https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80460
--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Actually, nothing I imagined wouldn't work for the case when the else branch is
dead :(.
A patch that helps with bogus warning for dead then branches:
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -1912,6 +1912,7 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_COND)
{
gcond *cond_stmt = as_a <gcond *> (gsi_stmt (*gsi_p));
+ bool false_p = gimple_cond_false_p (cond_stmt);
tree false_lab = gimple_cond_false_label (cond_stmt);
location_t if_loc = gimple_location (cond_stmt);
@@ -1956,7 +1957,9 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
= gimple_call_internal_p (gsi_stmt (*gsi_p), IFN_FALLTHROUGH);
gsi_next (gsi_p);
tree goto_dest = gimple_goto_dest (gsi_stmt (*gsi_p));
- if (!fallthru_before_dest)
+ /* If FALSE_P, the then branch is dead, do not collect
+ the label. */
+ if (!fallthru_before_dest && !false_p)
{
struct label_entry l = { goto_dest, if_loc };
labels->safe_push (l);
