On Thu, Aug 30, 2018 at 11:24:50PM +0200, Jakub Jelinek wrote:
> On Thu, Aug 30, 2018 at 05:17:03PM -0400, Marek Polacek wrote:
> > > 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;
>
> This looks incorrect. loc is an automatic variable in
> expand_FALLTHROUGH_r, you set wi->info to the address of that variable,
> then immediately return and then:
>
> > > @@ -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 "
>
> dereference it here, when the loc variable is no longer in scope.
> -fsanitize-use-after-scope should complain here...
>
> > > + "a case label or default label");
> > > + }
>
> If the only spot that ises wi->info is in these two new spots, can't you
> e.g. set in the expand_FALLTHROUGH function:
> location_t loc;
> wi.info = (void *) &loc;
> and then in expand_FALLTHROUGH_r do:
> *static_cast<location_t *>(wi.info) = gimple_location (stmt);
> ?
Sorry for the ridiculous delay and an embarassing thinko :(.
Here's an updated patch.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-02-28 Marek Polacek <pola...@redhat.com>
PR c++/87068 - missing diagnostic with fallthrough statement.
* 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 7e37e500d81..983635ba21f 100644
--- gcc/gimplify.c
+++ gcc/gimplify.c
@@ -2263,7 +2263,7 @@ 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);
@@ -2283,7 +2283,10 @@ expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p, bool
*handled_ops_p,
{
gsi_remove (gsi_p, true);
if (gsi_end_p (*gsi_p))
- return integer_zero_node;
+ {
+ *static_cast<location_t *>(wi->info) = gimple_location (stmt);
+ return integer_zero_node;
+ }
bool found = false;
location_t loc = gimple_location (stmt);
@@ -2347,8 +2350,15 @@ static void
expand_FALLTHROUGH (gimple_seq *seq_p)
{
struct walk_stmt_info wi;
+ location_t loc;
memset (&wi, 0, sizeof (wi));
+ wi.info = (void *) &loc;
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]. */
+ 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
new file mode 100644
index 00000000000..644003af47d
--- /dev/null
+++ 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" } */
+ }
+}
