Re: Detect EAF flags in ipa-modref

[Jan Hubicka <hubicka@ucw.cz>]

> > 
> > Richi, I think we can add "safe" parameter to gimple_call_arg_flags and
> > bypass this logic when we use it for warnings only (having body that
> > does not use the value is quite strong hint that it is unused by the
> > function).
> 
> Eh, please not.

OK, I do not care that much as long as we do not have false positives
everywhere :)

Hadling EAF_UNUSED and CONST functions is necessary so we do not get
false positive caused by us optimizing code out.  In this case of not
trusing EAF_UNUSED flag we will not optimize, so I do not really care.

Martin, we collected very many warnings when building with
configure --with-build-config=bootstrap-lto.mk
This patch fixes some of them, but there are many others, can you take a
look?

For the testcase in PR I think it is enough to use default_is_empty_type
to disable the warning, but it is not clear to me why the code uses
default_is_empty_record at first place.
> 
> > 
> > I played with bit more testcases and found that we also want to disable
> > warning for const functions and sometimes EAF_UNUSED flag is dropped
> > becaue of clobber that is not necessary to do.  If function only clobber
> > the target it can be considered unused past inlining.
> > 
> > I am testing this improved patch and plan to commit if there are no
> > complains, but still we need to handle binds_to_current_def.
> > 
> > On the other direction, Martin, I think we may also warn for args
> > that are !EAF_UNUSED and !EAF_NOCLOBBER.  This will catch some cases
> > where user did not add "const" specifier to the declaration but
> > parameter is detected to be readonly.
> > 
> > I also noticed that we do not detect EAF_UNUSED for fully unused
> > parameters (with no SSA names associated with them).  I will fix that
> > incrementally.
> 
> Make sure to not apply it based on that reason to aggregates ;)

Sure, we already have detection of unused params in ipa-prop, so I guess
we want is_giple_ref (parm) && !default_def to imply EAF_UNUSED.

Honza