debugging.xml 17 KB
Newer Older
1
<?xml version="1.0" encoding="iso-8859-1"?>
2 3 4 5 6 7 8
<sect1 id="options-debugging">
  <title>Debugging the compiler</title>

  <indexterm><primary>debugging options (for GHC)</primary></indexterm>

  <para>HACKER TERRITORY. HACKER TERRITORY.  (You were warned.)</para>

9
  <sect2 id="dumping-output">
10 11 12 13 14 15 16
    <title>Dumping out compiler intermediate structures</title>
    
    <indexterm><primary>dumping GHC intermediates</primary></indexterm>
    <indexterm><primary>intermediate passes, output</primary></indexterm>
    
    <variablelist>
      <varlistentry>
17 18 19 20
	<term>
          <option>-ddump-</option><replaceable>pass</replaceable>
          <indexterm><primary><option>-ddump</option> options</primary></indexterm>
        </term>
21 22 23 24 25
	<listitem>
	  <para>Make a debugging dump after pass
        <literal>&lt;pass&gt;</literal> (may be common enough to need
        a short form&hellip;).  You can get all of these at once
        (<emphasis>lots</emphasis> of output) by using
26 27
        <option>-v5</option>, or most of them with
        <option>-v4</option>.  Some of the most useful ones
28 29 30 31
        are:</para>

	  <variablelist>
	    <varlistentry>
32 33 34 35
	      <term>
	        <option>-ddump-parsed</option>:
                <indexterm><primary><option>-ddump-parsed</option></primary></indexterm>
	      </term>
36 37 38 39 40 41
	      <listitem>
		<para>parser output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
42 43 44 45
	      <term>
	        <option>-ddump-rn</option>:
                <indexterm><primary><option>-ddump-rn</option></primary></indexterm>
	      </term>
46 47 48 49 50 51
	      <listitem>
		<para>renamer output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
52 53 54 55
	      <term>
	        <option>-ddump-tc</option>:
                <indexterm><primary><option>-ddump-tc</option></primary></indexterm>
	      </term>
56 57 58 59 60 61
	      <listitem>
		<para>typechecker output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
62 63 64 65
	      <term>
	        <option>-ddump-types</option>:
                <indexterm><primary><option>-ddump-types</option></primary></indexterm>
	      </term>
66 67 68 69 70 71 72 73 74 75 76
	      <listitem>
		<para>Dump a type signature for each value defined at
              the top level of the module.  The list is sorted
              alphabetically.  Using <option>-dppr-debug</option>
              dumps a type signature for all the imported and
              system-defined things as well; useful for debugging the
              compiler.</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
77 78 79 80
	      <term>
	        <option>-ddump-deriv</option>:
                <indexterm><primary><option>-ddump-deriv</option></primary></indexterm>
	      </term>
81 82 83 84 85 86
	      <listitem>
		<para>derived instances</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
87 88 89 90
	      <term>
	        <option>-ddump-ds</option>:
                <indexterm><primary><option>-ddump-ds</option></primary></indexterm>
	      </term>
91 92 93 94 95 96
	      <listitem>
		<para>desugarer output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
97 98 99 100
	      <term>
	        <option>-ddump-spec</option>:
                <indexterm><primary><option>-ddump-spec</option></primary></indexterm>
	      </term>
101 102 103 104 105 106
	      <listitem>
		<para>output of specialisation pass</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
107 108 109 110
	      <term>
	        <option>-ddump-rules</option>:
                <indexterm><primary><option>-ddump-rules</option></primary></indexterm>
	      </term>
111 112 113 114 115 116 117
	      <listitem>
		<para>dumps all rewrite rules (including those generated
	      by the specialisation pass)</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
118 119 120 121
	      <term>
	        <option>-ddump-simpl</option>:
                <indexterm><primary><option>-ddump-simpl</option></primary></indexterm>
	      </term>
122
	      <listitem>
ross's avatar
ross committed
123
		<para>simplifier output (Core-to-Core passes)</para>
124 125 126 127
	      </listitem>
	    </varlistentry>

	    <varlistentry>
128 129 130 131
	      <term>
	        <option>-ddump-inlinings</option>:
                <indexterm><primary><option>-ddump-inlinings</option></primary></indexterm>
	      </term>
132 133 134 135 136 137
	      <listitem>
		<para>inlining info from the simplifier</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
138 139 140 141
	      <term>
	        <option>-ddump-cpranal</option>:
                <indexterm><primary><option>-ddump-cpranal</option></primary></indexterm>
	      </term>
142 143 144 145 146 147
	      <listitem>
		<para>CPR analyser output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
148 149 150 151
	      <term>
	        <option>-ddump-stranal</option>:
                <indexterm><primary><option>-ddump-stranal</option></primary></indexterm>
	      </term>
152 153 154 155 156 157
	      <listitem>
		<para>strictness analyser output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
158 159 160 161
	      <term>
	        <option>-ddump-cse</option>:
                <indexterm><primary><option>-ddump-cse</option></primary></indexterm>
	      </term>
162 163 164 165 166 167
	      <listitem>
		<para>CSE pass output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
168 169 170 171
	      <term>
	        <option>-ddump-workwrap</option>:
                <indexterm><primary><option>-ddump-workwrap</option></primary></indexterm>
	      </term>
172 173 174 175 176 177
	      <listitem>
		<para>worker/wrapper split output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
178 179 180 181
	      <term>
	        <option>-ddump-occur-anal</option>:
                <indexterm><primary><option>-ddump-occur-anal</option></primary></indexterm>
	      </term>
182 183 184 185 186 187
	      <listitem>
		<para>`occurrence analysis' output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
188 189 190 191
	      <term>
	        <option>-ddump-stg</option>:
                <indexterm><primary><option>-ddump-stg</option></primary></indexterm>
	      </term>
192 193 194 195 196 197
	      <listitem>
		<para>output of STG-to-STG passes</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
198 199 200 201
	      <term>
	        <option>-ddump-flatC</option>:
                <indexterm><primary><option>-ddump-flatC</option></primary></indexterm>
	      </term>
202 203 204 205 206 207
	      <listitem>
		<para><emphasis>flattened</emphasis> Abstract&nbsp;C</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
208 209 210 211
	      <term>
	        <option>-ddump-asm</option>:
                <indexterm><primary><option>-ddump-asm</option></primary></indexterm>
	      </term>
212 213 214 215 216 217
	      <listitem>
		<para>assembly language from the native-code generator</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
218 219 220 221
	      <term>
	        <option>-ddump-bcos</option>:
                <indexterm><primary><option>-ddump-bcos</option></primary></indexterm>
	      </term>
222 223 224 225 226 227
	      <listitem>
		<para>byte code compiler output</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
228 229 230 231
	      <term>
	        <option>-ddump-foreign</option>:
                <indexterm><primary><option>-ddump-foreign</option></primary></indexterm>
	      </term>
232 233 234 235 236 237 238 239
	      <listitem>
		<para>dump foreign export stubs</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</listitem>
      </varlistentry>
      
240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287
      <varlistentry>
	<term>
          <option>-ddump-simpl-iterations</option>:
          <indexterm><primary><option>-ddump-simpl-iterations</option></primary></indexterm>
        </term>
	<listitem>
	  <para>Show the output of each <emphasis>iteration</emphasis>
        of the simplifier (each run of the simplifier has a maximum
        number of iterations, normally 4).  Used when even
        <option>-dverbose-simpl</option> doesn't cut it.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>
          <option>-ddump-simpl-stats</option>
          <indexterm><primary><option>-ddump-simpl-stats option</option></primary></indexterm>
        </term>
	<listitem>
	  <para>Dump statistics about how many of each kind of
        transformation too place.  If you add
        <option>-dppr-debug</option> you get more detailed
        information.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>
          <option>-ddump-rn-trace</option>
          <indexterm><primary><option>-ddump-rn-trace</option></primary></indexterm>
        </term>
	<listitem>
	  <para>Make the renamer be *real* chatty about what it is
	upto.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>
          <option>-ddump-rn-stats</option>
          <indexterm><primary><option>-dshow-rn-stats</option></primary></indexterm>
        </term>
	<listitem>
	  <para>Print out summary of what kind of information the renamer
        had to bring in.</para>
	</listitem>
      </varlistentry>

288
      <varlistentry>
289 290 291 292 293 294 295 296
	<term>
          <option>-dverbose-core2core</option>
          <indexterm><primary><option>-dverbose-core2core</option></primary></indexterm>
        </term>
	<term>
          <option>-dverbose-stg2stg</option>
          <indexterm><primary><option>-dverbose-stg2stg</option></primary></indexterm>
        </term>
297 298 299 300 301
	<listitem>
	  <para>Show the output of the intermediate Core-to-Core and
        STG-to-STG passes, respectively.  (<emphasis>Lots</emphasis>
        of output!) So: when we're really desperate:</para>

302
	  <screen>
rrt's avatar
rrt committed
303
% ghc -noC -O -ddump-simpl -dverbose-simpl -dcore-lint Foo.hs
304
</screen>
rrt's avatar
rrt committed
305

306 307 308
	</listitem>
      </varlistentry>
      
Ian Lynagh's avatar
Ian Lynagh committed
309 310 311 312 313 314 315 316 317 318 319
      <varlistentry>
	<term>
          <option>-dfaststring-stats</option>
          <indexterm><primary><option>-dfaststring-stats</option></primary></indexterm>
        </term>
	<listitem>
	  <para>Show statistics for the usage of fast strings by the
          compiler</para>
	</listitem>
      </varlistentry>

320
      <varlistentry>
321 322 323 324
	<term>
          <option>-dppr-debug</option>
          <indexterm><primary><option>-dppr-debug</option></primary></indexterm>
        </term>
325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340
	<listitem>
	  <para>Debugging output is in one of several
          &ldquo;styles.&rdquo; Take the printing of types, for
          example.  In the &ldquo;user&rdquo; style (the default), the
          compiler's internal ideas about types are presented in
          Haskell source-level syntax, insofar as possible.  In the
          &ldquo;debug&rdquo; 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.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
341 342 343 344
	<term>
          <option>-dppr-user-length</option>
          <indexterm><primary><option>-dppr-user-length</option></primary></indexterm>
        </term>
345 346 347 348 349 350 351 352 353
	<listitem>
	  <para>In error messages, expressions are printed to a
	  certain &ldquo;depth&rdquo;, with subexpressions beyond the
	  depth replaced by ellipses.  This flag sets the
	  depth.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
354 355 356 357
	<term>
          <option>-dshow-unused-imports</option>
          <indexterm><primary><option>-dshow-unused-imports</option></primary></indexterm>
        </term>
358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374
	<listitem>
	  <para>Have the renamer report what imports does not
	contribute.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </sect2>

  <sect2 id="checking-consistency">
    <title>Checking for consistency</title>

    <indexterm><primary>consistency checks</primary></indexterm>
    <indexterm><primary>lint</primary></indexterm>

    <variablelist>

      <varlistentry>
375 376 377 378
	<term>
          <option>-dcore-lint</option>
          <indexterm><primary><option>-dcore-lint</option></primary></indexterm>
        </term>
379 380 381 382 383 384 385
	<listitem>
	  <para>Turn on heavyweight intra-pass sanity-checking within
          GHC, at Core level.  (It checks GHC's sanity, not yours.)</para>
	</listitem>
      </varlistentry>

      <varlistentry>
386 387 388 389
	<term>
          <option>-dstg-lint</option>:
          <indexterm><primary><option>-dstg-lint</option></primary></indexterm>
        </term>
390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406
	<listitem>
	  <para>Ditto for STG level. (NOTE: currently doesn't work).</para>
	</listitem>
      </varlistentry>

    </variablelist>
  </sect2>

  <sect2>
    <title>How to read Core syntax (from some <option>-ddump</option>
    flags)</title>

    <indexterm><primary>reading Core syntax</primary></indexterm>
    <indexterm><primary>Core syntax, how to read</primary></indexterm>

    <para>Let's do this by commenting an example.  It's from doing
    <option>-ddump-ds</option> on this code:
rrt's avatar
rrt committed
407

408
<programlisting>
rrt's avatar
rrt committed
409
skip2 m = m : skip2 (m+2)
410
</programlisting>
rrt's avatar
rrt committed
411

412 413 414 415 416 417 418 419 420 421 422 423 424 425 426
    Before we jump in, a word about names of things.  Within GHC,
    variables, type constructors, etc., are identified by their
    &ldquo;Uniques.&rdquo; These are of the form `letter' plus
    `number' (both loosely interpreted).  The `letter' gives some idea
    of where the Unique came from; e.g., <literal>&lowbar;</literal>
    means &ldquo;built-in type variable&rdquo;; <literal>t</literal>
    means &ldquo;from the typechecker&rdquo;; <literal>s</literal>
    means &ldquo;from the simplifier&rdquo;; and so on.  The `number'
    is printed fairly compactly in a `base-62' format, which everyone
    hates except me (WDP).</para>

    <para>Remember, everything has a &ldquo;Unique&rdquo; and it is
    usually printed out when debugging, in some form or another.  So
    here we go&hellip;</para>

427
<programlisting>
rrt's avatar
rrt committed
428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452
Desugared:
Main.skip2{-r1L6-} :: _forall_ a$_4 =&#62;{{Num a$_4}} -&#62; a$_4 -&#62; [a$_4]

--# `r1L6' is the Unique for Main.skip2;
--# `_4' is the Unique for the type-variable (template) `a'
--# `{{Num a$_4}}' is a dictionary argument

_NI_

--# `_NI_' means "no (pragmatic) information" yet; it will later
--# evolve into the GHC_PRAGMA info that goes into interface files.

Main.skip2{-r1L6-} =
    /\ _4 -&#62; \ d.Num.t4Gt -&#62;
        let {
          {- CoRec -}
          +.t4Hg :: _4 -&#62; _4 -&#62; _4
          _NI_
          +.t4Hg = (+{-r3JH-} _4) d.Num.t4Gt

          fromInt.t4GS :: Int{-2i-} -&#62; _4
          _NI_
          fromInt.t4GS = (fromInt{-r3JX-} _4) d.Num.t4Gt

--# The `+' class method (Unique: r3JH) selects the addition code
ross's avatar
ross committed
453
--# from a `Num' dictionary (now an explicit lambda'd argument).
rrt's avatar
rrt committed
454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496
--# Because Core is 2nd-order lambda-calculus, type applications
--# and lambdas (/\) are explicit.  So `+' is first applied to a
--# type (`_4'), then to a dictionary, yielding the actual addition
--# function that we will use subsequently...

--# We play the exact same game with the (non-standard) class method
--# `fromInt'.  Unsurprisingly, the type `Int' is wired into the
--# compiler.

          lit.t4Hb :: _4
          _NI_
          lit.t4Hb =
              let {
                ds.d4Qz :: Int{-2i-}
                _NI_
                ds.d4Qz = I#! 2#
              } in  fromInt.t4GS ds.d4Qz

--# `I# 2#' is just the literal Int `2'; it reflects the fact that
--# GHC defines `data Int = I# Int#', where Int# is the primitive
--# unboxed type.  (see relevant info about unboxed types elsewhere...)

--# The `!' after `I#' indicates that this is a *saturated*
--# application of the `I#' data constructor (i.e., not partially
--# applied).

          skip2.t3Ja :: _4 -&#62; [_4]
          _NI_
          skip2.t3Ja =
              \ m.r1H4 -&#62;
                  let { ds.d4QQ :: [_4]
                        _NI_
                        ds.d4QQ =
                    let {
                      ds.d4QY :: _4
                      _NI_
                      ds.d4QY = +.t4Hg m.r1H4 lit.t4Hb
                    } in  skip2.t3Ja ds.d4QY
                  } in
                  :! _4 m.r1H4 ds.d4QQ

          {- end CoRec -}
        } in  skip2.t3Ja
497
</programlisting>
rrt's avatar
rrt committed
498

499 500 501 502
    <para>(&ldquo;It's just a simple functional language&rdquo; is an
    unregisterised trademark of Peyton Jones Enterprises, plc.)</para>

  </sect2>
rrt's avatar
rrt committed
503

504 505 506 507 508 509 510 511 512 513 514 515
  <sect2 id="unreg">
    <title>Unregisterised compilation</title>
    <indexterm><primary>unregisterised compilation</primary></indexterm>

    <para>The term "unregisterised" really means "compile via vanilla
    C", disabling some of the platform-specific tricks that GHC
    normally uses to make programs go faster.  When compiling
    unregisterised, GHC simply generates a C file which is compiled
    via gcc.</para>

    <para>Unregisterised compilation can be useful when porting GHC to
    a new machine, since it reduces the prerequisite tools to
516 517
    <command>gcc</command>, <command>as</command>, and
    <command>ld</command> and nothing more, and furthermore the amount
518 519 520 521 522
    of platform-specific code that needs to be written in order to get
    unregisterised compilation going is usually fairly small.</para>

    <variablelist>
      <varlistentry>
523 524 525 526
	<term>
          <option>-unreg</option>:
          <indexterm><primary><option>-unreg</option></primary></indexterm>
        </term>
527 528 529 530 531 532 533 534 535 536 537
	<listitem>
	  <para>Compile via vanilla ANSI C only, turning off
	  platform-specific optimisations.  NOTE: in order to use
	  <option>-unreg</option>, you need to have a set of libraries
	  (including the RTS) built for unregisterised compilation.
	  This amounts to building GHC with way "u" enabled.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </sect2>

538
</sect1>
539 540 541

<!-- Emacs stuff:
     ;;; Local Variables: ***
542 543
     ;;; mode: xml ***
     ;;; sgml-parent-document: ("users_guide.xml" "book" "chapter" "sect1") ***
544 545
     ;;; End: ***
 -->