cost of Java "assert" when disabled?
ysr1729 at gmail.com
Thu Feb 16 16:39:48 PST 2012
Thanks to all for the prompt and enlightening discussion, and especially to
David for the succinct summary.
On Thu, Feb 16, 2012 at 3:15 PM, David Holmes <david.holmes at oracle.com>wrote:
> The corelibs side of things seems to have gotten dropped from the cc list
> - added back.
> On 17/02/2012 8:21 AM, Vitaly Davidovich wrote:
>> Don't want to sidetrack this thread but I really wish javac had proper
>> conditional compilation support, which would make this issue mostly moot.
> But the whole point of Java assertions is to make them available at
> runtime. I seem to recall a very similar question only recently on the
> core-libs mailing list.
> So summary is:
> - Every assert requires checking if asserts are enabled
> - JIT Compiler can elide the checks
> - Presence of assert related bytecodes can impact JIT compiler inlining
> Sent from my phone
>> On Feb 16, 2012 5:14 PM, "John Rose" <john.r.rose at oracle.com
>> <mailto:john.r.rose at oracle.com**>> wrote:
>> On Feb 16, 2012, at 1:59 PM, Vitaly Davidovich wrote:
>> I think one problem with them is that they count towards the
>>> inlining budget since their bytecodes still take up space. Not
>>> sure if newer C1/C2 compiler builds are "smarter" about this nowadays.
>> Optimized object code has (probably) no trace of the assertions
>> themselves, but as Vitaly said, they perturb the inlining budget.
>> Larger methods have a tendency to "discourage" the inliner from
>> inlining, causing more out-of-line calls and a rough net slowdown.
>> Currently, the non-executed bytecodes for assertions (which can be
>> arbitrarily complex) make methods look bigger than they really are.
>> This is (IMO) a bug in the inlining heuristics, which should be
>> fixed by examining inlining candidates with a little more care.
>> Since the escape analysis does a similar method summarization,
>> there isn't necessarily even a need for an extra pass over the methods.
>> -- John
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