https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77278
--- Comment #15 from rguenther at suse dot de <rguenther at suse dot de> --- On Tue, 4 Jun 2019, hubicka at ucw dot cz wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77278 > > --- Comment #14 from Jan Hubicka <hubicka at ucw dot cz> --- > > > > Yeah, I do remember this. I think we settled on the above > > (previously you had dim[7] in the library I think) to be > > compatible. Still a C simple testcase complains: > > > > typedef struct { int ndim; int dim[]; } *descp; > > void foo (descp d); > > > > void bar() > > { > > struct { int ndim; int dim[2]; } desc; > > desc.ndim = 2; > > foo (&desc); > > } > > > > t2.c: In function ‘bar’: > > t2.c:8:8: warning: passing argument 1 of ‘foo’ from incompatible pointer > > type [-Wincompatible-pointer-types] > > foo (&desc); > > ^~~~~ > > t2.c:2:17: note: expected ‘descp’ {aka ‘struct <anonymous> *’} but > > argument is of type ‘struct <anonymous> *’ > > void foo (descp d); > > ~~~~~~^ > > > > and we probably assign different alias sets to both. > > Curiously enough in C version of the LTO testcase I get no warning now > since we simplify function type and thus both pointers are turned into > incomplete pointers and considered TBAA compatible. > After lunch I will check why the warning triggers here. > > Still the alias set is different, so I think we more or less get lucky > by using base+offset tests first since array descriptors are accessed > directly after constant propagation of poointers. > > > > Now to make aliasing happy both the Frontend and LTO have to > > compute the same TYPE_CANONICAL for _all_ of the array > > descriptor types. You can either go and allocate > > dim always to the max size statically or in the Fortran > > FE use self-referential types (not sure if you then can > > statically instantiate an object of such type...) or > > rewrite all accesses to the fixed-dimension statically > > allocated array descriptors to go via the dim[] type > > (I think I suggested the latter elsewhere). > > > > So instantiate my_descriptor and then store for further > > use VIEW_CONVERT_EXPR <generic-descriptor-type> (my_descriptor). > > > > I hope that doesn't defeat [IPA] optimization ... > I think Martin's code generally gives up on type mismaches so it > is quite possible it gives up already. > > An option would be also to teach LTO that array descriptors are > special types aliasing with each other but not aliasing with > anything else. I'd rather not do that ;) Btw, I wonder what happens at the call boundary inside a single fortran module where the caller passes a dim[2] array to a subroutine handling arbitrary dimension arrays? I suspect the IL would have the very same TBAA issue. Can you produce a fortran testcase that exposes such a case so we can have a look into the details?
