[clang][Interp] Handle SubstNonTypeTemplateParmExprs

Differential Revision: https://reviews.llvm.org/D132831

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -231,6 +231,12 @@ bool ByteCodeExprGen<Emitter>::VisitImplicitValueInitExpr(const ImplicitValueIni
   return false;
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitSubstNonTypeTemplateParmExpr(
+    const SubstNonTypeTemplateParmExpr *E) {
+  return this->visit(E->getReplacement());
+}
+
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/true);

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -76,6 +76,7 @@ public:
   bool VisitUnaryOperator(const UnaryOperator *E);
   bool VisitDeclRefExpr(const DeclRefExpr *E);
   bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E);
+  bool VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/test/AST/Interp/functions.cpp

@@ -65,3 +65,11 @@ constexpr int recursion(int i) {
   return recursion(i);
 }
 static_assert(recursion(10) == 0, "");
+
+template<int N = 5>
+constexpr decltype(N) getNum() {
+  return N;
+}
+static_assert(getNum<-2>() == -2, "");
+static_assert(getNum<10>() == 10, "");
+static_assert(getNum() == 5, "");