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, 2 insertions, 2 deletions

diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/templates.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/templates.cpp
index e40761770d5..31213c9ebc3 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/templates.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/templates.cpp
@@ -139,11 +139,11 @@ namespace NonLocalLambdaInstantation {
   }
 
   template<typename T>
-  struct X2 { // expected-note{{in instantiation of default member initializer 'NonLocalLambdaInstantation::X2<int *>::x' requested here}}
+  struct X2 {
     int x = []{ return T(); }(); // expected-error{{cannot initialize a member subobject of type 'int' with an rvalue of type 'int *'}}
   };
 
   X2<int> x2i;
   X2<float> x2f;
-  X2<int*> x2ip; // expected-note{{implicit default constructor for 'NonLocalLambdaInstantation::X2<int *>' first required here}}
+  X2<int*> x2ip; // expected-note{{in instantiation of default member initializer 'NonLocalLambdaInstantation::X2<int *>::x'}}
 }