On 6/5/19 6:51 AM, Richard Biener wrote: > > The following was inspired by Marins work on escapes of locals > and the discussion there. It teaches points-to analysis that > the point of function return is special and thus escapes through > that a) do not influence other points-to solutions, b) can be > pruned of all locals. > > This is one example of reasonably simple "post-processing". > > The effects are small, I've done statistics, counting the number > of variables we do not mark escaped only after this patch. This > number is usually zero, sometimes one and a few cases more > (but never more than 11) during bootstrap: > > 0 95830 > 1 19268 > 2 19 > 3 2 > 5 2 > 6 1 > 8 1 > 11 1 > > so not sure if it is worth all the effort. It does allow us > to do more DSE but that requires the accesses to be indirect > which is not often true for locals. > > Bootstrapped / tested on x86_64-unknown-linux-gnu. > > Martin, does this help you at all? Anybody thinks this is > worth the trouble? > > Thanks, > Richard. > > 2019-06-05 Richard Biener <rguent...@suse.de> > > * tree-ssa-structalias.c: Include tree-cfg.h. > (make_heapvar): Do not make heap vars artificial. > (find_func_aliases_for_builtin_call): Handle stack allocation > functions. > (find_func_aliases): Delay processing of simple enough returns > in non-IPA mode. > (set_uids_in_ptset): Adjust. > (find_what_var_points_to): Likewise. > (solve_constraints): Do not dump points-to sets here. > (compute_points_to_sets): Post-process return statements, > amending the escaped solution. Dump points-to sets afterwards. > (ipa_pta_execute): Dump points-to sets. > > * gcc.dg/tree-ssa/alias-37.c: New testcase. > * gcc.dg/torture/20190604-1.c: Likewise. > * gcc.dg/tree-ssa/pta-callused.c: Adjust. It's a fair amount of code for a corner case, _but_ I think it's a step in the right direction. I suspect we ought to be using the alias oracle solutions for more than we are today and improved precision certainly doesn't hurt.
Jeff
