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Date: Tue, 11 Apr 2017 07:37:00 -0000
From: Richard Biener <rguenther@suse.de>
To: Pedro Alves <palves@redhat.com>
cc: Jason Merrill <jason@redhat.com>,     Bernd Edlinger <bernd.edlinger@hotmail.de>,     Jakub Jelinek <jakub@redhat.com>, Jonathan Wakely <jwakely@redhat.com>,     Florian Weimer <fweimer@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>,     Jeff Law <law@redhat.com>
Subject: Re: [PATCH] Add a new type attribute always_alias (PR79671)
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References: <AM4PR0701MB216292327A207737064C3CA3E40A0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <20170405160333.GR4425@redhat.com> <20170405160849.GV17461@tucnak> <AM4PR0701MB2162884DCF4538DC0FF5C2F1E40A0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <AM4PR0701MB21623337A5C0C1850D3DF4C7E40A0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <alpine.LSU.2.20.1704060925130.30715@zhemvz.fhfr.qr> <AM4PR0701MB2162E2D2B29F0C1495DC0EC3E40D0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <alpine.LSU.2.20.1704070850260.30715@zhemvz.fhfr.qr> <AM4PR0701MB2162B27950FE5CB041677DF0E40C0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <A970E82F-1A82-43A9-B283-06B71A1CBB7F@suse.de> <AM4PR0701MB2162DF600463D9C655DC8FA4E40C0@AM4PR0701MB2162.eurprd07.prod.outlook.com> <CADzB+2nbCg+vd+Q4PmGE6amfDapdksMC8ybLCrBzWDPjhBB8-A@mail.gmail.com> <alpine.LSU.2.20.1704101440150.30715@zhemvz.fhfr.qr> <aa639918-7ac8-f880-67f2-42f9ea4988f2@redhat.com>
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On Mon, 10 Apr 2017, Pedro Alves wrote:

> On 04/10/2017 01:50 PM, Richard Biener wrote:
> 
> > +void *operator new(__SIZE_TYPE__, void *p2) { return p2; }
> > +struct B { B(int i_) : i(i_) {} int i; };
> > +struct X
> > +{
> > +  unsigned char buf[sizeof (B)];
> > +};
> 
> Pedantically, shouldn't there be something here to enforce
> X's alignment to be at least the same as B's ?
> 
> > +
> > +int __attribute__((noinline)) foo()
> > +{
> > +  X x, y;
> > +  new (&x) B (0);

Right.  I'll do

  X x alignas(B), y alignas(B);

Meanwhile need to debug a LTO bootstrap failure caused by the patch.

Richard.