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From "Xiaoming Gu (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-6016) [drlvm][jit] An undetected interference in Graph Coloring register allocation
Date Thu, 13 Nov 2008 08:50:44 GMT
[drlvm][jit] An undetected interference in Graph Coloring register allocation

                 Key: HARMONY-6016
                 URL: https://issues.apache.org/jira/browse/HARMONY-6016
             Project: Harmony
          Issue Type: Bug
          Components: DRLVM
         Environment: IA32 Windows
            Reporter: Xiaoming Gu

When early_prop turned off in server_static mode, there is a NullPointerException during running
startup.helloworld. The bug comes from the last BB of DataInputStream.readByte(). Following
are the generated binary code for this bug:

  with early_prop
    	02D67855 I15: MOVSX t26(EAX):I_32,t12(EAX):I_32 

  without early_prop
	02D67865 I33: MOV t25(BH):I_8,t12(EAX):I_32 
	02D67867 I15: MOVSX t26(EAX):I_32,t25(BH):I_8 

BH is defined if no early_prop. But actually EBX is defined before the above part of code
and assumed to keep unmodifed and be used later. So some part of EBX (BH) is changed uncarefully
and an exception is thrown out finally. With early_prop the bug is gone because there is no
changes about EBX.

I verified my guess by changing server_static.emconf to only use bin packing register allocation
and found no bug when running startup.helloworld. My basic assumption is early_prop is NOT
indispensable and each optimization pass should be independent as much as possible.

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