RFR (L, tedious again, sorry) 8189610: Reconcile jvm.h and all jvm_md.h between java.base and hotspot

[David Holmes]

On 30/10/2017 10:15 PM, coleen.phillimore at oracle.com wrote:
> On 10/28/17 3:58 AM, David Holmes wrote:
>> On 28/10/2017 6:20 AM, coleen.phillimore at oracle.com wrote:
>>>
>>> Incremental webrev:
>>>
>>> http://cr.openjdk.java.net/~coleenp/8189610.incr.01/webrev/index.html
>>
>> That all looks fine - thanks.
>>
>> If I get a chance I'll look deeper into why the VS compiler needs 0 to 
>> be cast to jint (aka long) to avoid ambiguity with it being a NULL 
>> pointer. I could understand if it always needed the cast, but not only 
>> needing it for long, but not int.
> 
> Thanks,  Kim can probably tell you where in the spec this is.

Now I get it.

Given:

void x(int i) { ...}
void x(Foo* p) { ... }

a call x(0) is a call to x(int) because 0 is an int. No conversion needed.

But given:

void x(long i) { ...}
void x(Foo* p) { ... }

a call x(0) has no direct match (no int version) so standard conversions 
apply and IIUC conversion to long and conversion to Foo* have the same 
rank, so neither is preferred and the call is ambiguous.

David

> Coleen
> 
>>
>> Thanks,
>> David
>>
>>> thanks,
>>> Coleen
>>>
>>> On 10/27/17 11:13 AM, coleen.phillimore at oracle.com wrote:
>>>>
>>>>
>>>> On 10/27/17 9:37 AM, David Holmes wrote:
>>>>>>> src/hotspot/share/c1/c1_LinearScan.cpp
>>>>>>>
>>>>>>>  ConstantIntValue((jint)0);
>>>>>>>
>>>>>>> why is this cast needed? what causes the ambiguity? (If this was 
>>>>>>> a template I'd understand ;-) ). Also didn't you change that 
>>>>>>> constructor to take an int anyway - not that I think it should - 
>>>>>>> see below.
>>>>>>
>>>>>> Yes, it caused an ambiguity.  0 matches 'int' but it doesn't match 
>>>>>> 'long' better than any pointer type.  So this cast is needed.
>>>>>
>>>>> But you changed the constructor to take an int!
>>>>>
>>>>>  class ConstantIntValue: public ScopeValue {
>>>>>   private:
>>>>> -  jint _value;
>>>>> +  int _value;
>>>>>   public:
>>>>> -  ConstantIntValue(jint value)         { _value = value; }
>>>>> +  ConstantIntValue(int value)          { _value = value; }
>>>>>
>>>> I changed this back to not take an int and changed c1_LinearScan.cpp 
>>>> to have the (jint)0 cast and output.cp needed (jint)0 casts.  0L 
>>>> doesn't work for platforms where jint is an 'int' rather than a long 
>>>> because it's ambiguous with the functions that take a pointer type.
>>>> Probably better to keep the type of ConstantIntValue consistent with 
>>>> j types.
>>>>
>>>> Thanks,
>>>> Coleen
>>>
>