https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71166
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> --- (In reply to Nathan Sidwell from comment #4) > build_vec_init_elt (tree.c) says: > > /* Subroutine of build_vec_init_expr: Build up a single element > intialization as a proxy for the full array initialization to get things > marked as used and any appropriate diagnostics. > > Since we're deferring building the actual constructor calls until > gimplification time, we need to build one now and throw it away so > that the relevant constructor gets mark_used before cgraph decides > what functions are needed. Here we assume that init is either > NULL_TREE, void_type_node (indicating value-initialization), or > another array to copy. */ > > With constexprs now in play, that appears to be an incorrect approach. I'm > not sure why it's even sensible to go building things early only to throw > them away and redo it. It would seem better to just build the constructor > (or whatever) tree and keep it. I was trying with VEC_INIT_EXPR to get the same "floating initialization of an object to be determined later" semantics that we have with AGGR_INIT_EXPR, but indeed deferring all that building until after we've thrown away a lot of front end information doesn't make sense. For GCC 6 the minimal fix would be to disable try_const if (at_eof > 1), but for GCC 7 we should reconsider VEC_INIT_EXPR entirely.
