scudo: Re-order Allocator fields for improved performance. NFCI.

[pcc]

Summary

Move smaller and frequently-accessed fields near the beginning
of the data structure in order to improve locality and reduce
the number of instructions required to form an access to those
fields. With this change I measured a ~5% performance improvement on
BM_malloc_sql_trace_default on aarch64 Android devices (Pixel 4 and
DragonBoard 845c).

[cryptoad]

Thanks Peter!

[eugenis]

Nice.

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

private:
   static const sptr MemTagAllocationTraceIndex = -2;
   static const sptr MemTagAllocationTidIndex = -1;
   static const sptr MemTagDeallocationTraceIndex = 0;
   static const sptr MemTagDeallocationTidIndex = 1;
   static const sptr MemTagPrevTagIndex = 2;
 
   static const uptr MaxTraceSize = 64;
 
-  GlobalStats Stats;
-  TSDRegistryT TSDRegistry;
-  PrimaryT Primary;
-  SecondaryT Secondary;
-  QuarantineT Quarantine;
-
   u32 Cookie;
 
   struct {
     u8 MayReturnNull : 1;              // may_return_null
     FillContentsMode FillContents : 2; // zero_contents, pattern_fill_contents
     u8 DeallocTypeMismatch : 1;        // dealloc_type_mismatch
     u8 DeleteSizeMismatch : 1;         // delete_size_mismatch
     u8 TrackAllocationStacks : 1;
     u8 UseOddEvenTags : 1;
     u32 QuarantineMaxChunkSize; // quarantine_max_chunk_size
   } Options;
 
+  GlobalStats Stats;
+  PrimaryT Primary;
+  SecondaryT Secondary;
+  QuarantineT Quarantine;
+  TSDRegistryT TSDRegistry;
+
 #ifdef GWP_ASAN_HOOKS
   gwp_asan::GuardedPoolAllocator GuardedAlloc;
 #endif // GWP_ASAN_HOOKS
 
   StackDepot Depot;
 
   // The following might get optimized out by the compiler.
   NOINLINE void performSanityChecks() {