I've been experimenting with a change to make all inline functions
implicitly constexpr; this revealed that we are instantiating too
aggressively for speculative constant evaluation, leading to ordering
difficulties with e.g. is_a_helper<cgraph_node*>::test. This patch tries to
avoid such instantiation until we actually need the function definition to
determine whether a call is constant, by limiting the initial instantiation
of all used functions to manifestly-constant-evaluated expressions, and
checking whether the function arguments are constant before instantiating
the function.
This change resulted in a change in the diagnostics for a few library tests
due to instantiating the function with the static_assert later (during
constant evaluation) than we did before (during instantiation of the
intermediate function).
gcc/cp/ChangeLog:
* constexpr.c (cxx_bind_parameters_in_call): Replace
new_call parameter with fun.
(cxx_eval_call_expression): Call it before instantiation.
(cxx_eval_outermost_constant_expr): Only instantiate fns
when manifestly_const_eval.
* typeck2.c (check_narrowing): This context is manifestly
constant-evaluated.