> First, a belated follow-up to https://gcc.gnu.org/PR66512 . The bug is > asking why attribute-const appears to have a weaker effect in C++, compared > to C. The answer in that bug is that GCC assumes that attribute-const > function can terminate by throwing an exception.
FWIW there is an equivalent semantics in Ada: the "const" functions can throw and the language explicitly allows them to be CSEd in this case, etc. > That doesn't actually seem reasonable. Consider that C counterpart to > throwing is longjmp; it seems to me that GCC should behave consistently: > either assume that attribute-const may both longjmp and throw (I guess > nobody wants that), or that it may not longjmp nor throw. Intuitively, if > "const" means "free of side effects so that calls can be moved > speculatively or duplicated", then non-local control flow transfer via > throwing should be disallowed as well. This would pessimize a lot languages where exceptions are pervasive. > In any case, it would be nice the intended compiler behavior could be > explicitely stated in the manual. Agreed. -- Eric Botcazou
