[llvm] [ADT][NFCI]: Fix iterator category for graph iterators with external … (PR #116403)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-adt

Author: Mészáros Gergely (Maetveis)

<details>
<summary>Changes</summary>

…storage

Set the iterator category for graph iterators to input_iterator_tag when the visited set is stored externally. In that case we can't provide multi-pass guarantee, so we should not claim to be a forward iterator.

Fixes: #<!-- -->116400

---
Full diff: https://github.com/llvm/llvm-project/pull/116403.diff


2 Files Affected:

- (modified) llvm/include/llvm/ADT/DepthFirstIterator.h (+5-1) 
- (modified) llvm/include/llvm/ADT/PostOrderIterator.h (+5-1) 


``````````diff
diff --git a/llvm/include/llvm/ADT/DepthFirstIterator.h b/llvm/include/llvm/ADT/DepthFirstIterator.h
index 71053c2d0d8a8e..4ced758343806e 100644
--- a/llvm/include/llvm/ADT/DepthFirstIterator.h
+++ b/llvm/include/llvm/ADT/DepthFirstIterator.h
@@ -39,6 +39,7 @@
 #include "llvm/ADT/iterator_range.h"
 #include <iterator>
 #include <optional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -84,7 +85,10 @@ template <class GraphT,
           bool ExtStorage = false, class GT = GraphTraits<GraphT>>
 class df_iterator : public df_iterator_storage<SetType, ExtStorage> {
 public:
-  using iterator_category = std::forward_iterator_tag;
+  // When External storage is used we are not multi-pass safe.
+  using iterator_category =
+      std::conditional_t<ExtStorage, std::input_iterator_tag,
+                         std::forward_iterator_tag>;
   using value_type = typename GT::NodeRef;
   using difference_type = std::ptrdiff_t;
   using pointer = value_type *;
diff --git a/llvm/include/llvm/ADT/PostOrderIterator.h b/llvm/include/llvm/ADT/PostOrderIterator.h
index edf0401a751708..1cbd3c170052c7 100644
--- a/llvm/include/llvm/ADT/PostOrderIterator.h
+++ b/llvm/include/llvm/ADT/PostOrderIterator.h
@@ -23,6 +23,7 @@
 #include <iterator>
 #include <optional>
 #include <set>
+#include <type_traits>
 #include <utility>
 
 namespace llvm {
@@ -95,7 +96,10 @@ template <class GraphT,
           bool ExtStorage = false, class GT = GraphTraits<GraphT>>
 class po_iterator : public po_iterator_storage<SetType, ExtStorage> {
 public:
-  using iterator_category = std::forward_iterator_tag;
+  // When External storage is used we are not multi-pass safe.
+  using iterator_category =
+      std::conditional_t<ExtStorage, std::input_iterator_tag,
+                         std::forward_iterator_tag>;
   using value_type = typename GT::NodeRef;
   using difference_type = std::ptrdiff_t;
   using pointer = value_type *;

``````````

</details>


https://github.com/llvm/llvm-project/pull/116403