[compiler-rt] 8cd51a6 - [NFC][sanitizer] Use power of two in TwoLevelMap

[Vitaly Buka via llvm-commits]

Author: Vitaly Buka
Date: 2021-10-24T18:37:23-07:00
New Revision: 8cd51a69e5b4cf9513eb4f416f113058ebd8f257

URL: https://github.com/llvm/llvm-project/commit/8cd51a69e5b4cf9513eb4f416f113058ebd8f257
DIFF: https://github.com/llvm/llvm-project/commit/8cd51a69e5b4cf9513eb4f416f113058ebd8f257.diff

LOG: [NFC][sanitizer] Use power of two in TwoLevelMap

Using divisions by non power of two makes
a difference on x86_64 and aarch64 benchmarks.

Added: 
    

Modified: 
    compiler-rt/lib/sanitizer_common/sanitizer_flat_map.h

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/sanitizer_common/sanitizer_flat_map.h b/compiler-rt/lib/sanitizer_common/sanitizer_flat_map.h
index 038ee24e6bd8..0f7467c47e73 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_flat_map.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_flat_map.h
@@ -65,6 +65,10 @@ template <typename T, u64 kSize1, u64 kSize2,
           typename AddressSpaceViewTy = LocalAddressSpaceView,
           class MapUnmapCallback = NoOpMapUnmapCallback>
 class TwoLevelMap {
+  static_assert(IsPowerOfTwo(kSize2), "");
+  static constexpr uptr kSize2Shift = Log2(kSize2);
+  static constexpr uptr kSize2Mask = kSize2 - 1;
+
  public:
   using AddressSpaceView = AddressSpaceViewTy;
   void Init() {
@@ -100,19 +104,19 @@ class TwoLevelMap {
 
   bool contains(uptr idx) const {
     CHECK_LT(idx, kSize1 * kSize2);
-    return Get(idx / kSize2);
+    return Get(idx >> kSize2Shift);
   }
 
   const T &operator[](uptr idx) const {
     DCHECK_LT(idx, kSize1 * kSize2);
-    T *map2 = GetOrCreate(idx / kSize2);
-    return *AddressSpaceView::Load(&map2[idx % kSize2]);
+    T *map2 = GetOrCreate(idx >> kSize2Shift);
+    return *AddressSpaceView::Load(&map2[idx & kSize2Mask]);
   }
 
   T &operator[](uptr idx) {
     DCHECK_LT(idx, kSize1 * kSize2);
-    T *map2 = GetOrCreate(idx / kSize2);
-    return *AddressSpaceView::LoadWritable(&map2[idx % kSize2]);
+    T *map2 = GetOrCreate(idx >> kSize2Shift);
+    return *AddressSpaceView::LoadWritable(&map2[idx & kSize2Mask]);
   }
 
  private: