PR17800: When performing pack expansion, we must always rebuild the AST nodes
to avoid breaking AST invariants by reusing Stmt nodes within the same
function.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194217 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index 2d22e4c..52f6470 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -142,7 +142,11 @@
///
/// Subclasses may override this function to specify when the transformation
/// should rebuild all AST nodes.
- bool AlwaysRebuild() { return false; }
+ ///
+ /// We must always rebuild all AST nodes when performing variadic template
+ /// pack expansion, in order to avoid violating the AST invariant that each
+ /// statement node appears at most once in its containing declaration.
+ bool AlwaysRebuild() { return SemaRef.ArgumentPackSubstitutionIndex != -1; }
/// \brief Returns the location of the entity being transformed, if that
/// information was not available elsewhere in the AST.