Call the common case of AllocateBackingArray directly instead of through the function pointer.

Also remove ABSL_ATTRIBUTE_NOINLINE from AllocateBackingArray. I think that was copied unnecessarily from DeallocateBackingArray. DeallocateBackingArray is called directly in some places that we don't want it to be inlined, but AllocateBackingArray is only called by function pointer before this change so it wouldn't have had any effect.

Motivation: calling the allocation function through a function pointer prevents profile-guided-heap-optimization.
PiperOrigin-RevId: 834395282
Change-Id: I930757baf27784b81ee0a8e6596d5a3f31da528a

Author: ezbr

absl/container/internal/raw_hash_set.cc

@@ -19,6 +19,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
+#include <memory>
 #include <tuple>
 #include <utility>
 
@@ -763,7 +764,16 @@ BackingArrayPtrs AllocBackingArray(CommonFields& common,
                                    void* alloc) {
   RawHashSetLayout layout(new_capacity, policy.slot_size, policy.slot_align,
                           has_infoz);
-  char* mem = static_cast<char*>(policy.alloc(alloc, layout.alloc_size()));
+  // Perform a direct call in the common case to allow for profile-guided
+  // heap optimization (PGHO) to understand which allocation function is used.
+  constexpr size_t kDefaultAlignment = BackingArrayAlignment(alignof(size_t));
+  char* mem = static_cast<char*>(
+      ABSL_PREDICT_TRUE(
+          policy.alloc ==
+          (&AllocateBackingArray<kDefaultAlignment, std::allocator<char>>))
+          ? AllocateBackingArray<kDefaultAlignment, std::allocator<char>>(
+                alloc, layout.alloc_size())
+          : policy.alloc(alloc, layout.alloc_size()));
   const GenerationType old_generation = common.generation();
   common.set_generation_ptr(
       reinterpret_cast<GenerationType*>(mem + layout.generation_offset()));

absl/container/internal/raw_hash_set.h

@@ -1492,10 +1492,12 @@ constexpr bool ShouldSampleHashtablezInfoForAlloc() {
 
 // Allocates `n` bytes for a backing array.
 template <size_t AlignOfBackingArray, typename Alloc>
-ABSL_ATTRIBUTE_NOINLINE void* AllocateBackingArray(void* alloc, size_t n) {
+void* AllocateBackingArray(void* alloc, size_t n) {
   return Allocate<AlignOfBackingArray>(static_cast<Alloc*>(alloc), n);
 }
 
+// Note: we mark this function as ABSL_ATTRIBUTE_NOINLINE because we don't want
+// it to be inlined into e.g. the destructor to save code size.
 template <size_t AlignOfBackingArray, typename Alloc>
 ABSL_ATTRIBUTE_NOINLINE void DeallocateBackingArray(
     void* alloc, size_t capacity, ctrl_t* ctrl, size_t slot_size,