Fix PR13148, an inf-loop in StringMap.

StringMap suffered from the same bug as DenseMap: when you explicitly
construct it with a small number of buckets, you can arrange for the
tombstone-based growth path to be followed when the number of buckets
was less than '8'. In that case, even with a full map, it would compare
'0' as not less than '0', and refuse to grow the table, leading to
inf-loops trying to find an empty bucket on the next insertion. The fix
is very simple: use '<=' as the comparison. The same fix was applied to
DenseMap as well during its recent refactoring.

Thanks to Alex Bolz for the great report and test case. =]

llvm-svn: 158725

llvm/lib/Support/StringMap.cpp

@@ -189,7 +189,7 @@ void StringMapImpl::RehashTable() {
   // grow/rehash the table.
   if (NumItems*4 > NumBuckets*3) {
     NewSize = NumBuckets*2;
-  } else if (NumBuckets-(NumItems+NumTombstones) < NumBuckets/8) {
+  } else if (NumBuckets-(NumItems+NumTombstones) <= NumBuckets/8) {
     NewSize = NumBuckets;
   } else {
     return;