[compiler-rt] [msan] Mark allocator padding as uninitialized, with new origin tag (PR #157187)

[Vitaly Buka via llvm-commits]

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@@ -217,25 +217,52 @@ static void *MsanAllocate(BufferedStackTrace *stack, uptr size, uptr alignment,
   }
   auto *meta = reinterpret_cast<Metadata *>(allocator.GetMetaData(allocated));
   meta->requested_size = size;
+  uptr actually_allocated_size = allocator.GetActuallyAllocatedSize(allocated);
+  void* padding_start = reinterpret_cast<char*>(allocated) + size;
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vitalybuka wrote:

These used only in one branch of zero, declare it there

https://github.com/llvm/llvm-project/pull/157187