Inlining heuristic trouble

[Christian Thalinger]

On Jun 15, 2011, at 5:48 PM, Christian Thalinger wrote:
> On Jun 15, 2011, at 5:26 PM, Rémi Forax wrote:
>> I've just finished to code a sample for the cookbook that does
>> integer operation (+ and -) with overflow (to BigInteger).
>> 
>> https://code.google.com/p/jsr292-cookbook/source/browse/#svn%2Ftrunk%2Fbinary-operation%2Fsrc%2Fjsr292%2Fcookbook%2Fbinop
> 
> How do I build this thing?  -- Christian

Got it.  I thought there is probably something like a build.xml.  Investigating...

-- Christian

> 
>> 
>> For a code like this one:
>> max = ...
>> for(i=0; i<max; i = i + 1) {
>>  // do nothing
>> }
>> 
>> i + 1 is transformed to:
>> 
>> if (i.getClass() == Integer.class) {
>>  int j = i.intValue();
>>  if (j != MAXINT) {
>>    i = Integer.valueOf(j + 1);
>>  } else {
>>     fallback();
>>  }
>> } else {
>>  fallback();
>> }
>> 
>> but there is a bad news, perf of  i + 1 considering 1 as a constant
>> are *worst* (2 or 3 times !!) that using the double xor trick.
>> 
>> // with the optimization
>> [forax at localhost binary-operation]$ time java -cp .:classes PerfOpt
>> real    0m0.954s
>> user    0m1.030s
>> sys    0m0.087s
>> 
>> // without
>> [forax at localhost binary-operation]$ time java -cp .:classes Perf
>> real    0m0.378s
>> user    0m0.407s
>> sys    0m0.081s
>> 
>> Knowing that the double xor trick does 4 comparisons and
>> the constant trick only two, the problem comes from either
>> my code or the way the VM inlines the method handles.
>> 
>> I've found no problem in my code so ... :)
>> Playing with the VM logs, the method containing (j != MAXINT) is not inlined
>> because it hits the maximum depth (as far as I remember this problem
>> is new, the older algorithm, the one that didn't propagate MDO, didn't 
>> exhibit this problem).
>> Moreover, the VM tries to inline some parts of the fallback method 
>> (twice :( )
>> even if this code never called.
>> 
>> The way the VM decides to inline method handles in this case is not good 
>> at all.
>> 
>> Rémi
>> 
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> 
> 
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