HACKER TERRITORY. HACKER TERRITORY. (You were warned.)
Dump flags
-ddump-to-file Causes the output from all of the flags listed below to be dumped to a file. The file name depends upon the output produced; for instance, output from -ddump-simpl will end up in module.dump-simpl.
-ddump-json 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 -ddump-to-file.
-dshow-passes 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.
-dfaststring-stats Show statistics on the usage of fast strings by the compiler.
-dppr-debug 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.
-ddump-timings Show allocation and runtime statistics for various stages of compilation.
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 -ddump-to-file.
These flags dump various information from GHC’s frontend. This includes the parser and interface file reader.
-ddump-parsed Dump parser output
-ddump-parsed-ast Dump parser output as a syntax tree
-ddump-if-trace Make the interface loader be real chatty about what it is up to.
These flags dump various information from GHC’s typechecker and renamer.
-ddump-tc-trace Make the type checker be real chatty about what it is up to.
-ddump-rn-trace Make the renamer be real chatty about what it is up to.
-ddump-ec-trace Make the pattern match exhaustiveness checker be real chatty about what it is up to.
-ddump-rn-stats Print out summary of what kind of information the renamer had to bring in.
-ddump-rn Dump renamer output
-ddump-rn-ast Dump renamer output as a syntax tree
-ddump-tc Dump typechecker output
-ddump-tc-ast Dump typechecker output as a syntax tree
-ddump-splices Dump Template Haskell expressions that we splice in, and what Haskell code the expression evaluates to.
-dth-dec-file Dump expansions of all top-level Template Haskell splices into module.th.hs for each file module.hs.
-ddump-types Dump a type signature for each value defined at the top level of the module. The list is sorted alphabetically. Using -dppr-debug dumps a type signature for all the imported and system-defined things as well; useful for debugging the compiler.
-ddump-deriv Dump derived instances
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.
-ddump-core-stats Print a one-line summary of the size of the Core program at the end of the optimisation pipeline.
-ddump-ds -ddump-ds-preopt Dump desugarer output. -ddump-ds dumps the output after the very simple optimiser has run (which discards a lot of clutter and hence is a sensible default. -ddump-ds-preopt shows the output after desugaring but before the very simple optimiser.
-ddump-simpl-iterations Show the output of each iteration of the simplifier (each run of the simplifier has a maximum number of iterations, normally 4).
-ddump-simpl-stats Dump statistics about how many of each kind of transformation took place. If you add -dppr-debug you get more detailed information.
-dverbose-core2core Show the output of the intermediate Core-to-Core pass. (lots of output!) So: when we’re really desperate:
% ghc -noC -O -ddump-simpl -dverbose-core2core -dcore-lint Foo.hs
-ddump-spec Dump output of specialisation pass
-ddump-rules Dumps all rewrite rules specified in this module; see Controlling what’s going on in rewrite rules.
-ddump-rule-firings Dumps the names of all rules that fired in this module
-ddump-rule-rewrites Dumps detailed information about all rules that fired in this module
-drule-check=⟨str⟩ 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 file 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.
-dinline-check=⟨str⟩ 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.
-ddump-simpl Dump simplifier output (Core-to-Core passes)
-ddump-inlinings Dumps inlining info from the simplifier. Note that if used in conjunction with -dverbose-core2core the compiler will also dump the inlinings that it considers but passes up, along with its rationale.
-ddump-stranal Dump strictness analyser output
-ddump-str-signatures Dump strictness signatures
-ddump-cse Dump common subexpression elimination (CSE) pass output
-ddump-worker-wrapper Dump worker/wrapper split output
-ddump-occur-anal Dump “occurrence analysis” output
-ddump-prep Dump output of Core preparation pass
These flags dump various phases of GHC’s STG pipeline.
-ddump-stg Dump output of STG-to-STG passes
-dverbose-stg2stg Show the output of the intermediate STG-to-STG pass. (lots of output!)
These flags dump various phases of GHC’s C-\- pipeline.
-ddump-cmm-verbose Dump output from all C-\- pipeline stages. In case of .cmm compilation this also dumps the result of file parsing.
Cmm dumps don’t include unreachable blocks since we print blocks in reverse post-order.
-ddump-cmm-from-stg Dump the result of STG-to-C-\- conversion
-ddump-cmm-raw Dump the “raw” C-\-.
-ddump-cmm-cfg Dump the results of the C-\- control flow optimisation pass.
-ddump-cmm-cbe Dump the results of the C-\- Common Block Elimination (CBE) pass.
-ddump-cmm-switch Dump the results of the C-\- switch lowering pass.
-ddump-cmm-proc Dump the results of the C-\- proc-point analysis pass.
-ddump-cmm-sp Dump the results of the C-\- stack layout pass.
-ddump-cmm-sink Dump the results of the C-\- sinking pass.
-ddump-cmm-caf Dump the results of the C-\- CAF analysis pass.
-ddump-cmm-procmap Dump the results of the C-\- proc-point map pass.
-ddump-cmm-split Dump the results of the C-\- proc-point splitting pass.
-ddump-cmm-info Dump the results of the C-\- info table augmentation pass.
-ddump-cmm-cps Dump the results of the CPS pass.
-ddump-cmm Dump the result of the C-\- pipeline processing
-ddump-llvm | Implies: | -fllvm |
|---|
LLVM code from the LLVM code generator
These flags dump various stages of the native code generator’s pipeline, which starts with C-\- and produces native assembler.
-ddump-opt-cmm Dump the results of C-\- to C-\- optimising passes performed by the NCG.
-ddump-asm-native Dump the initial assembler output produced from C-\-.
-ddump-asm-liveness Dump the result of the register liveness pass.
-ddump-asm-regalloc Dump the result of the register allocation pass.
-ddump-asm-regalloc-stages Dump the build/spill stages of the -fregs-graph register allocator.
-ddump-asm-stats Dump statistics from the register allocator.
-ddump-asm-expanded Dump the result of the synthetic instruction expansion pass.
-ddump-asm Dump assembly language produced by the
These flags dump various bits of information from other backends.
-ddump-bcos Dump byte-code objects (BCOs) produced for the GHC’s byte-code interpreter.
-ddump-foreign Dump foreign export stubs.
-dppr-user-length 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.
-dppr-cols=⟨n⟩ Set the width of debugging output. Use this if your code is wrapping too much. For example: -dppr-cols=200.
-dppr-case-as-let Print single alternative case expressions as though they were strict let expressions. This is helpful when your code does a lot of unboxing.
-dhex-word-literals 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.
-dno-debug-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.
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.
-dsuppress-all 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.
-dsuppress-ticks Suppress “ticks” in the pretty-printer output.
-dsuppress-uniques 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 -dsuppress-uniques
-dsuppress-idinfo 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
-dsuppress-unfoldings Suppress the printing of the stable unfolding of a variable at its binding site.
-dsuppress-module-prefixes Suppress the printing of module qualification prefixes. This is the Data.List in Data.List.length.
-dsuppress-timestamps Suppress the printing of timestamps. This makes it easier to diff dumps.
-dsuppress-type-signatures Suppress the printing of type signatures.
-dsuppress-type-applications Suppress the printing of type applications.
-dsuppress-coercions Suppress the printing of type coercions.
-dsuppress-var-kinds Suppress the printing of variable kinds
-dsuppress-stg-free-vars Suppress the printing of closure free variable lists in STG output
-dcore-lint Turn on heavyweight intra-pass sanity-checking within GHC, at Core level. (It checks GHC’s sanity, not yours.)
-dstg-lint Ditto for STG level.
-dcmm-lint Ditto for C-\- level.
-fllvm-fill-undef-with-garbage 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 Trac #11487).
-falignment-sanitisation Compile with alignment checks for all info table dereferences. This can be useful when finding pointer tagging issues.
-fproc-alignment 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.
-fcatch-bottoms Instructs the simplifier to emit error expressions in the continuation of empty case analyses (which should bottom and consequently not return). This is helpful when debugging demand analysis bugs which can sometimes manifest as segmentation faults.
-dinitial-unique=⟨s⟩ Start UniqSupply allocation from ⟨s⟩.
-dunique-increment=⟨i⟩ Set the increment for the generated Unique‘s to ⟨i⟩.
This is useful in combination with -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
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Licensed under the Glasgow Haskell Compiler License.
https://downloads.haskell.org/~ghc/8.6.1/docs/html/users_guide/debugging.html