@c Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. @c This is part of the G77 manual. @c For copying conditions, see the file g77.texi. @c The text of this file appears in the file BUGS @c in the G77 distribution, as well as in the G77 manual. @c Keep this the same as the dates above, since it's used @c in the standalone derivations of this file (e.g. BUGS). @set copyrights-bugs 1995,1996,1997,1998,1999,2000,2001,2002 @set last-update-bugs 2002-02-01 @ifset DOC-BUGS @include root.texi @c The immediately following lines apply to the BUGS file @c which is derived from this file. @emph{Note:} This file is automatically generated from the files @file{bugs0.texi} and @file{bugs.texi}. @file{BUGS} is @emph{not} a source file, although it is normally included within source distributions. This file lists known bugs in the @value{which-g77} version of the GNU Fortran compiler. Copyright (C) @value{copyrights-bugs} Free Software Foundation, Inc. You may copy, distribute, and modify it freely as long as you preserve this copyright notice and permission notice. @node Top,,, (dir) @chapter Known Bugs In GNU Fortran @end ifset @ifset DOC-G77 @node Known Bugs @section Known Bugs In GNU Fortran @end ifset This section identifies bugs that @code{g77} @emph{users} might run into in the @value{which-g77} version of @code{g77}. This includes bugs that are actually in the @code{gcc} back end (GBE) or in @code{libf2c}, because those sets of code are at least somewhat under the control of (and necessarily intertwined with) @code{g77}, so it isn't worth separating them out. @ifset DOC-G77 For information on bugs in @emph{other} versions of @code{g77}, see @ref{News,,News About GNU Fortran}. There, lists of bugs fixed in various versions of @code{g77} can help determine what bugs existed in prior versions. @end ifset @ifset DOC-BUGS For information on bugs in @emph{other} versions of @code{g77}, see @file{@value{path-g77}/NEWS}. There, lists of bugs fixed in various versions of @code{g77} can help determine what bugs existed in prior versions. @end ifset @ifset DEVELOPMENT @emph{Warning:} The information below is still under development, and might not accurately reflect the @code{g77} code base of which it is a part. Efforts are made to keep it somewhat up-to-date, but they are particularly concentrated on any version of this information that is distributed as part of a @emph{released} @code{g77}. In particular, while this information is intended to apply to the @value{which-g77} version of @code{g77}, only an official @emph{release} of that version is expected to contain documentation that is most consistent with the @code{g77} product in that version. @end ifset An online, ``live'' version of this document (derived directly from the mainline, development version of @code{g77} within @code{gcc}) is available via @uref{http://gcc.gnu.org/onlinedocs/g77/Trouble.html}. Follow the ``Known Bugs'' link. The following information was last updated on @value{last-update-bugs}: @itemize @bullet @item @code{g77} fails to warn about use of a ``live'' iterative-DO variable as an implied-DO variable in a @code{WRITE} or @code{PRINT} statement (although it does warn about this in a @code{READ} statement). @item Something about @code{g77}'s straightforward handling of label references and definitions sometimes prevents the GBE from unrolling loops. Until this is solved, try inserting or removing @code{CONTINUE} statements as the terminal statement, using the @code{END DO} form instead, and so on. @item Some confusion in diagnostics concerning failing @code{INCLUDE} statements from within @code{INCLUDE}'d or @code{#include}'d files. @cindex integer constants @cindex constants, integer @item @code{g77} assumes that @code{INTEGER(KIND=1)} constants range from @samp{-2**31} to @samp{2**31-1} (the range for two's-complement 32-bit values), instead of determining their range from the actual range of the type for the configuration (and, someday, for the constant). Further, it generally doesn't implement the handling of constants very well in that it makes assumptions about the configuration that it no longer makes regarding variables (types). Included with this item is the fact that @code{g77} doesn't recognize that, on IEEE-754/854-compliant systems, @samp{0./0.} should produce a NaN and no warning instead of the value @samp{0.} and a warning. @cindex compiler speed @cindex speed, of compiler @cindex compiler memory usage @cindex memory usage, of compiler @cindex large aggregate areas @cindex initialization, bug @cindex DATA statement @cindex statements, DATA @item @code{g77} uses way too much memory and CPU time to process large aggregate areas having any initialized elements. For example, @samp{REAL A(1000000)} followed by @samp{DATA A(1)/1/} takes up way too much time and space, including the size of the generated assembler file. Version 0.5.18 improves cases like this---specifically, cases of @emph{sparse} initialization that leave large, contiguous areas uninitialized---significantly. However, even with the improvements, these cases still require too much memory and CPU time. (Version 0.5.18 also improves cases where the initial values are zero to a much greater degree, so if the above example ends with @samp{DATA A(1)/0/}, the compile-time performance will be about as good as it will ever get, aside from unrelated improvements to the compiler.) Note that @code{g77} does display a warning message to notify the user before the compiler appears to hang. @ifset DOC-G77 A warning message is issued when @code{g77} sees code that provides initial values (e.g. via @code{DATA}) to an aggregate area (@code{COMMON} or @code{EQUIVALENCE}, or even a large enough array or @code{CHARACTER} variable) that is large enough to increase @code{g77}'s compile time by roughly a factor of 10. This size currently is quite small, since @code{g77} currently has a known bug requiring too much memory and time to handle such cases. In @file{@value{path-g77}/data.c}, the macro @code{FFEDATA_sizeTOO_BIG_INIT_} is defined to the minimum size for the warning to appear. The size is specified in storage units, which can be bytes, words, or whatever, on a case-by-case basis. After changing this macro definition, you must (of course) rebuild and reinstall @code{g77} for the change to take effect. Note that, as of version 0.5.18, improvements have reduced the scope of the problem for @emph{sparse} initialization of large arrays, especially those with large, contiguous uninitialized areas. However, the warning is issued at a point prior to when @code{g77} knows whether the initialization is sparse, and delaying the warning could mean it is produced too late to be helpful. Therefore, the macro definition should not be adjusted to reflect sparse cases. Instead, adjust it to generate the warning when densely initialized arrays begin to cause responses noticeably slower than linear performance would suggest. @end ifset @cindex code, displaying main source @cindex displaying main source code @cindex debugging main source code @cindex printing main source @item When debugging, after starting up the debugger but before being able to see the source code for the main program unit, the user must currently set a breakpoint at @code{MAIN__} (or @code{MAIN___} or @code{MAIN_} if @code{MAIN__} doesn't exist) and run the program until it hits the breakpoint. At that point, the main program unit is activated and about to execute its first executable statement, but that's the state in which the debugger should start up, as is the case for languages like C. @cindex debugger @item Debugging @code{g77}-compiled code using debuggers other than @code{gdb} is likely not to work. Getting @code{g77} and @code{gdb} to work together is a known problem---getting @code{g77} to work properly with other debuggers, for which source code often is unavailable to @code{g77} developers, seems like a much larger, unknown problem, and is a lower priority than making @code{g77} and @code{gdb} work together properly. On the other hand, information about problems other debuggers have with @code{g77} output might make it easier to properly fix @code{g77}, and perhaps even improve @code{gdb}, so it is definitely welcome. Such information might even lead to all relevant products working together properly sooner. @cindex Alpha, support @cindex support, Alpha @item @code{g77} doesn't work perfectly on 64-bit configurations such as the Digital Semiconductor (``DEC'') Alpha. This problem is largely resolved as of version 0.5.23. @cindex padding @cindex structures @cindex common blocks @cindex equivalence areas @item @code{g77} currently inserts needless padding for things like @samp{COMMON A,IPAD} where @samp{A} is @code{CHARACTER*1} and @samp{IPAD} is @code{INTEGER(KIND=1)} on machines like x86, because the back end insists that @samp{IPAD} be aligned to a 4-byte boundary, but the processor has no such requirement (though it is usually good for performance). The @code{gcc} back end needs to provide a wider array of specifications of alignment requirements and preferences for targets, and front ends like @code{g77} should take advantage of this when it becomes available. @cindex complex performance @cindex aliasing @item The @code{libf2c} routines that perform some run-time arithmetic on @code{COMPLEX} operands were modified circa version 0.5.20 of @code{g77} to work properly even in the presence of aliased operands. While the @code{g77} and @code{netlib} versions of @code{libf2c} differ on how this is accomplished, the main differences are that we believe the @code{g77} version works properly even in the presence of @emph{partially} aliased operands. However, these modifications have reduced performance on targets such as x86, due to the extra copies of operands involved. @end itemize