This file lists known bugs in the GNU Fortran compiler. Copyright (C) 1995, 1996 Free Software Foundation, Inc. You may copy, distribute, and modify it freely as long as you preserve this copyright notice and permission notice. Bugs in GNU Fortran ******************* This section identifies bugs that `g77' *users* might run into in the `egcs'-1.1.2 version of `g77'. This includes bugs that are actually in the `gcc' back end (GBE) or in `libf2c', because those sets of code are at least somewhat under the control of (and necessarily intertwined with) `g77', so it isn't worth separating them out. For information on bugs in *other* versions of `g77', see `egcs/gcc/f/NEWS'. An online, "live" version of this document (derived directly from the up-to-date mainline version of `g77' within `egcs') is available at `http://egcs.cygnus.com/onlinedocs/g77_bugs.html'. For information on bugs that might afflict people who configure, port, build, and install `g77', see "Problems Installing" in `egcs/gcc/f/INSTALL'. * `g77' generates bad code for assignments, or other conversions, of `REAL' or `COMPLEX' constant expressions to type `INTEGER(KIND=2)' (often referred to as `INTEGER*8'). For example, `INTEGER*8 J; J = 4E10' is miscompiled on some systems--the wrong value is stored in J. * The `IDate' Intrinsic (VXT) fails to return the year in the documented, non-Y2K-compliant range of 0-99, instead returning 100 for the year 2000. * Year 2000 (Y2K) compliance information is missing from the documentation. * `g77' crashes when compiling I/O statements using keywords that define `INTEGER' values, such as `IOSTAT=J', where J is other than default `INTEGER' (such as `INTEGER*2'). * The `-ax' option is not obeyed when compiling Fortran programs. (It is not passed to the `f771' driver.) * `g77' fails to warn about a reference to a function when the corresponding *subsequent* function program unit disagrees with the reference concerning the type of the function. * Automatic arrays possibly aren't working on HP-UX systems, at least in HP-UX version 10.20. Writing into them apparently causes over-writing of statically declared data in the main program. This probably means the arrays themselves are being under-allocated, or pointers to them being improperly handled, e.g. not passed to other procedures as they should be. * `g77' fails to warn about use of a "live" iterative-DO variable as an implied-DO variable in a `WRITE' or `PRINT' statement (although it does warn about this in a `READ' statement). * Something about `g77''s straightforward handling of label references and definitions sometimes prevents the GBE from unrolling loops. Until this is solved, try inserting or removing `CONTINUE' statements as the terminal statement, using the `END DO' form instead, and so on. * Some confusion in diagnostics concerning failing `INCLUDE' statements from within `INCLUDE''d or `#include''d files. * `g77' assumes that `INTEGER(KIND=1)' constants range from `-2**31' to `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 `g77' doesn't recognize that, on IEEE-754/854-compliant systems, `0./0.' should produce a NaN and no warning instead of the value `0.' and a warning. This is to be fixed in version 0.6, when `g77' will use the `gcc' back end's constant-handling mechanisms to replace its own. * `g77' uses way too much memory and CPU time to process large aggregate areas having any initialized elements. For example, `REAL A(1000000)' followed by `DATA A(1)/1/' takes up way too much time and space, including the size of the generated assembler file. This is to be mitigated somewhat in version 0.6. Version 0.5.18 improves cases like this--specifically, cases of *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 `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 `g77' does display a warning message to notify the user before the compiler appears to hang. * `g77' doesn't emit variable and array members of common blocks for use with a debugger (the `-g' command-line option). The code is present to do this, but doesn't work with at least one debug format--perhaps it works with others. And it turns out there's a similar bug for local equivalence areas, so that has been disabled as well. As of Version 0.5.19, a temporary kludge solution is provided whereby some rudimentary information on a member is written as a string that is the member's value as a character string. * 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 `MAIN__' (or `MAIN___' or `MAIN_' if `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. * Debugging `g77'-compiled code using debuggers other than `gdb' is likely not to work. Getting `g77' and `gdb' to work together is a known problem--getting `g77' to work properly with other debuggers, for which source code often is unavailable to `g77' developers, seems like a much larger, unknown problem, and is a lower priority than making `g77' and `gdb' work together properly. On the other hand, information about problems other debuggers have with `g77' output might make it easier to properly fix `g77', and perhaps even improve `gdb', so it is definitely welcome. Such information might even lead to all relevant products working together properly sooner. * `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. Version 0.6 should solve most or all remaining problems (such as cross-compiling involving 64-bit machines). * Maintainers of gcc report that the back end definitely has "broken" support for `COMPLEX' types. Based on their input, it seems many of the problems affect only the more-general facilities for gcc's `__complex__' type, such as `__complex__ int' (where the real and imaginary parts are integers) that GNU Fortran does not use. Version 0.5.20 of `g77' works around this problem by not using the back end's support for `COMPLEX'. The new option `-fno-emulate-complex' avoids the work-around, reverting to using the same "broken" mechanism as that used by versions of `g77' prior to 0.5.20. * `g77' currently inserts needless padding for things like `COMMON A,IPAD' where `A' is `CHARACTER*1' and `IPAD' is `INTEGER(KIND=1)' on machines like x86, because the back end insists that `IPAD' be aligned to a 4-byte boundary, but the processor has no such requirement (though it is usually good for performance). The `gcc' back end needs to provide a wider array of specifications of alignment requirements and preferences for targets, and front ends like `g77' should take advantage of this when it becomes available. * The x86 target's `-malign-double' option no longer reliably aligns double-precision variables and arrays when they are placed in the stack frame. This can significantly reduce the performance of some applications, even on a run-to-run basis (that is, performance measurements can vary fairly widely depending on whether frequently used variables are properly aligned, and that can change from one program run to the next, even from one procedure call to the next). Versions 0.5.22 and earlier of `g77' included a patch to `gcc' that enabled this, but that patch has been deemed an improper (probably buggy) one for version 2.8 of `gcc' and for `egcs'. Note that version 1.1 of `egcs' aligns double-precision variables and arrays when they are in static storage even if `-malign-double' is not specified. There is ongoing investigation into how to make `-malign-double' work properly, also into how to make it unnecessary to get all double-precision variables and arrays aligned when such alignment would not violate the relevant specifications for processor and inter-procedural interfaces. For a suite of programs to test double-precision alignment, see `ftp://alpha.gnu.org/gnu/g77/align/'. * The `libf2c' routines that perform some run-time arithmetic on `COMPLEX' operands were modified circa version 0.5.20 of `g77' to work properly even in the presence of aliased operands. While the `g77' and `netlib' versions of `libf2c' differ on how this is accomplished, the main differences are that we believe the `g77' version works properly even in the presence of *partially* aliased operands. However, these modifications have reduced performance on targets such as x86, due to the extra copies of operands involved.