On Saturday 06 August 2011 17:39:06 Thomas Koenig wrote: > > As Thomas mentions, certain cases are still not handled correctly > > (e.g. A+B+C vs C+B+A, and other mathematical transformations), but I > > hope they are sufficiently exotic (so that we can wait for bug reports > > to roll in). In addition I expect people to declare overridden > > procedures analogously to the base procedure, and not use e.g. > > len=3*(x+1) in one case and len=3*x+3 in the other. > > Not OK. > > It is wrong to assume that expressions are unequal because we cannot > prove they are equal, with all the limitations that we currently > have. This will introduce rejects-valid bugs. In the PR at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49638#c8 I quote the standard:
4.5.7.3 (type-bound procedure overriding) has: • Either both shall be subroutines or both shall be functions having the same result characteristics (12.3.3). 12.3.3 (Characteristics of function results): If a type parameter of a function result or a bound of a function result array is not a constant expression, the exact dependence on the entities in the expression is a characteristic So the standards is more restrictive than expression values being the same. It requires _the exact same dependence on the entities_. My reading of this is that 3*(x+1) vs 3*x+3 is right to be rejected, same for (a+b)+c vs a+(b+c). The only worrying case that I see is the one you pointed out: a+b+c vs c+b+a (without brackets). Mikael
