On Tue, May 10, 2022 at 09:54:12AM -0400, Marek Polacek wrote:
> On Tue, May 10, 2022 at 08:58:46AM -0400, Jason Merrill wrote:
> > On 5/7/22 18:26, Marek Polacek wrote:
> > > Corrected version that avoids an uninitialized warning:
> > >
> > > This PR complains that we emit the "enumeration value not handled in
> > > switch" warning even though the enumerator was marked with the
> > > [[maybe_unused]] attribute.
> > >
> > > The first snag was that I couldn't just check TREE_USED, because
> > > the enumerator could have been used earlier in the function, which
> > > doesn't play well with the c_do_switch_warnings warning. Instead,
> > > I had to check the attributes on the CONST_DECL directly, which led
> > > to the second, and worse, snag: in C we don't have direct access to
> > > the CONST_DECL for the enumerator.
> >
> > I wonder if you want to change that instead of working around it?
>
> I wouldn't mind looking into that; I've hit this discrepancy numerous
> times throughout the years and it'd be good to unify it so that the
> c-common code doesn't need to hack around it.
>
> Let's see how far I'll get...
Now done (r13-575), which makes this patch a piece of cake.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
This PR complains that we emit the "enumeration value not handled in
switch" warning even though the enumerator was marked with the
[[maybe_unused]] attribute.
I couldn't just check TREE_USED, because the enumerator could have been
used earlier in the function, which doesn't play well with the
c_do_switch_warnings warning. Instead, I had to check the attributes on
the CONST_DECL. This is easy since the TYPE_VALUES of an enum type are
now consistent between C and C++, both of which store the CONST_DECL in
its TREE_VALUE.
PR c++/105497
gcc/c-family/ChangeLog:
* c-warn.cc (c_do_switch_warnings): Don't warn about unhandled
enumerator when it was marked with attribute unused.
gcc/testsuite/ChangeLog:
* c-c++-common/Wswitch-1.c: New test.
* g++.dg/warn/Wswitch-4.C: New test.
---
gcc/c-family/c-warn.cc | 11 +++++-
gcc/testsuite/c-c++-common/Wswitch-1.c | 29 ++++++++++++++
gcc/testsuite/g++.dg/warn/Wswitch-4.C | 52 ++++++++++++++++++++++++++
3 files changed, 90 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/c-c++-common/Wswitch-1.c
create mode 100644 gcc/testsuite/g++.dg/warn/Wswitch-4.C
diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index cae89294aea..ea7335f3edf 100644
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -1738,8 +1738,8 @@ c_do_switch_warnings (splay_tree cases, location_t
switch_location,
for (chain = TYPE_VALUES (type); chain; chain = TREE_CHAIN (chain))
{
tree value = TREE_VALUE (chain);
- if (TREE_CODE (value) == CONST_DECL)
- value = DECL_INITIAL (value);
+ tree attrs = DECL_ATTRIBUTES (value);
+ value = DECL_INITIAL (value);
node = splay_tree_lookup (cases, (splay_tree_key) value);
if (node)
{
@@ -1769,6 +1769,13 @@ c_do_switch_warnings (splay_tree cases, location_t
switch_location,
/* We've now determined that this enumerated literal isn't
handled by the case labels of the switch statement. */
+ /* Don't warn if the enumerator was marked as unused. We can't use
+ TREE_USED here: it could have been set on the enumerator if the
+ enumerator was used earlier. */
+ if (lookup_attribute ("unused", attrs)
+ || lookup_attribute ("maybe_unused", attrs))
+ continue;
+
/* If the switch expression is a constant, we only really care
about whether that constant is handled by the switch. */
if (cond && tree_int_cst_compare (cond, value))
diff --git a/gcc/testsuite/c-c++-common/Wswitch-1.c
b/gcc/testsuite/c-c++-common/Wswitch-1.c
new file mode 100644
index 00000000000..de9ee03b0a3
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wswitch-1.c
@@ -0,0 +1,29 @@
+/* PR c++/105497 */
+/* { dg-options "-Wswitch" } */
+
+enum E {
+ A,
+ B,
+ C __attribute((unused)),
+ D
+};
+
+void
+g (enum E e)
+{
+ switch (e)
+ {
+ case A:
+ case B:
+ case D:
+ break;
+ }
+
+ switch (e) // { dg-warning "not handled in switch" }
+ {
+ case A:
+ case B:
+ case C:
+ break;
+ }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wswitch-4.C
b/gcc/testsuite/g++.dg/warn/Wswitch-4.C
new file mode 100644
index 00000000000..553a57d777b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wswitch-4.C
@@ -0,0 +1,52 @@
+// PR c++/105497
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wswitch" }
+
+enum class Button
+{
+ Left,
+ Right,
+ Middle,
+ NumberOfButtons [[maybe_unused]]
+};
+
+enum class Sound
+{
+ Bark,
+ Meow,
+ Hiss,
+ Moo __attribute((unused))
+};
+
+enum class Chordata
+{
+ Urochordata,
+ Cephalochordata,
+ Vertebrata
+};
+
+int main()
+{
+ Button b = Button::Left;
+ switch (b) { // { dg-bogus "not handled" }
+ case Button::Left:
+ case Button::Right:
+ case Button::Middle:
+ break;
+ }
+
+ Sound s = Sound::Bark;
+ switch (s) { // { dg-bogus "not handled" }
+ case Sound::Bark:
+ case Sound::Meow:
+ case Sound::Hiss:
+ break;
+ }
+
+ Chordata c = Chordata::Vertebrata;
+ switch (c) { // { dg-warning "not handled" }
+ case Chordata::Cephalochordata:
+ case Chordata::Vertebrata:
+ break;
+ }
+}
base-commit: 1bfb823e2a7346ef55bd53a5354770599f7a550b
--
2.36.1
