[scudo] SizeClassAllocator64: dispatch all the classes in init()

[fabio-d]

Summary

This will make it easier to verify in a future patch that the ReservedMemory object has been fully dispatched.

[fabio-d]

Rebased

compiler-rt/lib/scudo/standalone/primary64.h

for (uptr I = 0; I < NumClasses; I++) {
       Region->RandState = getRandomU32(&Seed);
       // Releasing small blocks is expensive, set a higher threshold to avoid
       // frequent page releases.
       if (isSmallBlock(getSizeByClassId(I)))
         Region->TryReleaseThreshold = PageSize * SmallerBlockReleasePageDelta;
       else
         Region->TryReleaseThreshold = PageSize;
       Region->ReleaseInfo.LastReleaseAtNs = Time;
+
+      Region->MemMapInfo.MemMap = ReservedMemory.dispatch(
+          PrimaryBase + (I << Config::Primary::RegionSizeLog), RegionSize);
+      CHECK(Region->MemMapInfo.MemMap.isAllocated());
     }
     shuffle(RegionInfoArray, NumClasses, &Seed);
 
     setOption(Option::ReleaseInterval, static_cast<sptr>(ReleaseToOsInterval));
   }
 
   void unmapTestOnly() NO_THREAD_SAFETY_ANALYSIS {
     for (uptr I = 0; I < NumClasses; I++) {
if (TotalUserBytes > MappedUser) {
       // Do the mmap for the user memory.
       const uptr MapSize =
           roundUp(TotalUserBytes - MappedUser, MapSizeIncrement);
       const uptr RegionBase = RegionBeg - getRegionBaseByClassId(ClassId);
       if (UNLIKELY(RegionBase + MappedUser + MapSize > RegionSize)) {
         Region->Exhausted = true;
         return nullptr;
       }
-      // TODO: Consider allocating MemMap in init().
-      if (!Region->MemMapInfo.MemMap.isAllocated()) {
-        Region->MemMapInfo.MemMap = ReservedMemory.dispatch(
-            getRegionBaseByClassId(ClassId), RegionSize);
-      }
-      DCHECK(Region->MemMapInfo.MemMap.isAllocated());
 
       if (UNLIKELY(!Region->MemMapInfo.MemMap.remap(
               RegionBeg + MappedUser, MapSize, "scudo:primary",
               MAP_ALLOWNOMEM | MAP_RESIZABLE |
                   (useMemoryTagging<Config>(Options.load()) ? MAP_MEMTAG
                                                             : 0)))) {
         return nullptr;
       }