https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104377
--- Comment #2 from Martin Jambor <jamborm at gcc dot gnu.org> --- (In reply to Feng Xue from comment #1) > > OK. I does missed something. Here we could not hold assumption that > ipcp_decision_stage() only sees raw cgraph node, since sometime in the > future some new ipa pass may be added prior to ipa-cp, and this pass > introduces clone node. Right, initially IPA-SRA was developed as a pass before IPA-CP and it may well be that we decide to swap the order again. > > However, there is a questionable point about the code snippet > > if (!node->can_change_signature > || old_adj->op != IPA_PARAM_OP_COPY > || (!known_csts[old_adj->base_index] > && ipa_is_param_used (info, old_adj->base_index))) > > In ipa-cp, known_csts is for the node, has no relation to the node's origin > node, but here it is accessed via index of the latter (old_adj->base_index), > will this cause out-of-bound error? I think the code is correct. Assume IPA-SRA running before IPA-CP, and we're compiling a function with two argument, with indices 0 and 1. Analysis phases of both passes run before the IPA (WPA) phases of either. This is important to keep in mind. IPA SRA removes the first one with index zero as useless, IPA-CP wants to remove the second one with index 1, possibly because it is constant everywhere. In oder to that it has to combine the pre-existing adjustments with its own changes. Before create_specialized_node, the pass checks whether previous passes did not kill some parameters and stops caring about them, but it does not re-index anything, all lattices, jump functions, everything, still keep their positions (and thus indices) they got in the analysis phase. Then create_specialized_node hits this loop. For i=0 encounters an old_adj element that actually describes the parameter which originally had index 1. The pass looks up in base_index what the original (pre-IPA) index of the parameter was (1) and uses those to look up in its own structures whether it wants to remove it or not. Bounds should be always OK, base_index should never be greater than the original pre-IPA number of parameters (-1) and known_csts should always have just as many parameters. Does that make sense?
