Fix integer overflow in ConcurrentHashtTableByPtr

[andrew.w.kaylor]

Summary

This fixes a problem with potential integer overflow when multiplying two 32-bit values and assigning the result to a 64-bit value.

The potential overflow has been present since D132455 was re-landed. The initial version of the patch defined MaxBucketSize and NumberOfBuckets as size_t (which I guess would still be a problem for some targets). When the patch was re-landed they were defined as uint32_t, making the calculation of ExtHashMask subject to overflow.

[MaskRay]

While here, remove the parens as Multiplication having precedence over addition is well-known.

llvm/include/llvm/ADT/ConcurrentHashtable.h

ConcurrentHashTableByPtr(
     size_t LeadingZerosNumber = countl_zero(HashMask);
     HashBitsNum = 64 - LeadingZerosNumber;
 
     // We keep only high 32-bits of hash value. So bucket size cannot
     // exceed 2^31. Bucket size is always power of two.
     MaxBucketSize = 1Ull << (std::min((size_t)31, LeadingZerosNumber));
 
     // Calculate mask for extended hash bits.
-    ExtHashMask = (NumberOfBuckets * MaxBucketSize) - 1;
+    ExtHashMask = (uint64_t)NumberOfBuckets * MaxBucketSize - 1;
   }
 
   virtual ~ConcurrentHashTableByPtr() {
     // Deallocate buckets.
     for (uint32_t Idx = 0; Idx < NumberOfBuckets; Idx++) {
       delete[] BucketsArray[Idx].Hashes;
       delete[] BucketsArray[Idx].Entries;
     }