ipa: Prune any IPA-CP aggregate constants known by modref to be killed (111157)

PR 111157 shows that IPA-modref and IPA-CP (when plugged into value
numbering) can optimize out a store both before a call (because the
call will overwrite it) and in the call (because the store is of the
same value) and by eliminating both create miscompilation.

This patch fixes that by pruning any constants from the list of IPA-CP
aggregate value constants that it knows the contents of the memory can
be "killed."  Unfortunately, doing so is tricky.  First, IPA-modref
loads override kills and so only stores not loaded are truly not
necessary.  Looking stuff up there means doing what most of what
modref_may_alias may do but doing exactly what it does is tricky
because it takes also aliasing into account and has bail-out counters.

To err on the side of caution in order to avoid this miscompilation we
have to prune a constant when in doubt.  However, pruning can
interfere with the mechanism of how clone materialization
distinguishes between the cases when a parameter was entirely removed
and when it was both IPA-CPed and IPA-SRAed (in order to make up for
the removal in debug info, which can bump into an assert when
compiling g++.dg/torture/pr103669.C when we are not careful).

Therefore this patch:

  1) marks constants that IPA-modref has in its kill list with a new
     "killed" flag, and
  2) prunes the list from entries with this flag after materialization
     and IPA-CP transformation is done using the template introduced in
     the previous patch

It does not try to look up anything in the load lists, this will be
done as a follow-up in order to ease review.

gcc/ChangeLog:

2023-10-27  Martin Jambor  <mjambor@suse.cz>

	PR ipa/111157
	* ipa-prop.h (struct ipa_argagg_value): Newf flag killed.
	* ipa-modref.cc (ipcp_argagg_and_kill_overlap_p): New function.
	(update_signature): Mark any any IPA-CP aggregate constants at
	positions known to be killed as killed.  Move check that there is
	clone_info after this pruning.
	* ipa-cp.cc (ipa_argagg_value_list::dump): Dump the killed flag.
	(ipa_argagg_value_list::push_adjusted_values): Clear the new flag.
	(push_agg_values_from_plats): Likewise.
	(ipa_push_agg_values_from_jfunc): Likewise.
	(estimate_local_effects): Likewise.
	(push_agg_values_for_index_from_edge): Likewise.
	* ipa-prop.cc (write_ipcp_transformation_info): Stream the killed
	flag.
	(read_ipcp_transformation_info): Likewise.
	(ipcp_get_aggregate_const): Update comment, assert that encountered
	record does not have killed flag set.
	(ipcp_transform_function): Prune all aggregate constants with killed
	set.

gcc/testsuite/ChangeLog:

2023-09-18  Martin Jambor  <mjambor@suse.cz>

	PR ipa/111157
	* gcc.dg/lto/pr111157_0.c: New test.
	* gcc.dg/lto/pr111157_1.c: Second file of the same new test.

0 files changed, 0 insertions, 0 deletions