RFR (S) 8184753: Assert against MinObjectAlignmentMask to avoid integer division

Aleksey Shipilev shade at redhat.com
Tue Jul 18 08:02:28 UTC 2017

On 07/18/2017 09:58 AM, Mikael Gerdin wrote:
> Hi Aleksey,
> On 2017-07-18 09:51, Aleksey Shipilev wrote:
>> Hi Mikael,
>> On 07/18/2017 09:48 AM, Mikael Gerdin wrote:
>>>> Noticed two new asserts in arguments.cpp have excess whitespace, fixed:
>>>>     http://cr.openjdk.java.net/~shade/8184753/webrev.02
>>> Did you consider using is_object_aligned in the newly created align.hpp?
>>> http://hg.openjdk.java.net/jdk10/hs/hotspot/file/5e9c41536bd2/src/share/vm/utilities/align.hpp#l120
>>> inline bool is_object_aligned(size_t word_size) {
>>>    return is_aligned(word_size, MinObjAlignment);
>>> }
>> I did, but haven't done this for two reasons:
>>    a) The asserts are about object _sizes_, not the objects themselves;
>>    b) Doing *Mask fits other uses of MinObjAlignment(InBytes)(Mask) around HS;
> But the is_object_aligned(size_t) function _is_ about object sizes, it just has
> a weird naming and a weird overload with the void* variant which asserts that a
> pointer is correctly aligned.

Ah, unfortunate naming indeed. Let me try to switch to is_object_aligned.

> Another approach would be to just get rid of the weird one in align.hpp and use
> the MinObjAlignmentMask in plab.cpp instead.

If that was only plab.cpp, I'd try that. But there are more uses around HS now.


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