Use function attributes to mark functions as "const", "pure", and "nothrow"

[olly]

GCC allows functions to be annotate with attribute((const)) if they "do not examine any values except their arguments, and have no effects except the return value", which allows the compiler to use CSE to eliminate calls to them with identical arguments. This would probably be very useful for Xapian::Unicode::get_category() for example.

URL: http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Function-Attributes.html#Function-Attributes

[olly]

Oops, finger trouble...

attribute((const)) is available for (at least) GCC 2.95 onwards, which is all the versions we support.

There's also attribute((pure)) which is like const, but the function may also examine global memory, perhaps via pointer (or presumably reference) parameters. This is available from GCC 2.96 onwards.

MSVC doesn't seem to have equivalents for either of these.

Both GCC and MSVC support nothrow (as attribute and declspec respectively) to indicate a function doesn't throw exceptions. ISO C++ has "throw()" - not sure if this is the same or subtely different though.

GCC also allows functions to be marked listing pointer parameters which can't be NULL, which may be worth considering.

Marking this for consideration for 1.0.X.

[richard]

(In #120) Remove the unfixed dependencies so we can close this bug - they're all marked for the 1.1.0 milestone.

[olly]

Doing this to internal functions wouldn't affect the ABI and to external functions wouldn't affect the API so bumping to 1.1.1.