PR23135: Don't instantiate constexpr functions referenced in unevaluated operands where possible.

This implements something like the current direction of DR1581: we use a narrow
syntactic check to determine the set of places where a constant expression
could be evaluated, and only instantiate a constexpr function or variable if
it's referenced in one of those contexts, or is odr-used.

It's not yet clear whether this is the right set of syntactic locations; we
currently consider all contexts within templates that would result in odr-uses
after instantiation, and contexts within list-initialization (narrowing
conversions take another victim...), as requiring instantiation. We could in
principle restrict the former cases more (only const integral / reference
variable initializers, and contexts in which a constant expression is required,
perhaps). However, this is sufficient to allow us to accept libstdc++ code,
which relies on GCC's behavior (which appears to be somewhat similar to this
approach).

llvm-svn: 291318

1 files changed, 1 insertions, 2 deletions

diff --git a/clang/test/SemaTemplate/instantiate-init.cpp b/clang/test/SemaTemplate/instantiate-init.cpp
index e9be60d16c1..244e94f6d60 100644
--- a/clang/test/SemaTemplate/instantiate-init.cpp
+++ b/clang/test/SemaTemplate/instantiate-init.cpp
@@ -115,9 +115,8 @@ namespace PR13064 {
   struct A { explicit A(int); }; // expected-note{{here}}
   template<typename T> struct B { T a { 0 }; };
   B<A> b;
-  // expected-note@+1 {{in instantiation of default member initializer}}
   template<typename T> struct C { T a = { 0 }; }; // expected-error{{explicit}}
-  C<A> c; // expected-note{{here}}
+  C<A> c; // expected-note {{in instantiation of default member initializer}}
 }
 
 namespace PR16903 {