Ping.
On Thu, Aug 23, 2018 at 04:38:03PM -0400, Marek Polacek wrote:
> The C++ standard says that [[fallthrough]]; at the end of a switch statement
> is ill-formed: <http://eel.is/c++draft/dcl.attr.fallthrough>
>
> Currently we do check that the statement after a fallthrough statement is
> a labeled statement, but we didn't warn if a fallthrough statement is at
> the very end of a switch statement. This patch adds this warning.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-08-23 Marek Polacek <pola...@redhat.com>
>
> PR c++/87068
> * gimplify.c (expand_FALLTHROUGH_r): If IFN_FALLTHROUGH was found
> at the end of a seq, save its location to walk_stmt_info.
> (expand_FALLTHROUGH): Warn if IFN_FALLTHROUGH is at the end of
> a switch.
>
> * c-c++-common/Wimplicit-fallthrough-37.c: New test.
>
> diff --git gcc/gimplify.c gcc/gimplify.c
> index e35137aec2c..04c15016f18 100644
> --- gcc/gimplify.c
> +++ gcc/gimplify.c
> @@ -2231,7 +2231,7 @@ maybe_warn_implicit_fallthrough (gimple_seq seq)
>
> static tree
> expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
> - struct walk_stmt_info *)
> + struct walk_stmt_info *wi)
> {
> gimple *stmt = gsi_stmt (*gsi_p);
>
> @@ -2250,11 +2250,14 @@ expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p,
> bool *handled_ops_p,
> if (gimple_call_internal_p (stmt, IFN_FALLTHROUGH))
> {
> gsi_remove (gsi_p, true);
> + location_t loc = gimple_location (stmt);
> if (gsi_end_p (*gsi_p))
> - return integer_zero_node;
> + {
> + wi->info = &loc;
> + return integer_zero_node;
> + }
>
> bool found = false;
> - location_t loc = gimple_location (stmt);
>
> gimple_stmt_iterator gsi2 = *gsi_p;
> stmt = gsi_stmt (gsi2);
> @@ -2317,6 +2320,14 @@ expand_FALLTHROUGH (gimple_seq *seq_p)
> struct walk_stmt_info wi;
> memset (&wi, 0, sizeof (wi));
> walk_gimple_seq_mod (seq_p, expand_FALLTHROUGH_r, NULL, &wi);
> + if (wi.callback_result == integer_zero_node)
> + {
> + /* We've found [[fallthrough]]; at the end of a switch, which the C++
> + standard says is ill-formed; see [dcl.attr.fallthrough]. */
> + location_t *loc = static_cast<location_t *>(wi.info);
> + warning_at (*loc, 0, "attribute %<fallthrough%> not preceding "
> + "a case label or default label");
> + }
> }
>
>
> diff --git gcc/testsuite/c-c++-common/Wimplicit-fallthrough-37.c
> gcc/testsuite/c-c++-common/Wimplicit-fallthrough-37.c
> index e69de29bb2d..644003af47d 100644
> --- gcc/testsuite/c-c++-common/Wimplicit-fallthrough-37.c
> +++ gcc/testsuite/c-c++-common/Wimplicit-fallthrough-37.c
> @@ -0,0 +1,13 @@
> +/* PR c++/87068 */
> +/* { dg-do compile } */
> +
> +void
> +f (int n)
> +{
> + switch (n)
> + {
> + case 4:
> + ++n;
> + __attribute__((fallthrough)); /* { dg-warning "not preceding" } */
> + }
> +}
Marek
