Fix: make string indexing work with Infinity.

src/x64/codegen-x64.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 10917 matching lines @@
   // Index is not a smi.
   __ bind(&index_not_smi_);
   // If index is a heap number, try converting it to an integer.
   __ CheckMap(index_, Factory::heap_number_map(), index_not_number_, true);
   call_helper.BeforeCall(masm);
   __ push(object_);
   __ push(index_);
   __ push(result_);
   __ push(index_);  // Consumed by runtime conversion function.
   if (index_flags_ == STRING_INDEX_IS_NUMBER) {
-    // Strictly speaking, NumberToInteger should be called here, but
-    // our string lengths don't exceed 32 bits and using ToUint32 maps
-    // -0 to 0, which is what is required by the spec when accessing
-    // strings.
-    __ CallRuntime(Runtime::kNumberToJSUint32, 1);
+    __ CallRuntime(Runtime::kNumberToIntegerMapMinusZero, 1);
   } else {
     ASSERT(index_flags_ == STRING_INDEX_IS_ARRAY_INDEX);
     // NumberToSmi discards numbers that are not exact integers.
     __ CallRuntime(Runtime::kNumberToSmi, 1);
   }
   if (!scratch_.is(rax)) {
     // Save the conversion result before the pop instructions below
     // have a chance to overwrite it.
     __ movq(scratch_, rax);
   }
@@ skipping 925 matching lines @@
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64