[arm] Implement barriers on ARMv6 using CP15.

test/cctest/test-disasm-arm.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1147 matching lines @@
     COMPARE(dmb(LD),
             "f57ff05d       dmb ld");
     COMPARE(dmb(ST),
             "f57ff05e       dmb st");
     COMPARE(dmb(SY),
             "f57ff05f       dmb sy");
 
     COMPARE(dsb(ISH),
             "f57ff04b       dsb ish");
 
-    COMPARE(isb(ISH),
-            "f57ff06b       isb ish");
+    COMPARE(isb(SY),
+            "f57ff06f       isb sy");
+  } else {
+    // ARMv6 uses CP15 to implement barriers. The BarrierOption argument is
+    // ignored.
+    COMPARE(dmb(ISH),
+            "ee070fba       mcr (CP15DMB)");
+    COMPARE(dsb(OSH),
+            "ee070f9a       mcr (CP15DSB)");
+    COMPARE(isb(SY),
+            "ee070f95       mcr (CP15ISB)");
   }
 
+  // ARMv6 barriers.
+  // Details available in ARM DDI 0406C.b, B3-1750.
+  COMPARE(mcr(p15, 0, r0, cr7, cr10, 5), "ee070fba       mcr (CP15DMB)");
+  COMPARE(mcr(p15, 0, r0, cr7, cr10, 4), "ee070f9a       mcr (CP15DSB)");
+  COMPARE(mcr(p15, 0, r0, cr7, cr5, 4), "ee070f95       mcr (CP15ISB)");
+  // Rt is ignored.
+  COMPARE(mcr(p15, 0, lr, cr7, cr10, 5), "ee07efba       mcr (CP15DMB)");
+  COMPARE(mcr(p15, 0, lr, cr7, cr10, 4), "ee07ef9a       mcr (CP15DSB)");
+  COMPARE(mcr(p15, 0, lr, cr7, cr5, 4), "ee07ef95       mcr (CP15ISB)");
+  // The mcr instruction can be conditional.
+  COMPARE(mcr(p15, 0, r0, cr7, cr10, 5, eq), "0e070fba       mcreq (CP15DMB)");
+  COMPARE(mcr(p15, 0, r0, cr7, cr10, 4, ne), "1e070f9a       mcrne (CP15DSB)");
+  COMPARE(mcr(p15, 0, r0, cr7, cr5, 4, mi), "4e070f95       mcrmi (CP15ISB)");
+
   VERIFY_RUN();
 }
 
 
 TEST(LoadStoreExclusive) {
   SET_UP();
 
   COMPARE(ldrexb(r0, r1), "e1d10f9f       ldrexb r0, [r1]");
   COMPARE(strexb(r0, r1, r2), "e1c20f91       strexb r0, r1, [r2]");
   COMPARE(ldrexh(r0, r1), "e1f10f9f       ldrexh r0, [r1]");
   COMPARE(strexh(r0, r1, r2), "e1e20f91       strexh r0, r1, [r2]");
   COMPARE(ldrex(r0, r1), "e1910f9f       ldrex r0, [r1]");
   COMPARE(strex(r0, r1, r2), "e1820f91       strex r0, r1, [r2]");
 
   VERIFY_RUN();
 }