http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8081
--- Comment #26 from rguenther at suse dot de <rguenther at suse dot de> 2012-01-13 09:08:30 UTC --- On Fri, 13 Jan 2012, ebotcazou at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8081 > > Eric Botcazou <ebotcazou at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |ebotcazou at gcc dot > | |gnu.org > > --- Comment #25 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-13 > 08:36:56 UTC --- > > It's of course not that easy as we gimplify before un-nesting. The frontend > > would be responsible to arrange things that way, similar to how we pass > > a return slot in the C++ frontend (DECL_BY_REFERENCE on the DECL_RESULT > > variable). Like for the attached patch. Passes > > > > extern void abort (void); > > int > > main (int argc, char **argv) > > { > > int size = 10; > > typedef struct > > { > > char val[size]; > > } > > block; > > block a, b; > > block __attribute__((noinline)) > > retframe_block () > > { > > return *(block *) &b; > > } > > b.val[0] = -1; > > b.val[1] = -2; > > a=retframe_block (); > > if (a.val[0] != -1 > > || a.val[1] != -2) > > abort (); > > return 0; > > } > > > > I'm not sure if one can construct a testcase where using return-slot > > optimization causes wrong-code generation. Alternatively checking > > DECL_BY_REFERENCE on the callees DECL_RESULT instead of applying it to > > all VLA types could work (though not for indirect calls). > > You should ask specialists. :-) In Ada, we do this routinely and the strategy > used is that of the "forced RSO": we generate INIT_EXPR instead of MODIFY_EXPR > and we create an explicit temporary if we detect potential overlap. > > Btw, I don't understand why you're mixing DECL_BY_REFERENCE and RSO here, just > > Index: gimplify.c > =================================================================== > --- gimplify.c (revision 183104) > +++ gimplify.c (working copy) > @@ -4417,6 +4417,9 @@ gimplify_modify_expr_rhs (tree *expr_p, > /* It's OK to use the target directly if it's being > initialized. */ > use_target = true; > + else if (variably_modified_type_p (TREE_TYPE (*to_p), > NULL_TREE)) > + /* Always use the target for variable-sized types. */ > + use_target = true; > else if (TREE_CODE (*to_p) != SSA_NAME > && (!is_gimple_variable (*to_p) > || needs_to_live_in_memory (*to_p))) > > works for me on the testcase. Ah, ok. So I suppose the Frontend could force RSO here as well by just setting CALL_EXPR_RETURN_SLOT_OPT on the CALL_EXPR. Not sure which approach is better. -- Configure bugmail: http://gcc.gnu.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug. -- To UNSUBSCRIBE, email to debian-gcc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/bug-8081-5724-z3n43n1...@http.gcc.gnu.org/bugzilla/
