Re: [PATCH] tree-optimization/109304 - properly handle instrumented aliases

[Jan Hubicka <hubicka@ucw.cz>]

> On Tue, 28 Mar 2023, Richard Biener wrote:
> 
> > When adjusting calls to reflect instrumentation we failed to handle
> > calls to aliases since they appear to have no body.  Instead resort
> > to symtab node availability.  The patch also avoids touching
> > internal function calls in a more obvious way (builtins might
> > have a body available).
> > 
> > profiledbootstrap & regtest running on x86_64-unknown-linux-gnu.
> > 
> > Honza - does this look OK?
> > 	PR tree-optimization/109304
> > 	* tree-profile.cc (tree_profiling): Use symtab node
> > 	availability to decide whether to skip adjusting calls.
> > 	Do not adjust calls to internal functions.
> > @@ -842,12 +842,15 @@ tree_profiling (void)
> >  	    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> >  	      {
> >  		gcall *call = dyn_cast <gcall *> (gsi_stmt (gsi));
> > -		if (!call)
> > +		if (!call || gimple_call_internal_p (call))
> >  		  continue;
> >  
> >  		/* We do not clear pure/const on decls without body.  */
> >  		tree fndecl = gimple_call_fndecl (call);
> > -		if (fndecl && !gimple_has_body_p (fndecl))
> > +		cgraph_node *callee;
> > +		if (fndecl
> > +		    && (callee = cgraph_node::get (fndecl))
> > +		    && callee->get_availability (node) == AVAIL_NOT_AVAILABLE)

As discussed earlier, the testcase I posted can be adjusted to put the
const declared wrapper into another translation unit, so I think we will
need to drop the visibility check completely.  But as discussed, it is
wrong code issue, but not a regression, so we may go with the
availability check as you suggest. So the patch is OK. 


I wonder if we do not want to drop it everywhere (as we plan for next
stage1 anyway).  I think similar ICE as in the PR can be produced with
LTO. In normal situation declaration merging will do the right thing:
If you have unit A calling const foo externally, it won't get processed
by the code above.  However unit B declaring foo will get it downgraded
to non-const.

Now at WPA time we will read both A and B and in declaration merging B's
definition will prevail.  This won't happen if lto_symtab_merge_p
returns false which can probably be triggered by adding warning/error
attribute to B's declaration but not to A's.

It is however really side case and I am worried about dropping
pure/const from builtin declarations...

Honza