On Sun, Aug 24, 2025 at 5:12 PM Andrew Pinski
<andrew.pin...@oss.qualcomm.com> wrote:
>
> While looking at this code I noticed that we don't remove
> the old switch index assignment if it is only used in the switch
> after it is modified in simplify_gimple_switch.
> This fixes that by marking the old switch index for the dce worklist.
>
> Bootstrapped and tested on x86_64-linux-gnu.
OK.
Richard.
> gcc/ChangeLog:
>
> * tree-ssa-forwprop.cc (simplify_gimple_switch): Add
> simple_dce_worklist
> argument. Mark the old index when doing the replacement.
> (pass_forwprop::execute): Update call to simplify_gimple_switch.
>
> Signed-off-by: Andrew Pinski <andrew.pin...@oss.qualcomm.com>
> ---
> gcc/tree-ssa-forwprop.cc | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> index f7fb664a6b4..8bca917e722 100644
> --- a/gcc/tree-ssa-forwprop.cc
> +++ b/gcc/tree-ssa-forwprop.cc
> @@ -1054,7 +1054,8 @@ simplify_gimple_switch_label_vec (gswitch *stmt, tree
> index_type,
>
> static bool
> simplify_gimple_switch (gswitch *stmt,
> - vec<std::pair<int, int> > &edges_to_remove)
> + vec<std::pair<int, int> > &edges_to_remove,
> + bitmap simple_dce_worklist)
> {
> /* The optimization that we really care about is removing unnecessary
> casts. That will let us do much better in propagating the inferred
> @@ -1089,6 +1090,8 @@ simplify_gimple_switch (gswitch *stmt,
> if ((!min || int_fits_type_p (min, ti))
> && (!max || int_fits_type_p (max, ti)))
> {
> + bitmap_set_bit (simple_dce_worklist,
> + SSA_NAME_VERSION (cond));
> gimple_switch_set_index (stmt, def);
> simplify_gimple_switch_label_vec (stmt, ti,
> edges_to_remove);
> @@ -5170,7 +5173,8 @@ pass_forwprop::execute (function *fun)
>
> case GIMPLE_SWITCH:
> changed |= simplify_gimple_switch (as_a <gswitch *> (stmt),
> - edges_to_remove);
> + edges_to_remove,
> + simple_dce_worklist);
> break;
>
> case GIMPLE_COND:
> --
> 2.43.0
>
