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

src/a64/macro-assembler-a64.cc

Index: src/a64/macro-assembler-a64.cc
diff --git a/src/a64/macro-assembler-a64.cc b/src/a64/macro-assembler-a64.cc
index 623a54bd2d20edaa36718ec0b4d89df3ec2fd11f..90b7b26a5621f9062b2ac976b64324eec2a5bf83 100644
--- a/src/a64/macro-assembler-a64.cc
+++ b/src/a64/macro-assembler-a64.cc
@@ -2544,14 +2544,7 @@ void MacroAssembler::ECMA262ToInt32(Register result,
 
   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: