Use bit_cast for Runtime_Double{Hi,Lo}.

src/runtime/runtime-maths.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/arguments.h"
 #include "src/assembler.h"
 #include "src/codegen.h"
 #include "src/runtime/runtime-utils.h"
@@ skipping 16 matching lines @@
 RUNTIME_UNARY_MATH(Asin, asin)
 RUNTIME_UNARY_MATH(Atan, atan)
 RUNTIME_UNARY_MATH(LogRT, log)
 #undef RUNTIME_UNARY_MATH
 
 
 RUNTIME_FUNCTION(Runtime_DoubleHi) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
-  uint64_t integer = double_to_uint64(x);
-  integer = (integer >> 32) & 0xFFFFFFFFu;
-  return *isolate->factory()->NewNumber(static_cast<int32_t>(integer));
+  uint64_t unsigned64 = double_to_uint64(x);
+  uint32_t unsigned32 = static_cast<uint32_t>(unsigned64 >> 32);
+  int32_t signed32 = bit_cast<int32_t, uint32_t>(unsigned32);
+  return *isolate->factory()->NewNumber(signed32);
 }
 
 
 RUNTIME_FUNCTION(Runtime_DoubleLo) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
-  return *isolate->factory()->NewNumber(
-      static_cast<int32_t>(double_to_uint64(x) & 0xFFFFFFFFu));
+  uint64_t unsigned64 = double_to_uint64(x);
+  uint32_t unsigned32 = static_cast<uint32_t>(unsigned64);
+  int32_t signed32 = bit_cast<int32_t, uint32_t>(unsigned32);
+  return *isolate->factory()->NewNumber(signed32);
 }
 
 
 RUNTIME_FUNCTION(Runtime_ConstructDouble) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 2);
   CONVERT_NUMBER_CHECKED(uint32_t, hi, Uint32, args[0]);
   CONVERT_NUMBER_CHECKED(uint32_t, lo, Uint32, args[1]);
   uint64_t result = (static_cast<uint64_t>(hi) << 32) | lo;
   return *isolate->factory()->NewNumber(uint64_to_double(result));
@@ skipping 174 matching lines @@
 RUNTIME_FUNCTION(RuntimeReference_IsMinusZero) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_CHECKED(Object, obj, 0);
   if (!obj->IsHeapNumber()) return isolate->heap()->false_value();
   HeapNumber* number = HeapNumber::cast(obj);
   return isolate->heap()->ToBoolean(IsMinusZero(number->value()));
 }
 }
 }  // namespace v8::internal