RFR(S): 8029351: assert(bt != T_OBJECT) failed: Guard is incorrect in VM:defmeth

[David Chase]

I was attempting Christian's cleanup, and saw what would have been a nice one

  tag. basic_type() == T_OBJECT

but that did not evaluate the same condition -- it also includes

  is_klass_index() || is_string_index()

which is not in the generateOopMap code.  Is it wrong to include those, or did some Bright Boy
happen to know that he could save a few cycles by omitting those cases (and thus burn how many
beeelions of CPU cycles on testing etc as we wonder at his undocumented intent?)

bool is_object() const            { return is_klass() || is_unresolved_klass() ||
                                      is_string() || is_method_handle() || is_method_type() ||
                                      is_method_handle_in_error() || is_method_type_in_error(); }
  // But NOT is_klass_index or is_string_index, else we could use basic_type() == T_OBJECT?

Any idea?

David

On 2013-12-09, at 8:54 AM, Coleen Phillimore <coleen.phillimore at oracle.com> wrote:

> 
> This looks good.   I don't know why I decided that these weren't needed when I went through all of these with my previous bug fix, but apparently they are.
> Thanks for fixing these.
> Coleen
> 
> On 12/7/2013 10:12 PM, David Chase wrote:
>> RT-dev CC'd because this was more of a runtime bug, except that involved methodHandles.
>> 
>> bug: https://bugs.openjdk.java.net/browse/JDK-8029351
>> webrev: http://cr.openjdk.java.net/~drchase/8029351/webrev.01/
>> 
>> Running "defmeth", especially with -Xcomp and -XX:+AggressiveOpts, sometimes (1 in 25 to 1 in 50)
>> causes a crash in fastdebug, that in release builds is instead a signal-ignoring infinite loop.
>> 
>> The cause was failure to include the method_handle_in_error and method_type_in_error
>> cases in the "is this an object?" test.  This immediately led to a blown assertion in a debug build.
>> Fix was to add the obvious clauses to the if:
>> 
>>        tag.is_unresolved_klass() ||
>>        tag.is_string() ||
>>        tag.is_method_handle() ||
>> -      tag.is_method_type()) {
>> +      tag.is_method_type() ||
>> +      tag.is_method_handle_in_error() ||
>> +      tag.is_method_type_in_error()) {
>>      assert(bt == T_OBJECT, "Guard is incorrect");
>>      cts = CellTypeState::make_line_ref(bci);
>>    } else {
>> 
>> Testing:
>> defmeth, fastdebug build with bug-provoking flags , 1000 times.
>> All ran w/o crash (i.e., only with other existing known failures), all produced the same output.
>> 
>> David
>> 
> 

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