diff -r 0edd74a48586 src/cpu/x86/vm/stubGenerator_x86_64.cpp
--- a/src/cpu/x86/vm/stubGenerator_x86_64.cpp	Mon Mar 07 15:03:48 2016 -0800
+++ b/src/cpu/x86/vm/stubGenerator_x86_64.cpp	Tue Mar 08 22:32:15 2016 +0300
@@ -1329,7 +1329,6 @@
     }
   }
 
-
   // Copy big chunks forward
   //
   // Inputs:
@@ -1548,16 +1547,72 @@
     setup_arg_regs(); // from => rdi, to => rsi, count => rdx
                       // r9 and r10 may be used to save non-volatile registers
 
+    __ movptr(byte_count, count);
+    __ testptr(byte_count, byte_count);
+    __ jcc(Assembler::zero, L_exit);
+    
+    Label L_copy;
+    Label L_preloop;
+
+    __ xorptr(rscratch1, rscratch1);
+    __ BIND(L_preloop);
+      __ lea(rax, Address(to, rscratch1));
+      __ testptr(rax, 31);
+      __ jcc(Assembler::zero, L_copy);    
+    
+      __ movb(rax, Address(from, rscratch1));
+      __ movb(Address(to, rscratch1), rax);
+
+      __ increment(rscratch1);
+      __ decrement(byte_count);
+      __ jcc(Assembler::notZero, L_preloop);    
+    __ jmp(L_exit);
+
+    __ BIND(L_copy);
+    __ addptr(from, rscratch1);
+    __ addptr(to, rscratch1);
+    
     // 'from', 'to' and 'count' are now valid
-    __ movptr(byte_count, count);
-    __ shrptr(count, 3); // count => qword_count
+    __ movptr(qword_count, byte_count);
+    __ shrptr(qword_count, 3);
 
     // Copy from low to high addresses.  Use 'to' as scratch.
     __ lea(end_from, Address(from, qword_count, Address::times_8, -8));
     __ lea(end_to,   Address(to,   qword_count, Address::times_8, -8));
     __ negptr(qword_count); // make the count negative
+    
+    // Zero check
+    __ testptr(qword_count, qword_count);
+    __ jcc(Assembler::zero, L_copy_4_bytes);    
+
+  
+    // Enter the loop
     __ jmp(L_copy_bytes);
-
+    
+    Label L_bulk_loop;
+    __ align(OptoLoopAlignment);
+      
+    // Copy 32 bytes per iteration
+    __ BIND(L_bulk_loop);
+      __ vmovdqu(xmm3, Address(end_from, qword_count, Address::times_8, -120));
+      __ vmovdqu(Address(end_to, qword_count, Address::times_8, -120), xmm3);
+      __ vmovdqu(xmm2, Address(end_from, qword_count, Address::times_8, -88));
+      __ vmovdqu(Address(end_to, qword_count, Address::times_8, -88), xmm2);
+      __ vmovdqu(xmm1, Address(end_from, qword_count, Address::times_8, -56));
+      __ vmovdqu(Address(end_to, qword_count, Address::times_8, -56), xmm1);
+      __ vmovdqu(xmm0, Address(end_from, qword_count, Address::times_8, -24));
+      __ vmovdqu(Address(end_to, qword_count, Address::times_8, -24), xmm0);
+      __ BIND(L_copy_bytes);
+      __ addptr(qword_count, 4);
+      __ jcc(Assembler::lessEqual, L_bulk_loop);
+      __ vpxor(xmm0, xmm0);
+      __ vpxor(xmm1, xmm1);
+      __ vpxor(xmm2, xmm2);
+      __ vpxor(xmm3, xmm3);
+      
+    __ subptr(qword_count, 4);
+    __ jcc(Assembler::zero, L_copy_4_bytes);
+      
     // Copy trailing qwords
   __ BIND(L_copy_8_bytes);
     __ movq(rax, Address(end_from, qword_count, Address::times_8, 8));
@@ -1599,10 +1654,6 @@
     __ leave(); // required for proper stackwalking of RuntimeStub frame
     __ ret(0);
 
-    // Copy in multi-bytes chunks
-    copy_bytes_forward(end_from, end_to, qword_count, rax, L_copy_bytes, L_copy_8_bytes);
-    __ jmp(L_copy_4_bytes);
-
     return start;
   }