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Have
You Found a Bug?
If you are not sure whether
you have found a bug, the following documentation discusses some guidelines.
- If the compiler gets a fatal
signal, for any input whatever, that is a compiler bug. Reliable compilers
never crash.
- If the compiler produces
invalid assembly code, for any input what-ever (except an asm
statement), that is a compiler bug, unless the compiler reports errors
(not just warnings) which would ordinarily prevent the assembler from being
run.
- If the compiler produces
valid assembly code that does not correctly execute the input source code,
that is a compiler bug.
- However, you must double-check
to make sure, because you may have run into an incompatibility between
GNU C and traditional C (see Incompatibilities
of GNU CC). These incompatibilities might be considered bugs, but they
are inescapable consequences of valuable features. Or you may have a program
whose behavior is undefined, which happened by chance to give the desired
results with another C or C++ compiler.
- For example, in many nonoptimizing
compilers, you can write ‘x;’
at the end of a function instead of ‘return
x;’, with the
same results.
- But the value of the function
is undefined if return is omitted; it is not a bug when GNU CC produces
different results.
- Problems often result from
expressions with two increment operators, as in ‘f(*p++,
*p++)’. Your previous
compiler might have interpreted that expression the way you intended; GNU
CC might interpret it another way. Neither compiler is wrong. The bug is
in your code.
- After you have localized
the error to a single source line, it should be easy to check for these
things. If your program is correct and well defined, you have found a compiler
bug.
- If the compiler produces
an error message for valid input, that is a compiler bug.
- If the compiler does not
produce an error message for invalid input, that is a compiler bug. However,
you should note that your idea of “invalid input” might be my idea of “an
extension” or “support for traditional practice.”
- If you are an experienced
user of C or C++ compilers, your suggestions for improvement of GNU CC
or GNU C++ are welcome in any case.