constexpr: Implement DR1358: An instantiation of a constexpr function which

can't produce a constant expression is not ill-formed (so long as some
instantiation of that function can produce a constant expression).

llvm-svn: 149802

2 files changed, 4 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6b92b0ad67c..172e931153d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7302,7 +7302,7 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
     }
 
     if (FD && FD->isConstexpr() && !FD->isInvalidDecl() &&
-        !CheckConstexprFunctionBody(FD, Body))
+        !CheckConstexprFunctionBody(FD, Body, IsInstantiation))
       FD->setInvalidDecl();
 
     assert(ExprCleanupObjects.empty() && "Leftover temporaries in function");
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index a52d44c4f2e..10883af4b41 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -837,7 +837,8 @@ static void CheckConstexprCtorInitializer(Sema &SemaRef,
 /// the permitted types of statement. C++11 [dcl.constexpr]p3,p4.
 ///
 /// \return true if the body is OK, false if we have diagnosed a problem.
-bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body) {
+bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body,
+                                      bool IsInstantiation) {
   if (isa<CXXTryStmt>(Body)) {
     // C++11 [dcl.constexpr]p3:
     //  The definition of a constexpr function shall satisfy the following
@@ -989,7 +990,7 @@ bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body) {
   // can't produce constant expressions.
   llvm::SmallVector<PartialDiagnosticAt, 8> Diags;
   if (!Context.getSourceManager().isInSystemHeader(Dcl->getLocation()) &&
-      !Expr::isPotentialConstantExpr(Dcl, Diags)) {
+      !IsInstantiation && !Expr::isPotentialConstantExpr(Dcl, Diags)) {
     Diag(Dcl->getLocation(), diag::err_constexpr_function_never_constant_expr)
       << isa<CXXConstructorDecl>(Dcl);
     for (size_t I = 0, N = Diags.size(); I != N; ++I)