+ IPA_JF_CONST_MEMBER_PTR stands for C++ member pointers, it is a special
+ constant in this regard because it is in fact a structure consisting of two
+ values. Other constants are represented with IPA_JF_CONST.
+
+ IPA_JF_ANCESTOR is a special pass-through jump function, which means that
+ the result is an address of a part of the object pointed to by the formal
+ parameter to which the function refers. It is mainly intended to represent
+ getting addresses of of ancestor fields in C++
+ (e.g. &this_1(D)->D.1766.D.1756). Note that if the original pointer is
+ NULL, ancestor jump function must behave like a simple pass-through.
+
+ Other pass-through functions can either simply pass on an unchanged formal
+ parameter or can apply one simple binary operation to it (such jump
+ functions are called polynomial).
+
+ IPA_JF_KNOWN_TYPE is a special type of an "unknown" function that applies
+ only to pointer parameters. It means that even though we cannot prove that
+ the passed value is an interprocedural constant, we still know the exact
+ type of the containing object which may be valuable for devirtualization.
+
+ Jump functions are computed in ipa-prop.c by function
+ update_call_notes_after_inlining. Some information can be lost and jump
+ functions degraded accordingly when inlining, see
+ update_call_notes_after_inlining in the same file. */