> > Hmm, I see. I wonder how complex the expressions are and if we can't simply > > compare AO properties of MEM_REF at toplevel and then dispatch to > > operand_equal_p (..., OEP_ADDRESS_OF) > > which would make more sense to me. > > I can't see how we can do that comparison conservatively without resorting > to exact equality. The reason is that the two MEM_EXPRs e1 and e2 have > to behave equal TBAA-wise when compared against arbitrary e3. We
This is not very different from what we do at gimple level i.e. in tail merging, ipa-icf or load/store motion. Maybe we want something like OEP_ALIAS or OEP_STRUCTURAL flag to control this... > can be sure this is the case if e1 and e2 have alias-set zero or if > they are structurally equivalent. But that's all I think. > > > I would basically expect decls and mem_refs here. Reason why I started > > to look into that is that I added sanity check that operand_equal_p > > (...,0) is not called on things that do not have value (function types > > and incomplete types) and this is one of places that fires. > > MEM_EXPR can be arbitrarily complex (including array-refs with > variable index SSA name use for example). > > > > > > > > I will look more into nonoverlapping_memrefs_p and ao_ref_from_mem. The > > > > first > > > > one may need some update to tree-alias infrastructure.... > > > > > > I'd rather remove it completely (at least that was my plan eventually). > > > rtx_refs_may_alias_p is supposed to handle everything it handles. > > > > Yep, that was my feeling from looking into that yesterday.... > > So the experiment to carry out is (same for all other callers) > > Index: gcc/alias.c > =================================================================== > --- gcc/alias.c (revision 228597) > +++ gcc/alias.c (working copy) > @@ -2710,10 +2710,10 @@ true_dependence_1 (const_rtx mem, machin > if (mems_in_disjoint_alias_sets_p (x, mem)) > return 0; > > - if (nonoverlapping_memrefs_p (mem, x, false)) > - return 0; > - > - return rtx_refs_may_alias_p (x, mem, true); > + int tem = rtx_refs_may_alias_p (x, mem, true); > + if (tem) > + gcc_assert (!nonoverlapping_memrefs_p (mem, x, false)); > + return tem; > } > > /* True dependence: X is read after store in MEM takes place. */ > > and analyze what fires (or hope nothing does). OK, will give it a try... Honza > > Richard. > > > Honza > > > > > > -- > Richard Biener <rguent...@suse.de> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB > 21284 (AG Nuernberg)
