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From "Vyacheslav Shakin (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-2816) [drlvm][jit] Jitrino operand priority calculation in bin pack register allocator
Date Thu, 28 Dec 2006 12:38:28 GMT
    [ http://issues.apache.org/jira/browse/HARMONY-2816?page=comments#action_12461181 ] 
            
Vyacheslav Shakin commented on HARMONY-2816:
--------------------------------------------

I reviewed the patch and found it simple and correct, thanks a lot. The truncation often caused
rather strange prioritization of operands leading to inefficient register allocation, especially
with the static profile estimator. 

> [drlvm][jit] Jitrino operand priority calculation in bin pack register allocator
> --------------------------------------------------------------------------------
>
>                 Key: HARMONY-2816
>                 URL: http://issues.apache.org/jira/browse/HARMONY-2816
>             Project: Harmony
>          Issue Type: Bug
>          Components: DRLVM
>            Reporter: Ivashin Sergey
>         Attachments: H-2816.patch
>
>
> Calculation of operand's priority for register assignment is based on execution counters
and register pressures for all blocks where the operand is used. Block execution counter is
a float (double) value, but currently result of this calculation is truncated to integer value.
This truncation causes (1) errors in estimating priorities of operands and (2) different allocation
results for different compilers used (run-time routines from ICL and MSVC produce different
floating point results).
> Using floating point values for operand priorities (weight calculation) significantly
reduce numeric instability and help reproduce allocation results for different compilers.
It should not have a negative impact on performance, because double to integer truncation
is removed.

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