Re: Structure Return Testcase

[Jeffrey A Law <law at redhat dot com>]

  In message <Pine.LNX.4.32.0103151901200.20427-100000@kern.srcf.societies.cam.
ac.uk>you write:
  > On Thu, 15 Mar 2001, Jeffrey A Law wrote:
  > 
  > > According to the C standard (thanks Mark):
  > > 
  > >   If the value being stored in an object is accessed from another
  > >   object that overlaps in any way the storage of the first object,
  > >   then the overlap shall be exact and the two objects shall have
  > >   qualified or unqualified versions of a compatible type; otherwise,
  > >   the behavior is undefined.
  > > 
  > > 
  > > Given the definition of U we don't have an exact overlap between the lhs 
  > and
  > > rhs which violates the rule above, thus triggering undefined behavior.
  > 
  > As I've previously noted, this is essentially the testcase of DR#001, the
  > example added to 6.6.6.4 of the old standard by TC1, and the example of
  > 6.8.6.4 paragraph 4 in C99.  Footnote 135 seems quite clear.  "The return
  > statement is not an assignment.  The overlap restriction of subclause
  > 6.5.16.1 does not apply to the case of function return."
OK.  Ouch.  This likely means we're going to end up doing double copies for
most/all structure returns or using memmove which isn't too efficient either. 
Sigh.

jeff