RFR (S): 8024067: Missing replace_in_map() calls following null checks

Vladimir Kozlov vladimir.kozlov at oracle.com
Tue Sep 3 15:15:24 PDT 2013


Can you pass safe_for_replace into null_check_oop()? I want 
replace_in_map in one place.

Vladimir

On 9/3/13 2:49 PM, Roland Westrelin wrote:
>> Then why not do that in null_check_oop()? And why we need safe_for_replace?
>
> For instance, LibraryCallKit::inline_native_Class_query() for vmIntrinsics::_isInstance builds a region with 2 control paths. gen_instanceof() is used on one of the paths. gen_instanceof() calls null_check_oop(). If null_check_oop() does the replace_in_map then we can end up with a reference in the map after the isInstance that is only valid on one of the control paths. In general, null_check_oop() is called directly or indirectly from library_call.cpp where we build our own control flow and null_check_oop() can be only valid on one control path and so a replace_in_map cannot be safely performed.
>
> Roland.
>
>> PS: Roland, please, include previous mails text (with webrev link) in your responses.
>>
>> On 9/3/13 1:48 PM, Roland Westrelin wrote:
>>>
>>>> Why you need this when null_check_common() does this already?
>>>
>>> GraphKit::null_check_oop() sets (*null_control) = top()
>>> then GraphKit::null_check_common() does:
>>> if (null_control != NULL) {
>>> (*null_control) = null_true;
>>> so (*null_control) is no longer top and:
>>>
>>>     if (null_control == NULL || (*null_control) == top())
>>>        replace_in_map(value, cast);
>>>
>>> doesn't help. Back in GraphKit::null_check_oop():
>>>
>>>    if (never_see_null && (*null_control) != top()) {
>>>
>>> is where the uncommon trap is added and (*null_control) = top() is set back to top and nothing does the replace_in_map.
>>>
>>> Roland.
>>>
>


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