Java, Assertions and the JIT -


i'm trying reason how jit of hotspot reasons. i'm interested in latest compilation stage (c2 compiler). jit in java rely on assertions optimisations? if case, imagine there examples code run faster assertions enabled.

for example, in piece of code this:

static int getsumoffirstthree(int[] array) {    assert(array.length >= 3);    return array[0] + array[1] + array[2]; }
  • will jit, when assertions enabled, clever enough eliminate bounds checks on array accesses?
  • alternatively, there other cases can think of (practical or not) assertions improve native code jit compile?

in case, there multiple bounds checks made, , possible jit can coalesce them 1 check made, assertion doesn't avoid need make check.

assertions prevent optimisations inlining method larger , size factor in determining whether inline method. typically inlining improves performance in cases doesn't can cause l0 or l1 cpu caches become inefficient due larger code being generated.

an example of assertion can improve performance this.

boolean assertionon = false; assert assertionon = true; if (assertionon) {    assumedataisgood(); // due checks elsewhere } else {    expensivecheckthatdatamightnotbegood(); }

this perhaps anti-pattern using assertions, going cheaper assertions on intent.


Comments

Post a Comment

Popular posts from this blog

python - Operations inside variables -

this question has answer here: evaluating mathematical expression in string 12 answers i want make python script finds maximum possible output using 2 operations. problem says there syntax error @ 2nd last line, in b in there. how can fix it? x = 0 = int(input("1st number:")) c = int(input("2nd number:" )) e = int(input("3rd number:" )) in range(4): if == 0: b = "+" elif == 1: b = "-" elif == 2: b = "/" else: b = "*" j in range(4): if j == 0: d = "+" elif j == 1: d = "-" elif j == 2: d = "/" else: d = "*" k = b c d e print(k) if you're after variables e on single line, couldn...
Read more

Generic Map Parameter java -

i having lot of methods of type: public static list<eduusers> getdetails(class c, map<string, integer> params) { list<eduusers> details = null; session session = hibernateutil.getsessionfactory().opensession(); transaction tx = null; try { tx = session.begintransaction(); criteria cr = session.createcriteria(c); (map.entry<string, integer> entry : params.entryset()) { cr.add(restrictions.eq(entry.getkey(), entry.getvalue())); } details = cr.list(); tx.commit(); } catch (exception asd) { log.debug(asd.getmessage()); if (tx != null) { tx.commit(); } } { session.close(); } return details; } i trying have generic method them , have written far: public static <t> list<t> getdetails(class<t> c, class<t> b) { l...
Read more

arrays - What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? -

what arrayindexoutofboundsexception mean , how rid of it? here code sample triggers exception: string[] name = {"tom", "dick", "harry"}; for(int = 0; i<=name.length; i++) { system.out.print(name[i] +'\n'); } your first port of call should documentation explains reasonably clearly: thrown indicate array has been accessed illegal index. index either negative or greater or equal size of array. so example: int[] array = new int[5]; int boom = array[10]; // throws exception as how avoid it... um, don't that. careful array indexes. one problem people run thinking arrays 1-indexed, e.g. int[] array = new int[5]; // ... populate array here ... (int index = 1; index <= array.length; index++) { system.out.println(array[index]); } that miss out first element (index 0) , throw exception when index 5. valid indexes here 0-4 inclusive. correct, idiomatic for statement here be: for (int index = 0; index <...
Read more