[llvm] [Support] Consolidate the two implementations of Recycler::clear (NFC) (PR #165081)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/165081

This patch consolidates the two implementations of Recycler::clear
with "if constexpr" for simplicity.


>From d8c87ba110374acb5fb1d520f2ee666a96feba96 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Wed, 10 Sep 2025 20:30:25 -0700
Subject: [PATCH] [Support] Consolidate the two implementations of
 Recycler::clear (NFC)

This patch consolidates the two implementations of Recycler::clear
with "if constexpr" for simplicity.
---
 llvm/include/llvm/Support/Recycler.h | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/llvm/include/llvm/Support/Recycler.h b/llvm/include/llvm/Support/Recycler.h
index b51c58678e653..6502a70dbf89c 100644
--- a/llvm/include/llvm/Support/Recycler.h
+++ b/llvm/include/llvm/Support/Recycler.h
@@ -19,6 +19,7 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
+#include <type_traits>
 
 namespace llvm {
 
@@ -72,19 +73,19 @@ class Recycler {
   /// deleted; calling clear is one way to ensure this.
   template<class AllocatorType>
   void clear(AllocatorType &Allocator) {
-    while (FreeList) {
-      T *t = reinterpret_cast<T *>(pop_val());
-      Allocator.Deallocate(t, Size, Align);
+    if constexpr (std::is_same_v<std::decay_t<AllocatorType>,
+                                 BumpPtrAllocator>) {
+      // For BumpPtrAllocator, Deallocate is a no-op, so just drop the free
+      // list.
+      FreeList = nullptr;
+    } else {
+      while (FreeList) {
+        T *t = reinterpret_cast<T *>(pop_val());
+        Allocator.Deallocate(t, Size, Align);
+      }
     }
   }
 
-  /// Special case for BumpPtrAllocator which has an empty Deallocate()
-  /// function.
-  ///
-  /// There is no need to traverse the free list, pulling all the objects into
-  /// cache.
-  void clear(BumpPtrAllocator &) { FreeList = nullptr; }
-
   template<class SubClass, class AllocatorType>
   SubClass *Allocate(AllocatorType &Allocator) {
     static_assert(alignof(SubClass) <= Align,