[NFC][Asan] Remove chunk pointer from metadata

kAllocBegMagic should be enough.
kAllocBegMagic is already set for the Secondary allocations.
kAllocBegMagic is good enough for the Primary, but it's even safer for
the Secondary allocator as all allocated block are from mmap.

Depends on D87646.

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D87647

Author: vitalybuka

compiler-rt/lib/asan/asan_allocator.cpp

@@ -167,10 +167,10 @@ class LargeChunkHeader {
   AsanChunk *chunk_header;
 
  public:
-  AsanChunk *Get() {
+  AsanChunk *Get() const {
     return atomic_load(&magic, memory_order_acquire) == kAllocBegMagic
                ? chunk_header
-               : reinterpret_cast<AsanChunk *>(this);
+               : nullptr;
   }
 
   void Set(AsanChunk *p) {
@@ -510,13 +510,10 @@ struct Allocator {
     uptr needed_size = rounded_size + rz_size;
     if (alignment > min_alignment)
       needed_size += alignment;
-    bool using_primary_allocator = true;
     // If we are allocating from the secondary allocator, there will be no
     // automatic right redzone, so add the right redzone manually.
-    if (!PrimaryAllocator::CanAllocate(needed_size, alignment)) {
+    if (!PrimaryAllocator::CanAllocate(needed_size, alignment))
       needed_size += rz_size;
-      using_primary_allocator = false;
-    }
     CHECK(IsAligned(needed_size, min_alignment));
     if (size > kMaxAllowedMallocSize || needed_size > kMaxAllowedMallocSize ||
         size > max_user_defined_malloc_size) {
@@ -568,13 +565,6 @@ struct Allocator {
     m->alloc_type = alloc_type;
     CHECK(size);
     m->SetUsedSize(size);
-    if (using_primary_allocator) {
-      CHECK(allocator.FromPrimary(allocated));
-    } else {
-      CHECK(!allocator.FromPrimary(allocated));
-      uptr *meta = reinterpret_cast<uptr *>(allocator.GetMetaData(allocated));
-      meta[1] = chunk_beg;
-    }
     m->user_requested_alignment_log = user_requested_alignment_log;
 
     m->SetAllocContext(t ? t->tid() : 0, StackDepotPut(*stack));
@@ -782,15 +772,12 @@ struct Allocator {
   AsanChunk *GetAsanChunk(void *alloc_beg) {
     if (!alloc_beg)
       return nullptr;
-    AsanChunk *p = nullptr;
-    if (!allocator.FromPrimary(alloc_beg)) {
-      uptr *meta = reinterpret_cast<uptr *>(allocator.GetMetaData(alloc_beg));
-      p = reinterpret_cast<AsanChunk *>(meta[1]);
-    } else {
-      p = reinterpret_cast<LargeChunkHeader *>(alloc_beg)->Get();
+    AsanChunk *p = reinterpret_cast<LargeChunkHeader *>(alloc_beg)->Get();
+    if (!p) {
+      if (!allocator.FromPrimary(alloc_beg))
+        return nullptr;
+      p = reinterpret_cast<AsanChunk *>(alloc_beg);
     }
-    if (!p)
-      return nullptr;
     u8 state = atomic_load(&p->chunk_state, memory_order_relaxed);
     // It does not guaranty that Chunk is initialized, but it's
     // definitely not for any other value.