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Re: Should we compile Guile with -fno-strict-aliasing?

From: Ludovic Courtès
Subject: Re: Should we compile Guile with -fno-strict-aliasing?
Date: Sun, 29 Jan 2012 22:10:40 +0100
User-agent: Gnus/5.110018 (No Gnus v0.18) Emacs/24.0.90 (gnu/linux)


Andy Wingo <address@hidden> skribis:

> On Fri 27 Jan 2012 20:02, Mark H Weaver <address@hidden> writes:
>> For many years, Linux (the kernel) has used the -fno-strict-aliasing
>> compiler option to disable certain tricky optimizations that depend upon
>> a very strict reading of the aliasing rules of modern C standards.  It
>> turns out that it's quite difficult to write robust code in the presence
>> of those optimizations.  I have not researched this issue carefully, but
>> it seems that several Guile bugs may be related to this problem.
>> Perhaps we should simply add this compiler flag where its available, at
>> least in the short term.  What do you think?
> So, we added it, for GCC; cool.  I was wondering though whether we might
> be able to get by with something more limited, at least on GCC.  Have
> you looked at __attribute__((__may_alias__))?  It does seem like a good
> idea to add it to SCM, as we frequently alias SCM and scm_t_bits values
> at the very least.

Yes, why not, but post-2.0.4 maybe?

> Also adding it to struct scm_vm_frame would also fix the vm frame
> issue.

I’d say “may”, or “might”, rather than “would”.  ;-)


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