4 ms·

GCC has a 'pure' attribute. I don't know if it's only used for optimization, but it also serves as a kind of comment for whoever looks at the function in the fu

GCC has a 'pure' attribute. I don't know if it's only used for optimization, but it also serves as a kind of comment for whoever looks at the function in the future.

copx 14y ago
"pure" and "const" are GCC function attributes which are supposed to help the optimizer. Confusingly enough "const" demands a higher level of purity than "pure".. I would never use those attributes except - maybe - in the most critical loops and then only with a big "WARNING!!!" sign. Why? GCC does not / cannot enforce the guarantees given by "const" and "pure" yet the optimizer always assumes they are true. I.e. accidentally reduce the purity of a function decorated in this way.. and you might create very hard to find bugs. This is a general problem in C and C++, those languages simply weren't designed to enforce such contracts. C99's "restrict" has the same problem.
- jhasse 14y ago
  Since when is "const" a GCC function attribute?
  - scott_s 14y ago
    http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html This is, of course, in addition to its other meanings in the language.