[arm][arm64] Improve CountTrailingZero implementation.

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 212be80747a8dcba10ac041e074a2c7ba3ebc7f6..86cb7f1ef6f2c9a0d5b61c9a56865e186a6f6b5d 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -135,12 +135,15 @@ class MachineOperatorBuilder final : public ZoneObject {
     kWord64Ctz = 1u << 17,
     kWord32Popcnt = 1u << 18,
     kWord64Popcnt = 1u << 19,
+    kWord32ReverseBits = 1u << 20,
+    kWord64ReverseBits = 1u << 21,
     kAllOptionalOps = kFloat32Max | kFloat32Min | kFloat64Max | kFloat64Min |
                       kFloat32RoundDown | kFloat64RoundDown | kFloat32RoundUp |
                       kFloat64RoundUp | kFloat32RoundTruncate |
                       kFloat64RoundTruncate | kFloat64RoundTiesAway |
                       kFloat32RoundTiesEven | kFloat64RoundTiesEven |
-                      kWord32Ctz | kWord64Ctz | kWord32Popcnt | kWord64Popcnt
+                      kWord32Ctz | kWord64Ctz | kWord32Popcnt | kWord64Popcnt |
+                      kWord32ReverseBits | kWord64ReverseBits
   };
   typedef base::Flags<Flag, unsigned> Flags;
 
@@ -161,6 +164,8 @@ class MachineOperatorBuilder final : public ZoneObject {
   const OptionalOperator Word32Ctz();
   const OptionalOperator Word32Popcnt();
   const OptionalOperator Word64Popcnt();
+  const OptionalOperator Word32ReverseBits();
+  const OptionalOperator Word64ReverseBits();
   bool Word32ShiftIsSafe() const { return flags_ & kWord32ShiftIsSafe; }
 
   const Operator* Word64And();