[sbcl.git] / BUGS

REPORTING BUGS

Bugs can be reported on the help mailing list
  sbcl-help@lists.sourceforge.net
or on the development mailing list
  sbcl-devel@lists.sourceforge.net

Please include enough information in a bug report that someone reading
it can reproduce the problem, i.e. don't write
     Subject: apparent bug in PRINT-OBJECT (or *PRINT-LENGTH*?)
     PRINT-OBJECT doesn't seem to work with *PRINT-LENGTH*. Is this a bug?
but instead
     Subject: apparent bug in PRINT-OBJECT (or *PRINT-LENGTH*?)
     In sbcl-1.2.3 running under OpenBSD 4.5 on my Alpha box, when
     I compile and load the file
       (DEFSTRUCT (FOO (:PRINT-OBJECT (LAMBDA (X Y)
                                        (LET ((*PRINT-LENGTH* 4))
                                          (PRINT X Y)))))
         X Y)
     then at the command line type
       (MAKE-FOO)
     the program loops endlessly instead of printing the object.


NOTES:

There is also some information on bugs in the manual page and
in the TODO file. Eventually more such information may move here.

The gaps in the number sequence belong to old bug descriptions which
have gone away (typically because they were fixed, but sometimes for
other reasons, e.g. because they were moved elsewhere).


KNOWN BUGS OF NO SPECIAL CLASS:

2:
  DEFSTRUCT almost certainly should overwrite the old LAYOUT information
  instead of just punting when a contradictory structure definition
  is loaded. As it is, if you redefine DEFSTRUCTs in a way which 
  changes their layout, you probably have to rebuild your entire
  program, even if you know or guess enough about the internals of
  SBCL to wager that this (undefined in ANSI) operation would be safe.

3: "type checking of structure slots"
  a:
  ANSI specifies that a type mismatch in a structure slot
  initialization value should not cause a warning.
WORKAROUND:
  This one might not be fixed for a while because while we're big
  believers in ANSI compatibility and all, (1) there's no obvious
  simple way to do it (short of disabling all warnings for type
  mismatches everywhere), and (2) there's a good portable
  workaround, and (3) by their own reasoning, it looks as though
  ANSI may have gotten it wrong. ANSI justifies this specification
  by saying 
    The restriction against issuing a warning for type mismatches
    between a slot-initform and the corresponding slot's :TYPE
    option is necessary because a slot-initform must be specified
    in order to specify slot options; in some cases, no suitable
    default may exist.
  However, in SBCL (as in CMU CL or, for that matter, any compiler
  which really understands Common Lisp types) a suitable default
  does exist, in all cases, because the compiler understands the
  concept of functions which never return (i.e. has return type NIL).
  Thus, as a portable workaround, you can use a call to some
  known-never-to-return function as the default. E.g.
    (DEFSTRUCT FOO
      (BAR (ERROR "missing :BAR argument")
           :TYPE SOME-TYPE-TOO-HAIRY-TO-CONSTRUCT-AN-INSTANCE-OF))
  or 
    (DECLAIM (FTYPE (FUNCTION () NIL) MISSING-ARG))
    (DEFUN REQUIRED-ARG () ; workaround for SBCL non-ANSI slot init typing
      (ERROR "missing required argument")) 
    (DEFSTRUCT FOO
      (BAR (REQUIRED-ARG) :TYPE TRICKY-TYPE-OF-SOME-SORT)
      (BLETCH (REQUIRED-ARG) :TYPE TRICKY-TYPE-OF-SOME-SORT)
      (N-REFS-SO-FAR 0 :TYPE (INTEGER 0)))
  Such code should compile without complaint and work correctly either
  on SBCL or on any other completely compliant Common Lisp system.

  b: &AUX argument in a boa-constructor without a default value means
     "do not initilize this slot" and does not cause type error. But
     an error may be signalled at read time and it would be good if
     SBCL did it.

  d: (fixed in 0.8.1.5)

7:
  The "compiling top-level form:" output ought to be condensed.
  Perhaps any number of such consecutive lines ought to turn into a
  single "compiling top-level forms:" line.

11:
  It would be nice if the
        caught ERROR:
          (during macroexpansion)
  said what macroexpansion was at fault, e.g.
        caught ERROR:
          (during macroexpansion of IN-PACKAGE,
          during macroexpansion of DEFFOO)

19:
  (I *think* this is a bug. It certainly seems like strange behavior. But
  the ANSI spec is scary, dark, and deep.. -- WHN)
    (FORMAT NIL  "~,1G" 1.4) => "1.    "
    (FORMAT NIL "~3,1G" 1.4) => "1.    "

27:
  Sometimes (SB-EXT:QUIT) fails with 
        Argh! maximum interrupt nesting depth (4096) exceeded, exiting
        Process inferior-lisp exited abnormally with code 1
  I haven't noticed a repeatable case of this yet.

32:
  The printer doesn't report closures very well. This is true in 
  CMU CL 18b as well:
    (PRINT #'CLASS-NAME)
  gives
    #<Closure Over Function "DEFUN STRUCTURE-SLOT-ACCESSOR" {134D1A1}>
  It would be nice to make closures have a settable name slot,
  and make things like DEFSTRUCT and FLET, which create closures,
  set helpful values into this slot.

33:
  And as long as we're wishing, it would be awfully nice if INSPECT could
  also report on closures, telling about the values of the bound variables.

35:
  The compiler assumes that any time a function of declared FTYPE
  doesn't signal an error, its arguments were of the declared type.
  E.g. compiling and loading
    (DECLAIM (OPTIMIZE (SAFETY 3)))
    (DEFUN FACTORIAL (X) (GAMMA (1+ X)))
    (DEFUN GAMMA (X) X)
    (DECLAIM (FTYPE (FUNCTION (UNSIGNED-BYTE)) FACTORIAL))
    (DEFUN FOO (X)
      (COND ((> (FACTORIAL X) 1.0E6)
             (FORMAT T "too big~%"))
            ((INTEGERP X)
             (FORMAT T "exactly ~S~%" (FACTORIAL X)))
            (T
             (FORMAT T "approximately ~S~%" (FACTORIAL X)))))
  then executing
    (FOO 1.5)
  will cause the INTEGERP case to be selected, giving bogus output a la
    exactly 2.5
  This violates the "declarations are assertions" principle.
  According to the ANSI spec, in the section "System Class FUNCTION",
  this is a case of "lying to the compiler", but the lying is done
  by the code which calls FACTORIAL with non-UNSIGNED-BYTE arguments,
  not by the unexpectedly general definition of FACTORIAL. In any case,
  "declarations are assertions" means that lying to the compiler should
  cause an error to be signalled, and should not cause a bogus
  result to be returned. Thus, the compiler should not assume
  that arbitrary functions check their argument types. (It might
  make sense to add another flag (CHECKED?) to DEFKNOWN to 
  identify functions which *do* check their argument types.)
  (Also, verify that the compiler handles declared function
  return types as assertions.)

42:
  The definitions of SIGCONTEXT-FLOAT-REGISTER and
  %SET-SIGCONTEXT-FLOAT-REGISTER in x86-vm.lisp say they're not
  supported on FreeBSD because the floating point state is not saved,
  but at least as of FreeBSD 4.0, the floating point state *is* saved,
  so they could be supported after all. Very likely 
  SIGCONTEXT-FLOATING-POINT-MODES could now be supported, too.

45:
  a slew of floating-point-related errors reported by Peter Van Eynde
  on July 25, 2000:
        b: SBCL's value for LEAST-POSITIVE-SHORT-FLOAT on the x86 is 
           bogus, and should probably be 1.4012985e-45. In SBCL,
           (/ LEAST-POSITIVE-SHORT-FLOAT 2) returns a number smaller
           than LEAST-POSITIVE-SHORT-FLOAT. Similar problems 
           exist for LEAST-NEGATIVE-SHORT-FLOAT, LEAST-POSITIVE-LONG-FLOAT,
           and LEAST-NEGATIVE-LONG-FLOAT.
        c: Many expressions generate floating infinity on x86/Linux:
                (/ 1 0.0)
                (/ 1 0.0d0)
                (EXPT 10.0 1000)
                (EXPT 10.0d0 1000)
           PVE's regression tests want them to raise errors. sbcl-0.7.0.5
           on x86/Linux generates the infinities instead. That might or
           might not be conforming behavior, but it's also inconsistent,
           which is almost certainly wrong. (Inconsistency: (/ 1 0.0)
           should give the same result as (/ 1.0 0.0), but instead (/ 1 0.0)
           generates SINGLE-FLOAT-POSITIVE-INFINITY and (/ 1.0 0.0)
           signals an error.
        d: (in section12.erg) various forms a la 
                (FLOAT 1 DOUBLE-FLOAT-EPSILON)
           don't give the right behavior.

46:
  type safety errors reported by Peter Van Eynde July 25, 2000:
        k: READ-BYTE is supposed to signal TYPE-ERROR when its argument is 
           not a binary input stream, but instead cheerfully reads from
           character streams, e.g. (MAKE-STRING-INPUT-STREAM "abc").

60:
  The debugger LIST-LOCATIONS command doesn't work properly.
  (How should it work properly?)

61:
  Compiling and loading
    (DEFUN FAIL (X) (THROW 'FAIL-TAG X))
    (FAIL 12)
  then requesting a BACKTRACE at the debugger prompt gives no information
  about where in the user program the problem occurred.

64:
  Using the pretty-printer from the command prompt gives funny
  results, apparently because the pretty-printer doesn't know
  about user's command input, including the user's carriage return
  that the user, and therefore the pretty-printer thinks that
  the new output block should start indented 2 or more characters
  rightward of the correct location.

67:
  As reported by Winton Davies on a CMU CL mailing list 2000-01-10,
  and reported for SBCL by Martin Atzmueller 2000-10-20: (TRACE GETHASH)
  crashes SBCL. In general tracing anything which is used in the 
  implementation of TRACE is likely to have the same problem.

75:
  As reported by Martin Atzmueller on sbcl-devel 26 Dec 2000,
  ANSI says that WITH-OUTPUT-TO-STRING should have a keyword
  :ELEMENT-TYPE, but in sbcl-0.6.9 this is not defined for
  WITH-OUTPUT-TO-STRING.

78:
  ANSI says in one place that type declarations can be abbreviated even
  when the type name is not a symbol, e.g.
    (DECLAIM ((VECTOR T) *FOOVECTOR*))
  SBCL doesn't support this. But ANSI says in another place that this
  isn't allowed. So it's not clear this is a bug after all. (See the
  e-mail on cmucl-help@cons.org on 2001-01-16 and 2001-01-17 from WHN
  and Pierre Mai.)

79:
  as pointed out by Dan Barlow on sbcl-devel 2000-07-02:
  The PICK-TEMPORARY-FILE-NAME utility used by LOAD-FOREIGN uses
  an easily guessable temporary filename in a way which might open
  applications using LOAD-FOREIGN to hijacking by malicious users
  on the same machine. Incantations for doing this safely are
  floating around the net in various "how to write secure programs
  despite Unix" documents, and it would be good to (1) fix this in 
  LOAD-FOREIGN, and (2) hunt for any other code which uses temporary
  files and make it share the same new safe logic.

  (partially alleviated in sbcl-0.7.9.32 by a fix by Matthew Danish to
   make the temporary filename less easily guessable)

83:
  RANDOM-INTEGER-EXTRA-BITS=10 may not be large enough for the RANDOM
  RNG to be high quality near RANDOM-FIXNUM-MAX; it looks as though
  the mean of the distribution can be systematically O(0.1%) wrong.
  Just increasing R-I-E-B is probably not a good solution, since
  it would decrease efficiency more than is probably necessary. Perhaps
  using some sort of accept/reject method would be better.

85:
  Internally the compiler sometimes evaluates
    (sb-kernel:type/= (specifier-type '*) (specifier-type t))
  (I stumbled across this when I added an
    (assert (not (eq type1 *wild-type*)))
  in the NAMED :SIMPLE-= type method.) '* isn't really a type, and
  in a type context should probably be translated to T, and so it's
  probably wrong to ask whether it's equal to the T type and then (using
  the EQ type comparison in the NAMED :SIMPLE-= type method) return NIL.
  (I haven't tried to investigate this bug enough to guess whether
  there might be any user-level symptoms.)

  In fact, the type system is likely to depend on this inequality not
  holding... * is not equivalent to T in many cases, such as 
    (VECTOR *) /= (VECTOR T).

94a: 
  Inconsistencies between derived and declared VALUES return types for
  DEFUN aren't checked very well. E.g. the logic which successfully
  catches problems like
    (declaim (ftype (function (fixnum) float) foo))
    (defun foo (x)
      (declare (type integer x))
      (values x)) ; wrong return type, detected, gives warning, good!
  fails to catch
    (declaim (ftype (function (t) (values t t)) bar))
    (defun bar (x)
      (values x)) ; wrong number of return values, no warning, bad!
  The cause of this is seems to be that (1) the internal function 
  VALUES-TYPES-EQUAL-OR-INTERSECT used to make the check handles its
  arguments symmetrically, and (2) when the type checking code was
  written back when when SBCL's code was still CMU CL, the intent
  was that this case
    (declaim (ftype (function (t) t) bar))
    (defun bar (x)
      (values x x)) ; wrong number of return values; should give warning?
  not be warned for, because a two-valued return value is considered
  to be compatible with callers who expects a single value to be
  returned. That intent is probably not appropriate for modern ANSI
  Common Lisp, but fixing this might be complicated because of other
  divergences between auld-style and new-style handling of
  multiple-VALUES types. (Some issues related to this were discussed
  on cmucl-imp at some length sometime in 2000.)

95:
  The facility for dumping a running Lisp image to disk gets confused
  when run without the PURIFY option, and creates an unnecessarily large
  core file (apparently representing memory usage up to the previous
  high-water mark). Moreover, when the file is loaded, it confuses the
  GC, so that thereafter memory usage can never be reduced below that
  level.

98:
  In sbcl-0.6.11.41 (and in all earlier SBCL, and in CMU
  CL), out-of-line structure slot setters are horribly inefficient
  whenever the type of the slot is declared, because out-of-line
  structure slot setters are implemented as closures to save space,
  so the compiler doesn't compile the type test into code, but
  instead just saves the type in a lexical closure and interprets it
  at runtime.
    To exercise the problem, compile and load
      (cl:in-package :cl-user)
      (defstruct foo
        (bar (error "missing") :type bar))
      (defvar *foo*)
      (defun wastrel1 (x)
        (loop (setf (foo-bar *foo*) x)))
      (defstruct bar)
      (defvar *bar* (make-bar))
      (defvar *foo* (make-foo :bar *bar*))
      (defvar *setf-foo-bar* #'(setf foo-bar))
      (defun wastrel2 (x)
        (loop (funcall *setf-foo-bar* x *foo*)))
  then run (WASTREL1 *BAR*) or (WASTREL2 *BAR*), hit Ctrl-C, and
  use BACKTRACE, to see it's spending all essentially all its time
  in %TYPEP and VALUES-SPECIFIER-TYPE and so forth.
    One possible solution would be simply to give up on 
  representing structure slot accessors as functions, and represent
  them as macroexpansions instead. This can be inconvenient for users,
  but it's not clear that it's worse than trying to help by expanding
  into a horribly inefficient implementation.
    As a workaround for the problem, #'(SETF FOO) expressions
  can be replaced with (EFFICIENT-SETF-FUNCTION FOO), where
(defmacro efficient-setf-function (place-function-name)
  (or #+sbcl (and (sb-int:info :function :accessor-for place-function-name)
                  ;; a workaround for the problem, encouraging the
                  ;; inline expansion of the structure accessor, so
                  ;; that the compiler can optimize its type test
                  (let ((new-value (gensym "NEW-VALUE-"))
                        (structure-value (gensym "STRUCTURE-VALUE-")))
                    `(lambda (,new-value ,structure-value)
                       (setf (,place-function-name ,structure-value)
                             ,new-value))))
      ;; no problem, can just use the ordinary expansion
      `(function (setf ,place-function-name))))

100:
  There's apparently a bug in CEILING optimization which caused 
  Douglas Crosher to patch the CMU CL version. Martin Atzmueller
  applied the patches to SBCL and they didn't seem to cause problems
  (as reported sbcl-devel 2001-05-04). However, since the patches
  modify nontrivial code which was apparently written incorrectly
  the first time around, until regression tests are written I'm not 
  comfortable merging the patches in the CVS version of SBCL.

108:
  (TIME (ROOM T)) reports more than 200 Mbytes consed even for
  a clean, just-started SBCL system. And it seems to be right:
  (ROOM T) can bring a small computer to its knees for a *long*
  time trying to GC afterwards. Surely there's some more economical
  way to implement (ROOM T).

117:
  When the compiler inline expands functions, it may be that different
  kinds of return values are generated from different code branches.
  E.g. an inline expansion of POSITION generates integer results 
  from one branch, and NIL results from another. When that inline
  expansion is used in a context where only one of those results
  is acceptable, e.g.
    (defun foo (x)
      (aref *a1* (position x *a2*)))
  and the compiler can't prove that the unacceptable branch is 
  never taken, then bogus type mismatch warnings can be generated.
  If you need to suppress the type mismatch warnings, you can
  suppress the inline expansion,
    (defun foo (x)
      #+sbcl (declare (notinline position)) ; to suppress bug 117 bogowarnings
      (aref *a1* (position x *a2*)))
  or, sometimes, suppress them by declaring the result to be of an
  appropriate type,
    (defun foo (x)
      (aref *a1* (the integer (position x *a2*))))

  This is not a new compiler problem in 0.7.0, but the new compiler
  transforms for FIND, POSITION, FIND-IF, and POSITION-IF make it 
  more conspicuous. If you don't need performance from these functions,
  and the bogus warnings are a nuisance for you, you can return to
  your pre-0.7.0 state of grace with
    #+sbcl (declaim (notinline find position find-if position-if)) ; bug 117..

118:
   as reported by Eric Marsden on cmucl-imp@cons.org 2001-08-14:
     (= (FLOAT 1 DOUBLE-FLOAT-EPSILON)
        (+ (FLOAT 1 DOUBLE-FLOAT-EPSILON) DOUBLE-FLOAT-EPSILON)) => T
   when of course it should be NIL. (He says it only fails for X86,
   not SPARC; dunno about Alpha.)

   Also, "the same problem exists for LONG-FLOAT-EPSILON,
   DOUBLE-FLOAT-NEGATIVE-EPSILON, LONG-FLOAT-NEGATIVE-EPSILON (though
   for the -negative- the + is replaced by a - in the test)."

   Raymond Toy comments that this is tricky on the X86 since its FPU
   uses 80-bit precision internally.

120b:
   Even in sbcl-0.pre7.x, which is supposed to be free of the old
   non-ANSI behavior of treating the function return type inferred
   from the current function definition as a declaration of the
   return type from any function of that name, the return type of NIL
   is attached to FOO in 120a above, and used to optimize code which
   calls FOO. 

124:
   As of version 0.pre7.14, SBCL's implementation of MACROLET makes
   the entire lexical environment at the point of MACROLET available
   in the bodies of the macroexpander functions. In particular, it
   allows the function bodies (which run at compile time) to try to
   access lexical variables (which are only defined at runtime).
   It doesn't even issue a warning, which is bad.

   The SBCL behavior arguably conforms to the ANSI spec (since the
   spec says that the behavior is undefined, ergo anything conforms).
   However, it would be better to issue a compile-time error.
   Unfortunately I (WHN) don't see any simple way to detect this
   condition in order to issue such an error, so for the meantime
   SBCL just does this weird broken "conforming" thing.

   The ANSI standard says, in the definition of the special operator
   MACROLET,
       The macro-expansion functions defined by MACROLET are defined
       in the lexical environment in which the MACROLET form appears.
       Declarations and MACROLET and SYMBOL-MACROLET definitions affect
       the local macro definitions in a MACROLET, but the consequences
       are undefined if the local macro definitions reference any
       local variable or function bindings that are visible in that
       lexical environment.
   Then it seems to contradict itself by giving the example
        (defun foo (x flag)
           (macrolet ((fudge (z)
                         ;The parameters x and flag are not accessible
                         ; at this point; a reference to flag would be to
                         ; the global variable of that name.
                         ` (if flag (* ,z ,z) ,z)))
            ;The parameters x and flag are accessible here.
             (+ x
                (fudge x)
                (fudge (+ x 1)))))
   The comment "a reference to flag would be to the global variable
   of the same name" sounds like good behavior for the system to have.
   but actual specification quoted above says that the actual behavior
   is undefined.

   (Since 0.7.8.23 macroexpanders are defined in a restricted version
   of the lexical environment, containing no lexical variables and
   functions, which seems to conform to ANSI and CLtL2, but signalling
   a STYLE-WARNING for references to variables similar to locals might
   be a good thing.)

125:
   (as reported by Gabe Garza on cmucl-help 2001-09-21)
        (defvar *tmp* 3)
        (defun test-pred (x y)
          (eq x y))
        (defun test-case ()
          (let* ((x *tmp*)
                 (func (lambda () x)))
            (print (eq func func))
            (print (test-pred func func))
            (delete func (list func))))
   Now calling (TEST-CASE) gives output
     NIL
     NIL
     (#<FUNCTION {500A9EF9}>)
   Evidently Python thinks of the lambda as a code transformation so
   much that it forgets that it's also an object.

135:
  Ideally, uninterning a symbol would allow it, and its associated
  FDEFINITION and PROCLAIM data, to be reclaimed by the GC. However,
  at least as of sbcl-0.7.0, this isn't the case. Information about
  FDEFINITIONs and PROCLAIMed properties is stored in globaldb.lisp
  essentially in ordinary (non-weak) hash tables keyed by symbols.
  Thus, once a system has an entry in this system, it tends to live
  forever, even when it is uninterned and all other references to it
  are lost.

141: "pretty printing and backquote"
  a.
    * '``(FOO ,@',@S)
    ``(FOO SB-IMPL::BACKQ-COMMA-AT S)

  b.
    * (write '`(, .ala.) :readably t :pretty t)
    `(,.ALA.)

  (note the space between the comma and the point)

143:
  (reported by Jesse Bouwman 2001-10-24 through the unfortunately
  prominent SourceForge web/db bug tracking system, which is 
  unfortunately not a reliable way to get a timely response from
  the SBCL maintainers)
      In the course of trying to build a test case for an 
    application error, I encountered this behavior: 
      If you start up sbcl, and then lay on CTRL-C for a 
    minute or two, the lisp process will eventually say: 
         %PRIMITIVE HALT called; the party is over. 
    and throw you into the monitor. If I start up lisp, 
    attach to the process with strace, and then do the same 
    (abusive) thing, I get instead: 
         access failure in heap page not marked as write-protected 
    and the monitor again. I don't know enough to have the 
    faintest idea of what is going on here. 
      This is with sbcl 6.12, uname -a reports: 
         Linux prep 2.2.19 #4 SMP Tue Apr 24 13:59:52 CDT 2001 i686 unknown 
  I (WHN) have verified that the same thing occurs on sbcl-0.pre7.141
  under OpenBSD 2.9 on my X86 laptop. Do be patient when you try it:
  it took more than two minutes (but less than five) for me.

145:
  ANSI allows types `(COMPLEX ,FOO) to use very hairy values for
  FOO, e.g. (COMPLEX (AND REAL (SATISFIES ODDP))). The old CMU CL
  COMPLEX implementation didn't deal with this, and hasn't been
  upgraded to do so. (This doesn't seem to be a high priority
  conformance problem, since seems hard to construct useful code
  where it matters.)

146:
  Floating point errors are reported poorly. E.g. on x86 OpenBSD
  with sbcl-0.7.1, 
        * (expt 2.0 12777)
        debugger invoked on condition of type SB-KERNEL:FLOATING-POINT-EXCEPTION:
          An arithmetic error SB-KERNEL:FLOATING-POINT-EXCEPTION was signalled.
        No traps are enabled? How can this be?
  It should be possible to be much more specific (overflow, division
  by zero, etc.) and of course the "How can this be?" should be fixable.

  See also bugs #45.c and #183

162:
  (reported by Robert E. Brown 2002-04-16) 
  When a function is called with too few arguments, causing the
  debugger to be entered, the uninitialized slots in the bad call frame 
  seem to cause GCish problems, being interpreted as tagged data even
  though they're not. In particular, executing ROOM in the
  debugger at that point causes AVER failures:
    * (machine-type)
    "X86"
    * (lisp-implementation-version)
    "0.7.2.12"
    * (typep 10)
    ...
    0] (room)
    ...
    failed AVER: "(SAP= CURRENT END)"
  (Christophe Rhodes reports that this doesn't occur on the SPARC, which
  isn't too surprising since there are many differences in stack
  implementation and GC conservatism between the X86 and other ports.)

167:
  In sbcl-0.7.3.11, compiling the (illegal) code 
    (in-package :cl-user)
    (defmethod prove ((uustk uustk))
      (zap ((frob () nil))
        (frob)))
  gives the (not terribly clear) error message
    ; caught ERROR:
    ;   (during macroexpansion of (DEFMETHOD PROVE ...))
    ; can't get template for (FROB NIL NIL)
  The problem seems to be that the code walker used by the DEFMETHOD
  macro is unhappy with the illegal syntax in the method body, and
  is giving an unclear error message.

173:
  The compiler sometimes tries to constant-fold expressions before
  it checks to see whether they can be reached. This can lead to 
  bogus warnings about errors in the constant folding, e.g. in code
  like 
    (WHEN X
      (WRITE-STRING (> X 0) "+" "0"))
  compiled in a context where the compiler can prove that X is NIL,
  and the compiler complains that (> X 0) causes a type error because
  NIL isn't a valid argument to #'>. Until sbcl-0.7.4.10 or so this
  caused a full WARNING, which made the bug really annoying because then 
  COMPILE and COMPILE-FILE returned FAILURE-P=T for perfectly legal
  code. Since then the warning has been downgraded to STYLE-WARNING, 
  so it's still a bug but at least it's a little less annoying.

183: "IEEE floating point issues"
  Even where floating point handling is being dealt with relatively
  well (as of sbcl-0.7.5, on sparc/sunos and alpha; see bug #146), the
  accrued-exceptions and current-exceptions part of the fp control
  word don't seem to bear much relation to reality. E.g. on
  SPARC/SunOS:
  * (/ 1.0 0.0)

  debugger invoked on condition of type DIVISION-BY-ZERO:
    arithmetic error DIVISION-BY-ZERO signalled
  0] (sb-vm::get-floating-point-modes)

  (:TRAPS (:OVERFLOW :INVALID :DIVIDE-BY-ZERO)
          :ROUNDING-MODE :NEAREST
          :CURRENT-EXCEPTIONS NIL
          :ACCRUED-EXCEPTIONS (:INEXACT)
          :FAST-MODE NIL)
  0] abort
  * (sb-vm::get-floating-point-modes)
  (:TRAPS (:OVERFLOW :INVALID :DIVIDE-BY-ZERO)
          :ROUNDING-MODE :NEAREST
          :CURRENT-EXCEPTIONS (:INEXACT)
          :ACCRUED-EXCEPTIONS (:INEXACT)
          :FAST-MODE NIL)

188: "compiler performance fiasco involving type inference and UNION-TYPE"
    (time (compile
           nil
           '(lambda ()
             (declare (optimize (safety 3)))
             (declare (optimize (compilation-speed 2)))
             (declare (optimize (speed 1) (debug 1) (space 1)))
             (let ((start 4))
               (declare (type (integer 0) start))
               (print (incf start 22))
               (print (incf start 26))
               (print (incf start 28)))
             (let ((start 6))
               (declare (type (integer 0) start))
               (print (incf start 22))
               (print (incf start 26)))
             (let ((start 10))
               (declare (type (integer 0) start))
               (print (incf start 22))
               (print (incf start 26))))))

  This example could be solved with clever enough constraint
  propagation or with SSA, but consider

    (let ((x 0))
      (loop (incf x 2)))

  The careful type of X is {2k} :-(. Is it really important to be
  able to work with unions of many intervals?

190: "PPC/Linux pipe? buffer? bug"
  In sbcl-0.7.6, the run-program.test.sh test script sometimes hangs
  on the PPC/Linux platform, waiting for a zombie env process.  This
  is a classic symptom of buffer filling and deadlock, but it seems
  only sporadically reproducible.

191: "Miscellaneous PCL deficiencies"
  (reported by Alexey Dejneka sbcl-devel 2002-08-04)
  a. DEFCLASS does not inform the compiler about generated
     functions. Compiling a file with
       (DEFCLASS A-CLASS ()
         ((A-CLASS-X)))
       (DEFUN A-CLASS-X (A)
         (WITH-SLOTS (A-CLASS-X) A
           A-CLASS-X))
     results in a STYLE-WARNING:
       undefined-function 
         SB-SLOT-ACCESSOR-NAME::|COMMON-LISP-USER A-CLASS-X slot READER|

     APD's fix for this was checked in to sbcl-0.7.6.20, but Pierre
     Mai points out that the declamation of functions is in fact
     incorrect in some cases (most notably for structure
     classes).  This means that at present erroneous attempts to use
     WITH-SLOTS and the like on classes with metaclass STRUCTURE-CLASS
     won't get the corresponding STYLE-WARNING.
  c. the examples in CLHS 7.6.5.1 (regarding generic function lambda
     lists and &KEY arguments) do not signal errors when they should.

201: "Incautious type inference from compound types"
  a. (reported by APD sbcl-devel 2002-09-17)
    (DEFUN FOO (X)
      (LET ((Y (CAR (THE (CONS INTEGER *) X))))
        (SETF (CAR X) NIL)
        (FORMAT NIL "~S IS ~S, Y = ~S"
                (CAR X)
                (TYPECASE (CAR X)
                  (INTEGER 'INTEGER)
                  (T '(NOT INTEGER)))
                Y)))

    (FOO ' (1 . 2)) => "NIL IS INTEGER, Y = 1"

  b.
    * (defun foo (x)
        (declare (type (array * (4 4)) x))
        (let ((y x))
          (setq x (make-array '(4 4)))
          (adjust-array y '(3 5))
          (= (array-dimension y 0) (eval `(array-dimension ,y 0)))))
    FOO
    * (foo (make-array '(4 4) :adjustable t))
    NIL

205: "environment issues in cross compiler"
  (These bugs have no impact on user code, but should be fixed or
  documented.)
  a. Macroexpanders introduced with MACROLET are defined in the null
     lexical environment.
  b. The body of (EVAL-WHEN (:COMPILE-TOPLEVEL) ...) is evaluated in
     the null lexical environment.
  c. The cross-compiler cannot inline functions defined in a non-null
     lexical environment.

206: ":SB-FLUID feature broken"
  (reported by Antonio Martinez-Shotton sbcl-devel 2002-10-07)
  Enabling :SB-FLUID in the target-features list in sbcl-0.7.8 breaks
  the build.

207: "poorly distributed SXHASH results for compound data"
  SBCL's SXHASH could probably try a little harder. ANSI: "the
  intent is that an implementation should make a good-faith
  effort to produce hash-codes that are well distributed
  within the range of non-negative fixnums". But
        (let ((hits (make-hash-table)))
          (dotimes (i 16)
            (dotimes (j 16)
              (let* ((ij (cons i j))
                     (newlist (push ij (gethash (sxhash ij) hits))))
                (when (cdr newlist)
                  (format t "~&collision: ~S~%" newlist))))))
  reports lots of collisions in sbcl-0.7.8. A stronger MIX function
  would be an obvious way of fix. Maybe it would be acceptably efficient
  to redo MIX using a lookup into a 256-entry s-box containing
  29-bit pseudorandom numbers?

211: "keywords processing"
  a. :ALLOW-OTHER-KEYS T should allow a function to receive an odd
     number of keyword arguments.
  e. Compiling

      (flet ((foo (&key y) (list y)))
        (list (foo :y 1 :y 2)))

     issues confusing message

       ; in: LAMBDA NIL
       ;     (FOO :Y 1 :Y 2)
       ;
       ; caught STYLE-WARNING:
       ;   The variable #:G15 is defined but never used.

212: "Sequence functions and circular arguments"
  COERCE, MERGE and CONCATENATE go into an infinite loop when given
  circular arguments; it would be good for the user if they could be
  given an error instead (ANSI 17.1.1 allows this behaviour on the part
  of the implementation, as conforming code cannot give non-proper
  sequences to these functions.  MAP also has this problem (and
  solution), though arguably the convenience of being able to do
    (MAP 'LIST '+ FOO '#1=(1 . #1#))
  might be classed as more important (though signalling an error when
  all of the arguments are circular is probably desireable).

213: "Sequence functions and type checking"
  a. MAKE-SEQUENCE, COERCE, MERGE and CONCATENATE cannot deal with
     various complicated, though recognizeable, CONS types [e.g.
       (CONS * (CONS * NULL))
     which according to ANSI should be recognized] (and, in SAFETY 3
     code, should return a list of LENGTH 2 or signal an error)
  b. MAP, when given a type argument that is SUBTYPEP LIST, does not
     check that it will return a sequence of the given type.  Fixing
     it along the same lines as the others (cf. work done around
     sbcl-0.7.8.45) is possible, but doing so efficiently didn't look
     entirely straightforward.
  c. All of these functions will silently accept a type of the form
       (CONS INTEGER *)
     whether or not the return value is of this type.  This is
     probably permitted by ANSI (see "Exceptional Situations" under
     ANSI MAKE-SEQUENCE), but the DERIVE-TYPE mechanism does not
     know about this escape clause, so code of the form
       (INTEGERP (CAR (MAKE-SEQUENCE '(CONS INTEGER *) 2)))
     can erroneously return T.

214:
  SBCL 0.6.12.43 fails to compile

  (locally
      (declare (optimize (inhibit-warnings 0) (compilation-speed 2)))
    (flet ((foo (&key (x :vx x-p)) (list x x-p)))
      (foo 1 2)))

  or a more simple example:

  (locally
      (declare (optimize (inhibit-warnings 0) (compilation-speed 2)))
    (lambda (x) (declare (fixnum x)) (if (< x 0) 0 (1- x))))

215: ":TEST-NOT handling by functions"
  a. FIND and POSITION currently signal errors when given non-NIL for
     both their :TEST and (deprecated) :TEST-NOT arguments, but by
     ANSI 17.2 "the consequences are unspecified", which by ANSI 1.4.2
     means that the effect is "unpredictable but harmless".  It's not
     clear what that actually means; it may preclude conforming
     implementations from signalling errors.
  b. COUNT, REMOVE and the like give priority to a :TEST-NOT argument
     when conflict occurs.  As a quality of implementation issue, it
     might be preferable to treat :TEST and :TEST-NOT as being in some
     sense the same &KEY, and effectively take the first test function in
     the argument list.
  c. Again, a quality of implementation issue: it would be good to issue a
     STYLE-WARNING at compile-time for calls with :TEST-NOT, and a
     WARNING for calls with both :TEST and :TEST-NOT; possibly this
     latter should be WARNed about at execute-time too.

216: "debugger confused by frames with invalid number of arguments"
  In sbcl-0.7.8.51, executing e.g. (VECTOR-PUSH-EXTEND T), BACKTRACE, Q
  leaves the system confused, enough so that (QUIT) no longer works.
  It's as though the process of working with the uninitialized slot in
  the bad VECTOR-PUSH-EXTEND frame causes GC problems, though that may
  not be the actual problem. (CMU CL 18c doesn't have problems with this.)

217: "Bad type operations with FUNCTION types"
  In sbcl.0.7.7:

    * (values-type-union (specifier-type '(function (base-char)))
                         (specifier-type '(function (integer))))

    #<FUN-TYPE (FUNCTION (BASE-CHAR) *)>

  It causes insertion of wrong type assertions into generated
  code. E.g.

    (defun foo (x s)
      (let ((f (etypecase x
                 (character #'write-char)
                 (integer #'write-byte))))
        (funcall f x s)
        (etypecase x
          (character (write-char x s))
          (integer (write-byte x s)))))

   Then (FOO #\1 *STANDARD-OUTPUT*) signals type error.

  (In 0.7.9.1 the result type is (FUNCTION * *), so Python does not
  produce invalid code, but type checking is not accurate. Similar
  problems exist with VALUES-TYPE-INTERSECTION.)

220:
  Sbcl 0.7.9 fails to compile

  (multiple-value-call #'list
    (the integer (helper))
    nil)

  Type check for INTEGER, the result of which serves as the first
  argument of M-V-C, is inserted after evaluation of NIL. So arguments
  of M-V-C are pushed in the wrong order. As a temporary workaround
  type checking was disabled for M-V-Cs in 0.7.9.13. A better solution
  would be to put the check between evaluation of arguments, but it
  could be tricky to check result types of PROG1, IF etc.

233: bugs in constraint propagation
  a.
  (defun foo (x)
    (declare (optimize (speed 2) (safety 3)))
    (let ((y 0d0))
      (values
       (the double-float x)
       (setq y (+ x 1d0))
       (setq x 3d0)
       (quux y (+ y 2d0) (* y 3d0)))))
  (foo 4) => segmentation violation

  (see usage of CONTINUATION-ASSERTED-TYPE in USE-RESULT-CONSTRAINTS)
  (see also bug 236)

  b.
  (declaim (optimize (speed 2) (safety 3)))
  (defun foo (x y)
    (if (typep (prog1 x (setq x y)) 'double-float)
        (+ x 1d0)
        (+ x 2)))
  (foo 1d0 5) => segmentation violation

235: "type system and inline expansion"
  a.
  (declaim (ftype (function (cons) number) acc))
  (declaim (inline acc))
  (defun acc (c)
    (the number (car c)))

  (defun foo (x y)
    (values (locally (declare (optimize (safety 0)))
              (acc x))
            (locally (declare (optimize (safety 3)))
              (acc y))))

  (foo '(nil) '(t)) => NIL, T.

237: "Environment arguments to type functions"
  a. Functions SUBTYPEP, TYPEP, UPGRADED-ARRAY-ELEMENT-TYPE, and 
     UPGRADED-COMPLEX-PART-TYPE now have an optional environment
     argument, but they ignore it completely.  This is almost 
     certainly not correct.
  b. Also, the compiler's optimizers for TYPEP have not been informed
     about the new argument; consequently, they will not transform
     calls of the form (TYPEP 1 'INTEGER NIL), even though this is
     just as optimizeable as (TYPEP 1 'INTEGER).

238: "REPL compiler overenthusiasm for CLOS code"
  From the REPL,
    * (defclass foo () ())
    * (defmethod bar ((x foo) (foo foo)) (call-next-method))
  causes approximately 100 lines of code deletion notes.  Some
  discussion on this issue happened under the title 'Three "interesting"
  bugs in PCL', resulting in a fix for this oververbosity from the
  compiler proper; however, the problem persists in the interactor
  because the notion of original source is not preserved: for the
  compiler, the original source of the above expression is (DEFMETHOD
  BAR ((X FOO) (FOO FOO)) (CALL-NEXT-METHOD)), while by the time the
  compiler gets its hands on the code needing compilation from the REPL,
  it has been macroexpanded several times.

  A symptom of the same underlying problem, reported by Tony Martinez:
    * (handler-case
        (with-input-from-string (*query-io* "    no")
          (yes-or-no-p))
      (simple-type-error () 'error))
    ; in: LAMBDA NIL
    ;     (SB-KERNEL:FLOAT-WAIT)
    ; 
    ; note: deleting unreachable code
    ; compilation unit finished
    ;   printed 1 note

241: "DEFCLASS mysteriously remembers uninterned accessor names."
  (from tonyms on #lisp IRC 2003-02-25)
  In sbcl-0.7.12.55, typing
    (defclass foo () ((bar :accessor foo-bar)))
    (profile foo-bar)
    (unintern 'foo-bar)
    (defclass foo () ((bar :accessor foo-bar)))
  gives the error message
    "#:FOO-BAR already names an ordinary function or a macro."
  So it's somehow checking the uninterned old accessor name instead
  of the new requested accessor name, which seems broken to me (WHN).

242: "WRITE-SEQUENCE suboptimality"
  (observed from clx performance)
  In sbcl-0.7.13, WRITE-SEQUENCE of a sequence of type 
  (SIMPLE-ARRAY (UNSIGNED-BYTE 8) (*)) on a stream with element-type
  (UNSIGNED-BYTE 8) will write to the stream one byte at a time,
  rather than writing the sequence in one go, leading to severe
  performance degradation.

243: "STYLE-WARNING overenthusiasm for unused variables"
  (observed from clx compilation)
  In sbcl-0.7.14, in the presence of the macros
    (DEFMACRO FOO (X) `(BAR ,X))
    (DEFMACRO BAR (X) (DECLARE (IGNORABLE X)) 'NIL)
  somewhat surprising style warnings are emitted for
    (COMPILE NIL '(LAMBDA (Y) (FOO Y))):
  ; in: LAMBDA (Y)
  ;     (LAMBDA (Y) (FOO Y))
  ; 
  ; caught STYLE-WARNING:
  ;   The variable Y is defined but never used.

245: bugs in disassembler
  a. On X86 an immediate operand for IMUL is printed incorrectly.
  b. On X86 operand size prefix is not recognized.

248: "reporting errors in type specifier syntax"
  (TYPEP 1 '(SYMBOL NIL)) says something about "unknown type
  specifier".

251:
  (defun foo (&key (a :x))
    (declare (fixnum a))
    a)

  does not cause a warning. (BTW: old SBCL issued a warning, but for a
  function, which was never called!)

256:
  Compiler does not emit warnings for

  a. (lambda () (svref (make-array 8 :adjustable t) 1))

  b. (lambda (x)
       (list (let ((y (the real x)))
               (unless (floatp y) (error ""))
               y)
             (integer-length x)))

  c. (lambda (x)
       (declare (optimize (debug 0)))
       (declare (type vector x))
       (list (fill-pointer x)
             (svref x 1)))

257:
  Complex array type does not have corresponding type specifier.

  This is a problem because the compiler emits optimization notes when
  you use a non-simple array, and without a type specifier for hairy
  array types, there's no good way to tell it you're doing it
  intentionally so that it should shut up and just compile the code.

  Another problem is confusing error message "asserted type ARRAY
  conflicts with derived type (VALUES SIMPLE-VECTOR &OPTIONAL)" during
  compiling (LAMBDA (V) (VALUES (SVREF V 0) (VECTOR-POP V))).

  The last problem is that when type assertions are converted to type
  checks, types are represented with type specifiers, so we could lose
  complex attribute. (Now this is probably not important, because
  currently checks for complex arrays seem to be performed by
  callees.)

259:
  (compile nil '(lambda () (aref (make-array 0) 0))) compiles without
  warning.  Analogous cases with the index and length being equal and
  greater than 0 are warned for; the problem here seems to be that the
  type required for an array reference of this type is (INTEGER 0 (0))
  which is canonicalized to NIL.

260:
  a.
  (let* ((s (gensym))
         (t1 (specifier-type s)))
    (eval `(defstruct ,s))
    (type= t1 (specifier-type s)))
  => NIL, NIL

  (fixed in 0.8.1.24)

  b. The same for CSUBTYPEP.

261:
    * (let () (list (the (values &optional fixnum) (eval '(values)))))
    debugger invoked on condition of type TYPE-ERROR:
      The value NIL is not of type FIXNUM.

262: "yet another bug in inline expansion of local functions"
  Compiler fails on

    (defun foo (x y)
      (declare (integer x y))
      (+ (block nil
            (flet ((xyz (u)
                     (declare (integer u))
                     (if (> (1+ (the unsigned-byte u)) 0)
                         (+ 1 u)
                         (return (+ 38 (cos (/ u 78)))))))
              (declare (inline xyz))
              (return-from foo
                (* (funcall (eval #'xyz) x)
                   (if (> x 30)
                       (funcall (if (> x 5) #'xyz #'identity)
                                (+ x 13))
                       38)))))
         (sin (* x y))))

  Urgh... It's time to write IR1-copier.

265:
  SB-EXT:RUN-PROGRAM is currently non-functional on Linux/PPC;
  attempting to use it leads to segmentation violations.  This is
  probably because of a bogus implementation of
  os_restore_fp_control().

266:
  David Lichteblau provided (sbcl-devel 2003-06-01) a patch to fix
  behaviour of streams with element-type (SIGNED-BYTE 8).  The patch
  looks reasonable, if not obviously correct; however, it caused the
  PPC/Linux port to segfault during warm-init while loading
  src/pcl/std-class.fasl.  A workaround patch was made, but it would
  be nice to understand why the first patch caused problems, and to
  fix the cause if possible.

267:
  In
    (defun fact (x i)
      (if (= x 0)
          i
          (fact (1- x) (* x i))))
  sbcl does not convert the self-recursive call to a jump, though it
  is allowed to by CLHS 3.2.2.3.  CMUCL, however, does perform this
  optimization.

268: "wrong free declaration scope"
  The following code must signal type error:

    (locally (declare (optimize (safety 3)))
      (flet ((foo (x &optional (y (car x)))
               (declare (optimize (safety 0)))
               (list x y)))
        (funcall (eval #'foo) 1)))

DEFUNCT CATEGORIES OF BUGS
  IR1-#:
    These labels were used for bugs related to the old IR1 interpreter.
    The # values reached 6 before the category was closed down.