Change skip_empty_or_deleted to not use groups.

Motivation: this makes it simpler to change the iteration algorithm to allow for random iteration order for single group tables using aligned groups.
PiperOrigin-RevId: 783881315
Change-Id: I29d9d9584f677b2a809303c464dad093dd131746

Author: ezbr

absl/container/internal/raw_hash_set.cc

@@ -45,15 +45,9 @@ constexpr ctrl_t ZeroCtrlT() { return static_cast<ctrl_t>(0); }
 // uninitialized because reading this memory is a bug.
 ABSL_DLL ctrl_t kDefaultIterControl;
 
-// We need one full byte followed by a sentinel byte for iterator::operator++ to
-// work. We have a full group after kSentinel to be safe (in case operator++ is
-// changed to read a full group).
-ABSL_CONST_INIT ABSL_DLL const ctrl_t kSooControl[17] = {
-    ZeroCtrlT(),    ctrl_t::kSentinel, ZeroCtrlT(),    ctrl_t::kEmpty,
-    ctrl_t::kEmpty, ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty,
-    ctrl_t::kEmpty, ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty,
-    ctrl_t::kEmpty, ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty,
-    ctrl_t::kEmpty};
+// We need one full byte followed by a sentinel byte for iterator::operator++.
+ABSL_CONST_INIT ABSL_DLL const ctrl_t kSooControl[2] = {ZeroCtrlT(),
+                                                        ctrl_t::kSentinel};
 
 namespace {
 

absl/container/internal/raw_hash_set.h

@@ -389,7 +389,7 @@ inline ctrl_t* DefaultIterControl() { return &kDefaultIterControl; }
 // For use in SOO iterators.
 // TODO(b/289225379): we could potentially get rid of this by adding an is_soo
 // bit in iterators. This would add branches but reduce cache misses.
-ABSL_DLL extern const ctrl_t kSooControl[17];
+ABSL_DLL extern const ctrl_t kSooControl[2];
 
 // Returns a pointer to a full byte followed by a sentinel byte.
 inline ctrl_t* SooControl() {
@@ -2052,20 +2052,8 @@ class raw_hash_set {
     // `slot_` until they reach one.
     void skip_empty_or_deleted() {
       while (IsEmptyOrDeleted(*ctrl_)) {
-        auto mask = GroupFullEmptyOrDeleted{ctrl_}.MaskFullOrSentinel();
-        // Generally it is possible to compute `shift` branchless.
-        // This branch is useful to:
-        // 1. Avoid checking `IsEmptyOrDeleted` after the shift for the most
-        //    common dense table case.
-        // 2. Avoid the cost of `LowestBitSet` for extremely sparse tables.
-        if (ABSL_PREDICT_TRUE(mask)) {
-          auto shift = mask.LowestBitSet();
-          ctrl_ += shift;
-          slot_ += shift;
-          return;
-        }
-        ctrl_ += Group::kWidth;
-        slot_ += Group::kWidth;
+        ++ctrl_;
+        ++slot_;
       }
     }