A question about bytecodes + unsigned load performance ./. add performace

[John Rose]

On Jan 9, 2009, at 6:55 PM, Ulf Zibis wrote:

> Do you see any chance, that HotSpot optimizer could be enhanced in  
> that way, because the loop, we are speaking about, is the central  
> loop in all charset coders of the JVM.

It's already in there, to some degree, but hindered somehow by the  
peepholing problem.  See 'instruct loadUB' around line 6406 of:
   http://hg.openjdk.java.net/jdk7/hotspot/hotspot/file/tip/src/cpu/ 
x86/vm/x86_32.ad

What that does is, when it is time to "match" (or lower) ideal to  
machine nodes in the IR graph, if a suitable AndI and LoadB are  
adjacent, and if the LoadB is unshared, they are coalesced into a  
loadUB machine node.

It would be a detailed debugging exercise to find out why, in the  
case of your code, that optimization does not appear to kick in.

-- John
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