ADT: Make function_ref constexpr

[arsenm]

No description provided.

[arsenm]

• ADT: Make function_ref constexpr #155830 👈 (View in Graphite)
• main

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[llvmbot]

@llvm/pr-subscribers-llvm-adt

Author: Matt Arsenault (arsenm)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/155830.diff

1 Files Affected:

• (modified) llvm/include/llvm/ADT/STLFunctionalExtras.h (+8-8)

diff --git a/llvm/include/llvm/ADT/STLFunctionalExtras.h b/llvm/include/llvm/ADT/STLFunctionalExtras.h
index a4d50dc3648be..2c8d4e07fa5c0 100644
--- a/llvm/include/llvm/ADT/STLFunctionalExtras.h
+++ b/llvm/include/llvm/ADT/STLFunctionalExtras.h
@@ -41,18 +41,18 @@ class LLVM_GSL_POINTER function_ref<Ret(Params...)> {
   Ret (*callback)(intptr_t callable, Params ...params) = nullptr;
   intptr_t callable;
 
-  template<typename Callable>
-  static Ret callback_fn(intptr_t callable, Params ...params) {
+  template <typename Callable>
+  static constexpr Ret callback_fn(intptr_t callable, Params... params) {
     return (*reinterpret_cast<Callable*>(callable))(
         std::forward<Params>(params)...);
   }
 
 public:
-  function_ref() = default;
-  function_ref(std::nullptr_t) {}
+  constexpr function_ref() = default;
+  constexpr function_ref(std::nullptr_t) {}
 
   template <typename Callable>
-  function_ref(
+  constexpr function_ref(
       Callable &&callable LLVM_LIFETIME_BOUND,
       // This is not the copy-constructor.
       std::enable_if_t<!std::is_same<remove_cvref_t<Callable>,
@@ -65,13 +65,13 @@ class LLVM_GSL_POINTER function_ref<Ret(Params...)> {
       : callback(callback_fn<std::remove_reference_t<Callable>>),
         callable(reinterpret_cast<intptr_t>(&callable)) {}
 
-  Ret operator()(Params ...params) const {
+  constexpr Ret operator()(Params... params) const {
     return callback(callable, std::forward<Params>(params)...);
   }
 
-  explicit operator bool() const { return callback; }
+  explicit constexpr operator bool() const { return callback; }
 
-  bool operator==(const function_ref<Ret(Params...)> &Other) const {
+  constexpr bool operator==(const function_ref<Ret(Params...)> &Other) const {
     return callable == Other.callable;
   }
 };

[kuhar]

Can we add a unit test that shows how this is supposed to be used? I'm surprised using reinterpret_cast is allowed...

[jurahul]

Right, my earlier attempts to do the same ran into compiler errors, see https://discourse.llvm.org/t/constexpr-function-ref/87516

[arsenm]

Don't care enough about this to put any effort into it