http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54907
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-10-12 15:40:05 UTC --- I believe this code is well-defined. There are two objects modified, p and *p. p is modified by the assignment, and C11 6.5.16#3 says "The side effect of updating the stored value of the left operand is sequenced after the value computations of the left and right operands.". For postfix increment, which modifies *p, "The value computation of the result is sequenced before the side effect of updating the stored value of the operand.". Each object is modified only once, so there is no issue of two side effects on the same object being unsequenced. And the value computation of the RHS, using p, is sequenced before p is updated by the assignment; furthermore, 5.1.2.3#2 says "Value computation for an lvalue expression includes determining the identity of the designated object.". So I don't think either case of undefinedness in 6.5#2, "If a side effect on a scalar object is unsequenced relative to either a different side effect on the same scalar object or a value computation using the value of the same scalar object, the behavior is undefined.", applies here.
