[scudo] Separate Fuchsia & Default SizeClassMap

The Fuchsia allocator config was using the default size class map.

This CL gives Fuchsia its own size class map and changes a couple of
things in the default one:
- make `SizeDelta` configurable in `Config` for a fixed size class map
  as it currently is for a table size class map;
- switch `SizeDelta` to 0 for the default config, it allows for size
  classes that allow for power of 2s, and overall better wrt pages
  filling;
- increase the max number of caches pointers to 14 in the default,
  this makes the transfer batch 64/128 bytes on 32/64-bit platforms,
  which is cache-line friendly (previous size was 48/96 bytes).

The Fuchsia size class map remains untouched for now, this doesn't
impact Android which uses the table size class map.

Differential Revision: https://reviews.llvm.org/D102783

compiler-rt/lib/scudo/standalone/allocator_config.h

@@ -140,7 +140,7 @@ struct AndroidSvelteConfig {
 
 #if SCUDO_CAN_USE_PRIMARY64
 struct FuchsiaConfig {
-  using SizeClassMap = DefaultSizeClassMap;
+  using SizeClassMap = FuchsiaSizeClassMap;
   static const bool MaySupportMemoryTagging = false;
 
   typedef SizeClassAllocator64<FuchsiaConfig> Primary;

compiler-rt/lib/scudo/standalone/size_class_map.h

@@ -64,12 +64,10 @@ class FixedSizeClassMap : public SizeClassMapBase<Config> {
   static const u8 S = Config::NumBits - 1;
   static const uptr M = (1UL << S) - 1;
 
-  static const uptr SizeDelta = Chunk::getHeaderSize();
-
 public:
   static const u32 MaxNumCachedHint = Config::MaxNumCachedHint;
 
-  static const uptr MaxSize = (1UL << Config::MaxSizeLog) + SizeDelta;
+  static const uptr MaxSize = (1UL << Config::MaxSizeLog) + Config::SizeDelta;
   static const uptr NumClasses =
       MidClass + ((Config::MaxSizeLog - Config::MidSizeLog) << S) + 1;
   static_assert(NumClasses <= 256, "");
@@ -79,24 +77,22 @@ public:
   static uptr getSizeByClassId(uptr ClassId) {
     DCHECK_NE(ClassId, BatchClassId);
     if (ClassId <= MidClass)
-      return (ClassId << Config::MinSizeLog) + SizeDelta;
+      return (ClassId << Config::MinSizeLog) + Config::SizeDelta;
     ClassId -= MidClass;
     const uptr T = MidSize << (ClassId >> S);
-    return T + (T >> S) * (ClassId & M) + SizeDelta;
+    return T + (T >> S) * (ClassId & M) + Config::SizeDelta;
   }
 
   static u8 getSizeLSBByClassId(uptr ClassId) {
     return u8(getLeastSignificantSetBitIndex(getSizeByClassId(ClassId)));
   }
 
-  static constexpr bool usesCompressedLSBFormat() {
-    return false;
-  }
+  static constexpr bool usesCompressedLSBFormat() { return false; }
 
   static uptr getClassIdBySize(uptr Size) {
-    if (Size <= SizeDelta + (1 << Config::MinSizeLog))
+    if (Size <= Config::SizeDelta + (1 << Config::MinSizeLog))
       return 1;
-    Size -= SizeDelta;
+    Size -= Config::SizeDelta;
     DCHECK_LE(Size, MaxSize);
     if (Size <= MidSize)
       return (Size + MinSize - 1) >> Config::MinSizeLog;
@@ -227,12 +223,25 @@ struct DefaultSizeClassConfig {
   static const uptr MinSizeLog = 5;
   static const uptr MidSizeLog = 8;
   static const uptr MaxSizeLog = 17;
-  static const u32 MaxNumCachedHint = 10;
+  static const u32 MaxNumCachedHint = 14;
   static const uptr MaxBytesCachedLog = 10;
+  static const uptr SizeDelta = 0;
 };
 
 typedef FixedSizeClassMap<DefaultSizeClassConfig> DefaultSizeClassMap;
 
+struct FuchsiaSizeClassConfig {
+  static const uptr NumBits = 3;
+  static const uptr MinSizeLog = 5;
+  static const uptr MidSizeLog = 8;
+  static const uptr MaxSizeLog = 17;
+  static const u32 MaxNumCachedHint = 10;
+  static const uptr MaxBytesCachedLog = 10;
+  static const uptr SizeDelta = Chunk::getHeaderSize();
+};
+
+typedef FixedSizeClassMap<FuchsiaSizeClassConfig> FuchsiaSizeClassMap;
+
 struct AndroidSizeClassConfig {
 #if SCUDO_WORDSIZE == 64U
   static const uptr NumBits = 7;
@@ -285,6 +294,7 @@ struct SvelteSizeClassConfig {
   static const uptr MaxSizeLog = 14;
   static const u32 MaxNumCachedHint = 13;
   static const uptr MaxBytesCachedLog = 10;
+  static const uptr SizeDelta = Chunk::getHeaderSize();
 #else
   static const uptr NumBits = 4;
   static const uptr MinSizeLog = 3;
@@ -292,6 +302,7 @@ struct SvelteSizeClassConfig {
   static const uptr MaxSizeLog = 14;
   static const u32 MaxNumCachedHint = 14;
   static const uptr MaxBytesCachedLog = 10;
+  static const uptr SizeDelta = Chunk::getHeaderSize();
 #endif
 };
 

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

@@ -509,6 +509,7 @@ struct DeathSizeClassConfig {
   static const scudo::uptr MaxSizeLog = 13;
   static const scudo::u32 MaxNumCachedHint = 4;
   static const scudo::uptr MaxBytesCachedLog = 12;
+  static const scudo::uptr SizeDelta = 0;
 };
 
 static const scudo::uptr DeathRegionSizeLog = 20U;

compiler-rt/lib/scudo/standalone/tests/size_class_map_test.cpp

@@ -35,6 +35,7 @@ struct OneClassSizeClassConfig {
   static const scudo::uptr MaxSizeLog = 5;
   static const scudo::u32 MaxNumCachedHint = 0;
   static const scudo::uptr MaxBytesCachedLog = 0;
+  static const scudo::uptr SizeDelta = 0;
 };
 
 TEST(ScudoSizeClassMapTest, OneClassSizeClassMap) {
@@ -49,6 +50,7 @@ struct LargeMaxSizeClassConfig {
   static const scudo::uptr MaxSizeLog = 63;
   static const scudo::u32 MaxNumCachedHint = 128;
   static const scudo::uptr MaxBytesCachedLog = 16;
+  static const scudo::uptr SizeDelta = 0;
 };
 
 TEST(ScudoSizeClassMapTest, LargeMaxSizeClassMap) {