[llvm] [Diagnostics] Return rvalue reference from temporary argument (PR #127400)

[Jakub Kuderski via llvm-commits]

================
@@ -613,93 +613,47 @@ class DiagnosticInfoOptimizationBase : public DiagnosticInfoWithLocationBase {
 /// common base class.  This allows returning the result of the insertion
 /// directly by value, e.g. return OptimizationRemarkAnalysis(...) << "blah".
 template <class RemarkT>
-RemarkT &
-operator<<(RemarkT &R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               StringRef>
-               S) {
+decltype(auto) operator<<(
+    RemarkT &&R,
+    std::enable_if_t<std::is_base_of<DiagnosticInfoOptimizationBase,
+                                     std::remove_reference_t<RemarkT>>::value,
+                     StringRef>
+        S) {
   R.insert(S);
-  return R;
+  return std::forward<RemarkT>(R);
 }
 
-/// Also allow r-value for the remark to allow insertion into a
-/// temporarily-constructed remark.
 template <class RemarkT>
-RemarkT &&
-operator<<(RemarkT &&R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               StringRef>
-               S) {
-  R.insert(S);
-  return std::move(R);
-}
-
-template <class RemarkT>
-RemarkT &
-operator<<(RemarkT &R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::Argument>
-               A) {
-  R.insert(A);
-  return R;
-}
-
-template <class RemarkT>
-RemarkT &&
-operator<<(RemarkT &&R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::Argument>
-               A) {
+decltype(auto) operator<<(
+    RemarkT &&R,
+    std::enable_if_t<std::is_base_of<DiagnosticInfoOptimizationBase,
+                                     std::remove_reference_t<RemarkT>>::value,
+                     DiagnosticInfoOptimizationBase::Argument>
+        A) {
   R.insert(A);
-  return std::move(R);
+  return std::forward<RemarkT>(R);
 }
 
 template <class RemarkT>
-RemarkT &
-operator<<(RemarkT &R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::setIsVerbose>
-               V) {
+decltype(auto) operator<<(
+    RemarkT &&R,
+    std::enable_if_t<std::is_base_of<DiagnosticInfoOptimizationBase,
+                                     std::remove_reference_t<RemarkT>>::value,
+                     DiagnosticInfoOptimizationBase::setIsVerbose>
+        V) {
   R.insert(V);
-  return R;
-}
-
-template <class RemarkT>
-RemarkT &&
-operator<<(RemarkT &&R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::setIsVerbose>
-               V) {
-  R.insert(V);
-  return std::move(R);
-}
-
-template <class RemarkT>
-RemarkT &
-operator<<(RemarkT &R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::setExtraArgs>
-               EA) {
-  R.insert(EA);
-  return R;
+  return std::forward<RemarkT>(R);
 }
 
 template <class RemarkT>
-RemarkT &&
-operator<<(RemarkT &&R,
-           std::enable_if_t<
-               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
-               DiagnosticInfoOptimizationBase::setExtraArgs>
-               EA) {
+decltype(auto) operator<<(
+    RemarkT &&R,
+    std::enable_if_t<std::is_base_of<DiagnosticInfoOptimizationBase,
+                                     std::remove_reference_t<RemarkT>>::value,
----------------
kuhar wrote:

```suggestion
    std::enable_if_t<std::is_base_of_v<DiagnosticInfoOptimizationBase,
                                     std::remove_reference_t<RemarkT>>,
```

https://github.com/llvm/llvm-project/pull/127400