[ADT] Work around a bug in older compiler versions.

[lhames]

Summary

This patch works around a bug in clang-3.8 that made some uses of the DenseMap initializer list constructor ambiguous. The bug seems to be related to inheriting constructors, so this fix explicitly declares the necessary DenseMapPair constructors.

With my local clang-3.8 build, this change fixes the issue at http://lab.llvm.org:8011/builders/clang-x86_64-linux-abi-test/builds/33980/steps/build-unified-tree/logs/stdio.

Hopefully it will also fix the X-ray bugs we have seen on other builders.

[lhames]

Oops -- forgot to clang-format this. Will do so before applying if it is accepted though.

[dblaikie]

Patch description doesn't seem to immediately relate to the change - nor test cases demonstrating the connection?

[lhames]

• Add non templated constructors for DenseMap, clarify clang version in comment.
• clang-format

[lhames]

In D53726#1276405, @dblaikie wrote:

Patch description doesn't seem to immediately relate to the change - nor test cases demonstrating the connection?

Yep. I fail at 'arc diff' apparently. It seems to have dug up a message from a previous revision.

There is no test case for this issue, as it is a compile failure on currently supported compilers.

[dblaikie]

In D53726#1276569, @lhames wrote:

In D53726#1276405, @dblaikie wrote:

Patch description doesn't seem to immediately relate to the change - nor test cases demonstrating the connection?

Yep. I fail at 'arc diff' apparently. It seems to have dug up a message from a previous revision.

There is no test case for this issue, as it is a compile failure on currently supported compilers.

Ah, cool cool - I see the updated description & such. Makes sense - I'll leave this to @dberris to check on, since he's probably got more context on what the xray buildbots are running, etc.

[lhames]

• Fix a missing &&

[mclow.lists]

Looks promising. I will apply locally this afternoon/evening, and report back.

[mclow.lists]

Works for me! Thanks. Dean?

[dberris]

LGTM -- thanks!

[lhames]

Thanks everyone! Committed in r345411.

include/llvm/ADT/DenseMap.h

 
 namespace detail {
 
 // We extend a pair to allow users to override the bucket type with their own
 // implementation without requiring two members.
 template <typename KeyT, typename ValueT>
 struct DenseMapPair : public std::pair<KeyT, ValueT> {
 
-  using std::pair<KeyT, ValueT>::pair;
+  // FIXME: Switch to inheriting constructors when we drop support for older
+  //        clang versions.
+  // NOTE: This default constructor is declared with '{}' rather than
+  //       '= default' to work around a separate bug in clang-3.8. This can
+  //       also go when we switch to inheriting constructors.
+  DenseMapPair() {}
+
+  DenseMapPair(const KeyT &Key, const ValueT &Value)
+      : std::pair<KeyT, ValueT>(Key, Value) {}
+
+  DenseMapPair(KeyT &&Key, ValueT &&Value)
+      : std::pair<KeyT, ValueT>(std::move(Key), std::move(Value)) {}
+
+  template <typename AltKeyT, typename AltValueT>
+  DenseMapPair(AltKeyT &&AltKey, AltValueT &&AltValue,
+               typename std::enable_if<
+                   std::is_convertible<AltKeyT, KeyT>::value &&
+                   std::is_convertible<AltValueT, ValueT>::value>::type * = 0)
+      : std::pair<KeyT, ValueT>(std::forward<AltKeyT>(AltKey),
+                                std::forward<AltValueT>(AltValue)) {}
+
+  template <typename AltPairT>
+  DenseMapPair(AltPairT &&AltPair,
+               typename std::enable_if<std::is_convertible<
+                   AltPairT, std::pair<KeyT, ValueT>>::value>::type * = 0)
+      : std::pair<KeyT, ValueT>(std::forward<AltPairT>(AltPair)) {}
 
   KeyT &getFirst() { return std::pair<KeyT, ValueT>::first; }
   const KeyT &getFirst() const { return std::pair<KeyT, ValueT>::first; }
   ValueT &getSecond() { return std::pair<KeyT, ValueT>::second; }
   const ValueT &getSecond() const { return std::pair<KeyT, ValueT>::second; }
 };
 
 } // end namespace detail