[Bug middle-end/50325] [4.7 Regression] 76 new fails with rev. 177691

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50325

--- Comment #22 from rguenther at suse dot de <rguenther at suse dot de> 2011-12-01 09:22:19 UTC ---
On Thu, 17 Nov 2011, krebbel at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50325
> 
> --- Comment #14 from Andreas Krebbel <krebbel at gcc dot gnu.org> 2011-11-17 15:23:26 UTC ---
> As the tests from Ian Sandoe and Dominique d'Humieres show, the Darwin/AIX
> regressions disappear when limiting the extract_bit_field invocation to
> fieldmode == BLKmode (as it was in the "Experimental fix" attached to the
> bugzilla).
> 
> But I'm not sure this is the right fix. In general also the other modes need
> correct handling here. If the correct extraction of the source operand really
> depends on things like function arg padding the handling in store_bit_field is
> doomed to be incomplete.
> 
> Richard, could you please have a look!

Well, store_bit_field is supposed to do generic memory fiddling,
dependency on function arg padding is unwanted - and thus such
dependency has to be reflected by argument adjustments in the
caller.

[I can smell some weirdness we might have here though,
but surely latent - if you have such argument (small C testcase
I can look at with a cross?), take its address and perform
aggregate assignment through a pointer - does that still
work?  Thus, does the memory layout of s and q in

foo (struct S s)
{
  struct S q;
}

really differ?