1 <Sect1 id="options-debugging">
2 <Title>Debugging the compiler
6 <IndexTerm><Primary>debugging options (for GHC)</Primary></IndexTerm>
10 HACKER TERRITORY. HACKER TERRITORY.
14 <Sect2 id="replacing-phases">
15 <Title>Replacing the program for one or more phases.
19 <IndexTerm><Primary>GHC phases, changing</Primary></IndexTerm>
20 <IndexTerm><Primary>phases, changing GHC</Primary></IndexTerm>
21 You may specify that a different program be used for one of the phases
22 of the compilation system, in place of whatever the driver <Command>ghc</Command> has
23 wired into it. For example, you might want to try a different
25 <Option>-pgm<phase-code><program-name></Option><IndexTerm><Primary>-pgm<phase><stuff>
26 option</Primary></IndexTerm> option to <Command>ghc</Command> will cause it to use <Literal><program-name></Literal>
27 for phase <Literal><phase-code></Literal>, where the codes to indicate the phases are:
33 <ColSpec Align="Left" Colsep="0">
34 <ColSpec Align="Left" Colsep="0">
37 <Entry><Emphasis>code</Emphasis> </Entry>
38 <Entry><Emphasis>phase</Emphasis> </Entry>
44 <Entry> literate pre-processor </Entry>
49 <Entry> C pre-processor (if -cpp only) </Entry>
54 <Entry> Haskell compiler </Entry>
59 <Entry> C compiler</Entry>
64 <Entry> assembler </Entry>
69 <Entry> linker </Entry>
74 <Entry> Makefile dependency generator </Entry>
85 <Sect2 id="forcing-options-through">
86 <Title>Forcing options to a particular phase.
90 <IndexTerm><Primary>forcing GHC-phase options</Primary></IndexTerm>
94 The preceding sections describe driver options that are mostly
95 applicable to one particular phase. You may also <Emphasis>force</Emphasis> a
96 specific option <Option><option></Option> to be passed to a particular phase
97 <Literal><phase-code></Literal> by feeding the driver the option
98 <Option>-opt<phase-code><option></Option>.<IndexTerm><Primary>-opt<phase><stuff>
99 option</Primary></IndexTerm> The codes to indicate the phases are the same as in the
104 So, for example, to force an <Option>-Ewurble</Option> option to the assembler, you
105 would tell the driver <Option>-opta-Ewurble</Option> (the dash before the E is
110 Besides getting options to the Haskell compiler with <Option>-optC<blah></Option>,
111 you can get options through to its runtime system with
112 <Option>-optCrts<blah></Option><IndexTerm><Primary>-optCrts<blah> option</Primary></IndexTerm>.
116 So, for example: when I want to use my normal driver but with my
117 profiled compiler binary, I use this script:
121 exec /local/grasp_tmp3/simonpj/ghc-BUILDS/working-alpha/ghc/driver/ghc \
122 -pgmC/local/grasp_tmp3/simonpj/ghc-BUILDS/working-hsc-prof/hsc \
132 <Sect2 id="dumping-output">
133 <Title>Dumping out compiler intermediate structures
137 <IndexTerm><Primary>dumping GHC intermediates</Primary></IndexTerm>
138 <IndexTerm><Primary>intermediate passes, output</Primary></IndexTerm>
145 <Term><Option>-hi</Option>:</Term>
148 <IndexTerm><Primary>-hi option</Primary></IndexTerm>
149 <Emphasis>Do</Emphasis> generate an interface file. This would normally be used in
150 conjunction with <Option>-noC</Option>, which turns off interface generation;
151 thus: <Option>-noC -hi</Option>.
156 <Term><Option>-dshow-passes</Option>:</Term>
159 <IndexTerm><Primary>-dshow-passes option</Primary></IndexTerm>
160 Prints a message to stderr as each pass starts. Gives a warm but
161 undoubtedly misleading feeling that GHC is telling you what's
167 <Term><Option>-ddump-<pass></Option>:</Term>
170 <IndexTerm><Primary>-ddump-<pass> options</Primary></IndexTerm>
171 Make a debugging dump after pass <Literal><pass></Literal> (may be common enough to
172 need a short form…). You can get all of these at once (<Emphasis>lots</Emphasis> of
173 output) by using <Option>-ddump-all</Option>, or most of them with <Option>-ddump-most</Option>.
174 Some of the most useful ones are:
181 <Term><Option>-ddump-parsed</Option>:</Term>
190 <Term><Option>-ddump-rn</Option>:</Term>
199 <Term><Option>-ddump-minimal-imports</Option>:</Term>
202 Dump to the file "M.imports" (where M is the module being compiled)
203 a "minimal" set of import declarations. You can safely replace
204 all the import declarations in "M.hs" with those found in "M.imports".
205 Why would you want to do that? Because the "minimal" imports (a) import
206 everything explicitly, by name, and (b) import nothing that is not required.
207 It can be quite painful to maintain this property by hand, so this flag is
208 intended to reduce the labour.
214 <Term><Option>-ddump-hi-diffs</Option>:</Term>
217 Dump to stdout a summary of the differences between the existing interface file (if any)
218 for this module, and the new one.
224 <Term><Option>-ddump-tc</Option>:</Term>
233 <Term><Option>-ddump-types</Option>:</Term>
236 Dump a type signature for each value defined at the top level
237 of the module. The list is sorted alphabetically.
238 Using <Option>-dppr-debug</Option> dumps a type signature for
239 all the imported and system-defined things as well; useful
240 for debugging the compiler.
246 <Term><Option>-ddump-deriv</Option>:</Term>
254 <Term><Option>-ddump-ds</Option>:</Term>
262 <Term><Option>-ddump-spec</Option>:</Term>
265 output of specialisation pass
270 <Term><Option>-ddump-rules</Option>:</Term>
273 dumps all rewrite rules (including those generated by the specialisation pass)
278 <Term><Option>-ddump-simpl</Option>:</Term>
281 simplifer output (Core-to-Core passes)
286 <Term><Option>-ddump-usagesp</Option>:</Term>
289 UsageSP inference pre-inf and output
294 <Term><Option>-ddump-cpranal</Option>:</Term>
302 <Term><Option>-ddump-stranal</Option>:</Term>
305 strictness analyser output
310 <Term><Option>-ddump-workwrap</Option>:</Term>
313 worker/wrapper split output
318 <Term><Option>-ddump-occur-anal</Option>:</Term>
321 `occurrence analysis' output
326 <Term><Option>-ddump-stg</Option>:</Term>
329 output of STG-to-STG passes
334 <Term><Option>-ddump-absC</Option>:</Term>
337 <Emphasis>un</Emphasis>flattened Abstract C
342 <Term><Option>-ddump-flatC</Option>:</Term>
345 <Emphasis>flattened</Emphasis> Abstract C
350 <Term><Option>-ddump-realC</Option>:</Term>
353 same as what goes to the C compiler
358 <Term><Option>-ddump-asm</Option>:</Term>
361 assembly language from the native-code generator
366 <IndexTerm><Primary>-ddump-all option</Primary></IndexTerm>
367 <IndexTerm><Primary>-ddump-most option</Primary></IndexTerm>
368 <IndexTerm><Primary>-ddump-parsed option</Primary></IndexTerm>
369 <IndexTerm><Primary>-ddump-rn option</Primary></IndexTerm>
370 <IndexTerm><Primary>-ddump-tc option</Primary></IndexTerm>
371 <IndexTerm><Primary>-ddump-deriv option</Primary></IndexTerm>
372 <IndexTerm><Primary>-ddump-ds option</Primary></IndexTerm>
373 <IndexTerm><Primary>-ddump-simpl option</Primary></IndexTerm>
374 <IndexTerm><Primary>-ddump-cpranal option</Primary></IndexTerm>
375 <IndexTerm><Primary>-ddump-workwrap option</Primary></IndexTerm>
376 <IndexTerm><Primary>-ddump-rules option</Primary></IndexTerm>
377 <IndexTerm><Primary>-ddump-usagesp option</Primary></IndexTerm>
378 <IndexTerm><Primary>-ddump-stranal option</Primary></IndexTerm>
379 <IndexTerm><Primary>-ddump-occur-anal option</Primary></IndexTerm>
380 <IndexTerm><Primary>-ddump-spec option</Primary></IndexTerm>
381 <IndexTerm><Primary>-ddump-stg option</Primary></IndexTerm>
382 <IndexTerm><Primary>-ddump-absC option</Primary></IndexTerm>
383 <IndexTerm><Primary>-ddump-flatC option</Primary></IndexTerm>
384 <IndexTerm><Primary>-ddump-realC option</Primary></IndexTerm>
385 <IndexTerm><Primary>-ddump-asm option</Primary></IndexTerm>
390 <Term><Option>-dverbose-simpl</Option> and <Option>-dverbose-stg</Option>:</Term>
393 <IndexTerm><Primary>-dverbose-simpl option</Primary></IndexTerm>
394 <IndexTerm><Primary>-dverbose-stg option</Primary></IndexTerm>
395 Show the output of the intermediate Core-to-Core and STG-to-STG
396 passes, respectively. (<Emphasis>Lots</Emphasis> of output!) So: when we're
400 % ghc -noC -O -ddump-simpl -dverbose-simpl -dcore-lint Foo.hs
407 <Term><Option>-ddump-simpl-iterations</Option>:</Term>
410 <IndexTerm><Primary>-ddump-simpl-iterations option</Primary></IndexTerm>
411 Show the output of each <Emphasis>iteration</Emphasis> of the simplifier (each run of
412 the simplifier has a maximum number of iterations, normally 4). Used
413 when even <Option>-dverbose-simpl</Option> doesn't cut it.
418 <Term><Option>-dppr-{user,debug</Option>}:</Term>
421 <IndexTerm><Primary>-dppr-user option</Primary></IndexTerm>
422 <IndexTerm><Primary>-dppr-debug option</Primary></IndexTerm>
423 Debugging output is in one of several “styles.” Take the printing
424 of types, for example. In the “user” style, the compiler's internal
425 ideas about types are presented in Haskell source-level syntax,
426 insofar as possible. In the “debug” style (which is the default for
427 debugging output), the types are printed in with
428 explicit foralls, and variables have their unique-id attached (so you
429 can check for things that look the same but aren't).
434 <Term><Option>-ddump-simpl-stats</Option>:</Term>
437 <IndexTerm><Primary>-ddump-simpl-stats option</Primary></IndexTerm>
438 Dump statistics about how many of each kind
439 of transformation too place. If you add <Option>-dppr-debug</Option> you get more detailed information.
444 <Term><Option>-ddump-raw-asm</Option>:</Term>
447 <IndexTerm><Primary>-ddump-raw-asm option</Primary></IndexTerm>
448 Dump out the assembly-language stuff, before the “mangler” gets it.
453 <Term><Option>-ddump-rn-trace</Option>:</Term>
456 <IndexTerm><Primary>-ddump-rn-trace</Primary></IndexTerm>
457 Make the renamer be *real* chatty about what it is upto.
462 <Term><Option>-dshow-rn-stats</Option>:</Term>
465 <IndexTerm><Primary>-dshow-rn-stats</Primary></IndexTerm>
466 Print out summary of what kind of information the renamer had to bring
472 <Term><Option>-dshow-unused-imports</Option>:</Term>
475 <IndexTerm><Primary>-dshow-unused-imports</Primary></IndexTerm>
476 Have the renamer report what imports does not contribute.
485 <Sect2 id="checking-consistency">
486 <Title>Checking for consistency
490 <IndexTerm><Primary>consistency checks</Primary></IndexTerm>
491 <IndexTerm><Primary>lint</Primary></IndexTerm>
498 <Term><Option>-dcore-lint</Option>:</Term>
501 <IndexTerm><Primary>-dcore-lint option</Primary></IndexTerm>
502 Turn on heavyweight intra-pass sanity-checking within GHC, at Core
503 level. (It checks GHC's sanity, not yours.)
508 <Term><Option>-dstg-lint</Option>:</Term>
511 <IndexTerm><Primary>-dstg-lint option</Primary></IndexTerm>
517 <Term><Option>-dusagesp-lint</Option>:</Term>
520 <IndexTerm><Primary>-dstg-lint option</Primary></IndexTerm>
521 Turn on checks around UsageSP inference (<Option>-fusagesp</Option>). This verifies
522 various simple properties of the results of the inference, and also
523 warns if any identifier with a used-once annotation before the
524 inference has a used-many annotation afterwards; this could indicate a
525 non-worksafe transformation is being applied.
535 <Title>How to read Core syntax (from some <Option>-ddump-*</Option> flags)</Title>
538 <IndexTerm><Primary>reading Core syntax</Primary></IndexTerm>
539 <IndexTerm><Primary>Core syntax, how to read</Primary></IndexTerm>
543 Let's do this by commenting an example. It's from doing
544 <Option>-ddump-ds</Option> on this code:
547 skip2 m = m : skip2 (m+2)
553 Before we jump in, a word about names of things. Within GHC,
554 variables, type constructors, etc., are identified by their
555 “Uniques.” These are of the form `letter' plus `number' (both
556 loosely interpreted). The `letter' gives some idea of where the
557 Unique came from; e.g., <Literal>_</Literal> means “built-in type variable”;
558 <Literal>t</Literal> means “from the typechecker”; <Literal>s</Literal> means “from the
559 simplifier”; and so on. The `number' is printed fairly compactly in
560 a `base-62' format, which everyone hates except me (WDP).
564 Remember, everything has a “Unique” and it is usually printed out
565 when debugging, in some form or another. So here we go…
571 Main.skip2{-r1L6-} :: _forall_ a$_4 =>{{Num a$_4}} -> a$_4 -> [a$_4]
573 --# `r1L6' is the Unique for Main.skip2;
574 --# `_4' is the Unique for the type-variable (template) `a'
575 --# `{{Num a$_4}}' is a dictionary argument
579 --# `_NI_' means "no (pragmatic) information" yet; it will later
580 --# evolve into the GHC_PRAGMA info that goes into interface files.
583 /\ _4 -> \ d.Num.t4Gt ->
586 +.t4Hg :: _4 -> _4 -> _4
588 +.t4Hg = (+{-r3JH-} _4) d.Num.t4Gt
590 fromInt.t4GS :: Int{-2i-} -> _4
592 fromInt.t4GS = (fromInt{-r3JX-} _4) d.Num.t4Gt
594 --# The `+' class method (Unique: r3JH) selects the addition code
595 --# from a `Num' dictionary (now an explicit lamba'd argument).
596 --# Because Core is 2nd-order lambda-calculus, type applications
597 --# and lambdas (/\) are explicit. So `+' is first applied to a
598 --# type (`_4'), then to a dictionary, yielding the actual addition
599 --# function that we will use subsequently...
601 --# We play the exact same game with the (non-standard) class method
602 --# `fromInt'. Unsurprisingly, the type `Int' is wired into the
612 } in fromInt.t4GS ds.d4Qz
614 --# `I# 2#' is just the literal Int `2'; it reflects the fact that
615 --# GHC defines `data Int = I# Int#', where Int# is the primitive
616 --# unboxed type. (see relevant info about unboxed types elsewhere...)
618 --# The `!' after `I#' indicates that this is a *saturated*
619 --# application of the `I#' data constructor (i.e., not partially
622 skip2.t3Ja :: _4 -> [_4]
626 let { ds.d4QQ :: [_4]
632 ds.d4QY = +.t4Hg m.r1H4 lit.t4Hb
633 } in skip2.t3Ja ds.d4QY
643 (“It's just a simple functional language” is an unregisterised
644 trademark of Peyton Jones Enterprises, plc.)
649 <Sect2 id="source-file-options">
650 <Title>Command line options in source files
654 <IndexTerm><Primary>source-file options</Primary></IndexTerm>
658 Sometimes it is useful to make the connection between a source file
659 and the command-line options it requires quite tight. For instance,
660 if a (Glasgow) Haskell source file uses <Literal>casm</Literal>s, the C back-end
661 often needs to be told about which header files to include. Rather than
662 maintaining the list of files the source depends on in a
663 <Filename>Makefile</Filename> (using the <Option>-#include</Option> command-line option), it is
664 possible to do this directly in the source file using the <Literal>OPTIONS</Literal>
665 pragma <IndexTerm><Primary>OPTIONS pragma</Primary></IndexTerm>:
670 {-# OPTIONS -#include "foo.h" #-}
678 <Literal>OPTIONS</Literal> pragmas are only looked for at the top of your source
679 files, upto the first (non-literate,non-empty) line not containing
680 <Literal>OPTIONS</Literal>. Multiple <Literal>OPTIONS</Literal> pragmas are recognised. Note
681 that your command shell does not get to the source file options, they
682 are just included literally in the array of command-line arguments
683 the compiler driver maintains internally, so you'll be desperately
684 disappointed if you try to glob etc. inside <Literal>OPTIONS</Literal>.
688 NOTE: the contents of OPTIONS are prepended to the command-line
689 options, so you <Emphasis>do</Emphasis> have the ability to override OPTIONS settings
690 via the command line.
694 It is not recommended to move all the contents of your Makefiles into
695 your source files, but in some circumstances, the <Literal>OPTIONS</Literal> pragma
696 is the Right Thing. (If you use <Option>-keep-hc-file-too</Option> and have OPTION
697 flags in your module, the OPTIONS will get put into the generated .hc
704 <title>Unregisterised compilation</title>
705 <indexterm><primary>unregisterised compilation</primary></indexterm>
707 <para>The term "unregisterised" really means "compile via vanilla
708 C", disabling some of the platform-specific tricks that GHC
709 normally uses to make programs go faster. When compiling
710 unregisterised, GHC simply generates a C file which is compiled
713 <para>Unregisterised compilation can be useful when porting GHC to
714 a new machine, since it reduces the prerequisite tools to
715 <command>gcc</command>, <command>as</command>, and
716 <command>ld</command> and nothing more, and furthermore the amount
717 of platform-specific code that needs to be written in order to get
718 unregisterised compilation going is usually fairly small.</para>
722 <term><option>-unreg</option>:</term>
723 <indexterm><primary><option>-unreg</option></primary></indexterm>
725 <para>Compile via vanilla ANSI C only, turning off
726 platform-specific optimisations. NOTE: in order to use
727 <option>-unreg</option>, you need to have a set of libraries
728 (including the RTS) built for unregisterised compilation.
729 This amounts to building GHC with way "u" enabled.</para>
738 ;;; Local Variables: ***
740 ;;; sgml-parent-document: ("users_guide.sgml" "book" "chapter" "sect1") ***