Changes imported from Abseil "staging" branch:

  - 8320b38cd9f4f271fb6b278bd1e10d93f6ac3856 Use overloads for int32/int64/uint32/uint64 rather than i... by Jorg Brown <jorg@google.com>
  - f8b582b8deb3f78a3c6de2114b3ec4640f5427dd Internal change by Juemin Yang <jueminyang@google.com>
  - 240ff55ebf493ab1233ebe6976853a5fa2b3ec46 Remove the internal LowLevelAlloc's dependence on kLinker... by Greg Falcon <gfalcon@google.com>

GitOrigin-RevId: 8320b38cd9f4f271fb6b278bd1e10d93f6ac3856
Change-Id: If5004efa2b43856948390ab357b8e9403e4461b4

5 files changed, 231 insertions, 179 deletions

diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index 6f3cfe4cbdae..02bb030f5e5a 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -305,6 +305,7 @@
   __attribute__((section(#name))) __attribute__((noinline))
 #endif
 
+
 // ABSL_ATTRIBUTE_SECTION_VARIABLE
 //
 // Tells the compiler/linker to put a given variable into a section and define
@@ -344,6 +345,7 @@
   (reinterpret_cast<void *>(__start_##name))
 #define ABSL_ATTRIBUTE_SECTION_STOP(name) \
   (reinterpret_cast<void *>(__stop_##name))
+
 #else  // !ABSL_HAVE_ATTRIBUTE_SECTION
 
 #define ABSL_HAVE_ATTRIBUTE_SECTION 0
@@ -356,6 +358,7 @@
 #define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name)
 #define ABSL_ATTRIBUTE_SECTION_START(name) (reinterpret_cast<void *>(0))
 #define ABSL_ATTRIBUTE_SECTION_STOP(name) (reinterpret_cast<void *>(0))
+
 #endif  // ABSL_ATTRIBUTE_SECTION
 
 // ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC
diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index 8e2f9c98798b..962232433665 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -19,6 +19,9 @@
 
 #include "absl/base/internal/low_level_alloc.h"
 
+#include <type_traits>
+
+#include "absl/base/call_once.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/scheduling_mode.h"
 #include "absl/base/macros.h"
@@ -194,43 +197,80 @@ static void LLA_SkiplistDelete(AllocList *head, AllocList *e,
 // ---------------------------------------------------------------------------
 // Arena implementation
 
+// Metadata for an LowLevelAlloc arena instance.
 struct LowLevelAlloc::Arena {
-  // This constructor does nothing, and relies on zero-initialization to get
-  // the proper initial state.
-  Arena() : mu(base_internal::kLinkerInitialized) {}  // NOLINT
-  explicit Arena(int)  // NOLINT(readability/casting)
-      :  // Avoid recursive cooperative scheduling w/ kernel scheduling.
-        mu(base_internal::SCHEDULE_KERNEL_ONLY),
-        // Set pagesize to zero explicitly for non-static init.
-        pagesize(0),
-        random(0) {}
-
-  base_internal::SpinLock mu;   // protects freelist, allocation_count,
-                                // pagesize, roundup, min_size
-  AllocList freelist;           // head of free list; sorted by addr (under mu)
-  int32_t allocation_count;     // count of allocated blocks (under mu)
-  std::atomic<uint32_t> flags;  // flags passed to NewArena (ro after init)
-  size_t pagesize;              // ==getpagesize()  (init under mu, then ro)
-  size_t roundup;               // lowest 2^n >= max(16,sizeof (AllocList))
-                                // (init under mu, then ro)
-  size_t min_size;              // smallest allocation block size
-                                // (init under mu, then ro)
-  uint32_t random;              // PRNG state
+  // Constructs an arena with the given LowLevelAlloc flags.
+  explicit Arena(uint32_t flags_value);
+
+  base_internal::SpinLock mu;
+  // Head of free list, sorted by address
+  AllocList freelist GUARDED_BY(mu);
+  // Count of allocated blocks
+  int32_t allocation_count GUARDED_BY(mu);
+  // flags passed to NewArena
+  const uint32_t flags;
+  // Result of getpagesize()
+  const size_t pagesize;
+  // Lowest power of two >= max(16, sizeof(AllocList))
+  const size_t roundup;
+  // Smallest allocation block size
+  const size_t min_size;
+  // PRNG state
+  uint32_t random GUARDED_BY(mu);
 };
 
-// The default arena, which is used when 0 is passed instead of an Arena
-// pointer.
-static struct LowLevelAlloc::Arena default_arena;  // NOLINT
+namespace {
+using ArenaStorage = std::aligned_storage<sizeof(LowLevelAlloc::Arena),
+                                          alignof(LowLevelAlloc::Arena)>::type;
+
+// Static storage space for the lazily-constructed, default global arena
+// instances.  We require this space because the whole point of LowLevelAlloc
+// is to avoid relying on malloc/new.
+ArenaStorage default_arena_storage;
+ArenaStorage unhooked_arena_storage;
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
+ArenaStorage unhooked_async_sig_safe_arena_storage;
+#endif
+
+// We must use LowLevelCallOnce here to construct the global arenas, rather than
+// using function-level statics, to avoid recursively invoking the scheduler.
+absl::once_flag create_globals_once;
+
+void CreateGlobalArenas() {
+  new (&default_arena_storage)
+      LowLevelAlloc::Arena(LowLevelAlloc::kCallMallocHook);
+  new (&unhooked_arena_storage) LowLevelAlloc::Arena(0);
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
+  new (&unhooked_async_sig_safe_arena_storage)
+      LowLevelAlloc::Arena(LowLevelAlloc::kAsyncSignalSafe);
+#endif
+}
 
-// Non-malloc-hooked arenas: used only to allocate metadata for arenas that
-// do not want malloc hook reporting, so that for them there's no malloc hook
-// reporting even during arena creation.
-static struct LowLevelAlloc::Arena unhooked_arena;  // NOLINT
+// Returns a global arena that does not call into hooks.  Used by NewArena()
+// when kCallMallocHook is not set.
+LowLevelAlloc::Arena* UnhookedArena() {
+  base_internal::LowLevelCallOnce(&create_globals_once, CreateGlobalArenas);
+  return reinterpret_cast<LowLevelAlloc::Arena*>(&unhooked_arena_storage);
+}
 
 #ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
-static struct LowLevelAlloc::Arena unhooked_async_sig_safe_arena;  // NOLINT
+// Returns a global arena that is async-signal safe.  Used by NewArena() when
+// kAsyncSignalSafe is set.
+LowLevelAlloc::Arena *UnhookedAsyncSigSafeArena() {
+  base_internal::LowLevelCallOnce(&create_globals_once, CreateGlobalArenas);
+  return reinterpret_cast<LowLevelAlloc::Arena *>(
+      &unhooked_async_sig_safe_arena_storage);
+}
 #endif
 
+}  // namespace
+
+// Returns the default arena, as used by LowLevelAlloc::Alloc() and friends.
+LowLevelAlloc::Arena *LowLevelAlloc::DefaultArena() {
+  base_internal::LowLevelCallOnce(&create_globals_once, CreateGlobalArenas);
+  return reinterpret_cast<LowLevelAlloc::Arena*>(&default_arena_storage);
+}
+
 // magic numbers to identify allocated and unallocated blocks
 static const uintptr_t kMagicAllocated = 0x4c833e95U;
 static const uintptr_t kMagicUnallocated = ~kMagicAllocated;
@@ -242,9 +282,7 @@ class SCOPED_LOCKABLE ArenaLock {
       EXCLUSIVE_LOCK_FUNCTION(arena->mu)
       : arena_(arena) {
 #ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
-    if (arena == &unhooked_async_sig_safe_arena ||
-        (arena->flags.load(std::memory_order_relaxed) &
-         LowLevelAlloc::kAsyncSignalSafe) != 0) {
+    if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
       sigset_t all;
       sigfillset(&all);
       mask_valid_ = pthread_sigmask(SIG_BLOCK, &all, &mask_) == 0;
@@ -281,118 +319,107 @@ inline static uintptr_t Magic(uintptr_t magic, AllocList::Header *ptr) {
   return magic ^ reinterpret_cast<uintptr_t>(ptr);
 }
 
-// Initialize the fields of an Arena
-static void ArenaInit(LowLevelAlloc::Arena *arena) {
-  if (arena->pagesize == 0) {
+namespace {
+size_t GetPageSize() {
 #ifdef _WIN32
-    SYSTEM_INFO system_info;
-    GetSystemInfo(&system_info);
-    arena->pagesize = std::max(system_info.dwPageSize,
-                               system_info.dwAllocationGranularity);
+  SYSTEM_INFO system_info;
+  GetSystemInfo(&system_info);
+  return std::max(system_info.dwPageSize, system_info.dwAllocationGranularity);
 #else
-    arena->pagesize = getpagesize();
-#endif
-    // Round up block sizes to a power of two close to the header size.
-    arena->roundup = 16;
-    while (arena->roundup < sizeof (arena->freelist.header)) {
-      arena->roundup += arena->roundup;
-    }
-    // Don't allocate blocks less than twice the roundup size to avoid tiny
-    // free blocks.
-    arena->min_size = 2 * arena->roundup;
-    arena->freelist.header.size = 0;
-    arena->freelist.header.magic =
-        Magic(kMagicUnallocated, &arena->freelist.header);
-    arena->freelist.header.arena = arena;
-    arena->freelist.levels = 0;
-    memset(arena->freelist.next, 0, sizeof (arena->freelist.next));
-    arena->allocation_count = 0;
-    if (arena == &default_arena) {
-      // Default arena should be hooked, e.g. for heap-checker to trace
-      // pointer chains through objects in the default arena.
-      arena->flags.store(LowLevelAlloc::kCallMallocHook,
-                         std::memory_order_relaxed);
-    }
-#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
-    else if (arena ==  // NOLINT(readability/braces)
-             &unhooked_async_sig_safe_arena) {
-      arena->flags.store(LowLevelAlloc::kAsyncSignalSafe,
-                         std::memory_order_relaxed);
-    }
+  return getpagesize();
 #endif
-    else {  // NOLINT(readability/braces)
-      // other arenas' flags may be overridden by client,
-      // but unhooked_arena will have 0 in 'flags'.
-      arena->flags.store(0, std::memory_order_relaxed);
-    }
+}
+
+size_t RoundedUpBlockSize() {
+  // Round up block sizes to a power of two close to the header size.
+  size_t roundup = 16;
+  while (roundup < sizeof(AllocList::Header)) {
+    roundup += roundup;
   }
+  return roundup;
+}
+
+}  // namespace
+
+LowLevelAlloc::Arena::Arena(uint32_t flags_value)
+    : mu(base_internal::SCHEDULE_KERNEL_ONLY),
+      allocation_count(0),
+      flags(flags_value),
+      pagesize(GetPageSize()),
+      roundup(RoundedUpBlockSize()),
+      min_size(2 * roundup),
+      random(0) {
+  freelist.header.size = 0;
+  freelist.header.magic =
+      Magic(kMagicUnallocated, &freelist.header);
+  freelist.header.arena = this;
+  freelist.levels = 0;
+  memset(freelist.next, 0, sizeof(freelist.next));
 }
 
 // L < meta_data_arena->mu
 LowLevelAlloc::Arena *LowLevelAlloc::NewArena(int32_t flags,
                                               Arena *meta_data_arena) {
   ABSL_RAW_CHECK(meta_data_arena != nullptr, "must pass a valid arena");
-  if (meta_data_arena == &default_arena) {
+  if (meta_data_arena == DefaultArena()) {
 #ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
-      meta_data_arena = &unhooked_async_sig_safe_arena;
+      meta_data_arena = UnhookedAsyncSigSafeArena();
     } else  // NOLINT(readability/braces)
 #endif
         if ((flags & LowLevelAlloc::kCallMallocHook) == 0) {
-      meta_data_arena = &unhooked_arena;
+      meta_data_arena = UnhookedArena();
     }
   }
-  // Arena(0) uses the constructor for non-static contexts
   Arena *result =
-    new (AllocWithArena(sizeof (*result), meta_data_arena)) Arena(0);
-  ArenaInit(result);
-  result->flags.store(flags, std::memory_order_relaxed);
+    new (AllocWithArena(sizeof (*result), meta_data_arena)) Arena(flags);
   return result;
 }
 
 // L < arena->mu, L < arena->arena->mu
 bool LowLevelAlloc::DeleteArena(Arena *arena) {
   ABSL_RAW_CHECK(
-      arena != nullptr && arena != &default_arena && arena != &unhooked_arena,
+      arena != nullptr && arena != DefaultArena() && arena != UnhookedArena(),
       "may not delete default arena");
   ArenaLock section(arena);
-  bool empty = (arena->allocation_count == 0);
-  section.Leave();
-  if (empty) {
-    while (arena->freelist.next[0] != nullptr) {
-      AllocList *region = arena->freelist.next[0];
-      size_t size = region->header.size;
-      arena->freelist.next[0] = region->next[0];
-      ABSL_RAW_CHECK(
-          region->header.magic == Magic(kMagicUnallocated, &region->header),
-          "bad magic number in DeleteArena()");
-      ABSL_RAW_CHECK(region->header.arena == arena,
-                     "bad arena pointer in DeleteArena()");
-      ABSL_RAW_CHECK(size % arena->pagesize == 0,
-                     "empty arena has non-page-aligned block size");
-      ABSL_RAW_CHECK(reinterpret_cast<uintptr_t>(region) % arena->pagesize == 0,
-                     "empty arena has non-page-aligned block");
-      int munmap_result;
+  if (arena->allocation_count != 0) {
+    section.Leave();
+    return false;
+  }
+  while (arena->freelist.next[0] != nullptr) {
+    AllocList *region = arena->freelist.next[0];
+    size_t size = region->header.size;
+    arena->freelist.next[0] = region->next[0];
+    ABSL_RAW_CHECK(
+        region->header.magic == Magic(kMagicUnallocated, &region->header),
+        "bad magic number in DeleteArena()");
+    ABSL_RAW_CHECK(region->header.arena == arena,
+                   "bad arena pointer in DeleteArena()");
+    ABSL_RAW_CHECK(size % arena->pagesize == 0,
+                   "empty arena has non-page-aligned block size");
+    ABSL_RAW_CHECK(reinterpret_cast<uintptr_t>(region) % arena->pagesize == 0,
+                   "empty arena has non-page-aligned block");
+    int munmap_result;
 #ifdef _WIN32
-      munmap_result = VirtualFree(region, 0, MEM_RELEASE);
-      ABSL_RAW_CHECK(munmap_result != 0,
-                     "LowLevelAlloc::DeleteArena: VitualFree failed");
+    munmap_result = VirtualFree(region, 0, MEM_RELEASE);
+    ABSL_RAW_CHECK(munmap_result != 0,
+                   "LowLevelAlloc::DeleteArena: VitualFree failed");
 #else
-      if ((arena->flags.load(std::memory_order_relaxed) &
-           LowLevelAlloc::kAsyncSignalSafe) == 0) {
-        munmap_result = munmap(region, size);
-      } else {
-        munmap_result = MallocHook::UnhookedMUnmap(region, size);
-      }
-      if (munmap_result != 0) {
-        ABSL_RAW_LOG(FATAL, "LowLevelAlloc::DeleteArena: munmap failed: %d",
-                     errno);
-      }
-#endif
+    if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
+      munmap_result = munmap(region, size);
+    } else {
+      munmap_result = MallocHook::UnhookedMUnmap(region, size);
+    }
+    if (munmap_result != 0) {
+      ABSL_RAW_LOG(FATAL, "LowLevelAlloc::DeleteArena: munmap failed: %d",
+                   errno);
     }
-    Free(arena);
+#endif
   }
-  return empty;
+  section.Leave();
+  arena->~Arena();
+  Free(arena);
+  return true;
 }
 
 // ---------------------------------------------------------------------------
@@ -479,7 +506,7 @@ void LowLevelAlloc::Free(void *v) {
     ABSL_RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header),
                    "bad magic number in Free()");
     LowLevelAlloc::Arena *arena = f->header.arena;
-    if ((arena->flags.load(std::memory_order_relaxed) & kCallMallocHook) != 0) {
+    if ((arena->flags & kCallMallocHook) != 0) {
       MallocHook::InvokeDeleteHook(v);
     }
     ArenaLock section(arena);
@@ -497,7 +524,6 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
   if (request != 0) {
     AllocList *s;       // will point to region that satisfies request
     ArenaLock section(arena);
-    ArenaInit(arena);
     // round up with header
     size_t req_rnd = RoundUp(CheckedAdd(request, sizeof (s->header)),
                              arena->roundup);
@@ -526,8 +552,7 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
                                MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
       ABSL_RAW_CHECK(new_pages != nullptr, "VirtualAlloc failed");
 #else
-      if ((arena->flags.load(std::memory_order_relaxed) &
-           LowLevelAlloc::kAsyncSignalSafe) != 0) {
+      if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
         new_pages = MallocHook::UnhookedMMap(nullptr, new_pages_size,
             PROT_WRITE|PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
       } else {
@@ -570,20 +595,18 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
 }
 
 void *LowLevelAlloc::Alloc(size_t request) {
-  void *result = DoAllocWithArena(request, &default_arena);
-  if ((default_arena.flags.load(std::memory_order_relaxed) &
-       kCallMallocHook) != 0) {
-    // this call must be directly in the user-called allocator function
-    // for MallocHook::GetCallerStackTrace to work properly
-    MallocHook::InvokeNewHook(result, request);
-  }
+  void *result = DoAllocWithArena(request, DefaultArena());
+  // The default arena always calls the malloc hook.
+  // This call must be directly in the user-called allocator function
+  // for MallocHook::GetCallerStackTrace to work properly
+  MallocHook::InvokeNewHook(result, request);
   return result;
 }
 
 void *LowLevelAlloc::AllocWithArena(size_t request, Arena *arena) {
   ABSL_RAW_CHECK(arena != nullptr, "must pass a valid arena");
   void *result = DoAllocWithArena(request, arena);
-  if ((arena->flags.load(std::memory_order_relaxed) & kCallMallocHook) != 0) {
+  if ((arena->flags & kCallMallocHook) != 0) {
     // this call must be directly in the user-called allocator function
     // for MallocHook::GetCallerStackTrace to work properly
     MallocHook::InvokeNewHook(result, request);
@@ -591,10 +614,6 @@ void *LowLevelAlloc::AllocWithArena(size_t request, Arena *arena) {
   return result;
 }
 
-LowLevelAlloc::Arena *LowLevelAlloc::DefaultArena() {
-  return &default_arena;
-}
-
 }  // namespace base_internal
 }  // namespace absl
 
diff --git a/absl/strings/numbers.cc b/absl/strings/numbers.cc
index ac73f5308225..31f07c72c949 100644
--- a/absl/strings/numbers.cc
+++ b/absl/strings/numbers.cc
@@ -135,16 +135,12 @@ bool SimpleAtob(absl::string_view str, bool* value) {
 }
 
 // ----------------------------------------------------------------------
-// FastInt32ToBuffer()
-// FastUInt32ToBuffer()
-// FastInt64ToBuffer()
-// FastUInt64ToBuffer()
+// FastIntToBuffer() overloads
 //
 // Like the Fast*ToBuffer() functions above, these are intended for speed.
 // Unlike the Fast*ToBuffer() functions, however, these functions write
-// their output to the beginning of the buffer (hence the name, as the
-// output is left-aligned).  The caller is responsible for ensuring that
-// the buffer has enough space to hold the output.
+// their output to the beginning of the buffer.  The caller is responsible
+// for ensuring that the buffer has enough space to hold the output.
 //
 // Returns a pointer to the end of the std::string (i.e. the null character
 // terminating the std::string).
@@ -160,7 +156,7 @@ const char one_ASCII_final_digits[10][2] {
 
 }  // namespace
 
-char* numbers_internal::FastUInt32ToBuffer(uint32_t i, char* buffer) {
+char* numbers_internal::FastIntToBuffer(uint32_t i, char* buffer) {
   uint32_t digits;
   // The idea of this implementation is to trim the number of divides to as few
   // as possible, and also reducing memory stores and branches, by going in
@@ -230,7 +226,7 @@ char* numbers_internal::FastUInt32ToBuffer(uint32_t i, char* buffer) {
   goto lt100_000_000;
 }
 
-char* numbers_internal::FastInt32ToBuffer(int32_t i, char* buffer) {
+char* numbers_internal::FastIntToBuffer(int32_t i, char* buffer) {
   uint32_t u = i;
   if (i < 0) {
     *buffer++ = '-';
@@ -239,12 +235,12 @@ char* numbers_internal::FastInt32ToBuffer(int32_t i, char* buffer) {
     // we write the equivalent expression "0 - u" instead.
     u = 0 - u;
   }
-  return numbers_internal::FastUInt32ToBuffer(u, buffer);
+  return numbers_internal::FastIntToBuffer(u, buffer);
 }
 
-char* numbers_internal::FastUInt64ToBuffer(uint64_t i, char* buffer) {
+char* numbers_internal::FastIntToBuffer(uint64_t i, char* buffer) {
   uint32_t u32 = static_cast<uint32_t>(i);
-  if (u32 == i) return numbers_internal::FastUInt32ToBuffer(u32, buffer);
+  if (u32 == i) return numbers_internal::FastIntToBuffer(u32, buffer);
 
   // Here we know i has at least 10 decimal digits.
   uint64_t top_1to11 = i / 1000000000;
@@ -252,12 +248,12 @@ char* numbers_internal::FastUInt64ToBuffer(uint64_t i, char* buffer) {
   uint32_t top_1to11_32 = static_cast<uint32_t>(top_1to11);
 
   if (top_1to11_32 == top_1to11) {
-    buffer = numbers_internal::FastUInt32ToBuffer(top_1to11_32, buffer);
+    buffer = numbers_internal::FastIntToBuffer(top_1to11_32, buffer);
   } else {
     // top_1to11 has more than 32 bits too; print it in two steps.
     uint32_t top_8to9 = static_cast<uint32_t>(top_1to11 / 100);
     uint32_t mid_2 = static_cast<uint32_t>(top_1to11 - top_8to9 * 100);
-    buffer = numbers_internal::FastUInt32ToBuffer(top_8to9, buffer);
+    buffer = numbers_internal::FastIntToBuffer(top_8to9, buffer);
     PutTwoDigits(mid_2, buffer);
     buffer += 2;
   }
@@ -283,13 +279,13 @@ char* numbers_internal::FastUInt64ToBuffer(uint64_t i, char* buffer) {
   return buffer + 1;
 }
 
-char* numbers_internal::FastInt64ToBuffer(int64_t i, char* buffer) {
+char* numbers_internal::FastIntToBuffer(int64_t i, char* buffer) {
   uint64_t u = i;
   if (i < 0) {
     *buffer++ = '-';
     u = 0 - u;
   }
-  return numbers_internal::FastUInt64ToBuffer(u, buffer);
+  return numbers_internal::FastIntToBuffer(u, buffer);
 }
 
 // Returns the number of leading 0 bits in a 64-bit value.
diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
index 1f3bbcfae596..adf706a4e26e 100644
--- a/absl/strings/numbers.h
+++ b/absl/strings/numbers.h
@@ -81,14 +81,6 @@ bool safe_strto64_base(absl::string_view text, int64_t* value, int base);
 bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base);
 bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base);
 
-// These functions are intended for speed. All functions take an output buffer
-// as an argument and return a pointer to the last byte they wrote, which is the
-// terminating '\0'. At most `kFastToBufferSize` bytes are written.
-char* FastInt32ToBuffer(int32_t i, char* buffer);
-char* FastUInt32ToBuffer(uint32_t i, char* buffer);
-char* FastInt64ToBuffer(int64_t i, char* buffer);
-char* FastUInt64ToBuffer(uint64_t i, char* buffer);
-
 static const int kFastToBufferSize = 32;
 static const int kSixDigitsToBufferSize = 16;
 
@@ -100,6 +92,16 @@ static const int kSixDigitsToBufferSize = 16;
 // Required buffer size is `kSixDigitsToBufferSize`.
 size_t SixDigitsToBuffer(double d, char* buffer);
 
+// These functions are intended for speed. All functions take an output buffer
+// as an argument and return a pointer to the last byte they wrote, which is the
+// terminating '\0'. At most `kFastToBufferSize` bytes are written.
+char* FastIntToBuffer(int32_t, char*);
+char* FastIntToBuffer(uint32_t, char*);
+char* FastIntToBuffer(int64_t, char*);
+char* FastIntToBuffer(uint64_t, char*);
+
+// For enums and integer types that are not an exact match for the types above,
+// use templates to call the appropriate one of the four overloads above.
 template <typename int_type>
 char* FastIntToBuffer(int_type i, char* buffer) {
   static_assert(sizeof(i) <= 64 / 8,
@@ -109,15 +111,15 @@ char* FastIntToBuffer(int_type i, char* buffer) {
   // If one day something like std::is_signed<enum E> works, switch to it.
   if (static_cast<int_type>(1) - 2 < 0) {  // Signed
     if (sizeof(i) > 32 / 8) {           // 33-bit to 64-bit
-      return numbers_internal::FastInt64ToBuffer(i, buffer);
+      return FastIntToBuffer(static_cast<int64_t>(i), buffer);
     } else {  // 32-bit or less
-      return numbers_internal::FastInt32ToBuffer(i, buffer);
+      return FastIntToBuffer(static_cast<int32_t>(i), buffer);
     }
   } else {                     // Unsigned
     if (sizeof(i) > 32 / 8) {  // 33-bit to 64-bit
-      return numbers_internal::FastUInt64ToBuffer(i, buffer);
+      return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
     } else {  // 32-bit or less
-      return numbers_internal::FastUInt32ToBuffer(i, buffer);
+      return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
     }
   }
 }
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
index ff3120f5c57b..a705255c706d 100644
--- a/absl/strings/numbers_test.cc
+++ b/absl/strings/numbers_test.cc
@@ -110,13 +110,38 @@ TEST(ToString, PerfectDtoa) {
   }
 }
 
+template <typename integer>
+struct MyInteger {
+  integer i;
+  explicit constexpr MyInteger(integer i) : i(i) {}
+  constexpr operator integer() const { return i; }
+
+  constexpr MyInteger operator+(MyInteger other) const { return i + other.i; }
+  constexpr MyInteger operator-(MyInteger other) const { return i - other.i; }
+  constexpr MyInteger operator*(MyInteger other) const { return i * other.i; }
+  constexpr MyInteger operator/(MyInteger other) const { return i / other.i; }
+
+  constexpr bool operator<(MyInteger other) const { return i < other.i; }
+  constexpr bool operator<=(MyInteger other) const { return i <= other.i; }
+  constexpr bool operator==(MyInteger other) const { return i == other.i; }
+  constexpr bool operator>=(MyInteger other) const { return i >= other.i; }
+  constexpr bool operator>(MyInteger other) const { return i > other.i; }
+  constexpr bool operator!=(MyInteger other) const { return i != other.i; }
+
+  integer as_integer() const { return i; }
+};
+
+typedef MyInteger<int64_t> MyInt64;
+typedef MyInteger<uint64_t> MyUInt64;
+
 void CheckInt32(int32_t x) {
   char buffer[absl::numbers_internal::kFastToBufferSize];
-  char* actual = absl::numbers_internal::FastInt32ToBuffer(x, buffer);
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
   std::string expected = std::to_string(x);
-  ASSERT_TRUE(expected == std::string(buffer, actual))
-      << "Expected \"" << expected << "\", Actual \"" << actual << "\", Input "
-      << x;
+  EXPECT_EQ(expected, std::string(buffer, actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  EXPECT_EQ(expected, std::string(buffer, generic_actual)) << " Input " << x;
 }
 
 void CheckInt64(int64_t x) {
@@ -124,40 +149,47 @@ void CheckInt64(int64_t x) {
   buffer[0] = '*';
   buffer[23] = '*';
   buffer[24] = '*';
-  char* actual = absl::numbers_internal::FastInt64ToBuffer(x, &buffer[1]);
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
   std::string expected = std::to_string(x);
-  ASSERT_TRUE(expected == std::string(&buffer[1], actual))
-      << "Expected \"" << expected << "\", Actual \"" << actual << "\", Input "
-      << x;
-  ASSERT_EQ(buffer[0], '*');
-  ASSERT_EQ(buffer[23], '*');
-  ASSERT_EQ(buffer[24], '*');
+  EXPECT_EQ(expected, std::string(&buffer[1], actual)) << " Input " << x;
+  EXPECT_EQ(buffer[0], '*');
+  EXPECT_EQ(buffer[23], '*');
+  EXPECT_EQ(buffer[24], '*');
+
+  char* my_actual =
+      absl::numbers_internal::FastIntToBuffer(MyInt64(x), &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], my_actual)) << " Input " << x;
 }
 
 void CheckUInt32(uint32_t x) {
   char buffer[absl::numbers_internal::kFastToBufferSize];
-  char* actual = absl::numbers_internal::FastUInt32ToBuffer(x, buffer);
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
   std::string expected = std::to_string(x);
-  ASSERT_TRUE(expected == std::string(buffer, actual))
-      << "Expected \"" << expected << "\", Actual \"" << actual << "\", Input "
-      << x;
+  EXPECT_EQ(expected, std::string(buffer, actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  EXPECT_EQ(expected, std::string(buffer, generic_actual)) << " Input " << x;
 }
 
 void CheckUInt64(uint64_t x) {
   char buffer[absl::numbers_internal::kFastToBufferSize + 1];
-  char* actual = absl::numbers_internal::FastUInt64ToBuffer(x, &buffer[1]);
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
   std::string expected = std::to_string(x);
-  ASSERT_TRUE(expected == std::string(&buffer[1], actual))
-      << "Expected \"" << expected << "\", Actual \"" << actual << "\", Input "
-      << x;
+  EXPECT_EQ(expected, std::string(&buffer[1], actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], generic_actual)) << " Input " << x;
+
+  char* my_actual =
+      absl::numbers_internal::FastIntToBuffer(MyUInt64(x), &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], my_actual)) << " Input " << x;
 }
 
 void CheckHex64(uint64_t v) {
   char expected[16 + 1];
   std::string actual = absl::StrCat(absl::Hex(v, absl::kZeroPad16));
   snprintf(expected, sizeof(expected), "%016" PRIx64, static_cast<uint64_t>(v));
-  ASSERT_TRUE(expected == actual)
-      << "Expected \"" << expected << "\", Actual \"" << actual << "\"";
+  EXPECT_EQ(expected, actual) << " Input " << v;
 }
 
 TEST(Numbers, TestFastPrints) {