https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48885
--- Comment #14 from vries at gcc dot gnu.org --- (In reply to rguent...@suse.de from comment #13) > On Wed, 23 Sep 2015, vries at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48885 > > > > --- Comment #12 from vries at gcc dot gnu.org --- > > (In reply to Richard Biener from comment #11) > > > I'm testing the above simple fix and amend the comment. > > > > Consider the example with functions f and g I gave in comment 10. Using the > > patch from comment 11, I get at ealias: > > ... > > void f(int* __restrict__&, int*) (intD.9 * restrict & restrict pD.2252, > > intD.9 > > * p2D.2253) > > { > > intD.9 * _3; > > > > # VUSE <.MEM_1(D)> > > # PT = { D.2265 } (nonlocal) > > _3 = MEM[(intD.9 * restrict &)p_2(D) clique 1 base 1]; > > > > # .MEM_4 = VDEF <.MEM_1(D)> > > MEM[(intD.9 *)_3 clique 1 base 2] = 1; > > > > # .MEM_6 = VDEF <.MEM_4> > > MEM[(intD.9 *)p2_5(D) clique 1 base 0] = 2; > > ... > > > > AFAIU, this is incorrect. The two stores can be now disambiguated based on > > same > > clique/different base, but in fact the stores can alias (in fact they do, in > > the "f (gp, gp)" call from g). > > How is this a valid testcase? > You are accessing g()s *gp through > p and p2 even though p is marked as restrict. To be exact, p is a restrict reference to a restrict pointer. And AFAIU it's a valid test-case. > Did you mean to write > > void > f (int *&__restrict__ p, int *p2) > > ? No. I'll try explain, renaming variables to help clarification, and adding a call to g for completeness: ... void f (int *__restrict__ &__restrict__ fp, int *fp2) { *fp = 1; *fp2 = 2; } void g (int *__restrict__ gp) { f (gp, gp); } void h (void) { int ha; g (&ha); } ... Let's look at the three restricts in the example. First, there's the second restrict in "int *__restrict &__restrict fp", which is a reference to object gp. Since object gp is not modified during f, the restrict has no consequence. Then there's the restrict in "int *__restrict__ gp". The object pointed to is ha, and it's modified during g. So all accesses to ha during g need to be based on gp. And that is the case. The '*fp2 = 1' is based on gp. And the '*fp2 = 2' is based on gp. Finally, there's the first restrict in "int *__restrict &__restrict fp". That's a copy of the type of gp.
