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From Tim Ellison <t.p.elli...@gmail.com>
Subject Re: [classlib][performance] @Inline and @NoBoundsCheck annotation support
Date Mon, 28 Apr 2008 15:20:10 GMT
Ian Rogers wrote:
> Aleksey Shipilev wrote:
>> Hi,
>>
>> I had returned to idea to have @Inline and @NoBoundCheck annotation
>> support in classlib and Jitrino.
>> I will try to summarize the rationale for both these annotations:
>>
>>  1. @Inline. There are places where we're creating small methods to
>> get more consistent code, while we expect JIT should inline them to
>> reduce call penalty. Unfortunately, this is not always the case and
>> any JIT can miss the opportunities for inline. As classlib developers
>> we can dope our code with the hints saying "this method is really
>> should be inlined, as we know it would be the penalty leaving it not
>> inlined, just do it even when inline budget is exhausted". Jitrino
>> really have @Inline already as the part of vmmagic package, but I want
>> to see these annotations visible from the classlib part.
>>
>> That's the case of new HashMap [1] for example:
>>
>>     /*
>>      * Contract-related functionality
>>      */
>>     static int computeHashCode(Object key) {
>>         return key.hashCode();
>>     }
>>
>>     static boolean areEqualKeys(Object key1, Object key2) {
>>         return key1.equals(key2);
>>     }
>>
>>     static boolean areEqualValues(Object value1, Object value2) {
>>         return value1.equals(value2);
>>     }
>>
>>
>>  2. @NoBoundCheck. There are also cases in which we definitely know
>> that no bound check need to be performed. This is the case of HashMap
>> again:
>>
>>     ...
>>             int hash = computeHashCode(key);
>>             index = hash & (elementData.length - 1);
>>             entry = elementData[index];
>>     ...
>>
>>    Of course, good JIT compiler should also resolve such patterns and
>> eliminate bounds check here, but we can again hint the compiler they
>> are not necessary. There's a complication though that such pragma
>> could violate security if used in user code, but we could restrict its
>> usage to bootstrap classes only. ABCD gurus (Egor?) could shed more
>> light whether it's possible to implement on JIT side.
>>
>> What do you think? I can elaborate with proof-of-concept patches to
>> see what advantage it would bring.
>>
>> Thanks,
>> Aleksey.
>>
>> [1] https://issues.apache.org/jira/browse/HARMONY-5791
>>   
> Hi Aleksey,
> 
> an alternate approach may be to use a bytecode engineering library. For 
> example, Jikes RVM uses ASM to add annotations to the library during 
> bootstrap compilation [1]. 

Are you advocating using bytecode modification specifically over source 
annotations, or just pointing it out as an alternative?

Since Harmony has the class library implementation I'm more inclined to 
consider this directly in the source code.

Regards,
Tim

> A few of the other annotations we use are:
> 
> @Pure to indicate that a method can be called at compile time if its 
> arguments are constants. This allows us to turn 
> BigInteger.ONE.add(BigInteger.TEN) into a literal BigInteger holding the 
> value 11.
> 
> @NoEscapes indicates that if an aggregate (object or array) is passed as 
> an argument to a method, and this call is the sole reason an aggregate 
> escapes, the object can be replaced by scalars. We use this to avoid 
> stack trace generation when the stack trace is never read.
> 
> Regards,
> Ian Rogers
> 
> [1] 
> http://jikesrvm.svn.sourceforge.net/viewvc/jikesrvm/rvmroot/trunk/tools/asm-tasks/src/org/jikesrvm/tools/asm/AnnotationAdder.java?revision=14102&view=markup

> 

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