1 files changed, 21 insertions, 1 deletions
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 8b77e01f4e8..1b744c82a09 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2245,12 +2245,16 @@ void VarDecl::setInit(Expr *I) {
   Init = I;
 }
 
-bool VarDecl::isUsableInConstantExpressions(ASTContext &C) const {
+bool VarDecl::mightBeUsableInConstantExpressions(ASTContext &C) const {
   const LangOptions &Lang = C.getLangOpts();
 
   if (!Lang.CPlusPlus)
     return false;
 
+  // Function parameters are never usable in constant expressions.
+  if (isa<ParmVarDecl>(this))
+    return false;
+
   // In C++11, any variable of reference type can be used in a constant
   // expression if it is initialized by a constant expression.
   if (Lang.CPlusPlus11 && getType()->isReferenceType())
@@ -2272,6 +2276,22 @@ bool VarDecl::isUsableInConstantExpressions(ASTContext &C) const {
   return Lang.CPlusPlus11 && isConstexpr();
 }
 
+bool VarDecl::isUsableInConstantExpressions(ASTContext &Context) const {
+  // C++2a [expr.const]p3:
+  //   A variable is usable in constant expressions after its initializing
+  //   declaration is encountered...
+  const VarDecl *DefVD = nullptr;
+  const Expr *Init = getAnyInitializer(DefVD);
+  if (!Init || Init->isValueDependent())
+    return false;
+  //   ... if it is a constexpr variable, or it is of reference type or of
+  //   const-qualified integral or enumeration type, ...
+  if (!DefVD->mightBeUsableInConstantExpressions(Context))
+    return false;
+  //   ... and its initializer is a constant initializer.
+  return DefVD->checkInitIsICE();
+}
+
 /// Convert the initializer for this declaration to the elaborated EvaluatedStmt
 /// form, which contains extra information on the evaluated value of the
 /// initializer.