns warn when a pattern match could fail dynamic -Wno-incomplete-patterns
-Wincomplete-record-selectors warn when a record selector application could fail dynamic -Wno-incomplete-record-selectors
-Wincomplete-record-updates warn when a record update could fail dynamic -Wno-incomplete-record-updates
-Wincomplete-uni-patterns warn when a pattern match in a lambda expression, pattern binding or a lazy pattern could fail dynamic -Wno-incomplete-uni-patterns
-Winconsistent-flags warn when command line options are inconsistent in some way. dynamic -Wno-inconsistent-flags
-Winferred-safe-imports warn when an explicitly Safe Haskell module imports a Safe-Inferred one dynamic -Wno-inferred-safe-imports
-Winline-rule-shadowing Warn if a rewrite RULE might fail to fire because the function might be inlined before the rule has a chance to fire. See How rules interact with INLINE/NOINLINE pragmas. dynamic -Wno-inline-rule-shadowing
-Winvalid-haddock warn when a Haddock comment occurs in an invalid position dynamic -Wno-invalid-haddock
-Wloopy-superclass-solve (deprecated) warn when creating potentially-loopy superclass constraint evidence dynamic -Wno-loopy-superclass-solve
-Wmisplaced-pragmas warn about uses of file header pragmas in the module body dynamic -Wno-misplaced-pragmas
-Wmissed-extra-shared-lib Warn when GHCi can't load a shared lib. dynamic -Wno-missed-extra-shared-lib
-Wmissed-specialisations warn when specialisation of an imported, overloaded function fails. dynamic -Wno-missed-specialisations
-Wmissed-specializations alias for -Wmissed-specialisations dynamic -Wno-missed-specializations
-Wmissing-deriving-strategies warn when a deriving clause is missing a deriving strategy dynamic -Wno-missing-deriving-strategies
-Wmissing-export-lists warn when a module declaration does not explicitly list all exports dynamic -Wno-missing-export-lists
-Wmissing-exported-pattern-synonym-signatures warn about pattern synonyms without signatures, only if they are exported dynamic -Wno-missing-exported-pattern-synonym-signatures
-Wmissing-exported-signatures warn about top-level functions without signatures, only if they are exported dynamic -Wno-missing-exported-signatures
-Wmissing-exported-sigs (deprecated) warn about top-level functions without signatures, only if they are exported. takes precedence over -Wmissing-signatures dynamic -Wno-missing-exported-sigs
-Wmissing-fields warn when fields of a record are uninitialised dynamic -Wno-missing-fields
-Wmissing-home-modules warn when encountering a home module imported, but not listed on the command line. Useful for cabal to ensure GHC won't pick up modules, not listed neither in exposed-modules, nor in other-modules. dynamic -Wno-missing-home-modules
-Wmissing-import-lists warn when an import declaration does not explicitly list all the names brought into scope dynamic -Wno-missing-import-lists
-Wmissing-kind-signatures warn when type declarations don't have kind signatures nor CUSKs dynamic -Wno-missing-kind-signatures
-Wmissing-local-signatures warn about polymorphic local bindings without signatures dynamic -Wno-missing-local-signatures
-Wmissing-local-sigs (deprecated) warn about polymorphic local bindings without signatures dynamic -Wno-missing-local-sigs
-Wmissing-methods warn when class methods are undefined dynamic -Wno-missing-methods
-Wmissing-monadfail-instances (deprecated) Warn when a failable pattern is used in a do-block that does not have a MonadFail instance. dynamic -Wno-missing-monadfail-instances
-Wmissing-pattern-synonym-signatures warn when pattern synonyms do not have type signatures dynamic -Wno-missing-pattern-synonym-signatures
-Wmissing-poly-kind-signatures warn when inferred polykinded type or class declaration don't have kind signatures nor CUSKs dynamic -Wno-missing-poly-kind-signatures
-Wmissing-role-annotations warn when type declarations don't have role annotations dynamic -Wno-role-annotations-signatures
-Wmissing-safe-haskell-mode warn when the Safe Haskell mode is not explicitly specified. dynamic -Wno-missing-safe-haskell-mode
-Wmissing-signatures warn about top-level functions without signatures dynamic -Wno-missing-signatures
-Wmissing-space-after-bang (deprecated) Does nothing dynamic
-Wmonomorphism-restriction warn when the Monomorphism Restriction is applied dynamic -Wno-monomorphism-restriction
-Wname-shadowing warn when names are shadowed dynamic -Wno-name-shadowing
-Wnoncanonical-monad-instances warn when Applicative or Monad instances have noncanonical definitions of return, pure, (>>), or (*>). See flag description in Warnings and sanity-checking for more details. dynamic -Wno-noncanonical-monad-instances
-Wnoncanonical-monadfail-instances (deprecated) warn when Monad or MonadFail instances have noncanonical definitions of fail. dynamic -Wno-noncanonical-monadfail-instances
-Wnoncanonical-monoid-instances warn when Semigroup or Monoid instances have noncanonical definitions of (<>) or mappend. See flag description in Warnings and sanity-checking for more details. dynamic -Wno-noncanonical-monoid-instances
-Wnot (deprecated) Alias for -w dynamic
-Woperator-whitespace warn on prefix, suffix, and tight infix uses of infix operators dynamic -Wno-operator-whitespace
-Woperator-whitespace-ext-conflict warn on uses of infix operators that would be parsed differently were a particular GHC extension enabled dynamic -Wno-operator-whitespace-ext-conflict
-Worphans warn when the module contains orphan instance declarations or rewrite rules dynamic -Wno-orphans
-Woverflowed-literals warn about literals that will overflow their type dynamic -Wno-overflowed-literals
-Woverlapping-patterns warn about overlapping patterns dynamic -Wno-overlapping-patterns
-Wpartial-fields warn when defining a partial record field. dynamic -Wno-partial-fields
-Wpartial-type-signatures warn about holes in partial type signatures when PartialTypeSignatures is enabled. Not applicable when PartialTypeSignatures is not enabled, in which case errors are generated for such holes. dynamic -Wno-partial-type-signatures
-Wprepositive-qualified-module Report imports with a leading/prepositive "qualified" dynamic -Wno-prepositive-qualified-module
-Wredundant-bang-patterns Warn about redundant bang patterns. dynamic -Wno-redundant-bang-patterns
-Wredundant-constraints Have the compiler warn about redundant constraints in type signatures. dynamic -Wno-redundant-constraints
-Wredundant-record-wildcards Warn about record wildcard matches when the wildcard binds no patterns. dynamic -Wno-redundant-record-wildcards
-Wredundant-strictness-flags Warn about redundant strictness flags. dynamic -Wno-redundant-strictness-flags
-Wsafe warn if the module being compiled is regarded to be safe. dynamic -Wno-safe
-Wsemigroup (deprecated) Warn when a Monoid is not Semigroup, and on non-Semigroup definitions of (<>) dynamic -Wno-semigroup
-Wsimplifiable-class-constraints Warn about class constraints in a type signature that can be simplified using a top-level instance declaration. dynamic -Wno-simplifiable-class-constraints
-Wstar-binder warn about binding the (*) type operator despite StarIsType dynamic -Wno-star-binder
-Wstar-is-type warn when * is used to mean Data.Kind.Type dynamic -Wno-star-is-type
-Wtabs warn if there are tabs in the source file dynamic -Wno-tabs
-Wterm-variable-capture warn when an implicitly quantified type variable captures a term's name dynamic
-Wtrustworthy-safe warn if the module being compiled is marked as Trustworthy but it could instead be marked as Safe, a more informative bound. dynamic -Wno-safe
-Wtype-defaults warn when defaulting happens dynamic -Wno-type-defaults
-Wtype-equality-out-of-scope warn when type equality a ~ b is used despite being out of scope dynamic -Wno-type-equality-out-of-scope
-Wtype-equality-requires-operators warn when type equality a ~ b is used despite being out of scope dynamic -Wno-type-equality-requires-operators
-Wtyped-holes Report warnings when typed hole errors are deferred until runtime. See -fdefer-typed-holes. dynamic -Wno-typed-holes
-Wunbanged-strict-patterns warn on pattern bind of unlifted variable that is neither bare nor banged dynamic -Wno-unbanged-strict-patterns
-Wunicode-bidirectional-format-characters warn about the usage of unicode bidirectional layout override characters dynamic
-Wunrecognised-pragmas warn about uses of pragmas that GHC doesn't recognise dynamic -Wno-unrecognised-pragmas
-Wunrecognised-warning-flags throw a warning when an unrecognised -W... flag is encountered on the command line. dynamic -Wno-unrecognised-warning-flags
-Wunsafe warn if the module being compiled is regarded to be unsafe. See Safe Haskell dynamic -Wno-unsafe
-Wunsupported-calling-conventions warn about use of an unsupported calling convention dynamic -Wno-unsupported-calling-conventions
-Wunsupported-llvm-version Warn when using -fllvm with an unsupported version of LLVM. dynamic -Wno-unsupported-llvm-version
-Wunticked-promoted-constructors warn if promoted constructors are not ticked dynamic -Wno-unticked-promoted-constructors
-Wunused-binds warn about bindings that are unused. Alias for -Wunused-top-binds, -Wunused-local-binds and -Wunused-pattern-binds dynamic -Wno-unused-binds
-Wunused-do-bind warn about do bindings that appear to throw away values of types other than () dynamic -Wno-unused-do-bind
-Wunused-foralls warn about type variables in user-written forall\s that are unused dynamic -Wno-unused-foralls
-Wunused-imports warn about unnecessary imports dynamic -Wno-unused-imports
-Wunused-local-binds warn about local bindings that are unused dynamic -Wno-unused-local-binds
-Wunused-matches warn about variables in patterns that aren't used dynamic -Wno-unused-matches
-Wunused-packages warn when package is requested on command line, but not needed. dynamic -Wno-unused-packages
-Wunused-pattern-binds warn about pattern match bindings that are unused dynamic -Wno-unused-pattern-binds
-Wunused-record-wildcards Warn about record wildcard matches when none of the bound variables are used. dynamic -Wno-unused-record-wildcards
-Wunused-top-binds warn about top-level bindings that are unused dynamic -Wno-unused-top-binds
-Wunused-type-patterns warn about unused type variables which arise from patterns in in type family and data family instances dynamic -Wno-unused-type-patterns
-Wwarn make warnings non-fatal dynamic -Werror
-Wwarnings-deprecations warn about uses of functions & types that have DEPRECATED pragmas, or WARNING pragmas with the deprecated category. Alias for -Wdeprecations. dynamic -Wno-warnings-deprecations
-Wwrong-do-bind warn about do bindings that appear to throw away monadic values that you should have bound instead dynamic -Wno-wrong-do-bind
-Wx-⟨category⟩ warn about uses of functions & types that have WARNING pragmas with the given category dynamic -Wno-x-⟨category⟩

5.6.15. Optimisation levels

These options are described in more detail in Optimisation (code improvement).

See Individual optimisations for a list of optimisations enabled on level 1 and level 2.

Flag Description Type Reverse
-O, -O1 Enable level 1 optimisations dynamic -O0
-O0 Disable optimisations (default) dynamic
-O2 Enable level 2 optimisations dynamic -O0
-O⟨n⟩ Any -On where n > 2 is the same as -O2. dynamic -O0

5.6.16. Individual optimisations

These options are described in more detail in -f*: platform-independent flags. If a flag is implied by -O then it is also implied by -O2 (unless flag description explicitly says otherwise). If a flag is implied by -O0 only then the flag is not implied by -O and -O2.

Flag Description Type Reverse
-fasm-shortcutting Enable shortcutting on assembly. Implied by -O2. dynamic -fno-asm-shortcutting
-fbinary-blob-threshold=⟨n⟩ default: 500K. Tweak assembly generator for binary blobs. dynamic
-fblock-layout-cfg Use the new cfg based block layout algorithm. Implied by -O. dynamic -fno-block-layout-cfg
-fblock-layout-weightless Ignore cfg weights for code layout. dynamic -fno-block-layout-weightless
-fblock-layout-weights Sets edge weights used by the new code layout algorithm. dynamic
-fcall-arity Enable call-arity optimisation. Implied by -O. dynamic -fno-call-arity
-fcase-folding Enable constant folding in case expressions. Implied by -O. dynamic -fno-case-folding
-fcase-merge Enable case-merging. Implied by -O. dynamic -fno-case-merge
-fcmm-control-flow Enable control flow optimisation in the Cmm backend. Implied by -O. dynamic -fno-cmm-control-flow
-fcmm-elim-common-blocks Enable Cmm common block elimination. Implied by -O. dynamic -fno-cmm-elim-common-blocks
-fcmm-sink Enable Cmm sinking. Implied by -O. dynamic -fno-cmm-sink
-fcmm-static-pred Enable static control flow prediction. Implied by -O. dynamic -fno-cmm-static-pred
-fcore-constant-folding Enable constant folding in Core. Implied by -O. dynamic -fno-core-constant-folding
-fcpr-anal Turn on Constructed Product Result analysis. Implied by -O. dynamic -fno-cpr-anal
-fcross-module-specialise Turn on specialisation of overloaded functions imported from other modules. Implied by -O. dynamic -fno-cross-module-specialise
-fcse Enable common sub-expression elimination. Implied by -O. dynamic -fno-cse
-fdicts-cheap Make dictionary-valued expressions seem cheap to the optimiser. dynamic -fno-dicts-cheap
-fdicts-strict Make dictionaries strict. Implied by -O2. dynamic -fno-dicts-strict
-fdmd-tx-dict-sel (deprecated) Use a special demand transformer for dictionary selectors. dynamic -fno-dmd-tx-dict-sel
-fdmd-unbox-width=⟨n⟩ default: 3. Boxity analysis pretends that returned records with this many fields can be unboxed. dynamic
-fdo-clever-arg-eta-expansion Enable sophisticated argument eta-expansion. Implied by -O2. dynamic -fno-do-clever-arg-eta-expansion
-fdo-eta-reduction Enable eta-reduction. Always enabled by default. dynamic -fno-do-eta-reduction
-fdo-lambda-eta-expansion Enable lambda eta-expansion. Always enabled by default. dynamic -fno-do-lambda-eta-expansion
-feager-blackholing Turn on eager blackholing dynamic
-fenable-rewrite-rules Switch on all rewrite rules (including rules generated by automatic specialisation of overloaded functions). Implied by -O. dynamic -fno-enable-rewrite-rules
-fexcess-precision Enable excess intermediate precision dynamic -fno-excess-precision
-fexitification Enables exitification optimisation. Implied by -O. dynamic -fno-exitification
-fexpose-all-unfoldings Expose all unfoldings, even for very large or recursive functions. dynamic -fno-expose-all-unfoldings
-ffloat-in Turn on the float-in transformation. Implied by -O. dynamic -fno-float-in
-ffull-laziness Turn on full laziness (floating bindings outwards). Implied by -O. dynamic -fno-full-laziness
-ffun-to-thunk (deprecated) superseded by -ffull-laziness. dynamic -fno-fun-to-thunk
-fignore-asserts Ignore assertions in the source. Implied by -O. dynamic -fno-ignore-asserts
-fignore-interface-pragmas Ignore pragmas in interface files. Implied by -O0 only. dynamic -fno-ignore-interface-pragmas
-finline-generics Annotate methods of derived Generic and Generic1 instances with INLINE[1] pragmas based on heuristics. Implied by -O. dynamic -fno-inline-generics
-finline-generics-aggressively Annotate methods of all derived Generic and Generic1 instances with INLINE[1] pragmas. dynamic -fno-inline-generics-aggressively
-fkeep-auto-rules Keep all "auto" rules, generated by specialisation dynamic -fno-keep-auto-rules
-flate-dmd-anal Run demand analysis again, at the end of the simplification pipeline dynamic -fno-late-dmd-anal
-flate-specialise Run a late specialisation pass dynamic -fno-late-specialise
-fliberate-case Turn on the liberate-case transformation. Implied by -O2. dynamic -fno-liberate-case
-fliberate-case-threshold=⟨n⟩ default: 2000. Set the size threshold for the liberate-case transformation to ⟨n⟩ dynamic -fno-liberate-case-threshold
-fllvm-pass-vectors-in-regs (deprecated) Does nothing dynamic
-flocal-float-out Enable local floating definitions out of let-binds. dynamic -fno-local-float-out
-flocal-float-out-top-level Enable local floating to float top-level bindings dynamic -fno-local-float-out-top-level
-floopification Turn saturated self-recursive tail-calls into local jumps in the generated assembly. Implied by -O. dynamic -fno-loopification
-fmax-inline-alloc-size=⟨n⟩ default: 128. Set the maximum size of inline array allocations to ⟨n⟩ bytes (default: 128). dynamic
-fmax-inline-memcpy-insns=⟨n⟩ default: 32. Inline memcpy calls if they would generate no more than ⟨n⟩ pseudo instructions. dynamic
-fmax-inline-memset-insns=⟨n⟩ default: 32. Inline memset calls if they would generate no more than ⟨n⟩ pseudo instructions dynamic
-fmax-simplifier-iterations=⟨n⟩ default: 4. Set the max iterations for the simplifier. dynamic
-fmax-uncovered-patterns=⟨n⟩ default: 4. Set the maximum number of patterns to display in warnings about non-exhaustive ones. dynamic
-fmax-worker-args=⟨n⟩ default: 10. Maximum number of value arguments for a worker. dynamic
-fno-opt-coercion Turn off the coercion optimiser dynamic
-fno-pre-inlining Turn off pre-inlining dynamic
-fno-state-hack Turn off the state hackwhereby any lambda with a real-world state token as argument is considered to be single-entry. Hence OK to inline things inside it. dynamic
-fomit-interface-pragmas Don't generate interface pragmas. Implied by -O0 only. dynamic -fno-omit-interface-pragmas
-fomit-yields Omit heap checks when no allocation is being performed. dynamic -fno-omit-yields
-foptimal-applicative-do Use a slower but better algorithm for ApplicativeDo dynamic -fno-optimal-applicative-do
-fpedantic-bottoms Make GHC be more precise about its treatment of bottom (but see also -fno-state-hack). In particular, GHC will not eta-expand through a case expression. dynamic -fno-pedantic-bottoms
-fpolymorphic-specialisation Allow specialisation to abstract over free type variables dynamic -fno-polymorphic-specialisation
-fregs-graph Use the graph colouring register allocator for register allocation in the native code generator. dynamic -fno-regs-graph
-fregs-iterative Use the iterative coalescing graph colouring register allocator in the native code generator. dynamic -fno-regs-iterative
-fsimpl-tick-factor=⟨n⟩ default: 100. Set the percentage factor for simplifier ticks. dynamic
-fsimplifier-phases=⟨n⟩ default: 2. Set the number of phases for the simplifier. Ignored with -O0. dynamic
-fsolve-constant-dicts When solving constraints, try to eagerly solve super classes using available dictionaries. Implied by -O. dynamic -fno-solve-constant-dicts
-fspec-constr Turn on the SpecConstr transformation. Implied by -O2. dynamic -fno-spec-constr
-fspec-constr-count=⟨n⟩ default: 3.* Set to ⟨n⟩ the maximum number of specialisations that will be created for any one function by the SpecConstr transformation. dynamic -fno-spec-constr-count
-fspec-constr-keen Specialize a call with an explicit constructor argument, even if the argument is not scrutinised in the body of the function dynamic -fno-spec-constr-keen
-fspec-constr-threshold=⟨n⟩ default: 2000. Set the size threshold for the SpecConstr transformation to ⟨n⟩. dynamic -fno-spec-constr-threshold
-fspecialise Turn on specialisation of overloaded functions. Implied by -O. dynamic -fno-specialise
-fspecialise-aggressively Turn on specialisation of overloaded functions regardless of size, if unfolding is available dynamic -fno-specialise-aggressively
-fspecialise-incoherents Enable specialisation on incoherent instances dynamic -fno-specialise-incoherents
-fstatic-argument-transformation Turn on the static argument transformation. dynamic -fno-static-argument-transformation
-fstg-cse Enable common sub-expression elimination on the STG intermediate language. Implied by -O. dynamic -fno-stg-cse
-fstg-lift-lams Enable late lambda lifting on the STG intermediate language. Implied by -O2. dynamic -fno-stg-lift-lams
-fstg-lift-lams-known Allow turning known into unknown calls while performing late lambda lifting. dynamic -fno-stg-lift-lams-known
-fstg-lift-lams-non-rec-args Create top-level non-recursive functions with at most <n> parameters while performing late lambda lifting. dynamic -fstg-lift-lams-non-rec-args-any
-fstg-lift-lams-rec-args Create top-level recursive functions with at most <n> parameters while performing late lambda lifting. dynamic -fstg-lift-lams-rec-args-any
-fstrictness Turn on demand analysis. Implied by -O. Implies -fworker-wrapper dynamic -fno-strictness
-fstrictness-before=⟨n⟩ Run an additional demand analysis before simplifier phase ⟨n⟩ dynamic
-funbox-small-strict-fields Flatten strict constructor fields with a pointer-sized representation. Implied by -O. dynamic -fno-unbox-small-strict-fields
-funbox-strict-fields Flatten strict constructor fields dynamic -fno-unbox-strict-fields
-funfolding-case-scaling=⟨n⟩ default: 30. Apply a penalty of (inlining_cost * 1/n) for each level of case nesting. dynamic
-funfolding-case-threshold=⟨n⟩ default: 2. Reduce inlining for cases nested deeper than n. dynamic
-funfolding-creation-threshold=⟨n⟩ default: 750. Tweak unfolding settings. dynamic
-funfolding-dict-discount=⟨n⟩ default: 30. Tweak unfolding settings. dynamic
-funfolding-fun-discount=⟨n⟩ default: 60. Tweak unfolding settings. dynamic
-funfolding-keeness-factor=⟨n⟩ This has been deprecated in GHC 9.0.1. dynamic
-funfolding-use-threshold=⟨n⟩ default: 80. Tweak unfolding settings. dynamic
-fworker-wrapper Enable the worker/wrapper transformation. Implied by -O and by -fstrictness. dynamic
-fworker-wrapper-cbv Enable w/w splits for wrappers whos sole purpose is evaluating arguments. dynamic

5.6.17. Profiling options

More details in Profiling

Flag Description Type Reverse
-auto (deprecated) Alias for -fprof-auto-exported dynamic
-auto-all (deprecated) Alias for -fprof-auto dynamic
-caf-all (deprecated) Alias for -fprof-cafs dynamic
-fno-prof-count-entries Do not collect entry counts dynamic -fprof-count-entries
-fprof-auto Auto-add SCC\ s to all bindings not marked INLINE dynamic -fno-prof-auto
-fprof-auto-calls Auto-add SCC\ s to all call sites dynamic -fno-prof-auto
-fprof-auto-exported Auto-add SCC\ s to all exported bindings not marked INLINE dynamic -fno-prof-auto
-fprof-auto-top Auto-add SCC\ s to all top-level bindings not marked INLINE dynamic -fno-prof-auto
-fprof-cafs Auto-add SCC\ s to all CAFs dynamic -fno-prof-cafs
-fprof-callers=⟨name⟩ Auto-add SCC\ s to all call-sites of the named function. dynamic
-fprof-late Auto-add SCC\ s to all top level bindings after the core pipeline has run. dynamic -fno-prof-late
-fprof-late-inline Auto-add SCC\ s to all top level bindings after the optimizer has run and retain them when inlining. dynamic -fno-prof-late-inline
-fprof-late-overloaded Auto-add SCC\ s to all top level overloaded bindings after the core pipeline has run. dynamic -fno-prof-late-overloaded
-fprof-late-overloaded-calls Auto-add SCC\ s to all call sites that include dictionary arguments after the core pipeline has run. dynamic -fno-prof-late-overloaded-calls
-fprof-manual Process manual SCC annotations. dynamic -fno-prof-manual
-no-auto (deprecated) Alias for -fno-prof-auto dynamic
-no-auto-all (deprecated) Alias for -fno-prof-auto dynamic
-no-caf-all (deprecated) Alias for -fno-prof-cafs dynamic
-prof Turn on profiling dynamic
-ticky Turn on ticky-ticky profiling dynamic
-ticky-allocd Track the number of times each closure type is allocated. dynamic
-ticky-ap-thunk Don't use standard AP thunks on order to get more reliable entry counters. dynamic
-ticky-dyn-thunk Track allocations of dynamic thunks dynamic
-ticky-LNE Treat join point binders similar to thunks/functions. dynamic
-ticky-tag-checks Emit dummy ticky counters to record how many tag-inference checks tag inference avoided. dynamic

5.6.18. Program coverage options

More details in Observing Code Coverage

Flag Description Type Reverse
-fhpc Turn on Haskell program coverage instrumentation dynamic
-hpcdir⟨dir⟩ Set the directory where GHC places .mix files. dynamic

5.6.19. C pre-processor options

More details in Options affecting the C pre-processor

Flag Description Type Reverse
-cpp Run the C pre-processor on Haskell source files dynamic
-D⟨symbol⟩[=⟨value⟩] Define a symbol in the C pre-processor dynamic -U⟨symbol⟩
-I⟨dir⟩ Add ⟨dir⟩ to the directory search list for #include files dynamic
-U⟨symbol⟩ Undefine a symbol in the C pre-processor dynamic

5.6.20. Code generation options

More details in Options affecting code generation

Flag Description Type Reverse
-dynamic-too Build dynamic object files as well as static object files during compilation dynamic
-fasm Use the native code generator dynamic -fllvm
-fbyte-code Generate byte-code dynamic
-fbyte-code-and-object-code Generate object code and byte-code dynamic
-fexpose-internal-symbols Produce symbols for all functions, including internal functions. dynamic
-fexternal-dynamic-refs Generate code for linking against dynamic libraries dynamic
-fllvm Compile using the LLVM code generator dynamic -fasm
-fno-code Omit code generation dynamic
-fobject-code Generate object code dynamic
-fPIC Generate position-independent code (where available) dynamic
-fPIE Generate code for a position-independent executable (where available) dynamic
-fprefer-byte-code Use byte-code if it is available to evaluate TH splices dynamic
-fwrite-if-simplified-core Write an interface file containing the simplified core of the module. dynamic
-fwrite-interface Always write interface files dynamic

5.6.21. Linking options

More details in Options affecting linking

Flag Description Type Reverse
-c Stop after generating object (.o) file mode
-debug Use the debugging runtime dynamic
-dylib-install-name ⟨path⟩ Set the install name (via -install_name passed to Apple's linker), specifying the full install path of the library file. Any libraries or executables that link with it later will pick up that path as their runtime search location for it. (Darwin/OS X only) dynamic
-dynamic Build dynamically-linked object files and executables dynamic
-dynload Selects one of a number of modes for finding shared libraries at runtime. dynamic
-eventlog Enable runtime event tracing dynamic
-fcompact-unwind Instruct the linker to produce a __compact_unwind section. dynamic
-fkeep-cafs Do not garbage-collect CAFs (top-level expressions) at runtime dynamic
-flink-rts Link the runtime when generating a shared or static library dynamic
-fno-embed-manifest Do not embed the manifest in the executable (Windows only) dynamic
-fno-gen-manifest Do not generate a manifest file (Windows only) dynamic
-fno-shared-implib Don't generate an import library for a DLL (Windows only) dynamic
-framework ⟨name⟩ On Darwin/OS X/iOS only, link in the framework ⟨name⟩. This option corresponds to the -framework option for Apple's Linker. dynamic
-framework-path ⟨dir⟩ On Darwin/OS X/iOS only, add ⟨dir⟩ to the list of directories searched for frameworks. This option corresponds to the -F option for Apple's Linker. dynamic
-fsplit-sections, -split-sections Split sections for link-time dead-code stripping dynamic -fno-split-sections
-fuse-rpaths Set the rpath based on -L flags dynamic
-fwhole-archive-hs-libs When linking a binary executable, this inserts the flag -Wl,--whole-archive before any -l flags for Haskell libraries, and -Wl,--no-whole-archive afterwards dynamic
-L ⟨dir⟩ Add ⟨dir⟩ to the list of directories searched for libraries dynamic
-l ⟨lib⟩ Link in library ⟨lib⟩ dynamic
-main-is ⟨thing⟩ Set main module and function dynamic
-no-hs-main Don't assume this program contains main dynamic
-no-pie Don't instruct the linker to produce a position-independent executable. dynamic -pie
-no-rtsopts-suggestions Don't print RTS suggestions about linking with -rtsopts[=⟨none|some|all|ignore|ignoreAll⟩]. dynamic
-package ⟨name⟩ Expose package ⟨pkg⟩ dynamic
-pie Instruct the linker to produce a position-independent executable. dynamic -no-pie
-rdynamic This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. Currently Linux and Windows/MinGW32 only. This is equivalent to using -optl -rdynamic on Linux, and -optl -export-all-symbols on Windows. dynamic
-rtsopts[=⟨none|some|all|ignore|ignoreAll⟩] Control whether the RTS behaviour can be tweaked via command-line flags and the GHCRTS environment variable. Using none means no RTS flags can be given; some means only a minimum of safe options can be given (the default); all (or no argument at all) means that all RTS flags are permitted; ignore means RTS flags can be given, but are treated as regular arguments and passed to the Haskell program as arguments; ignoreAll is the same as ignore, but GHCRTS is also ignored. -rtsopts does not affect -with-rtsopts behavior; flags passed via -with-rtsopts are used regardless of -rtsopts. dynamic
-shared Generate a shared library (as opposed to an executable) dynamic
-single-threaded Use the single-threaded runtime dynamic -threaded
-static Use static Haskell libraries dynamic
-staticlib Generate a standalone static library (as opposed to an executable). This is useful when cross compiling. The library together with all its dependencies ends up in in a single static library that can be linked against. dynamic
-threaded Use the threaded runtime dynamic -single-threaded
-with-rtsopts=⟨opts⟩ Set the default RTS options to ⟨opts⟩. dynamic

5.6.22. Plugin options

More details in Compiler Plugins

Flag Description Type Reverse
-fclear-plugins Clear the list of active plugins dynamic
-fplugin-library=⟨file-path⟩;⟨unit-id⟩;⟨module⟩;⟨args⟩ Load a pre-compiled static plugin from an external library dynamic
-fplugin-opt=⟨module⟩:⟨args⟩ Give arguments to a plugin module; module must be specified with -fplugin=⟨module⟩ dynamic
-fplugin-trustworthy Trust the used plugins and no longer mark the compiled module as unsafe dynamic
-fplugin=⟨module⟩ Load a plugin exported by a given module dynamic
-hide-all-plugin-packages Hide all packages for plugins by default dynamic
-plugin-package ⟨pkg⟩ Expose ⟨pkg⟩ for plugins dynamic
-plugin-package-id ⟨pkg-id⟩ Expose ⟨pkg-id⟩ for plugins dynamic

5.6.23. Replacing phases

More details in Replacing the program for one or more phases

Flag Description Type Reverse
-pgma ⟨cmd⟩ Use ⟨cmd⟩ as the assembler dynamic
-pgmc ⟨cmd⟩ Use ⟨cmd⟩ as the C compiler dynamic
-pgmcxx ⟨cmd⟩ Use ⟨cmd⟩ as the C++ compiler dynamic
-pgmF ⟨cmd⟩ Use ⟨cmd⟩ as the pre-processor (with -F only) dynamic
-pgmi ⟨cmd⟩ Use ⟨cmd⟩ as the external interpreter command. dynamic
-pgminstall_name_tool ⟨cmd⟩ Use ⟨cmd⟩ as the program to inject runpath into mach-o dylibs on macOS dynamic
-pgmL ⟨cmd⟩ Use ⟨cmd⟩ as the literate pre-processor dynamic
-pgml ⟨cmd⟩ Use ⟨cmd⟩ as the linker dynamic
-pgmlas ⟨cmd⟩ Use ⟨cmd⟩ as the LLVM assembler dynamic
-pgmlc ⟨cmd⟩ Use ⟨cmd⟩ as the LLVM compiler dynamic
-pgmlm ⟨cmd⟩ Use ⟨cmd⟩ as the linker when merging object files dynamic
-pgmlo ⟨cmd⟩ Use ⟨cmd⟩ as the LLVM optimiser dynamic
-pgmotool ⟨cmd⟩ Use ⟨cmd⟩ as the program to inspect mach-o dylibs on macOS dynamic
-pgmP ⟨cmd⟩ Use ⟨cmd⟩ as the C pre-processor (with -cpp only) dynamic
-pgms ⟨cmd⟩ Use ⟨cmd⟩ as the splitter dynamic
-pgmwindres ⟨cmd⟩ Use ⟨cmd⟩ as the program for embedding manifests on Windows. dynamic

5.6.24. Forcing options to particular phases

More details in Forcing options to a particular phase

Flag Description Type Reverse
-opta ⟨option⟩ pass ⟨option⟩ to the assembler dynamic
-optc ⟨option⟩ pass ⟨option⟩ to the C compiler dynamic
-optcxx ⟨option⟩ pass ⟨option⟩ to the C++ compiler dynamic
-optF ⟨option⟩ pass ⟨option⟩ to the custom pre-processor dynamic
-opti ⟨option⟩ pass ⟨option⟩ to the interpreter sub-process. dynamic
-optL ⟨option⟩ pass ⟨option⟩ to the literate pre-processor dynamic
-optl ⟨option⟩ pass ⟨option⟩ to the linker dynamic
-optlas ⟨option⟩ pass ⟨option⟩ to the LLVM assembler dynamic
-optlc ⟨option⟩ pass ⟨option⟩ to the LLVM compiler dynamic
-optlm ⟨option⟩ pass ⟨option⟩ to the linker when merging object files. dynamic
-optlo ⟨option⟩ pass ⟨option⟩ to the LLVM optimiser dynamic
-optP ⟨option⟩ pass ⟨option⟩ to cpp (with -cpp only) dynamic
-optwindres ⟨option⟩ pass ⟨option⟩ to windres. dynamic
-pgmc-supports-no-pie (deprecated) Indicate that the linker supports -no-pie dynamic
-pgml-supports-no-pie Indicate that the linker supports -no-pie dynamic

5.6.25. Platform-specific options

More details in Platform-specific Flags

Flag Description Type Reverse
-mavx (x86 only) Enable support for AVX SIMD extensions dynamic
-mavx2 (x86 only) Enable support for AVX2 SIMD extensions dynamic
-mavx512cd (x86 only) Enable support for AVX512-CD SIMD extensions dynamic
-mavx512er (x86 only) Enable support for AVX512-ER SIMD extensions dynamic
-mavx512f (x86 only) Enable support for AVX512-F SIMD extensions dynamic
-mavx512pf (x86 only) Enable support for AVX512-PF SIMD extensions dynamic
-mbmi (x86 only) Use BMI1 for bit manipulation operations dynamic
-mbmi2 (x86 only) Use BMI2 for bit manipulation operations dynamic
-mfma Use native FMA instructions for fused multiply-add floating-point operations dynamic
-msse (x86 only) Use SSE for floating-point operations dynamic
-msse2 (x86 only) Use SSE2 for floating-point operations dynamic
-msse3 (x86 only) Use SSE3 for floating-point operations dynamic
-msse4 (x86 only) Use SSE4 for floating-point operations dynamic
-msse4.2 (x86 only) Use SSE4.2 for floating-point operations dynamic

5.6.26. Compiler debugging options

More details in Debugging the compiler

Flag Description Type Reverse
-dasm-lint ASM pass sanity checking dynamic
-dcmm-lint C-\- pass sanity checking dynamic
-dcore-lint Turn on internal sanity checking dynamic
-ddisable-js-c-sources Disable the link with C sources compiled to JavaScript dynamic
-ddisable-js-minifier Generate pretty-printed JavaScript code instead of minified (compacted) code. dynamic
-ddump-asm Dump final assembly dynamic
-ddump-asm-conflicts Dump register conflicts from the register allocator. dynamic
-ddump-asm-liveness Dump assembly augmented with register liveness dynamic
-ddump-asm-native Dump initial assembly dynamic
-ddump-asm-regalloc Dump the result of register allocation dynamic
-ddump-asm-regalloc-stages Dump the build/spill stages of the -fregs-graph register allocator. dynamic
-ddump-asm-stats Dump statistics from the register allocator. dynamic
-ddump-bcos Dump interpreter byte code dynamic
-ddump-c-backend Dump C code produced by the C (unregisterised) backend. dynamic
-ddump-call-arity Dump output of the call arity analysis pass. dynamic
-ddump-cfg-weights Dump the assumed weights of the CFG. dynamic
-ddump-cmm Dump the final C-\- output dynamic
-ddump-cmm-caf Dump the results of the C-\- CAF analysis pass. dynamic
-ddump-cmm-cbe Dump the results of common block elimination dynamic
-ddump-cmm-cfg Dump the results of the C-\- control flow optimisation pass. dynamic
-ddump-cmm-cps Dump the results of the CPS pass dynamic
-ddump-cmm-from-stg Dump STG-to-C-\- output dynamic
-ddump-cmm-info Dump the results of the C-\- info table augmentation pass. dynamic
-ddump-cmm-opt Dump the results of C-\- to C-\- optimising passes dynamic
-ddump-cmm-proc Dump the results of proc-point analysis dynamic
-ddump-cmm-procmap Dump the results of the C-\- proc-point map pass. dynamic
-ddump-cmm-raw Dump raw C-\- dynamic
-ddump-cmm-sink Dump the results of the C-\- sinking pass. dynamic
-ddump-cmm-sp Dump the results of the C-\- stack layout pass. dynamic
-ddump-cmm-split Dump the results of the C-\- proc-point splitting pass. dynamic
-ddump-cmm-switch Dump the results of switch lowering passes dynamic
-ddump-cmm-thread-sanitizer Dump the results of the C-\- ThreadSanitizer elaboration pass. dynamic
-ddump-cmm-verbose Write output from main C-\- pipeline passes to files dynamic
-ddump-cmm-verbose-by-proc Show output from main C-\- pipeline passes (grouped by proc) dynamic
-ddump-core-stats Print a one-line summary of the size of the Core program at the end of the optimisation pipeline dynamic
-ddump-cpr-signatures Dump CPR signatures dynamic
-ddump-cpranal Dump CPR analysis output dynamic
-ddump-cs-trace Trace constraint solver dynamic
-ddump-cse Dump CSE output dynamic
-ddump-debug Dump generated DWARF debug information dynamic
-ddump-deriv Dump deriving output dynamic
-ddump-dmd-signatures Dump top-level demand signatures dynamic
-ddump-dmdanal Dump demand analysis output dynamic
-ddump-ds, -ddump-ds-preopt Dump desugarer output. dynamic
-ddump-ec-trace Trace exhaustiveness checker dynamic
-ddump-exitify Dump output of the exitification pass. dynamic
-ddump-faststrings Dump the whole FastString table when finished dynamic
-ddump-file-prefix=⟨str⟩ Set the prefix of the filenames used for debugging output. dynamic
-ddump-float-in Dump float in output dynamic
-ddump-foreign Dump foreign export stubs dynamic
-ddump-full-laziness, -ddump-float-out Dump full laziness pass output dynamic
-ddump-hie Dump the hie file syntax tree dynamic
-ddump-hpc An alias for -ddump-ticked. dynamic
-ddump-if-trace Trace interface files dynamic
-ddump-inlinings Dump inlinings performed by the simplifier. dynamic
-ddump-js Dump final JavaScript code dynamic
-ddump-json (deprecated) Use -fdiagnostics-as-json instead dynamic
-ddump-late-cc Dump core with late cost centres added dynamic
-ddump-liberate-case Dump liberate case output dynamic
-ddump-llvm Dump LLVM intermediate code. dynamic
-ddump-mod-map Dump the state of the module mapping database. dynamic
-ddump-occur-anal Dump occurrence analysis output dynamic
-ddump-opt-cmm Dump the results of C-\- to C-\- optimising passes dynamic
-ddump-parsed Dump parse tree dynamic
-ddump-parsed-ast Dump parser output as a syntax tree dynamic
-ddump-prep Dump prepared core dynamic
-ddump-rn Dump renamer output dynamic
-ddump-rn-ast Dump renamer output as a syntax tree dynamic
-ddump-rn-stats Renamer stats dynamic
-ddump-rn-trace Trace renamer dynamic
-ddump-rtti Trace runtime type inference dynamic
-ddump-rule-firings Dump rule firing info dynamic
-ddump-rule-rewrites Dump detailed rule firing info dynamic
-ddump-rules Dump rewrite rules dynamic
-ddump-simpl Dump final simplifier output dynamic
-ddump-simpl-iterations Dump output from each simplifier iteration dynamic
-ddump-simpl-stats Dump simplifier stats dynamic
-ddump-simpl-trace Dump trace messages in simplifier dynamic
-ddump-spec Dump specialiser output dynamic
-ddump-spec-constr Dump specialiser output from SpecConstr dynamic
-ddump-splices Dump TH spliced expressions, and what they evaluate to dynamic
-ddump-static-argument-transformation Dump static argument transformation output dynamic
-ddump-stg (deprecated) Alias for -ddump-stg-from-core dynamic
-ddump-stg-cg Show output after Stg2Stg dynamic
-ddump-stg-final Show output of last STG pass. dynamic
-ddump-stg-from-core Show CoreToStg output dynamic
-ddump-stg-tags Show output of the tag inference pass. dynamic
-ddump-stg-unarised Show unarised STG dynamic
-ddump-str-signatures (deprecated) Alias for -ddump-dmd-signatures dynamic
-ddump-stranal (deprecated) Alias for -ddump-dmdanal dynamic
-ddump-tc Dump typechecker output dynamic
-ddump-tc-ast Dump typechecker output as a syntax tree dynamic
-ddump-tc-trace Trace typechecker dynamic
-ddump-ticked Dump the code instrumented by HPC (Observing Code Coverage). dynamic
-ddump-timings Dump per-pass timing and allocation statistics dynamic
-ddump-to-file Dump to files instead of stdout dynamic
-ddump-types Dump type signatures dynamic
-ddump-verbose-inlinings Dump all considered inlinings dynamic
-ddump-view-pattern-commoning Dump commoned view patterns dynamic
-ddump-worker-wrapper Dump worker-wrapper output dynamic
-dfaststring-stats Show statistics for fast string usage when finished dynamic
-dhex-word-literals Print values of type Word# in hexadecimal. dynamic
-dinitial-unique=⟨s⟩ Start UniqSupply allocation from ⟨s⟩. dynamic
-dinline-check=⟨str⟩ Dump information about inlining decisions dynamic
-dipe-stats Show statistics about IPE information dynamic
-dkeep-comments Include comments in the parser. Useful in combination with -ddump-parsed-ast. dynamic
-dlinear-core-lint Turn on internal sanity checking dynamic
-dlint Enable several common internal sanity checkers dynamic
-dno-debug-output Suppress unsolicited debugging output dynamic -ddebug-output
-dno-typeable-binds Don't generate bindings for Typeable methods dynamic
-dppr-case-as-let Print single alternative case expressions as strict lets. dynamic
-dppr-cols=⟨n⟩ Set the width of debugging output. For example -dppr-cols200 dynamic
-dppr-debug Turn on debug printing (more verbose) dynamic
-dppr-user-length Set the depth for printing expressions in error msgs dynamic
-drule-check=⟨str⟩ Dump information about potential rule application dynamic
-dshow-passes Print out each pass name as it happens dynamic
-dstg-lint STG pass sanity checking dynamic
-dsuppress-all In dumps, suppress everything (except for uniques) that is suppressible. dynamic
-dsuppress-coercion-types Suppress the printing of coercion types in Core dumps to make them shorter dynamic
-dsuppress-coercions Suppress the printing of coercions in Core dumps to make them shorter dynamic
-dsuppress-core-sizes Suppress the printing of core size stats per binding (since 9.4) dynamic
-dsuppress-idinfo Suppress extended information about identifiers where they are bound dynamic
-dsuppress-module-prefixes Suppress the printing of module qualification prefixes dynamic
-dsuppress-stg-free-vars Suppress the printing of closure free variable lists in STG output dynamic
-dsuppress-stg-reps Suppress rep annotations on STG args. dynamic
-dsuppress-ticks Suppress "ticks" in the pretty-printer output. dynamic
-dsuppress-timestamps Suppress timestamps in dumps dynamic
-dsuppress-type-applications Suppress type applications dynamic
-dsuppress-type-signatures Suppress type signatures dynamic
-dsuppress-unfoldings Suppress the printing of the stable unfolding of a variable at its binding site dynamic
-dsuppress-uniques Suppress the printing of uniques in debug output (easier to use diff) dynamic
-dsuppress-var-kinds Suppress the printing of variable kinds dynamic
-dtag-inference-checks Affirm tag inference results are correct at runtime. dynamic
-dth-dec-file Dump evaluated TH declarations into *.th.hs files dynamic
-dunique-increment=⟨i⟩ Set the increment for the generated Unique's to ⟨i⟩. dynamic
-dverbose-core2core Show output from each core-to-core pass dynamic
-dverbose-stg2stg Show output from each STG-to-STG pass dynamic
-falignment-sanitisation Compile with alignment checks for all info table dereferences. dynamic
-fcatch-nonexhaustive-cases Add a default error alternative to case expressions without a default alternative. dynamic
-fcheck-prim-bounds Instrument array primops with bounds checks. dynamic
-fcmm-thread-sanitizer Enable ThreadSanitizer instrumentation of memory accesses. dynamic
-fdistinct-constructor-tables Generate a fresh info table for each usage of a data constructor. dynamic
-fdump-with-ways Include the tag of the enabled ways in the extension of dump files. dynamic
-finfo-table-map Embed a lookup table in the generated binary which maps the address of an info table to the source position the closure originated from. dynamic
-finfo-table-map-with-fallback Include info tables with no source location information in the info table map. dynamic -fno-info-table-map-with-fallback
-finfo-table-map-with-stack Include info tables for STACK closures in the info table map. dynamic -fno-info-table-map-with-stack
-fllvm-fill-undef-with-garbage Intruct LLVM to fill dead STG registers with garbage dynamic
-fno-info-table-map-with-fallback Omit info tables with no source location information from the info table map. dynamic -finfo-table-map-with-fallback
-fno-info-table-map-with-stack Omit info tables for STACK closures from the info table map. dynamic -finfo-table-map-with-stack
-forig-thunk-info Generate stg_orig_thunk_info stack frames on thunk entry dynamic
-fproc-alignment Align functions at given boundary. dynamic
-funoptimized-core-for-interpreter Disable optimizations with the interpreter dynamic -fno-unoptimized-core-for-interpreter
-g, -g⟨n⟩ Produce DWARF debug information in compiled object files. ⟨n⟩ can be 0, 1, or 2, with higher numbers producing richer output. If ⟨n⟩ is omitted, level 2 is assumed. dynamic

5.6.27. Miscellaneous compiler options

Flag Description Type Reverse
-ddump-mod-cycles Dump module cycles dynamic
-fdefer-out-of-scope-variables Convert variable out of scope variables errors into warnings. Implied by -fdefer-type-errors. See also -Wdeferred-out-of-scope-variables. dynamic -fno-defer-out-of-scope-variables
-fdefer-type-errors Turn type errors into warnings, deferring the error until runtime. Implies -fdefer-typed-holes and -fdefer-out-of-scope-variables. See also -Wdeferred-type-errors. dynamic -fno-defer-type-errors
-fdefer-typed-holes Convert typed hole errors into warnings, deferring the error until runtime. Implied by -fdefer-type-errors. See also -Wtyped-holes. dynamic -fno-defer-typed-holes
-fexternal-interpreter Run interpreted code in a separate process dynamic
-ffamily-application-cache Use a cache when reducing type family applications dynamic -fno-family-application-cache
-fglasgow-exts Deprecated. Enable most language extensions; see Controlling editions and extensions for exactly which ones. dynamic -fno-glasgow-exts
-fno-safe-haskell Disable Safe Haskell dynamic
-ghcversion-file ⟨path to ghcversion.h⟩ (GHC as a C compiler only) Use this ghcversion.h file dynamic
-H ⟨size⟩ Set the minimum size of the heap to ⟨size⟩ dynamic
-hidden-module ⟨module name⟩ A module which should not be visible outside its unit. dynamic
-j[⟨n⟩] When compiling with --make, compile ⟨n⟩ modules in parallel. dynamic
-jsem When compiling with --make, coordinate with other processes through the semaphore ⟨sem⟩ to compile modules in parallel. dynamic
-reexported-module ⟨module name⟩ A module which should be reexported from this unit. dynamic
-this-package-name ⟨unit-id⟩ The name of the package which this module would be part of when installed. dynamic
-unit @⟨filename⟩ Specify the options to build a specific unit. dynamic
-working-dir ⟨dir⟩ Specify the directory a unit is expected to be compiled in. dynamic