llvm dev - May 2016 - struct layout in AIX

Hi.

Is the alignment of a struct be computed in the constructor of StructLayout
class? I wonder that the position of a member in the struct has been
considered in llvm? Because the alignment of a member is dependent to the
position in the struct in AIX platform according to the table in
http://www.ibm.com/support/knowledgecenter/SSGH2K_13.1.2/com.ibm.xlc131.aix.doc/proguide/alignment.html
(`power` alignment setting)


   1. In aggregates, the first member of this data type is aligned
   according to its natural alignment value; subsequent members of the
   aggregate are aligned on 4-byte boundaries.


Thanks
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For C code, record layout decisions are made here:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/RecordLayoutBuilder.cpp?view=markup

LLVM's struct layout rules are only important if you aren't using clang.

On Wed, May 4, 2016 at 8:06 PM, Zeson Wu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi.
>
> Is the alignment of a struct be computed in the constructor of
> StructLayout class? I wonder that the position of a member in the struct
> has been considered in llvm? Because the alignment of a member is dependent
> to the position in the struct in AIX platform according to the table in
>
http://www.ibm.com/support/knowledgecenter/SSGH2K_13.1.2/com.ibm.xlc131.aix.doc/proguide/alignment.html
> (`power` alignment setting)
>
>
>    1. In aggregates, the first member of this data type is aligned
>    according to its natural alignment value; subsequent members of the
>    aggregate are aligned on 4-byte boundaries.
>
>
> Thanks
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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> Because the alignment of a member is dependent to the position in the
struct in AIX platform according to the table in
http://www.ibm.com/support/knowledgecenter/SSGH2K_13.1.2/com.ibm.xlc131.aix.doc/proguide/alignment.html
And on the -qalign and #pragma options, which do get used. The commercial
product I work on needs to be compiled -qalign=natural on AIX, or it doesn’t
work (I can explain the reasons if anyone's interested, but they're
complex, boring, and hard to work around).

--
John Dallman

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