https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85827
--- Comment #3 from Matthias Kretz <kretz at kde dot org> --- But macros are different. They remove the code before the C++ parser sees it (at least as-if). One great improvement of constexpr-if over macros is that all the other branches are parsed and their syntax checked. E.g. it requires the mentioned names to exist. This doesn't compile (cf. https://godbolt.org/g/iCRPDv): #ifdef HAVE_FOO constexpr bool have_foo = true; void foo(); #else constexpr bool have_foo = false; #endif void f() { if constexpr (have_foo) { foo(); } } So, the frontend parses all branches anyway. It should be able to see that _2 and _3 are referenced in f<1>().
