On Fri, Nov 25, 2022 at 09:26:34PM +0100, Richard Biener via Gcc-patches wrote:
> > We could
> > probably keep tract if any instrumented code was ever inlined into a
> > given function and perhaps just start ignoring attributes set on types?
>
> But ignoring attributes on types makes all indirect calls not
> const/pure annotatable (OK, they are not pure annotatable because of
> the above bug). I really don't see how to conservatively solve this
> issue?
> Maybe we can ignore all pure/const when the cgraph state is
> in profile-instrumented state? Of course we have multiple "APIs"
> to query that.
I think that's the way to go. But we'd need to arrange somewhere during IPA
to add vops to all those pure/const calls if -fprofile-generate (direct or
indirect; not sure what exact flags) and after that make sure all our APIs
don't return ECF_CONST, ECF_PURE or ECF_LOOPING_CONST_OR_PURE.
Could be e.g.
if (whatever)
flags &= ~(ECF_CONST | ECF_PURE | ECF_LOOPING_CONST_OR_PURE);
at the end of flags_from_decl_or_type, internal_fn_flags, what else?
Although, perhaps internal_fn_flags don't need to change, because internal
calls don't really have callees.
Or is just ECF_CONST enough given that ECF_PURE is on fndecls and not
types?
Or perhaps just start ignoring TYPE_READONLY -> ECF_CONST in
flags_from_decl_or_type if that flag is on?
Is that rewriting currently what tree_profiling does in the
/* Update call statements and rebuild the cgraph. */
FOR_EACH_DEFINED_FUNCTION (node)
spot where it calls update_stmt on all call statements?
If so, could we just set that global? flag instead or in addition to
doing those node->set_const_flag (false, false); calls and
change flags_from_decl_or_type, plus I guess lto1 should set that
flag if it is global on start as well if
!flag_auto_profile
&& (flag_branch_probabilities || flag_test_coverage || profile_arc_flag)
?
I think just ignoring ECF_CONST from TYPE_READONLY might be best, if we
have external functions like builtins from libc/libm and don't have their
bodies, we can still treat them as const, the only problem is with the
indirect calls where we don't know if we do or don't have a body for
the callees and whether we've instrumented those or not.
Jakub
