[llvm] [Support] Use "inline static" to initialize Registry (NFC) (PR #160235)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/160235

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.


>From a5f1e9d6e8a9ee0ca0a73ae4e8049e6385dc5f2f Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Sun, 21 Sep 2025 12:41:03 -0700
Subject: [PATCH] [Support] Use "inline static" to initialize Registry (NFC)

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.
---
 llvm/include/llvm/Support/Registry.h | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

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