[arm64] Use exclusive instructions in exchange

src/arm64/constants-arm64.h

Index: src/arm64/constants-arm64.h
diff --git a/src/arm64/constants-arm64.h b/src/arm64/constants-arm64.h
index 23d4db44a052d0ddfb53569d55709047247ce296..7b10ca36a73e88cc074822b03f025e503addf486 100644
--- a/src/arm64/constants-arm64.h
+++ b/src/arm64/constants-arm64.h
@@ -864,7 +864,7 @@ enum LoadStoreRegisterOffset {
   #undef LOAD_STORE_REGISTER_OFFSET
 };
 
-// Load/store acquire/release
+// Load/store acquire/release.
 enum LoadStoreAcquireReleaseOp {
   LoadStoreAcquireReleaseFixed = 0x08000000,
   LoadStoreAcquireReleaseFMask = 0x3F000000,
@@ -887,6 +887,21 @@ enum LoadStoreAcquireReleaseOp {
   LDAR_x  = LoadStoreAcquireReleaseFixed | 0xC0C08000,
 };
 
+// Load/store exclusive.
+enum LoadStoreExclusiveOp {
+  LoadStoreExclusiveFixed = 0x08000000,
+  LoadStoreExclusiveFMask = 0x3F808000,
+  LoadStoreExclusiveMask = 0xFFE08000,
+  STXRB = LoadStoreExclusiveFixed,
+  LDXRB = LoadStoreExclusiveFixed | 0x00400000,
+  STXRH = LoadStoreExclusiveFixed | 0x40000000,
+  LDXRH = LoadStoreExclusiveFixed | 0x40400000,
+  STXR_w = LoadStoreExclusiveFixed | 0x80000000,
+  LDXR_w = LoadStoreExclusiveFixed | 0x80400000,
+  STXR_x = LoadStoreExclusiveFixed | 0xC0000000,
+  LDXR_x = LoadStoreExclusiveFixed | 0xC0400000,
+};
+
 // Conditional compare.
 enum ConditionalCompareOp {
   ConditionalCompareMask = 0x60000000,