.. _options-debugging: Debugging the compiler ====================== .. index:: single: debugging options (for GHC) .. It is not necessary to provide :category: tags for ``ghc-flag:``s defined in this file; a default is specified in ``flags.py``. HACKER TERRITORY. HACKER TERRITORY. (You were warned.) .. contents:: Dump flags .. _dumping-output: Dumping out compiler intermediate structures -------------------------------------------- .. index:: single: dumping GHC intermediates single: intermediate passes, output .. ghc-flag:: -ddump-to-file :shortdesc: Dump to files instead of stdout :type: dynamic Causes the output from each of flags starting with "-ddump", to be dumped to a file or files. If you want to have all the output from one single flag saved to one file, use :ghc-flag:`-ddump-file-prefix=⟨str⟩` (see descriptions below). Otherwise, the output will go to several files, including one for non-module specific and several for module specific. The suffix of a dump file depends on the flag turned on, for instance, output from :ghc-flag:`-ddump-simpl` will end up in :file:`prefix.dump-simpl`. .. ghc-flag:: -ddump-file-prefix=⟨str⟩ :shortdesc: Set the prefix of the filenames used for debugging output. :type: dynamic Set the prefix of the filenames used for debugging output. For example, ``-ddump-file-prefix=Foo`` will cause the output from :ghc-flag:`-ddump-simpl` to be dumped to :file:`Foo.dump-simpl`. .. ghc-flag:: -fdump-with-ways :shortdesc: Include the tag of the enabled ways in the extension of dump files. :type: dynamic :default: enabled When compiling Main.hs with profiling and without this will now produce ``Main.p.dump-simpl`` and ``Main.dump-simpl`` instead of overwriting the output of one way with the output of another. .. ghc-flag:: -ddump-json :shortdesc: Dump error messages as JSON documents :type: dynamic Dump error messages as JSON documents. This is intended to be consumed by external tooling. A good way to use it is in conjunction with :ghc-flag:`-ddump-to-file`. .. ghc-flag:: -dshow-passes :shortdesc: Print out each pass name as it happens :type: dynamic Print out each pass name, its runtime and heap allocations as it happens. Note that this may come at a slight performance cost as the compiler will be a bit more eager in forcing pass results to more accurately account for their costs. Two types of messages are produced: Those beginning with ``***`` do denote the beginning of a compilation phase whereas those starting with ``!!!`` mark the end of a pass and are accompanied by allocation and runtime statistics. .. ghc-flag:: -dfaststring-stats :shortdesc: Show statistics for fast string usage when finished :type: dynamic Show statistics on the usage of fast strings by the compiler. .. ghc-flag:: -ddump-faststrings :shortdesc: Dump the whole FastString table when finished :type: dynamic Dump the whole FastString table when finished. Consider using :ghc-flag:`-ddump-file-prefix=⟨str⟩` to dump it into a file. .. ghc-flag:: -dppr-debug :shortdesc: Turn on debug printing (more verbose) :type: dynamic Debugging output is in one of several "styles." Take the printing of types, for example. In the "user" style (the default), the compiler's internal ideas about types are presented in Haskell source-level syntax, insofar as possible. In the "debug" style (which is the default for debugging output), the types are printed in with explicit foralls, and variables have their unique-id attached (so you can check for things that look the same but aren't). This flag makes debugging output appear in the more verbose debug style. .. ghc-flag:: -ddump-timings :shortdesc: Dump per-pass timing and allocation statistics :type: dynamic Show allocation and runtime statistics for various stages of compilation. Allocations are measured in bytes. Timings are measured in milliseconds. GHC is a large program consisting of a number of stages. You can tell GHC to dump information from various stages of compilation using the ``-ddump-⟨pass⟩`` flags listed below. Note that some of these tend to produce a lot of output. You can prevent them from clogging up your standard output by passing :ghc-flag:`-ddump-to-file`. Front-end ~~~~~~~~~ These flags dump various information from GHC's frontend. This includes the parser and interface file reader. .. ghc-flag:: -ddump-parsed :shortdesc: Dump parse tree :type: dynamic Dump parser output .. ghc-flag:: -ddump-parsed-ast :shortdesc: Dump parser output as a syntax tree :type: dynamic Dump parser output as a syntax tree .. ghc-flag:: -dkeep-comments :shortdesc: Include comments in the parser. Useful in combination with :ghc-flag:`-ddump-parsed-ast`. :type: dynamic Include comments in the parser. Useful in combination with :ghc-flag:`-ddump-parsed-ast`. .. ghc-flag:: -ddump-if-trace :shortdesc: Trace interface files :type: dynamic Make the interface loader be *real* chatty about what it is up to. Type-checking and renaming ~~~~~~~~~~~~~~~~~~~~~~~~~~ These flags dump various information from GHC's typechecker and renamer. .. ghc-flag:: -ddump-tc-trace :shortdesc: Trace typechecker :type: dynamic Make the type checker be *real* chatty about what it is up to. .. ghc-flag:: -ddump-rn-trace :shortdesc: Trace renamer :type: dynamic Make the renamer be *real* chatty about what it is up to. .. ghc-flag:: -ddump-ec-trace :shortdesc: Trace exhaustiveness checker :type: dynamic Make the pattern match exhaustiveness checker be *real* chatty about what it is up to. .. ghc-flag:: -ddump-cs-trace :shortdesc: Trace constraint solver :type: dynamic Make the constraint solver be *real* chatty about what it is up to. .. ghc-flag:: -ddump-rn-stats :shortdesc: Renamer stats :type: dynamic Print out summary of what kind of information the renamer had to bring in. .. ghc-flag:: -ddump-rn :shortdesc: Dump renamer output :type: dynamic Dump renamer output .. ghc-flag:: -ddump-rn-ast :shortdesc: Dump renamer output as a syntax tree :type: dynamic Dump renamer output as a syntax tree .. ghc-flag:: -ddump-tc :shortdesc: Dump typechecker output :type: dynamic Dump typechecker output. Note that this hides a great deal of detail by default; you might consider using this with :ghc-flag:`-fprint-typechecker-elaboration`. .. ghc-flag:: -ddump-tc-ast :shortdesc: Dump typechecker output as a syntax tree :type: dynamic Dump typechecker output as a syntax tree .. ghc-flag:: -ddump-hie :shortdesc: Dump the hie file syntax tree :type: dynamic Dump the hie file syntax tree if we are generating extended interface files .. ghc-flag:: -ddump-splices :shortdesc: Dump TH spliced expressions, and what they evaluate to :type: dynamic Dump Template Haskell expressions that we splice in, and what Haskell code the expression evaluates to. .. ghc-flag:: -dth-dec-file :shortdesc: Dump evaluated TH declarations into `*.th.hs` files :type: dynamic Dump expansions of all top-level Template Haskell splices into :file:`{module}.th.hs` for each file :file:`{module}.hs`. .. ghc-flag:: -ddump-types :shortdesc: Dump type signatures :type: dynamic Dump a type signature for each value defined at the top level of the module. The list is sorted alphabetically. Using :ghc-flag:`-dppr-debug` dumps a type signature for all the imported and system-defined things as well; useful for debugging the compiler. .. ghc-flag:: -ddump-deriv :shortdesc: Dump deriving output :type: dynamic Dump derived instances Core representation and simplification ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ These flags dump various phases of GHC's Core-to-Core pipeline. This begins with the desugarer and includes the simplifier, worker-wrapper transformation, the rule engine, the specialiser, the strictness/occurrence analyser, and a common subexpression elimination pass. .. ghc-flag:: -ddump-call-arity :shortdesc: Dump output of the call arity analysis pass. :type: dynamic Dump output of the call arity analysis pass (:ghc-flag:`-fcall-arity`). .. ghc-flag:: -ddump-core-stats :shortdesc: Print a one-line summary of the size of the Core program at the end of the optimisation pipeline :type: dynamic Print a one-line summary of the size of the Core program at the end of the optimisation pipeline. .. ghc-flag:: -ddump-ds -ddump-ds-preopt :shortdesc: Dump desugarer output. :type: dynamic Dump desugarer output. :ghc-flag:`-ddump-ds` dumps the output after the very simple optimiser has run (which discards a lot of clutter and hence is a sensible default. :ghc-flag:`-ddump-ds-preopt` shows the output after desugaring but before the very simple optimiser. .. ghc-flag:: -ddump-exitify :shortdesc: Dump output of the exitification pass. :type: dynamic Dump output of the exitification pass (:ghc-flag:`-fexitification`), which tries to pull out code out of recursive functions. .. ghc-flag:: -ddump-simpl-iterations :shortdesc: Dump output from each simplifier iteration :type: dynamic Show the output of each *iteration* of the simplifier (each run of the simplifier has a maximum number of iterations, normally 4). .. ghc-flag:: -ddump-simpl-stats :shortdesc: Dump simplifier stats :type: dynamic Dump statistics about how many of each kind of transformation took place. If you add :ghc-flag:`-dppr-debug` you get more detailed information. .. ghc-flag:: -ddump-simpl-trace :shortdesc: Dump trace messages in simplifier :type: dynamic Dump trace messages from various functions of the simplifier. Produces quite a lot of output. .. ghc-flag:: -dverbose-core2core :shortdesc: Show output from each core-to-core pass :type: dynamic Show the output of the intermediate Core-to-Core pass. (*lots* of output!) So: when we're really desperate: .. code-block:: sh % ghc -noC -O -ddump-simpl -dverbose-core2core -dcore-lint Foo.hs .. ghc-flag:: -ddump-spec :shortdesc: Dump specialiser output :type: dynamic Dump output of typeclass specialisation pass .. ghc-flag:: -ddump-spec-constr :shortdesc: Dump specialiser output from SpecConstr :type: dynamic :since: 9.8.1 Dump output of the SpecConstr specialisation pass .. ghc-flag:: -ddump-rules :shortdesc: Dump rewrite rules :type: dynamic Dumps all rewrite rules specified in this module; see :ref:`controlling-rules`. .. ghc-flag:: -ddump-rule-firings :shortdesc: Dump rule firing info :type: dynamic Dumps the names of all rules that fired in this module .. ghc-flag:: -ddump-rule-rewrites :shortdesc: Dump detailed rule firing info :type: dynamic Dumps detailed information about all rules that fired in this module .. ghc-flag:: -drule-check=⟨str⟩ :shortdesc: Dump information about potential rule application :type: dynamic This flag is useful for debugging why a rule you expect to be firing isn't. Rules are filtered by the user provided string, a rule is kept if a prefix of its name matches the string. The pass then checks whether any of these rules could apply to the program but which didn't fire for some reason. For example, specifying ``-drule-check=SPEC`` will check whether there are any applications which might be subject to a rule created by specialisation. .. ghc-flag:: -dinline-check=⟨str⟩ :shortdesc: Dump information about inlining decisions :type: dynamic This flag is useful for debugging why a definition is not inlined. When a string is passed to this flag we report information about all functions whose name shares a prefix with the string. For example, if you are inspecting the core of your program and you observe that ``foo`` is not being inlined. You can pass ``-dinline-check foo`` and you will see a report about why ``foo`` is not inlined. .. ghc-flag:: -ddump-simpl :shortdesc: Dump final simplifier output :type: dynamic Dump simplifier output (Core-to-Core passes) .. ghc-flag:: -ddump-inlinings :shortdesc: Dump inlinings performed by the simplifier. :type: dynamic Dumps inlinings performed by the simplifier. .. ghc-flag:: -ddump-verbose-inlinings :shortdesc: Dump all considered inlinings :type: dynamic Dumps all inlinings considered by the simplifier, even those ultimately not performed. This output includes various information that the simplifier uses to determine whether the inlining is beneficial. .. ghc-flag:: -ddump-stranal :shortdesc: Dump demand analysis output :type: dynamic Dump demand analysis output. See :ghc-flag:`-fstrictness` for the syntax and semantics of demand annotations. .. ghc-flag:: -ddump-str-signatures :shortdesc: Dump top-level demand signatures :type: dynamic Dump top-level demand signatures as produced by demand analysis. See :ghc-flag:`-fstrictness` for the syntax and semantics of demand annotations. .. ghc-flag:: -ddump-cpranal :shortdesc: Dump CPR analysis output :type: dynamic Dump Constructed Product Result analysis output .. ghc-flag:: -ddump-cpr-signatures :shortdesc: Dump CPR signatures :type: dynamic Dump Constructed Product Result signatures .. ghc-flag:: -ddump-cse :shortdesc: Dump CSE output :type: dynamic Dump common subexpression elimination (CSE) pass output .. ghc-flag:: -ddump-full-laziness -ddump-float-out :shortdesc: Dump full laziness pass output :type: dynamic Dump full laziness pass (also known as float-out) output (see :ghc-flag:`-ffull-laziness`) .. ghc-flag:: -ddump-float-in :shortdesc: Dump float in output :type: dynamic Dump float-in pass output (see :ghc-flag:`-ffloat-in`) .. ghc-flag:: -ddump-liberate-case :shortdesc: Dump liberate case output :type: dynamic Dump liberate case pass output (see :ghc-flag:`-fliberate-case`) .. ghc-flag:: -ddump-static-argument-transformation :shortdesc: Dump static argument transformation output :type: dynamic Dump static argument transformation pass output (see :ghc-flag:`-fstatic-argument-transformation`) .. ghc-flag:: -ddump-worker-wrapper :shortdesc: Dump worker-wrapper output :type: dynamic Dump worker/wrapper split output .. ghc-flag:: -ddump-occur-anal :shortdesc: Dump occurrence analysis output :type: dynamic Dump "occurrence analysis" output .. ghc-flag:: -ddump-prep :shortdesc: Dump prepared core :type: dynamic Dump output of Core preparation pass .. ghc-flag:: -ddump-late-cc :shortdesc: Dump core with late cost centres added :type: dynamic Dump output of LateCC pass after cost centres have been added. .. ghc-flag:: -ddump-view-pattern-commoning :shortdesc: Dump commoned view patterns :type: dynamic Print the view patterns that are commoned. STG representation ~~~~~~~~~~~~~~~~~~ These flags dump various phases of GHC's STG pipeline. .. ghc-flag:: -ddump-stg-from-core :shortdesc: Show CoreToStg output :type: dynamic Show the output of CoreToStg pass. .. ghc-flag:: -dverbose-stg2stg :shortdesc: Show output from each STG-to-STG pass :type: dynamic Show the output of the intermediate STG-to-STG pass. (*lots* of output!) .. ghc-flag:: -ddump-stg-unarised :shortdesc: Show unarised STG :type: dynamic Show the output of the unarise pass. .. ghc-flag:: -ddump-stg-cg :shortdesc: Show output after Stg2Stg :type: dynamic Show the output of the STG after Stg2Stg. This is the result after applying the Stg2Stg optimization passes. .. ghc-flag:: -ddump-stg-tags :shortdesc: Show output of the tag inference pass. :type: dynamic Show the output of the tag inference pass. .. ghc-flag:: -ddump-stg-final :shortdesc: Show output of last STG pass. :type: dynamic Show the output of the last STG pass before we generate Cmm. .. ghc-flag:: -ddump-stg :shortdesc: *(deprecated)* Alias for :ghc-flag:`-ddump-stg-from-core` :type: dynamic Alias for :ghc-flag:`-ddump-stg-from-core`. Deprecated in favor of more explicit flags: :ghc-flag:`-ddump-stg-from-core`, :ghc-flag:`-ddump-stg-final`, etc. C-\\- representation ~~~~~~~~~~~~~~~~~~~~ These flags dump various phases of GHC's C-\\- pipeline. .. ghc-flag:: -ddump-cmm-verbose-by-proc :shortdesc: Show output from main C-\\- pipeline passes (grouped by proc) :type: dynamic Dump output from main C-\\- pipeline stages. In case of ``.cmm`` compilation this also dumps the result of file parsing. Not included are passes run by the chosen backend. Currently only the NCG backends runs additional passes ( :ghc-flag:`-ddump-opt-cmm` ). Cmm dumps don't include unreachable blocks since we print blocks in reverse post-order. .. ghc-flag:: -ddump-cmm-verbose :shortdesc: Write output from main C-\\- pipeline passes to files :type: dynamic If used in conjunction with :ghc-flag:`-ddump-to-file`, writes dump output from main C-\\- pipeline stages to files (each stage per file). .. ghc-flag:: -ddump-cmm-from-stg :shortdesc: Dump STG-to-C-\\- output :type: dynamic Dump the result of STG-to-C-\\- conversion .. ghc-flag:: -ddump-cmm-raw :shortdesc: Dump raw C-\\- :type: dynamic Dump the “raw” C-\\-. .. ghc-flag:: -ddump-cmm-cfg :shortdesc: Dump the results of the C-\\- control flow optimisation pass. :type: dynamic Dump the results of the C-\\- control flow optimisation pass. .. ghc-flag:: -ddump-cmm-thread-sanitizer :shortdesc: Dump the results of the C-\\- ThreadSanitizer elaboration pass. :type: dynamic Dump the results of the C-\\- pass responsible for adding instrumentation added by :ghc-flag:`-fcmm-thread-sanitizer`. .. ghc-flag:: -ddump-cmm-cbe :shortdesc: Dump the results of common block elimination :type: dynamic Dump the results of the C-\\- Common Block Elimination (CBE) pass. .. ghc-flag:: -ddump-cmm-switch :shortdesc: Dump the results of switch lowering passes :type: dynamic Dump the results of the C-\\- switch lowering pass. .. ghc-flag:: -ddump-cmm-proc :shortdesc: Dump the results of proc-point analysis :type: dynamic Dump the results of the C-\\- proc-point analysis pass. .. ghc-flag:: -ddump-cmm-sp :shortdesc: Dump the results of the C-\\- stack layout pass. :type: dynamic Dump the results of the C-\\- stack layout pass. .. ghc-flag:: -ddump-cmm-sink :shortdesc: Dump the results of the C-\\- sinking pass. :type: dynamic Dump the results of the C-\\- sinking pass. .. ghc-flag:: -ddump-cmm-caf :shortdesc: Dump the results of the C-\\- CAF analysis pass. :type: dynamic Dump the results of the C-\\- CAF analysis pass. .. ghc-flag:: -ddump-cmm-procmap :shortdesc: Dump the results of the C-\\- proc-point map pass. :type: dynamic Dump the results of the C-\\- proc-point map pass. .. ghc-flag:: -ddump-cmm-split :shortdesc: Dump the results of the C-\\- proc-point splitting pass. :type: dynamic Dump the results of the C-\\- proc-point splitting pass. .. ghc-flag:: -ddump-cmm-info :shortdesc: Dump the results of the C-\\- info table augmentation pass. :type: dynamic Dump the results of the C-\\- info table augmentation pass. .. ghc-flag:: -ddump-cmm-cps :shortdesc: Dump the results of the CPS pass :type: dynamic Dump the results of the CPS pass. .. ghc-flag:: -ddump-cmm :shortdesc: Dump the final C-\\- output :type: dynamic Dump the result of the C-\\- pipeline processing .. ghc-flag:: -ddump-cfg-weights :shortdesc: Dump the assumed weights of the CFG. :type: dynamic Dumps the CFG with weights used by the new block layout code. Each CFG is dumped in dot format graph making it easy to visualize them. LLVM code generator ~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -ddump-llvm :shortdesc: Dump LLVM intermediate code. :type: dynamic :implies: :ghc-flag:`-fllvm` LLVM code from the :ref:`LLVM code generator ` C code generator ~~~~~~~~~~~~~~~~ .. ghc-flag:: -ddump-c-backend :shortdesc: Dump C code produced by the C (unregisterised) backend. :type: dynamic :shortdesc: Dump C code produced by the C (unregisterised) backend. Native code generator ~~~~~~~~~~~~~~~~~~~~~ These flags dump various stages of the :ref:`native code generator's ` pipeline, which starts with C-\\- and produces native assembler. .. ghc-flag:: -ddump-cmm-opt :shortdesc: Dump the results of C-\\- to C-\\- optimising passes :type: dynamic Dump the results of C-\\- to C-\\- optimising passes performed by the NCG. .. ghc-flag:: -ddump-opt-cmm :shortdesc: Dump the results of C-\\- to C-\\- optimising passes :type: dynamic Alias for :ghc-flag:`-ddump-cmm-opt` .. ghc-flag:: -ddump-asm-conflicts :shortdesc: Dump register conflicts from the register allocator. :type: dynamic Dump (virtual) register conflicts ("interferences") from the graph coloring register allocator (:ghc-flag:`-fregs-graph`). .. ghc-flag:: -ddump-asm-native :shortdesc: Dump initial assembly :type: dynamic Dump the initial assembler output produced from C-\\-. .. ghc-flag:: -ddump-asm-liveness :shortdesc: Dump assembly augmented with register liveness :type: dynamic Dump the result of the register liveness pass. .. ghc-flag:: -ddump-asm-regalloc :shortdesc: Dump the result of register allocation :type: dynamic Dump the result of the register allocation pass. .. ghc-flag:: -ddump-asm-regalloc-stages :shortdesc: Dump the build/spill stages of the :ghc-flag:`-fregs-graph` register allocator. :type: dynamic Dump the build/spill stages of the :ghc-flag:`-fregs-graph` register allocator. .. ghc-flag:: -ddump-asm-stats :shortdesc: Dump statistics from the register allocator. :type: dynamic Dump statistics from the register allocator. .. ghc-flag:: -ddump-asm :shortdesc: Dump final assembly :type: dynamic Dump the final assembly produced by the native code generator. .. ghc-flag:: -ddump-js :shortdesc: Dump final JavaScript code :type: dynamic Dump the final JavaScript code produced by the JavaScript code generator. JavaScript code generator ~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -ddisable-js-minifier :shortdesc: Generate pretty-printed JavaScript code instead of minified (compacted) code. :type: dynamic Include human-readable spacing and indentation when generating JavaScript. Miscellaneous backend dumps ~~~~~~~~~~~~~~~~~~~~~~~~~~~ These flags dump various bits of information from other backends. .. ghc-flag:: -ddump-bcos :shortdesc: Dump interpreter byte code :type: dynamic Dump byte-code objects (BCOs) produced for the GHC's byte-code interpreter. .. ghc-flag:: -ddump-debug :shortdesc: Dump generated DWARF debug information :type: dynamic Dump generated debug information (DWARF) produced with the :ghc-flag:`-g` flag. .. ghc-flag:: -ddump-rtti :shortdesc: Trace runtime type inference :type: dynamic Trace runtime type inference done by various interpreter commands. .. ghc-flag:: -ddump-foreign :shortdesc: Dump ``foreign export`` stubs :type: dynamic Dump foreign export stubs. .. ghc-flag:: -ddump-ticked :shortdesc: Dump the code instrumented by HPC (:ref:`hpc`). :type: dynamic Dump the code instrumented by HPC (:ref:`hpc`). .. ghc-flag:: -ddump-hpc :shortdesc: An alias for :ghc-flag:`-ddump-ticked`. :type: dynamic An alias for :ghc-flag:`-ddump-ticked`. .. ghc-flag:: -ddump-mod-map :shortdesc: Dump the state of the module mapping database. :type: dynamic Dump a mapping of modules to where they come from, and how: - ``(hidden module)``: Module is hidden, and thus will never be available for import. - ``(unusable module)``: Module is unavailable because the package is unusable. - ``(hidden package)``: This module is in someone's exported-modules list, but that package is hidden. - ``(exposed package)``: Module is available for import. - ``(reexport by )``: This module is available from a reexport of some set of exposed packages. - ``(hidden reexport by )``: This module is available from a reexport of some set of hidden packages. - ``(package flag)``: This module export comes from a package flag. .. _formatting dumps: Formatting dumps ---------------- .. index:: single: formatting dumps .. ghc-flag:: -dppr-user-length :shortdesc: Set the depth for printing expressions in error msgs :type: dynamic In error messages, expressions are printed to a certain "depth", with subexpressions beyond the depth replaced by ellipses. This flag sets the depth. Its default value is 5. .. ghc-flag:: -dppr-cols=⟨n⟩ :shortdesc: Set the width of debugging output. For example ``-dppr-cols200`` :type: dynamic Set the width of debugging output. Use this if your code is wrapping too much. For example: ``-dppr-cols=200``. .. ghc-flag:: -dppr-case-as-let :shortdesc: Print single alternative case expressions as strict lets. :type: dynamic Print single alternative case expressions as though they were strict let expressions. This is helpful when your code does a lot of unboxing. .. ghc-flag:: -dhex-word-literals :shortdesc: Print values of type `Word#` in hexadecimal. :type: dynamic Print values of type `Word#` and `Word64#` (but not values of type `Int#` and `Int64#`) in hexadecimal instead of decimal. The hexadecimal is zero-padded to make the length of the representation a power of two. For example: `0x0A0A##`, `0x000FFFFF##`, `0xC##`. This flag may be helpful when you are producing a bit pattern that to expect to work correctly on a 32-bit or a 64-bit architecture. Dumping hexadecimal literals after optimizations and constant folding makes it easier to confirm that the generated bit pattern is correct. .. ghc-flag:: -dno-debug-output :shortdesc: Suppress unsolicited debugging output :type: dynamic :reverse: -ddebug-output Suppress any unsolicited debugging output. When GHC has been built with the ``DEBUG`` option it occasionally emits debug output of interest to developers. The extra output can confuse the testing framework and cause bogus test failures, so this flag is provided to turn it off. .. _suppression: Suppressing unwanted information -------------------------------- .. index:: single: suppression; of unwanted dump output Core dumps contain a large amount of information. Depending on what you are doing, not all of it will be useful. Use these flags to suppress the parts that you are not interested in. .. ghc-flag:: -dsuppress-all :shortdesc: In dumps, suppress everything (except for uniques) that is suppressible. :type: dynamic Suppress everything that can be suppressed, except for unique ids as this often makes the printout ambiguous. If you just want to see the overall structure of the code, then start here. .. ghc-flag:: -dsuppress-ticks :shortdesc: Suppress "ticks" in the pretty-printer output. :type: dynamic Suppress "ticks" in the pretty-printer output. .. ghc-flag:: -dsuppress-uniques :shortdesc: Suppress the printing of uniques in debug output (easier to use ``diff``) :type: dynamic Suppress the printing of uniques. This may make the printout ambiguous (e.g. unclear where an occurrence of 'x' is bound), but it makes the output of two compiler runs have many fewer gratuitous differences, so you can realistically apply ``diff``. Once ``diff`` has shown you where to look, you can try again without :ghc-flag:`-dsuppress-uniques` .. ghc-flag:: -dsuppress-idinfo :shortdesc: Suppress extended information about identifiers where they are bound :type: dynamic Suppress extended information about identifiers where they are bound. This includes strictness information and inliner templates. Using this flag can cut the size of the core dump in half, due to the lack of inliner templates .. ghc-flag:: -dsuppress-unfoldings :shortdesc: Suppress the printing of the stable unfolding of a variable at its binding site :type: dynamic Suppress the printing of the stable unfolding of a variable at its binding site. .. ghc-flag:: -dsuppress-module-prefixes :shortdesc: Suppress the printing of module qualification prefixes :type: dynamic Suppress the printing of module qualification prefixes. This is the ``Data.List`` in ``Data.List.length``. .. ghc-flag:: -dsuppress-timestamps :shortdesc: Suppress timestamps in dumps :type: dynamic Suppress the printing of timestamps. This makes it easier to diff dumps. .. ghc-flag:: -dsuppress-type-signatures :shortdesc: Suppress type signatures :type: dynamic Suppress the printing of type signatures. .. ghc-flag:: -dsuppress-type-applications :shortdesc: Suppress type applications :type: dynamic Suppress the printing of type applications. .. ghc-flag:: -dsuppress-coercions :shortdesc: Suppress the printing of coercions in Core dumps to make them shorter :type: dynamic Suppress the printing of type coercions. .. ghc-flag:: -dsuppress-coercion-types :shortdesc: Suppress the printing of coercion types in Core dumps to make them shorter :type: dynamic .. ghc-flag:: -dsuppress-var-kinds :shortdesc: Suppress the printing of variable kinds :type: dynamic Suppress the printing of variable kinds .. ghc-flag:: -dsuppress-stg-free-vars :shortdesc: Suppress the printing of closure free variable lists in STG output :type: dynamic Suppress the printing of closure free variable lists in STG output .. ghc-flag:: -dsuppress-core-sizes :shortdesc: Suppress the printing of core size stats per binding (since 9.4) :type: dynamic :since: 9.4.1 Suppress the printing of core size stats per binding .. ghc-flag:: -dsuppress-stg-reps :shortdesc: Suppress rep annotations on STG args. :type: dynamic :since: 9.6.1 default: enabled Disabling this will annoate certain stg arguments with their prim rep. .. _checking-consistency: Checking for consistency ------------------------ .. index:: single: consistency checks single: lint .. ghc-flag:: -dlint :shortdesc: Enable several common internal sanity checkers :type: dynamic :implies: -dcore-lint, -dstg-lint, -dcmm-lint, -dasm-lint, -fllvm-fill-undef-with-garbage, -debug :since: 9.4.1 Turn on various heavy-weight intra-pass sanity-checking measures within GHC and its runtime system. Notably, this does not include :ghc-flag:`-falignment-sanitisation` as it incurs a rather hefty runtime cost. .. ghc-flag:: -dcore-lint :shortdesc: Turn on internal sanity checking :type: dynamic Turn on heavyweight intra-pass sanity-checking within GHC, at Core level. (It checks GHC's sanity, not yours.) .. ghc-flag:: -dlinear-core-lint :shortdesc: Turn on internal sanity checking :type: dynamic Turn on linearity checking in GHC. Currently, some optimizations in GHC might not preserve linearity and there are valid programs that fail Linear Core Lint. In the near future, this option will be removed and folded into normal Core Lint. .. ghc-flag:: -dstg-lint :shortdesc: STG pass sanity checking :type: dynamic Ditto for STG level. .. ghc-flag:: -dcmm-lint :shortdesc: C-\\- pass sanity checking :type: dynamic Ditto for C-\\- level. .. ghc-flag:: -dasm-lint :shortdesc: ASM pass sanity checking :type: dynamic Turn on intra-pass sanity-checking within GHC, at the code generator level. .. ghc-flag:: -fllvm-fill-undef-with-garbage :shortdesc: Intruct LLVM to fill dead STG registers with garbage :type: dynamic Instructs the LLVM code generator to fill dead STG registers with garbage instead of ``undef`` in calls. This makes it easier to catch subtle code generator and runtime system bugs (e.g. see :ghc-ticket:`11487`). .. ghc-flag:: -falignment-sanitisation :shortdesc: Compile with alignment checks for all info table dereferences. :type: dynamic Compile with alignment checks for all info table dereferences. This can be useful when finding pointer tagging issues. .. ghc-flag:: -fproc-alignment :shortdesc: Align functions at given boundary. :type: dynamic :since: 8.6.1 Align functions to multiples of the given value. Only valid values are powers of two. ``-fproc-alignment=64`` can be used to limit alignment impact on performance as each function will start at a cache line. However forcing larger alignments in general reduces performance. .. ghc-flag:: -fcatch-nonexhaustive-cases :shortdesc: Add a default ``error`` alternative to case expressions without a default alternative. :type: dynamic GHC generates case expressions without a default alternative in some cases: - When the demand analysis thinks that the scrutinee does not return (i.e. a bottoming expression) - When the scrutinee is a GADT and its type rules out some constructors, and others constructors are already handled by the case expression. With this flag GHC generates a default alternative with ``error`` in these cases. This is helpful when debugging demand analysis or type checker bugs which can sometimes manifest as segmentation faults. .. ghc-flag:: -fcheck-prim-bounds :shortdesc: Instrument array primops with bounds checks. :type: dynamic Typically primops operations like ``writeArray#`` exhibit unsafe behavior, relying on the user to perform any bounds checking. This flag instructs the code generator to instrument such operations with bound checking logic which aborts the program when an out-of-bounds access is detected. Note that this is only intended to be used as a debugging measure, not as the primary means of catching out-of-bounds accesses. .. ghc-flag:: -fcmm-thread-sanitizer :shortdesc: Enable ThreadSanitizer instrumentation of memory accesses. :type: dynamic This enables generation of `ThreadSanitizer ` instrumentation of memory accesses. Requires use of ``-fsanitize=thread`` or similar when compiling and linking. .. _checking-determinism: Checking for determinism ------------------------ .. index:: single: deterministic builds .. ghc-flag:: -dinitial-unique=⟨s⟩ :shortdesc: Start ``UniqSupply`` allocation from ⟨s⟩. :type: dynamic Start ``UniqSupply`` allocation from ⟨s⟩. .. ghc-flag:: -dunique-increment=⟨i⟩ :shortdesc: Set the increment for the generated ``Unique``'s to ⟨i⟩. :type: dynamic Set the increment for the generated ``Unique``'s to ⟨i⟩. This is useful in combination with :ghc-flag:`-dinitial-unique=⟨s⟩` to test if the generated files depend on the order of ``Unique``'s. Some interesting values: * ``-dinitial-unique=0 -dunique-increment=1`` - current sequential ``UniqSupply`` * ``-dinitial-unique=16777215 -dunique-increment=-1`` - ``UniqSupply`` that generates in decreasing order * ``-dinitial-unique=1 -dunique-increment=PRIME`` - where PRIME big enough to overflow often - nonsequential order Other ----- .. ghc-flag:: -dno-typeable-binds :shortdesc: Don't generate bindings for Typeable methods :type: dynamic This avoids generating Typeable-related bindings for modules and types. This is useful when debugging because it gives smaller modules and dumps, but the compiler will panic if you try to use Typeable instances of things that you built with this flag. .. ghc-flag:: -dtag-inference-checks :shortdesc: Affirm tag inference results are correct at runtime. :type: dynamic When tag inference tells as a specific value is supposed to be tagged then generate code to check this at runtime. If the check fails the program will be terminated. This helps narrowing down if an issue is due to tag inference if things go wrong. Which would otherwise be quite difficult. .. ghc-flag:: -funoptimized-core-for-interpreter :shortdesc: Disable optimizations with the interpreter :reverse: -fno-unoptimized-core-for-interpreter :type: dynamic :since: 9.8.1 default: enabled At the moment, ghci disables optimizations, because not all passes are compatible with the interpreter. This option can be used to override this check, e.g. ``ghci -O2 -fno-unoptimized-core-for-interpreter``. It is not recommended for normal use and can cause a compiler panic. Note that this has an effect on the debugger interface: With optimizations in play, free variables in breakpoints may now be substituted with complex expressions. Those cannot be stored in breakpoints, so any free variable that refers to optimized code will not be inspectable when this flag is enabled.