ARM64: Use UntagSmi helpers and clean up assertions.

src/arm64/macro-assembler-arm64-inl.h

Index: src/arm64/macro-assembler-arm64-inl.h
diff --git a/src/arm64/macro-assembler-arm64-inl.h b/src/arm64/macro-assembler-arm64-inl.h
index fd5172bb0daca27237a59ca5dce311a365dbe91a..6071aa3d1a8afb0f5025a051343be70b93e07055 100644
--- a/src/arm64/macro-assembler-arm64-inl.h
+++ b/src/arm64/macro-assembler-arm64-inl.h
@@ -1304,6 +1304,7 @@ void MacroAssembler::InitializeRootRegister() {
 
 
 void MacroAssembler::SmiTag(Register dst, Register src) {
+  STATIC_ASSERT(kSmiValueSize + kSmiShift == kXRegSizeInBits);
   ASSERT(dst.Is64Bits() && src.Is64Bits());
   Lsl(dst, src, kSmiShift);
 }
@@ -1313,6 +1314,7 @@ void MacroAssembler::SmiTag(Register smi) { SmiTag(smi, smi); }
 
 
 void MacroAssembler::SmiUntag(Register dst, Register src) {
+  STATIC_ASSERT(kSmiValueSize + kSmiShift == kXRegSizeInBits);
   ASSERT(dst.Is64Bits() && src.Is64Bits());
   if (FLAG_enable_slow_asserts) {
     AssertSmi(src);
@@ -1347,13 +1349,17 @@ void MacroAssembler::SmiUntagToFloat(FPRegister dst,
 
 
 void MacroAssembler::SmiTagAndPush(Register src) {
-  STATIC_ASSERT((kSmiShift == 32) && (kSmiTag == 0));
+  STATIC_ASSERT((kSmiShift == kWRegSizeInBits) &&
+                (kSmiValueSize == kWRegSizeInBits) &&
+                (kSmiTag == 0));
   Push(src.W(), wzr);
 }
 
 
 void MacroAssembler::SmiTagAndPush(Register src1, Register src2) {
-  STATIC_ASSERT((kSmiShift == 32) && (kSmiTag == 0));
+  STATIC_ASSERT((kSmiShift == kWRegSizeInBits) &&
+                (kSmiValueSize == kWRegSizeInBits) &&
+                (kSmiTag == 0));
   Push(src1.W(), wzr, src2.W(), wzr);
 }