[PATCH] fix struct alignment problem with empty base class

[Andrea_DiBiagio at sn.scee.net]

Hi Eli,

> From: Eli Friedman <eli.friedman at gmail.com>
> On Fri, Jul 12, 2013 at 6:46 AM,  <Andrea_DiBiagio at sn.scee.net> wrote:
> > Hi,
> > attached is a patch to fix an alignment problem affecting classes 
derived
> > from a base with no fields but with strong alignment constraints.
> >
> > Let A be a strongly aligned struct/class with no fields.
> > Let B be a derived class with A as its direct base class.
> >
> > When performing the layout of B, A is correctly placed at offset 0 of 
B.
> > However, the alignment of B is wrongly left unchanged.
> >
> > <snip>
> >
> > This patch fixes the problem with the alignment and adds a test case 
to
> > verify that the alignment info is correctly updated.
> > One thing to note is that this change may have an effect on binary
> > compatibility between obj/libs built with and without this change (but
> > only in the - hopefully rare - case described above).
> 
> Index: test/CodeGenCXX/alignof.cpp
> ===================================================================
> --- test/CodeGenCXX/alignof.cpp (revision 0)
> +++ test/CodeGenCXX/alignof.cpp (revision 0)
> 
> Please move the test into SemaCXX, and use static_assert to verify the
> alignment instead of checking the IR.

I moved the test from CodeGenCXX to SemaCXX.
I renamed the test file into "alignment-of-derived-class.cpp" because I 
noticed that there was already a test called alignof.cpp in SemaCXX  which 
however tested something completely different.

> 
> +    // Remember max struct/class alignment.
> 
> This comment is useless.

I removed the comment above from the patch.

> 
> Otherwise, looks fine.
> 

Thanks!
In case, if this new version of the patch is ok, could you please commit 
it for me?

Thanks in advance,
Andrea Di Biagio
SN Systems - Sony Computer Entertainment Group.



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