cost of Java "assert" when disabled?
david.holmes at oracle.com
Thu Feb 16 23:15:39 UTC 2012
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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