sra: Avoid creating TBAA hazards (PR118924)

The testcase in PR 118924, when compiled on Aarch64, contains an
gimple aggregate assignment statement in between different types which
are types_compatible_p but behave differently for the purposes of
alias analysis.

SRA replaces the statement with a series of scalar assignments which
however have LHSs access chains modeled on the RHS type and so do not
alias with a subsequent reads and so are DSEd.

SRA clearly gets its "same_access_path" logic subtly wrong.  One issue
is that the same_access_path_p function probably should be implemented
more along the lines of (parts of ao_compare::compare_ao_refs) instead
of internally relying on operand_equal_p.  That is however not the
problem in the PR and so I will deal with it only later.

The issue here is that even when the access path is the same, it must
not be bolted on an aggregate type that does not match.  This patch
does that, taking just one simple function from the
ao_compare::compare_ao_refs machinery and using it to detect the
situation.  The rest is just merging the information in between
accesses of the same access group.

I looked at how many times we come across such assignment during
"make stage2-bubble" of GCC (configured with only c and C++ and
without multilib and libsanitizers) and on an x86_64 there were 87924
such assignments (though now I realize not all of them had to be
aggregate), so they do happen.  The patch leads to about 5% increase
of cases where we don't use an "access path" but resort to a
MEM_REF (from 90209 to 95204).  On an Aarch64, there were 92268 such
assignments and the increase of falling back to MEM_REFs was by
4% (but from a bigger base 132983 to 107991).

gcc/ChangeLog:

2025-04-04  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/118924
	* tree-ssa-alias-compare.h (types_equal_for_same_type_for_tbaa_p):
	Declare.
	* tree-ssa-alias.cc: Include ipa-utils.h.
	(types_equal_for_same_type_for_tbaa_p): New public overloaded variant.
	* tree-sra.cc: Include tree-ssa-alias-compare.h.
	(create_access): Initialzie grp_same_access_path to true.
	(build_accesses_from_assign): Detect tbaa hazards and clear
	grp_same_access_path fields of involved accesses when they occur.
	(sort_and_splice_var_accesses): Take previous values of
	grp_same_access_path into account.

gcc/testsuite/ChangeLog:

2025-03-25  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/118924
	* g++.dg/tree-ssa/pr118924.C: New test.

0 files changed, 0 insertions, 0 deletions