[Bug target/120241] bpf: problem with preserve_access_index in "nested" struct types

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120241

--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Cupertino Miranda <cupermir@gcc.gnu.org>:

https://gcc.gnu.org/g:fb7bfbaa9192a8055683447810f08b9fa352e402

commit r16-7698-gfb7bfbaa9192a8055683447810f08b9fa352e402
Author: Cupertino Miranda <cupertino.miranda@oracle.com>
Date:   Tue Oct 21 13:33:58 2025 +0100

    bpf: Split expressions for proper CO-RE code generation

    This patch corrects CO-RE generation for the cases where an expression
    starts with a non-CO-RE access, but in the middle it requires to
    generate CO-RE to correctly compute the access location.

    It fixes it by splitting the expression into their CO-RE and non-CO-RE
    counterparts. It performs this by walking gimple expressions, and for
    each field access to which its type is a struct or union, it verifies if
    both the types for the base and field are attributed similarly.
    Otherwise, it splits the expression at this location by creating a
    temporary variable and performing any required pointer conversions.
    This smaller expressions are converted to CO-RE in the subsequent
    gimple walker.

    There is no way in GCC to distinguish nested struct/union definitions
    from non-nested ones.
    This patch simplifies code and enforces that all preserve_access_index
    structs/unions would be attributed explicitly.
    Previous approach was error prone as it would extend CO-RE accesses to
    structures which would not be attributed.

    All GCC BPF dejagnu passes tests:
      # of expected passes          553
      # of expected failures                6

    kernel-next bpf selftests:
     before: Summary: 543/4888 PASSED, 113 SKIPPED, 136 FAILED
     after:  Summary: 545/4893 PASSED, 113 SKIPPED, 134 FAILED

    gcc/ChangeLog:
            PR target/120241
            * config/bpf/core-builtins.cc
            (is_attr_preserve_access): Correct for pointer types.
            (maybe_get_base_for_field_expr, core_access_index_map,
            core_access_clean, core_is_access_index,
core_mark_as_access_index):
            Remove.
            (make_gimple_core_safe_access_index): Remove function.
            (struct walker_data): New struct to pass data to tree walker.
            (callback_should_do_core_access, should_do_core_access): Add
            function to identify expressions that should not be converted to
            CO-RE.
            (core_make_builtins): Add callback tree walker function to
            convert expressions to CO-RE.
            (callback_find_next_split_location, core_should_split_expr,
            find_next_split_location, gimple_core_early_split_expr): Add
            function to split expressions in CO-RE and non-CO-RE
            expressions.
            (execute_lower_bpf_core): Adapt to new code.
            * config/bpf/bpf.opt: Add option Wco-re.
            * doc/invoke.texi: Add documentation for Wco-re.

    gcc/testsuite/ChangeLog:
            PR target/120241
            * gcc.target/bpf/core-attr-3.c: Add attribute.
            * gcc.target/bpf/core-attr-4.c: Add attribute.
            * gcc.target/bpf/core-attr-5.c: Add attribute.
            * gcc.target/bpf/core-attr-6.c: Add attribute.
            * gcc.target/bpf/core-attr-7.c: New test.
            * gcc.target/bpf/core-attr-calls.c: Adapt.