On further thought, it seems better to maintain the index array from the start, allowing complete replacement of the linear list searches. We can add a separate bool flag to denote frozen-ness.
+1 for 0001 patch. Now we process plain Vars and PlaceHolderVars in a more consistent way when building joinrel's tlist. And this change would make it easier to build up phnullingrels for PHVs as we climb up the join tree.
BTW, the comment just above the two calls to build_joinrel_tlist says:
* Create a new tlist containing just the vars that need to be output from
Here by 'vars' it means both plain Vars and PlaceHolderVars, right? If not we may need to adjust this comment to also include PlaceHolderVars.
0002 patch looks good to me. Glad we can get rid of create_new_ph flag. A minor comment is that seems we can get rid of phid inside PlaceHolderInfo, since we do not do linear list searches any more. It's some duplicate to the phid inside PlaceHolderVar. Currently there are two places referencing PlaceHolderInfo->phid, remove_rel_from_query and find_placeholder_info. We can use PlaceHolderVar->phid instead in both the two places.
