Can access by local method variables be faster then access by member variables ?

[Ulf Zibis]

Thanks for your answer.

It's hard to follow for me in detail. What's C1 and C2 ?

-Ulf


Am 16.08.2008 01:16, Tom Rodriguez schrieb:
> What pushes and pops are you talking about?  You should consider stack 
> and local variable access to be completely free when any reasonable 
> JIT is involved.  The bytecodes that operate on the stack and locals 
> don't correspond to any code that it's emitted by C1 or C2.  
> Operations on member variables are definitely not free, though 
> depending on how good your JIT is it may be able to reduce the number 
> of actuals loads and stores that are issued.  In general though the 
> number issued will never become zero.  C2 is fairly good at this and 
> C1 does ok for simple cases but doesn't include any loop optimizations 
> so it will be much less efficient for loopy code like you're showing.
>
> Basically the revision 302 code could be transformed into the revision 
> 291 by a good compiler.  291 will definitely run faster with C1 
> because it doesn't have any loop optimizations around memory 
> operations.  C2 might be able to reproduce equivalent code, though I'm 
> not positive it can delay the stores implied by the srcPos++ dstPos++ 
> until the whole loop has completed.
>
> tom
>
> On Aug 15, 2008, at 3:02 PM, Ulf Zibis wrote:
>
>> Hi experts,
>>
>> to avoid stack push + pop of src, dst I have refactored my code in 
>> moving the local method variables (sp, ...) to member variables 
>> (srcPos, ...).
>>
>> After this I have experienced that my code was little slower.
>>
>> For full source code see:
>> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/src/sun/nio/cs/SingleByteEncoder.java?rev=291&view=markup 
>>
>> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/src/sun/nio/cs/SingleByteEncoder.java?rev=302&view=markup 
>>
>>
>> ======================================== revisions 291 
>> ========================================
>>
>>   private CoderResult encodeArraysLoop(CharBuffer src, ByteBuffer dst) {
>>       char[] sa = src.array();
>>       int sp = src.arrayOffset() + src.position();
>>       int sl = src.arrayOffset() + src.limit();
>>       assert (sp <= sl);
>>       byte[] da = dst.array();
>>       int dp = dst.arrayOffset() + dst.position();
>>       int dl = dst.arrayOffset() + dst.limit();
>>       assert (dp <= dl);
>>       try {
>>           for (; sp < sl; sp++) {
>>               current = sa[sp];
>>               byte b = encodeSingle();
>>               if (dp >= dl)
>>                   return CoderResult.OVERFLOW;
>>               da[dp++] = b;
>>           }
>>           return CoderResult.UNDERFLOW;
>>       } catch (UnmappableCharacterException e) {
>>           if (Surrogate.isLow(current) || current >= '\uFFFE')
>>               return CODERRESULT_MALFORMED;
>>           if (Surrogate.isHigh(current))
>>               try {
>>                   if (sp+1 >= sl)
>>                       return CoderResult.UNDERFLOW;
>>                   encodeSurrogate(sa[sp+1]);
>>               } catch (UnmappableCharacterException e2) {
>>                   return CODERRESULT_UNMAPPABLE2;
>>               } catch (MalformedInputException e2) {
>>                   return CODERRESULT_MALFORMED2;
>>               }
>>           return CODERRESULT_UNMAPPABLE;
>>       } finally {
>>           src.position(sp - src.arrayOffset());
>>           dst.position(dp - dst.arrayOffset());
>>       }
>>   }
>>
>> ======================================== revisions 302 
>> ========================================
>>
>>   private CoderResult encodeArraysLoop() throws RuntimeException, 
>> UnmappableCharacterException {
>>       for (; srcPos < srcLimit; srcPos++) {
>>           current = srcArray[srcPos];
>>           byte b = encodeSingle();
>>           if (dstPos < dstLimit)
>>               dstArray[dstPos++] = b;
>>           else
>>               return CoderResult.OVERFLOW;
>>       }
>>       return CoderResult.UNDERFLOW;
>>   }
>>
>> =============================================================================================== 
>>
>>
>>
>> Thanks for your explanations,
>>
>> Ulf
>>
>>
>>
>>
>
>