Re: PATCH to fix bogus -Wimplicit-fallthrough warning (PR c++/77803)

[Marek Polacek <polacek@redhat.com>]

On Sat, Oct 01, 2016 at 07:17:50AM +0200, Markus Trippelsdorf wrote:
> On 2016.09.30 at 23:31 +0200, Marek Polacek wrote:
> > This PR reports a bogus -Wimplicit-fallthrough warning on the attached test.
> > The problem is that last_stmt_in_scope should for GIMPLE_TRY, if the last
> > statement of the eval part can't fallthrough, return this statement and don't
> > warn.  And the same should be true for FALLTHROUGH ().   This patch fixes it.
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> Try to compile the testcase without the fallthrough attribute...

Nuts.  Forgot that gimple_call_internal_p doesn't handle NULL.

Bootstrapped/regtested on x86_64-linux and ppc64-linux, ok for trunk?

2016-10-01  Marek Polacek  <polacek@redhat.com>

	PR c++/77803
	* gimplify.c (last_stmt_in_scope): Add check for FALLTHROUGH ().

	* g++.dg/warn/Wimplicit-fallthrough-1.C: New test.

diff --git gcc/gimplify.c gcc/gimplify.c
index 66bb8be..a60d947 100644
--- gcc/gimplify.c
+++ gcc/gimplify.c
@@ -1687,6 +1687,8 @@ last_stmt_in_scope (gimple *stmt)
 	stmt = gimple_seq_last_stmt (gimple_try_eval (try_stmt));
 	gimple *last_eval = last_stmt_in_scope (stmt);
 	if (gimple_stmt_may_fallthru (last_eval)
+	    && (last_eval == NULL
+		|| !gimple_call_internal_p (last_eval, IFN_FALLTHROUGH))
 	    && gimple_try_kind (try_stmt) == GIMPLE_TRY_FINALLY)
 	  {
 	    stmt = gimple_seq_last_stmt (gimple_try_cleanup (try_stmt));
diff --git gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-1.C gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-1.C
index e69de29..053ed68 100644
--- gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-1.C
+++ gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-1.C
@@ -0,0 +1,33 @@
+// PR c++/77803
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wimplicit-fallthrough" }
+
+struct A {};
+int a;
+
+void
+fn1 ()
+{
+  switch (0) {
+  case 0:
+  {
+    A b;
+    [[fallthrough]];
+  }
+  default:
+    a = 0;
+  }
+}
+
+void
+fn2 ()
+{
+  switch (0) {
+  case 0:
+  {
+    A b; // { dg-warning "statement may fall through" }
+  }
+  default:
+    a = 0;
+  }
+}

	Marek