[clang][Interp] Fix SourceLocExpr used in CXXDefaultInitExprs

... when initializing.

Fixes a problem pointed out in https://reviews.llvm.org/D156045/

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2152,12 +2152,11 @@ bool ByteCodeExprGen<Emitter>::VisitCXXMemberCallExpr(
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCXXDefaultInitExpr(
     const CXXDefaultInitExpr *E) {
-
+  SourceLocScope<Emitter> SLS(this, E);
   if (Initializing)
     return this->visitInitializer(E->getExpr());
 
   assert(classify(E->getType()));
-  SourceLocScope<Emitter> SLS(this, E);
   return this->visit(E->getExpr());
 }
 

clang/test/AST/Interp/builtin-functions.cpp

@@ -248,4 +248,15 @@ namespace SourceLocation {
   };
 
   static_assert(Foo{}.a == __LINE__, "");
+
+  struct AA {
+    int n = __builtin_LINE();
+  };
+  struct B {
+    AA a = {};
+  };
+  constexpr void f() {
+    constexpr B c = {};
+    static_assert(c.a.n == __LINE__ - 1, "");
+  }
 }