Index: include/clang/AST/Stmt.h
===================================================================
--- include/clang/AST/Stmt.h
+++ include/clang/AST/Stmt.h
@@ -577,13 +577,24 @@
   /// @endcode
   bool HasLeadingEmptyMacro = false;
 
+  /// \brief True if the null statement was produced by folding a part of the
+  ///        code away, e.g:
+  /// @code
+  ///   if constexpr(0 > 1) { willBeFoldedAway(); }
+  ///   // After constexpr evaluation:
+  ///   if constexpr(0 > 1) ;
+  /// @endcode
+  bool ResultOfConstexprFolding = false;
+
 public:
   friend class ASTStmtReader;
   friend class ASTStmtWriter;
 
-  NullStmt(SourceLocation L, bool hasLeadingEmptyMacro = false)
+  NullStmt(SourceLocation L, bool hasLeadingEmptyMacro = false,
+           bool resultOfConstexprFolding = false)
       : Stmt(NullStmtClass), SemiLoc(L),
-        HasLeadingEmptyMacro(hasLeadingEmptyMacro) {}
+        HasLeadingEmptyMacro(hasLeadingEmptyMacro),
+        ResultOfConstexprFolding(resultOfConstexprFolding) {}
 
   /// \brief Build an empty null statement.
   explicit NullStmt(EmptyShell Empty) : Stmt(NullStmtClass, Empty) {}
@@ -592,6 +603,7 @@
   void setSemiLoc(SourceLocation L) { SemiLoc = L; }
 
   bool hasLeadingEmptyMacro() const { return HasLeadingEmptyMacro; }
+  bool resultOfConstexprFolding() const { return ResultOfConstexprFolding; }
 
   SourceLocation getLocStart() const LLVM_READONLY { return SemiLoc; }
   SourceLocation getLocEnd() const LLVM_READONLY { return SemiLoc; }
Index: lib/Sema/TreeTransform.h
===================================================================
--- lib/Sema/TreeTransform.h
+++ lib/Sema/TreeTransform.h
@@ -6605,7 +6605,9 @@
     if (Then.isInvalid())
       return StmtError();
   } else {
-    Then = new (getSema().Context) NullStmt(S->getThen()->getLocStart());
+    Then = new (getSema().Context) NullStmt(S->getThen()->getLocStart(),
+                                            /*hasLeadingEmptyMacro=*/false,
+                                            /*resultOfConstexprFolding=*/true);
   }
 
   // Transform the "else" branch.