[Support] Use "inline static" to initialize Registry (NFC)

[kazutakahirata]

In C++17, we can initialize a static member variable with "inline
static" as part of the class definition. With this, we can eliminate
the out-of-line static initializers involving boilerplate template
code.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Kazu Hirata (kazutakahirata)

Changes

In C++17, we can initialize a static member variable with "inline
static" as part of the class definition. With this, we can eliminate
the out-of-line static initializers involving boilerplate template
code.

---

Full diff: https://github.com/llvm/llvm-project/pull/160235.diff

1 Files Affected:

• (modified) llvm/include/llvm/Support/Registry.h (+2-10)

diff --git a/llvm/include/llvm/Support/Registry.h b/llvm/include/llvm/Support/Registry.h
index ff9226c39359c..e77a794a12994 100644
--- a/llvm/include/llvm/Support/Registry.h
+++ b/llvm/include/llvm/Support/Registry.h
@@ -58,8 +58,8 @@ namespace llvm {
     // declaration causing error C2487 "member of dll interface class may not
     // be declared with dll interface".
     // https://developercommunity.visualstudio.com/t/c2487-in-dllexport-class-with-static-members/69878
-    static node *Head;
-    static node *Tail;
+    inline static node *Head = nullptr;
+    inline static node *Tail = nullptr;
 
   public:
     /// Node in linked list of entries.
@@ -143,19 +143,11 @@ namespace llvm {
 /// Instantiate a registry class.
 #define LLVM_INSTANTIATE_REGISTRY(REGISTRY_CLASS)                              \
   namespace llvm {                                                             \
-  template <typename T>                                                        \
-  typename Registry<T>::node *Registry<T>::Head = nullptr;                     \
-  template <typename T>                                                        \
-  typename Registry<T>::node *Registry<T>::Tail = nullptr;                     \
   template class LLVM_ABI_EXPORT Registry<REGISTRY_CLASS::type>;               \
   }
 #else
 #define LLVM_INSTANTIATE_REGISTRY(REGISTRY_CLASS)                              \
   namespace llvm {                                                             \
-  template <typename T>                                                        \
-  typename Registry<T>::node *Registry<T>::Head = nullptr;                     \
-  template <typename T>                                                        \
-  typename Registry<T>::node *Registry<T>::Tail = nullptr;                     \
   template class Registry<REGISTRY_CLASS::type>;                               \
   }
 #endif