https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69960
--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #14) > C++ FE's constexpr.c has bool lval argument to many recursive functions, so > it can differentiate between cases where you don't want to fold "str"[0] to > 's' and cases where you can do that. It is among other cases set when > processing ADDR_EXPR's operand. But c_fully_fold_internal doesn't have > anything like that, so that would need to be introduced there. >From the related PR66618, it seems that if we had such an argument properly propagated, we could as well use decl_constant_value_for_optimization during c_fully_fold_internal (if not pedantic?) centrally for VAR_DECLs, rather then just using it on selected operands where we basically know for sure we don't need an lvalue. Without such changes, a hack could be to add the ARRAY_REF of STRING_CST with constant index folding into decl_constant_value_for_optimization.
