[Qemu-devel] git commit c832e3de chokes gcc-4.5.2 (out of memory error)

[Qemu-devel] git commit c832e3de chokes gcc-4.5.2 (out of memory error)

[walt]

Hi qemu team,

The following commit has a strange side-effect on gcc-4.5.2:

commit c832e3de64f1069313fc0672087791cc3dd5b4d8
Author: Richard Henderson
Date:   Mon Jan 10 19:23:47 2011 -0800

     target-i386: Use deposit operation.
     
     Use this for assignment to the low byte or low word of a register.
     
     Acked-by: Aurelien Jarno
     Signed-off-by: Richard Henderson
     Signed-off-by: Edgar E. Iglesias


The new code in 'target-i386/translate.c' compiles just fine with gcc-4.4.4,
using less than 1GB of RAM, but gcc-4.5.2 uses the whole GB and then fills
up 2GB of swap space in addition while the machine grinds slowly to a halt.

I'm using the latest qemu.git, and when I revert that one commit, gcc-4.5.2
chugs along just fine with my puny 1GB of RAM.

I filed a bug against gcc-4.5.2 a few hours ago, but I notice that another
ten or fifteen bugs were filed *after* mine, so I don't have much hope that
anyone will pay much attention :(

I'm hoping someone here might know how to find the source of the problem
so I can add some helpful details to my bug report.

Thanks for any suggestions, and thanks for qemu :)

Re: [Qemu-devel] git commit c832e3de chokes gcc-4.5.2 (out of memory error)

[Peter Maydell]

On 18 March 2011 23:31, walt <w41ter@gmail.com> wrote:
> The following commit has a strange side-effect on gcc-4.5.2:
> The new code in 'target-i386/translate.c' compiles just fine with gcc-4.4.4,
> using less than 1GB of RAM, but gcc-4.5.2 uses the whole GB and then fills
> up 2GB of swap space in addition while the machine grinds slowly to a halt.

I'm wondering whether this is
https://bugs.launchpad.net/gcc-linaro/+bug/714921
again (an upstream gcc bug, fix in-progress).

> I'm hoping someone here might know how to find the source of the problem
> so I can add some helpful details to my bug report.

1. If you compile with -fno-var-tracking does it still use lots
of memory?

2. (for the ludicrously enthusiastic only) build a gcc with the patches
listed in that bug report and see if the problem goes away...

-- PMM

[Qemu-devel] Re: git commit c832e3de chokes gcc-4.5.2 (out of memory error)

[walt]

On 03/18/2011 03:44 PM, Peter Maydell wrote:
> On 18 March 2011 23:31, walt<w41ter@gmail.com>  wrote:
>> The following commit has a strange side-effect on gcc-4.5.2:
>> The new code in 'target-i386/translate.c' compiles just fine with gcc-4.4.4,
>> using less than 1GB of RAM, but gcc-4.5.2 uses the whole GB and then fills
>> up 2GB of swap space in addition while the machine grinds slowly to a halt.
>
> I'm wondering whether this is
> https://bugs.launchpad.net/gcc-linaro/+bug/714921
> again (an upstream gcc bug, fix in-progress).
>
>> I'm hoping someone here might know how to find the source of the problem
>> so I can add some helpful details to my bug report.
>
> 1. If you compile with -fno-var-tracking does it still use lots
> of memory?

That flag fixes the memory problem, so my bug must be the same, I think.

> 2. (for the ludicrously enthusiastic only) build a gcc with the patches
> listed in that bug report and see if the problem goes away...

I fetched the patch and found that it doesn't apply cleanly to the heavily
patched gentoo sources :(

Many thanks for the excellent clue.