A64: When truncating to an int, store the result in a 64bit register

src/a64/macro-assembler-a64.cc

 // Copyright 2013 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 2526 matching lines @@
   Cneg(mantissa, mantissa, ne);
 
   // Shift the mantissa bits in the correct place. We know that we have to shift
   // it left here, because exponent >= 63 >= kMantissaBits.
   Sub(exponent, exponent,
       HeapNumber::kExponentBias + HeapNumber::kMantissaBits);
   Lsl(result, mantissa, exponent);
 
   Bind(&tag);
   switch (format) {
-    case INT32_IN_W:
-      // There is nothing to do; the upper 32 bits are undefined.
-      if (emit_debug_code()) {
-        __ Mov(scratch1, 0x55555555);
-        __ Bfi(result, scratch1, 32, 32);
-      }
-      break;
-    case INT32_IN_X:
+    case INT32:
       Sxtw(result, result);
       break;
     case SMI:
       SmiTag(result);
       break;
   }
 
   Bind(&done);
 }
 
@@ skipping 2231 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64