[LLVMdev] Language lawyer question

Daniel Berlin dberlin at dberlin.org
Wed Mar 12 13:05:27 PDT 2008

On Wed, Mar 12, 2008 at 3:49 PM, Mike Stump <mrs at apple.com> wrote:
> On Mar 11, 2008, at 8:42 PM, Dale Johannesen wrote:
>  > Looking through the gcc testsuite turned up an interesting edge
>  > case.  Let's assume our target leaves a hole for alignment in struct
>  > x, as do x86 and powerpc.  Do you think the following code can
>  > validly abort?
>  No.  The value of the object referred to be the left hand side must be
>  replaced by the object on the right.  The objects are defined to be a
>  sequence of sizeof(x) bytes (I'm assuming the testcase does struct x
>  X, Y;).  If a byte isn't so updated, trivially, the object has not
>  been replaced.

Except that the standard specifically says the value of the padding
bytes are undefined, and that you can do structure copies by member.

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