Make UBSan happy.

src/runtime.cc

 // Copyright 2012 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 <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 6991 matching lines @@
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
   CONVERT_DOUBLE_ARG_CHECKED(y, 1);
   return *isolate->factory()->NewNumber(modulo(x, y));
 }
 
 
 RUNTIME_FUNCTION(Runtime_NumberImul) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
 
-  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
-  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
-  return *isolate->factory()->NewNumberFromInt(x * y);
+  // We rely on implementation-defined behavior below, but at least not on
+  // undefined behavior.
+  CONVERT_NUMBER_CHECKED(uint32_t, x, Int32, args[0]);
+  CONVERT_NUMBER_CHECKED(uint32_t, y, Int32, args[1]);
+  int32_t product = static_cast<int32_t>(x * y);
+  return *isolate->factory()->NewNumberFromInt(product);
 }
 
 
 RUNTIME_FUNCTION(Runtime_StringAdd) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(String, str1, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, str2, 1);
   isolate->counters()->string_add_runtime()->Increment();
   Handle<String> result;
@@ skipping 8080 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal