PATCH for c++/87068, missing diagnostic with fallthrough statement
Marek Polacek
polacek@redhat.com
Thu Aug 23 20:38:00 GMT 2018
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 <polacek@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" } */
+ }
+}
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