X64: A bunch of small fixes.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index f195439eba9f91866206bff06362edc2e0a28a2c..1bddea4bf65241af0d1d8c847270dac62e66e402 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -46,23 +46,23 @@ namespace internal {
 
 // Test whether a 64-bit value is in a specific range.
 static inline bool is_uint32(int64_t x) {
-  static const int64_t kUInt32Mask = V8_INT64_C(0xffffffff);
-  return x == (x & kUInt32Mask);
+  static const uint64_t kMaxUInt32 = V8_UINT64_C(0xffffffff);
+  return static_cast<uint64_t>(x) <= kMaxUInt32;
 }
 
 static inline bool is_int32(int64_t x) {
-  static const int64_t kMinIntValue = V8_INT64_C(-0x80000000);
-  return is_uint32(x - kMinIntValue);
+  static const int64_t kMinInt32 = -V8_INT64_C(0x80000000);
+  return is_uint32(x - kMinInt32);
 }
 
 static inline bool uint_is_int32(uint64_t x) {
-  static const uint64_t kMaxIntValue = V8_UINT64_C(0x80000000);
-  return x < kMaxIntValue;
+  static const uint64_t kMaxInt32 = V8_UINT64_C(0x7fffffff);
+  return x <= kMaxInt32;
 }
 
 static inline bool is_uint32(uint64_t x) {
-  static const uint64_t kMaxUIntValue = V8_UINT64_C(0x100000000);
-  return x < kMaxUIntValue;
+  static const uint64_t kMaxUInt32 = V8_UINT64_C(0xffffffff);
+  return x <= kMaxUInt32;
 }
 
 // CPU Registers.