RFR(XXS) 8249087 Symbol constructor unnecessarily initializes _body[0]

[Ioi Lam]

Hi please review this very simple fix:

diff -r 19f26d72a8d0 src/hotspot/share/oops/symbol.cpp
--- a/src/hotspot/share/oops/symbol.cpp    Mon Jul 20 14:24:19 2020 -0700
+++ b/src/hotspot/share/oops/symbol.cpp    Mon Jul 20 17:11:57 2020 -0700
@@ -51,8 +51,11 @@
  Symbol::Symbol(const u1* name, int length, int refcount) {
    _hash_and_refcount = pack_hash_and_refcount((short)os::random(), 
refcount);
    _length = length;
-  _body[0] = 0;  // in case length == 0
    memcpy(_body, name, length);
+  // For symbols of length 0 and 1: _body[0] (and _body[1]) are 
uninitialized and may
+  // contain random values, which will only be read by 
Symbol::identity_hash(),
+  // which would tolerate such randomness. These values never change 
during the lifetime
+  // of the Symbol.
  }


Passed hs tiers 1/2. Running tiers 3/4 now.

Thanks
- Ioi