>From CVS HEAD lib/autoconf/c.m4: > # AC_LANG_BOOL_COMPILE_TRY(C)(PROLOGUE, EXPRESSION) > # ------------------------------------------------- > # The C standard does not require a diagnostic when we compute 1 / 0 > # at compile-time, but we don't know of any compiler that fails to > # diagnose this. Diagnostics are required for some other expressions > # (e.g., ((EXPRESSION) ? 0 : (0, 0)), INT_MAX + !!(EXPRESSION)), > # but they don't work as well in practice. > m4_define([AC_LANG_BOOL_COMPILE_TRY(C)], > [AC_LANG_PROGRAM([$1], [static int v = 1 / !!($2); > v = 0; > ])]) Though all compilers do seem to issue at least at warning for a guaranteed division by zero, some (HP/UX 11.23 cc/aCC and Tru64 4.0 cc) do not return non-zero on that account. This makes tests that depend upon the above macro unreliable with these compilers. The side effects work out to be fairly harmless. Affected Autoconf configure script runs never define __CHAR_UNSIGNED__ and always define HAVE_LONG_DOUBLE. When cross-compiling, every AC_CHECK_SIZEOF will return zero. Since nearly all cross compilation of GNU software uses gcc, the last issue may be more of a theoretical eyesore than anything else. Even the others will affect only a few programs on few platforms with a few compilers. That said, I'd like to fix it. Would one of the following be appropriate? 1) Change the test such that it creates truly invalid C in the false case. I don't know how to do this, but perhaps a reader does. Ideas? 2) Test for the switch (including none) that makes the compiler driver return a nonzero status when a division by zero exists in the code. Use that switch in compilations from AC_LANG_BOOL_TRY_COMPILE(C). If ``configure'' finds no such switch, it will print a stern warning. This switches I know of are as follows; when more than one switch works for a particular compiler, I list both. If you can provide the flags for vendor compilers I have not listed (at least IBM, Sun, and SGI would be nice), please do so. **Compiler** **Switch** Compaq C V6.5-207 (dtk) on Digital UNIX V4.0G (Rev. 1530) -msg_fatal zerodiv Compaq C V6.5-207 (dtk) on Digital UNIX V4.0G (Rev. 1530) -w3 HP aC++/ANSI C B3910B A.05.56 [June 09 2004] [aCC6_beta] +We HP aC++/ANSI C B3910B A.05.56 [June 09 2004] [aCC6_beta] +We2039 HP aC++/ANSI C B3910B A.05.55 [Dec 04 2003] +We HP aC++/ANSI C B3910B A.05.55 [Dec 04 2003] +We155 icc 8.0 for ia64 Linux none needed gcc 2.95.3 none needed gcc 3.X none needed OpenVMS CC none available(?) 3) Don't bother. The code uglification is not worth the small reduction in bugs. Perhaps just document the limitation and print a warning upon use of an affected test with a non-gcc compiler. 4) I have better idea _______. Thanks. _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx http://lists.gnu.org/mailman/listinfo/autoconf
