[sanitizer] Size class map & local cache improvements

Summary:
- Reland rL324263, this time allowing for a compile-time decision as to whether
  or not use the 32-bit division. A single test is using a class map covering
  a maximum size greater than 4GB, this can be checked via the template
  parameters, and allows SizeClassAllocator64PopulateFreeListOOM to pass;
- `MaxCachedHint` is always called on a class id for which we have already
  computed the size, but we still recompute `Size(class_id)`. Change the
  prototype of the function to work on sizes instead of class ids. This also
  allows us to get rid of the `kBatchClassID` special case. Update the callers
  accordingly;
- `InitCache` and `Drain` will start iterating at index 1: index 0 contents are
  unused and can safely be left to be 0. Plus we do not pay the cost of going
  through an `UNLIKELY` in `MaxCachedHint`, and touching memory that is
  otherwise not used;
- `const` some variables in the areas modified;
- Remove an spurious extra line at the end of a file.

Reviewers: alekseyshl, tl0gic, dberris

Reviewed By: alekseyshl, dberris

Subscribers: dberris, kubamracek, delcypher, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D43088

llvm-svn: 324906

compiler-rt/lib/sanitizer_common/sanitizer_allocator_local_cache.h

@@ -70,7 +70,7 @@ struct SizeClassAllocator64LocalCache {
   }
 
   void Drain(SizeClassAllocator *allocator) {
-    for (uptr i = 0; i < kNumClasses; i++) {
+    for (uptr i = 1; i < kNumClasses; i++) {
       PerClass *c = &per_class_[i];
       while (c->count > 0)
         Drain(c, allocator, i, c->count);
@@ -94,10 +94,11 @@ struct SizeClassAllocator64LocalCache {
   void InitCache(PerClass *c) {
     if (LIKELY(c->max_count))
       return;
-    for (uptr i = 0; i < kNumClasses; i++) {
+    for (uptr i = 1; i < kNumClasses; i++) {
       PerClass *c = &per_class_[i];
-      c->max_count = 2 * SizeClassMap::MaxCachedHint(i);
-      c->class_size = Allocator::ClassIdToSize(i);
+      const uptr size = Allocator::ClassIdToSize(i);
+      c->max_count = 2 * SizeClassMap::MaxCachedHint(size);
+      c->class_size = size;
     }
     DCHECK_NE(c->max_count, 0UL);
   }
@@ -185,7 +186,7 @@ struct SizeClassAllocator32LocalCache {
   }
 
   void Drain(SizeClassAllocator *allocator) {
-    for (uptr i = 0; i < kNumClasses; i++) {
+    for (uptr i = 1; i < kNumClasses; i++) {
       PerClass *c = &per_class_[i];
       while (c->count > 0)
         Drain(c, allocator, i);
@@ -217,11 +218,12 @@ struct SizeClassAllocator32LocalCache {
     if (LIKELY(c->max_count))
       return;
     const uptr batch_class_id = SizeClassMap::ClassID(sizeof(TransferBatch));
-    for (uptr i = 0; i < kNumClasses; i++) {
+    for (uptr i = 1; i < kNumClasses; i++) {
       PerClass *c = &per_class_[i];
-      uptr max_cached = TransferBatch::MaxCached(i);
+      const uptr size = Allocator::ClassIdToSize(i);
+      const uptr max_cached = TransferBatch::MaxCached(size);
       c->max_count = 2 * max_cached;
-      c->class_size = Allocator::ClassIdToSize(i);
+      c->class_size = size;
       // Precompute the class id to use to store batches for the current class
       // id. 0 means the class size is large enough to store a batch within one
       // of the chunks. If using a separate size class, it will always be
@@ -229,7 +231,7 @@ struct SizeClassAllocator32LocalCache {
       if (kUseSeparateSizeClassForBatch) {
         c->batch_class_id = (i == kBatchClassID) ? 0 : kBatchClassID;
       } else {
-        c->batch_class_id = (c->class_size <
+        c->batch_class_id = (size <
           TransferBatch::AllocationSizeRequiredForNElements(max_cached)) ?
               batch_class_id : 0;
       }
@@ -266,4 +268,3 @@ struct SizeClassAllocator32LocalCache {
     allocator->DeallocateBatch(&stats_, class_id, b);
   }
 };
-

compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h

@@ -84,8 +84,8 @@ class SizeClassAllocator32 {
     static uptr AllocationSizeRequiredForNElements(uptr n) {
       return sizeof(uptr) * 2 + sizeof(void *) * n;
     }
-    static uptr MaxCached(uptr class_id) {
-      return Min(kMaxNumCached, SizeClassMap::MaxCachedHint(class_id));
+    static uptr MaxCached(uptr size) {
+      return Min(kMaxNumCached, SizeClassMap::MaxCachedHint(size));
     }
 
     TransferBatch *next;
@@ -156,10 +156,11 @@ class SizeClassAllocator32 {
     CHECK_LT(class_id, kNumClasses);
     SizeClassInfo *sci = GetSizeClassInfo(class_id);
     SpinMutexLock l(&sci->mutex);
-    if (sci->free_list.empty() &&
-        UNLIKELY(!PopulateFreeList(stat, c, sci, class_id)))
+    if (sci->free_list.empty()) {
+      if (UNLIKELY(!PopulateFreeList(stat, c, sci, class_id)))
         return nullptr;
-    CHECK(!sci->free_list.empty());
+      DCHECK(!sci->free_list.empty());
+    }
     TransferBatch *b = sci->free_list.front();
     sci->free_list.pop_front();
     return b;
@@ -275,7 +276,7 @@ class SizeClassAllocator32 {
   COMPILER_CHECK(sizeof(SizeClassInfo) == kCacheLineSize);
 
   uptr ComputeRegionId(uptr mem) {
-    uptr res = mem >> kRegionSizeLog;
+    const uptr res = mem >> kRegionSizeLog;
     CHECK_LT(res, kNumPossibleRegions);
     return res;
   }
@@ -329,22 +330,22 @@ class SizeClassAllocator32 {
 
   bool PopulateFreeList(AllocatorStats *stat, AllocatorCache *c,
                         SizeClassInfo *sci, uptr class_id) {
-    uptr size = ClassIdToSize(class_id);
-    uptr reg = AllocateRegion(stat, class_id);
-    if (UNLIKELY(!reg))
+    const uptr region = AllocateRegion(stat, class_id);
+    if (UNLIKELY(!region))
       return false;
     if (kRandomShuffleChunks)
       if (UNLIKELY(sci->rand_state == 0))
         // The random state is initialized from ASLR (PIE) and time.
         sci->rand_state = reinterpret_cast<uptr>(sci) ^ NanoTime();
-    uptr n_chunks = kRegionSize / (size + kMetadataSize);
-    uptr max_count = TransferBatch::MaxCached(class_id);
-    CHECK_GT(max_count, 0);
+    const uptr size = ClassIdToSize(class_id);
+    const uptr n_chunks = kRegionSize / (size + kMetadataSize);
+    const uptr max_count = TransferBatch::MaxCached(size);
+    DCHECK_GT(max_count, 0);
     TransferBatch *b = nullptr;
-    const uptr kShuffleArraySize = 48;
+    constexpr uptr kShuffleArraySize = 48;
     uptr shuffle_array[kShuffleArraySize];
     uptr count = 0;
-    for (uptr i = reg; i < reg + n_chunks * size; i += size) {
+    for (uptr i = region; i < region + n_chunks * size; i += size) {
       shuffle_array[count++] = i;
       if (count == kShuffleArraySize) {
         if (UNLIKELY(!PopulateBatches(c, sci, class_id, &b, max_count,

compiler-rt/lib/sanitizer_common/sanitizer_allocator_size_class_map.h

@@ -161,23 +161,24 @@ class SizeClassMap {
       return 0;
     if (size <= kMidSize)
       return (size + kMinSize - 1) >> kMinSizeLog;
-    uptr l = MostSignificantSetBitIndex(size);
-    uptr hbits = (size >> (l - S)) & M;
-    uptr lbits = size & ((1 << (l - S)) - 1);
-    uptr l1 = l - kMidSizeLog;
+    const uptr l = MostSignificantSetBitIndex(size);
+    const uptr hbits = (size >> (l - S)) & M;
+    const uptr lbits = size & ((1U << (l - S)) - 1);
+    const uptr l1 = l - kMidSizeLog;
     return kMidClass + (l1 << S) + hbits + (lbits > 0);
   }
 
-  static uptr MaxCachedHint(uptr class_id) {
-    // Estimate the result for kBatchClassID because this class does not know
-    // the exact size of TransferBatch. We need to cache fewer batches than user
-    // chunks, so this number can be small.
-    if (UNLIKELY(class_id == kBatchClassID))
-      return 16;
-    if (UNLIKELY(class_id == 0))
+  static uptr MaxCachedHint(uptr size) {
+    DCHECK_LE(size, kMaxSize);
+    if (UNLIKELY(size == 0))
       return 0;
-    uptr n = (1UL << kMaxBytesCachedLog) / Size(class_id);
-    return Max<uptr>(1, Min(kMaxNumCachedHint, n));
+    uptr n;
+    // Force a 32-bit division if the template parameters allow for it.
+    if (kMaxBytesCachedLog > 31 || kMaxSizeLog > 31)
+      n = (1UL << kMaxBytesCachedLog) / size;
+    else
+      n = (1U << kMaxBytesCachedLog) / static_cast<u32>(size);
+    return Max<uptr>(1U, Min(kMaxNumCachedHint, n));
   }
 
   static void Print() {
@@ -190,12 +191,12 @@ class SizeClassMap {
       uptr d = s - prev_s;
       uptr p = prev_s ? (d * 100 / prev_s) : 0;
       uptr l = s ? MostSignificantSetBitIndex(s) : 0;
-      uptr cached = MaxCachedHint(i) * s;
+      uptr cached = MaxCachedHint(s) * s;
       if (i == kBatchClassID)
         d = p = l = 0;
       Printf("c%02zd => s: %zd diff: +%zd %02zd%% l %zd "
              "cached: %zd %zd; id %zd\n",
-             i, Size(i), d, p, l, MaxCachedHint(i), cached, ClassID(s));
+             i, Size(i), d, p, l, MaxCachedHint(s), cached, ClassID(s));
       total_cached += cached;
       prev_s = s;
     }