RFR: 8241825: Make compressed oops and compressed class pointers independent on x86_64 (closed)

[coleen.phillimore at oracle.com]

On 4/28/20 1:25 PM, coleen.phillimore at oracle.com wrote:
> Okay. Your incremental is 4040 but looks good to me.
10 times 404 I mean.
> Thanks,
> Coleen
>
> On 4/28/20 12:30 PM, Erik Österlund wrote:
>> Hi Coleen,
>>
>> Thanks for the review.
>>
>> Here is a new webrev:
>> http://cr.openjdk.java.net/~eosterlund/8241825/webrev.01/
>>
>> Incremental:
>> http://cr.openjdk.java.net/~eosterlund/8241825/webrev.00_01/
>>
>> On 2020-04-28 16:15, coleen.phillimore at oracle.com wrote:
>>> Sorry, this went to the wrong list.
>>>
>>> Coleen
>>>
>>> On 4/24/20 11:17 AM, coleen.phillimore at oracle.comwrote:
>>>>
>>>> Hi Erik, well the interpreter code isn't as bad as I thought it 
>>>> would be.  We tied UseCompressedKlassPointers to UseCompressedOops 
>>>> because we couldn't imagine why someone would care about 4 bytes 
>>>> per object with all 8 byte pointers to oops.  But maybe you do care.
>>>>
>>>> http://cr.openjdk.java.net/~eosterlund/8241825/webrev.00/src/hotspot/cpu/x86/interp_masm_x86.cpp.udiff.html 
>>>>
>>>>
>>>>        if (UseBiasedLocking) {
>>>> - biased_locking_enter(lock_reg, obj_reg, swap_reg, tmp_reg, false, 
>>>> done, &slow_case);
>>>> + Register rklass_decode_tmp = LP64_ONLY(rscratch1) NOT_LP64(noreg);
>>>> + biased_locking_enter(lock_reg, obj_reg, swap_reg, tmp_reg, 
>>>> rscratch1, false, done, &slow_case);
>>>>        }
>>>> You didn't use rklass_decode_tmp here.
>>
>> Nice catch. Fixed.
>>
>>>> http://cr.openjdk.java.net/~eosterlund/8241825/webrev.00/src/hotspot/cpu/x86/templateTable_x86.cpp.udiff.html 
>>>>
>>>>
>>>>
>>>> + Register tmp_load_klass = LP64_ONLY(rscratch1) NOT_LP64(noreg);
>>>>
>>>> I wonder if you couldn't just pass rscratch1 into load_klass and 
>>>> handle ignoring it inside the load_klass function, ie. fix the 
>>>> asserts.  This gets repetitive in the templateTable and other 
>>>> code.  Maybe people may have the opposite opinion though.
>>
>> Unfortunately, that won't compile in code that is shared between 32 
>> bit and 64 bit. In 32 bit-only code I just pass in noreg, and in 
>> 64-bit only code I just send in the temp. But for shared code, I have 
>> to do the macro dance, because rscratch1 does not exist on 32 bit.
>>
>>>> This is quite nice that UseCompressedKlassPointers doesn't have to 
>>>> reinit_heapbase. The interpreter code looks good.
>>
>> Thanks!
>>
>>>> http://cr.openjdk.java.net/~eosterlund/8241825/webrev.00/src/hotspot/share/memory/metaspace.cpp.frames.html 
>>>>
>>>>
>>>> I don't know if base = HeapBaseMinAddress is right for the 
>>>> compressed class space.  It's reserved but not committed as 1G.  
>>>> Maybe it makes sense since the heap without UseCompressedOops 
>>>> should be above the class space.
>>
>> Thomas had a similar comment. I think the summary is that yes it is 
>> the right thing to use, but the naming is unfortunate.
>>
>> Hope I fixed it all.
>>
>> Thanks,
>> /Erik
>>
>>>> Coleen
>>>>
>>>> On 4/24/20 4:25 AM, Erik Österlund wrote:
>>>>> Hi,
>>>>>
>>>>> This is the closed version of the mostly open change. There are 
>>>>> some @Contended tests in closed
>>>>> that needed some love with my change to make compressed class 
>>>>> pointers usable with compressed
>>>>> oops disabled. In particular, these tests perform calculations to 
>>>>> ensure that things are padded
>>>>> as expected. Part of those calculations makes assumptions about 
>>>>> how large the object header is,
>>>>> presuming that the number is a constant that is the same for all 
>>>>> objects, and is determinable
>>>>> by checking the offset of the first field. However, with my 
>>>>> changes, the first field will end
>>>>> up either in the klass gap, or after, depending on the field size. 
>>>>> I updated the tests to consider
>>>>> different header sizes depending on the type of fields being used. 
>>>>> It still isn't perfect, but
>>>>> it is clever enough for the purposes of the tests; they pass with 
>>>>> these changes.
>>>>>
>>>>> Bug:
>>>>> https://bugs.openjdk.java.net/browse/JDK-8241825
>>>>>
>>>>> Webrev:
>>>>> http://wikifiles.se.oracle.com/dev/eosterlund/8241825/webrev.00/
>>>>>
>>>>> Thanks,
>>>>> /Erik
>>>>
>>>
>>
>