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From "Xiao-Feng Li" <xiaofeng...@gmail.com>
Subject Re: [jira] Created: (HARMONY-6016) [drlvm][jit] An undetected interference in Graph Coloring register allocation
Date Thu, 13 Nov 2008 09:58:45 GMT
Good catch! It is a really hard bug. Thanks.


On Thu, Nov 13, 2008 at 4:50 PM, Xiaoming Gu (JIRA) <jira@apache.org> wrote:
> [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.
> --
> This message is automatically generated by JIRA.
> -
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