Relaxed memory barriers for x86

X86 provides stronger memory guarantees and thus the memory barriers can be
optimized. This patch ensures that all memory barriers for x86 are treated
as scheduling barriers. And in cases where a barrier is needed (StoreLoad case),
an mfence is used.

Change-Id: I13d02bf3f152083ba9f358052aedb583b0d48640
Signed-off-by: Razvan A Lupusoru <razvan.a.lupusoru@intel.com>
diff --git a/compiler/dex/quick/x86/codegen_x86.h b/compiler/dex/quick/x86/codegen_x86.h
index 275a2d9..f2654b9 100644
--- a/compiler/dex/quick/x86/codegen_x86.h
+++ b/compiler/dex/quick/x86/codegen_x86.h
@@ -372,6 +372,8 @@
     void OpVectorRegCopyWide(uint8_t fp_reg, uint8_t low_reg, uint8_t high_reg);
     void GenConstWide(RegLocation rl_dest, int64_t value);
 
+    static bool ProvidesFullMemoryBarrier(X86OpCode opcode);
+
     /*
      * @brief generate inline code for fast case of Strng.indexOf.
      * @param info Call parameters