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, 0 deletions

diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 806a3d813ee..c9aa99ee383 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -134,6 +134,7 @@ static IMAKind ClassifyImplicitMemberAccess(Sema &SemaRef,
   assert(!AbstractInstanceResult);
   switch (SemaRef.ExprEvalContexts.back().Context) {
   case Sema::Unevaluated:
+  case Sema::UnevaluatedList:
     if (isField && SemaRef.getLangOpts().CPlusPlus11)
       AbstractInstanceResult = IMA_Field_Uneval_Context;
     break;