commit daff1b1a9cd5cf32c7d5409b4844e32e92dde461
author Vitaly Goldshteyn <goldvitaly@google.com> Thu Jun 05 15:20:43 2025 -0700
committer Copybara-Service <copybara-worker@google.com> Thu Jun 05 15:21:30 2025 -0700
tree 767b9690db78910605b88f2ae836d24c4b31b0cd
parent f8c9a088d66521aacde14357d05c6b2a69000b26

Remove unnecessary modification of growth info in small table case.

We still allocate and allow modifying GrowthInfo in some codepathes. In most of the hottest codepathes we know that we don't need to modify or read growth_info for small tables.

It is still allowed to use `ResetGrowthLeft` and get access via `GetGrowthInfoFromControl`. That simplifies general function and avoids extra complexity. In case we decide to go all the way to allocate only a single slot that will need to be changed.

PiperOrigin-RevId: 767785846
Change-Id: Ia66be1044f06ab43d36064edfc8007ea5ae3767e

absl/container/internal/raw_hash_set.cc

diff --git a/absl/container/internal/raw_hash_set.cc b/absl/container/internal/raw_hash_set.cc
index f332320..daa9ff6 100644
--- a/absl/container/internal/raw_hash_set.cc
+++ b/absl/container/internal/raw_hash_set.cc
@@ -522,7 +522,6 @@
 
   if (c.is_small()) {
     SanitizerPoisonMemoryRegion(c.slot_array(), slot_size);
-    c.growth_info().OverwriteFullAsEmpty();
     return;
   }
 
@@ -1433,10 +1432,6 @@
 
   static_assert(NextCapacity(0) == 1);
   PrepareInsertCommon(common);
-  // TODO(b/413062340): maybe don't allocate growth info for capacity 1 tables.
-  // Doing so may require additional branches/complexity so it might not be
-  // worth it.
-  GetGrowthInfoFromControl(new_ctrl).InitGrowthLeftNoDeleted(0);
 
   if (ABSL_PREDICT_FALSE(has_infoz)) {
     ReportSingleGroupTableGrowthToInfoz(common, infoz, get_hash());
@@ -1857,8 +1852,7 @@
   ABSL_SWISSTABLE_ASSERT(!common.empty() || cap > policy.soo_capacity());
   ABSL_SWISSTABLE_ASSERT(cap > 0);
   const size_t max_size_before_growth =
-      cap <= policy.soo_capacity() ? policy.soo_capacity()
-                                   : common.size() + common.growth_left();
+      IsSmallCapacity(cap) ? cap : common.size() + common.growth_left();
   if (new_size <= max_size_before_growth) {
     return;
   }

absl/container/internal/raw_hash_set.h

diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index e9486c3..8228151 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -806,6 +806,9 @@
 // Helper class for computing offsets and allocation size of hash set fields.
 class RawHashSetLayout {
  public:
+  // TODO(b/413062340): maybe don't allocate growth info for capacity 1 tables.
+  // Doing so may require additional branches/complexity so it might not be
+  // worth it.
   explicit RawHashSetLayout(size_t capacity, size_t slot_size,
                             size_t slot_align, bool has_infoz)
       : control_offset_(ControlOffset(has_infoz)),
@@ -965,12 +968,6 @@
       generate_new_seed();
     }
   }
-  void* backing_array_start() const {
-    // growth_info (and maybe infoz) is stored before control bytes.
-    ABSL_SWISSTABLE_ASSERT(
-        reinterpret_cast<uintptr_t>(control()) % alignof(size_t) == 0);
-    return control() - ControlOffset(has_infoz());
-  }
 
   // Note: we can't use slots() because Qt defines "slots" as a macro.
   void* slot_array() const { return heap_or_soo_.slot_array().get(); }
@@ -1031,6 +1028,7 @@
   size_t growth_left() const { return growth_info().GetGrowthLeft(); }
 
   GrowthInfo& growth_info() {
+    ABSL_SWISSTABLE_ASSERT(!is_small());
     return GetGrowthInfoFromControl(control());
   }
   GrowthInfo growth_info() const {
@@ -1040,14 +1038,21 @@
   bool has_infoz() const { return size_.has_infoz(); }
   void set_has_infoz() { size_.set_has_infoz(); }
 
+  HashtablezInfoHandle* infoz_ptr() const {
+    // growth_info is stored before control bytes.
+    ABSL_SWISSTABLE_ASSERT(
+        reinterpret_cast<uintptr_t>(control()) % alignof(size_t) == 0);
+    ABSL_SWISSTABLE_ASSERT(has_infoz());
+    return reinterpret_cast<HashtablezInfoHandle*>(
+        control() - ControlOffset(/*has_infoz=*/true));
+  }
+
   HashtablezInfoHandle infoz() {
-    return has_infoz()
-               ? *reinterpret_cast<HashtablezInfoHandle*>(backing_array_start())
-               : HashtablezInfoHandle();
+    return has_infoz() ? *infoz_ptr() : HashtablezInfoHandle();
   }
   void set_infoz(HashtablezInfoHandle infoz) {
     ABSL_SWISSTABLE_ASSERT(has_infoz());
-    *reinterpret_cast<HashtablezInfoHandle*>(backing_array_start()) = infoz;
+    *infoz_ptr() = infoz;
   }
 
   bool should_rehash_for_bug_detection_on_insert() const {
@@ -3430,16 +3435,13 @@
   //
   // See `CapacityToGrowth()`.
   size_t growth_left() const {
-    ABSL_SWISSTABLE_ASSERT(!is_soo());
     return common().growth_left();
   }
 
   GrowthInfo& growth_info() {
-    ABSL_SWISSTABLE_ASSERT(!is_soo());
     return common().growth_info();
   }
   GrowthInfo growth_info() const {
-    ABSL_SWISSTABLE_ASSERT(!is_soo());
     return common().growth_info();
   }
 
@@ -3485,7 +3487,6 @@
     SooEnabled() ? common().set_empty_soo() : common().decrement_size();
     if (!SooEnabled()) {
       SanitizerPoisonObject(single_slot());
-      growth_info().OverwriteFullAsEmpty();
     }
   }
   iterator single_iterator() {