From 5fc99498fc68f9c00d4c478efcddbfe5bd3fb602 Mon Sep 17 00:00:00 2001
From: Daniel Varga <dvarga@mozilla.com>
Date: Sat, 20 Jul 2019 02:03:50 +0300
Subject: [PATCH] Backed out changeset 1f9ee99573c0 (bug 1566195) for build
 bustage at workspace/build/src/js/src/ds/BitArray.h. On a CLOSED TREE

---
 js/src/ds/BitArray.h    | 30 +-----------------------------
 js/src/gc/Marking.cpp   |  9 +++------
 js/src/gc/StoreBuffer.h | 10 +---------
 3 files changed, 5 insertions(+), 44 deletions(-)

diff --git a/js/src/ds/BitArray.h b/js/src/ds/BitArray.h
index 8105ac5f2ab3..e5e8d032ad4b 100644
--- a/js/src/ds/BitArray.h
+++ b/js/src/ds/BitArray.h
@@ -7,7 +7,6 @@
 #ifndef ds_BitArray_h
 #define ds_BitArray_h
 
-#include "mozilla/MathAlgorithms.h"
 #include "mozilla/TemplateLib.h"
 
 #include <limits.h>
@@ -17,34 +16,15 @@
 
 namespace js {
 
-namespace detail {
-
-template <typename WordT>
-uint8_fast_t CountTrailingZeroes(WordT word);
-
-template<>
-uint8_fast_t CountTrailingZeroes(uint32_t word) {
-  return mozilla::CountTrailingZeroes32(word);
-}
-
-template<>
-uint8_fast_t CountTrailingZeroes(uint64_t word) {
-  return mozilla::CountTrailingZeroes64(word);
-}
-
-} // namespace detail
-
 template <size_t nbits>
 class BitArray {
- public:
+ private:
   // Use a 32 bit word to make it easier to access a BitArray from JIT code.
   using WordT = uint32_t;
 
   static const size_t bitsPerElement = sizeof(WordT) * CHAR_BIT;
   static const size_t numSlots =
       nbits / bitsPerElement + (nbits % bitsPerElement == 0 ? 0 : 1);
-
- private:
   static const size_t paddingBits = (numSlots * bitsPerElement) - nbits;
   static_assert(paddingBits < bitsPerElement,
                 "More padding bits than expected.");
@@ -66,7 +46,6 @@ class BitArray {
     size_t index;
     WordT mask;
     getIndexAndMask(offset, &index, &mask);
-    MOZ_ASSERT(index < numSlots);
     return map[index] & mask;
   }
 
@@ -93,14 +72,7 @@ class BitArray {
     return true;
   }
 
-  // For iterating over the set bits in the bit array, get a word at a time.
-  WordT getWord(size_t elementIndex) const {
-    MOZ_ASSERT(elementIndex < numSlots);
-    return map[elementIndex];
-  }
-
   static void getIndexAndMask(size_t offset, size_t* indexp, WordT* maskp) {
-    MOZ_ASSERT(offset < numSlots);
     static_assert(bitsPerElement == 32, "unexpected bitsPerElement value");
     *indexp = offset / bitsPerElement;
     *maskp = WordT(1) << (offset % bitsPerElement);
diff --git a/js/src/gc/Marking.cpp b/js/src/gc/Marking.cpp
index 51dc9baf309a..c2f2a3182a05 100644
--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -2883,14 +2883,11 @@ static inline void TraceWholeCell(TenuringTracer& mover,
 template <typename T>
 static void TraceBufferedCells(TenuringTracer& mover, Arena* arena,
                                ArenaCellSet* cells) {
-  for (size_t i = 0; i < MaxArenaCellIndex; i += cells->BitsPerWord) {
-    ArenaCellSet::WordT bitset = cells->getWord(i / cells->BitsPerWord);
-    while (bitset) {
-      int bit = i + js::detail::CountTrailingZeroes(bitset);
+  for (size_t i = 0; i < MaxArenaCellIndex; i++) {
+    if (cells->hasCell(i)) {
       auto cell =
-          reinterpret_cast<T*>(uintptr_t(arena) + ArenaCellIndexBytes * bit);
+          reinterpret_cast<T*>(uintptr_t(arena) + ArenaCellIndexBytes * i);
       TraceWholeCell(mover, cell);
-      bitset &= bitset - 1;  // Clear the low bit.
     }
   }
 }
diff --git a/js/src/gc/StoreBuffer.h b/js/src/gc/StoreBuffer.h
index 294f1c0b37de..585f119116c7 100644
--- a/js/src/gc/StoreBuffer.h
+++ b/js/src/gc/StoreBuffer.h
@@ -504,8 +504,6 @@ class StoreBuffer {
 class ArenaCellSet {
   friend class StoreBuffer;
 
-  using ArenaCellBits = BitArray<MaxArenaCellIndex>;
-
   // The arena this relates to.
   Arena* arena;
 
@@ -513,7 +511,7 @@ class ArenaCellSet {
   ArenaCellSet* next;
 
   // Bit vector for each possible cell start position.
-  ArenaCellBits bits;
+  BitArray<MaxArenaCellIndex> bits;
 
 #ifdef DEBUG
   // The minor GC number when this was created. This object should not survive
@@ -533,10 +531,6 @@ class ArenaCellSet {
   }
 
  public:
-  using WordT = ArenaCellBits::WordT;
-  const size_t BitsPerWord = ArenaCellBits::bitsPerElement;
-  const size_t NumWords = ArenaCellBits::numSlots;
-
   ArenaCellSet(Arena* arena, ArenaCellSet* next);
 
   bool hasCell(const TenuredCell* cell) const {
@@ -553,8 +547,6 @@ class ArenaCellSet {
 
   void check() const;
 
-  WordT getWord(size_t wordIndex) const { return bits.getWord(wordIndex); }
-
   // Sentinel object used for all empty sets.
   //
   // We use a sentinel because it simplifies the JIT code slightly as we can