optimization/9904: aliasing proböem

optimization/9904: aliasing proböem

[andreas]

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>Number:         9904
>Category:       optimization
>Synopsis:       aliasing proböem
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Mar 02 17:36:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Andreas Bogk
>Release:        3.2.2 20030109 (Debian prerelease), and actually all versions of gcc 3 before that I've tested
>Organization:
>Environment:
Debian-unstable on x86, also reported on a wide range of other systems
>Description:
I'm having a hard time nailing this one down in a
conveniently-reproducible form.  I'm sending you this mail anyways, in
the hope that it will be useful to you.

We're seeing a problem with gcc 3 when being used on the output of
d2c, the Dylan-to-C-translator from the Gwydion project.  The code
works fine when compiled with gcc 2.95; or with gcc 3 and reduced
optimizer settings, but reports internal errors where there should be
none when compiled with -O2.

In particular, the code works when compiled with '-O2
-fno-strict-aliasing', and doesn't work when compiled with '-O2'.  The
piece of code that gets confused is appended.  I have marked the
branches that are taken.  Functions called are from a different
library.  The behaviour does not depend on whether that other library
is compiled with -fno-strict-aliasing or not.

The function values_sequence returns its first argument plus or minus
an offset, creating an alias for the first argument.
>How-To-Repeat:
I can't provide a self-contained example of the bug at the moment, but I'll keep trying. I'm pretty sure that the provided code snippet is the one that's problematic, though.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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