Re: [Valgrind-developers] wrong diagnostics off uninitialised value if using incw

[Julian S. <js...@ac...>]

Yes, please submit a bug report.  It would also be good to have
a C program which reproduced the problem, if you can construct
one.=20

J


On Tuesday 24 October 2006 21:41, Rafael Esp=EDndola wrote:
> Generally when compiling a ((short|1) =3D=3D constant) compression, gcc
> generates this code:
>
> ---------------------------------------
>         movl    (%rdi), %eax
>         orl     $1, %eax
>         cmpw    $43, %ax
>         je      .L17
> ---------------------------------------
>
> This works correctly on valgrind even if the second half of eax is
> undefined (cmpw doesn't use it).
>
> But if the constant is 0xffff, the generated code is
>
> ------------------------------------
>         movl    (%rdi), %eax
>         orl     $1, %eax
>         incw    %ax
>         je      .L17
> ------------------------------------
>
> In this case valgrind prints the warning
> ------------------------------------
> Conditional jump or move depends on uninitialised value(s)
> ------------------------------------
>
> But the Z flag doesn't depend on the high part of eax. So the jump
> doesn't depend on uninitialized values.
>
> Should I submit a bug report? Where should I look in the code to try
> to fix this?
>
> Thanks,
> Rafael
>
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