On 17/02/2012 9:40 AM, Vitaly Davidovich wrote:
The asserts can be enabled/disabled at startup time, but I don't consider
that an advantage over conditional compilation. In fact, it's less
convenient in some cases, e.g. you can't conditionally add/remove class
fields, can't surround blocks of code with condition, etc. There are
workarounds, but it's not ideal.
I'm not going to get drawn into the whole "conditional compilation is
[not] evil" debate. :) If I recall correctly the suggested buld-time
idiom was to do:
static final boolean ASSERT = true; // or false
...
if (ASSERT)
assert ...
that way you could compile with ASSERT set true to get assertions in the
code; or false to have them elided by javac.
C#/.Net have conditional compilation (conditional blocks + assert
statements) and it's a handy tool and no need to worry about dead IL code
causing opto issues - don't see a reason why java couldn't have done the
same from the beginning.
Simply because the people defining the language didn't want it. I
suspect there's a blog or two out there somewhere discussing this.
David
-----
Sent from my phone
On Feb 16, 2012 6:16 PM, "David Holmes"<[email protected]> 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
decisions
David
Sent from my phone
On Feb 16, 2012 5:14 PM, "John Rose"<[email protected]
<mailto:[email protected]**>> 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
