RFR(S): 8213419: C2 may hang in MulLNode::Ideal()/MulINode::Ideal() with gcc 8.2.1

[dean.long at oracle.com]

On 11/9/18 2:38 AM, Roland Westrelin wrote:
>> It looks like log2_intptr() here is converting bit1 from unsigned to signed:
> I changed the signature of log2_intptr() to take an unsigned int so I
> don't think there's any conversion.

OK, I missed that.  That addresses my concern.

>> and bit1 can be 0x80000000 unless I'm missing something.  If INT_MIN
>> is the only problem, can we just have special handling for INT_MIN, and
>> leave the rest of the code unchanged:
>>
>>       if (con == INT_MIN) {
>>           ...
>>           return ...
>>       }
>>
>>       bool sign_flip = false;
>> if( con < 0 ) {
>> con = -con;
>>
>>         sign_flip = true;
>>       }
>> [...]
> Right. That's another way of dealing with this. But introducing uabs()
> and changing the log2_intptr() signature is also likely required for
> other part of the code.

OK.  I'll leave it up to you which way you want to go with this fix.

dl

> Roland.