Re: [PATCH 5/7] rtl: Verify shared jump tables after each pass [PR middle-end/126236]

[Jeff Law]

On 9/22/26 3:33 AM, ktkac...@nvidia.com wrote:

From: Kyrylo Tkachov <ktkac...@nvidia.com>

A broken table reference can make tablejump_p stop recognizing a dispatch,
which bypasses its CFG checks.  Those checks also stop when free_cfg removes
the CFG before machine reorganization and branch shortening.

Check table references from both instruction patterns and JUMP_LABEL in the
existing post-pass RTL verifier.  Require live table, base and case labels,
label-to-table adjacency, and a shared flag for tables with several repeatable
users.  Honor the existing target copy restriction when counting users.
An uncopyable dispatch can also have an out-of-line execution template.
Handle jumps in delay-slot sequences.  Allow a shared table to lose users
and to change entry width.

Run the structural check on hook-enabled targets in linear RTL, including
after free_cfg.  Strengthen the CFG check to compare complete destination
sets, including casesi default and exceptional edges.

Plugin tests damage individual invariants and check the diagnostics at pass
boundaries.  Positive tests cover repeated entries, zero or one remaining
user, target copy restrictions, shortened tables, delay-slot sequences and
casesi default edges.

Bootstrapped on aarch64-linux-gnu with RTL and extra checking.

gcc/ChangeLog:

        PR middle-end/126236
        * cfgrtl.cc (rtl_verify_edges): Compare all shared-table destinations
        with the dispatch's successors.
        * passes.cc (execute_function_todo): Verify tablejump links before
        CFG verification and after CFG teardown.
        * rtl.h (verify_jump_tables): Declare.
        * rtlanal.cc (verify_jump_tables): New function.

gcc/testsuite/ChangeLog:

        PR middle-end/126236
        * gcc.dg/plugin/plugin.exp: Register the tablejump tests.
        * gcc.dg/plugin/tablejump_plugin.cc: New plugin.
        * gcc.dg/plugin/tablejump-valid.c: New test.
        * gcc.dg/plugin/tablejump-missing-edge.c: Likewise.
        * gcc.dg/plugin/tablejump-extra-edge.c: Likewise.
        * gcc.dg/plugin/tablejump-null-label.c: Likewise.
        * gcc.dg/plugin/tablejump-stale-label.c: Likewise.
        * gcc.dg/plugin/tablejump-missing-ref.c: Likewise.
        * gcc.dg/plugin/tablejump-detached-label.c: Likewise.
        * gcc.dg/plugin/tablejump-detached-table.c: Likewise.
        * gcc.dg/plugin/tablejump-detached-pair.c: Likewise.
        * gcc.dg/plugin/tablejump-deleted-table.c: Likewise.
        * gcc.dg/plugin/tablejump-unmarked.c: Likewise.
        * gcc.dg/plugin/tablejump-case-label.c: Likewise.
        * gcc.dg/plugin/tablejump-base-label.c: Likewise.

Signed-off-by: Kyrylo Tkachov <ktkac...@nvidia.com>

OK if and when prereqs are approved.

jeff