[PATCH] c, c++: -Wswitch warning on [[maybe_unused]] enumerator [PR105497]
Marek Polacek
polacek@redhat.com
Sat May 7 22:14:56 GMT 2022
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 had to handle that by adding
a new function that extracts the decl from an identifier's binding.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/105497
gcc/c-family/ChangeLog:
* c-common.h (get_decl_for_identifier): Declare.
* c-warn.cc (c_do_switch_warnings): Don't warn about unhandled
enumerator when it was marked as unused.
gcc/c/ChangeLog:
* c-decl.cc (get_decl_for_identifier): New.
gcc/cp/ChangeLog:
* tree.cc (get_decl_for_identifier): New.
gcc/testsuite/ChangeLog:
* c-c++-common/Wswitch-1.c: New test.
* g++.dg/warn/Wswitch-4.C: New test.
---
gcc/c-family/c-common.h | 1 +
gcc/c-family/c-warn.cc | 24 ++++++++++--
gcc/c/c-decl.cc | 10 +++++
gcc/cp/tree.cc | 8 ++++
gcc/testsuite/c-c++-common/Wswitch-1.c | 29 ++++++++++++++
gcc/testsuite/g++.dg/warn/Wswitch-4.C | 52 ++++++++++++++++++++++++++
6 files changed, 121 insertions(+), 3 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-common.h b/gcc/c-family/c-common.h
index f10be9bd67e..c4221089a18 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -831,6 +831,7 @@ extern tree (*make_fname_decl) (location_t, tree, int);
/* In c-decl.cc and cp/tree.cc. FIXME. */
extern void c_register_addr_space (const char *str, addr_space_t as);
+extern tree get_decl_for_identifier (tree);
/* In c-common.cc. */
extern bool in_late_binary_op;
diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index cae89294aea..01765624eb5 100644
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -1738,8 +1738,23 @@ 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);
+ tree id = TREE_PURPOSE (chain);
+ tree attrs;
+ /* In C++, the TREE_VALUE is a CONST_DECL. */
if (TREE_CODE (value) == CONST_DECL)
- value = DECL_INITIAL (value);
+ {
+ attrs = DECL_ATTRIBUTES (value);
+ value = DECL_INITIAL (value);
+ }
+ /* In C, the TREE_VALUE is an integer constant. The TREE_PURPOSE is
+ an identifier from which we must tease out the CONST_DECL. */
+ else if (tree decl = get_decl_for_identifier (id))
+ attrs = DECL_ATTRIBUTES (decl);
+ /* Track 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. */
+ const bool unused_p = (lookup_attribute ("unused", attrs)
+ || lookup_attribute ("maybe_unused", attrs));
node = splay_tree_lookup (cases, (splay_tree_key) value);
if (node)
{
@@ -1769,6 +1784,10 @@ 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. */
+ if (unused_p)
+ 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))
@@ -1791,8 +1810,7 @@ c_do_switch_warnings (splay_tree cases, location_t switch_location,
(default_node || !warn_switch
? OPT_Wswitch_enum
: OPT_Wswitch),
- "enumeration value %qE not handled in switch",
- TREE_PURPOSE (chain));
+ "enumeration value %qE not handled in switch", id);
}
/* Warn if there are case expressions that don't correspond to
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index c701f07befe..c2c813d922a 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -12466,4 +12466,14 @@ c_check_in_current_scope (tree decl)
return b != NULL && B_IN_CURRENT_SCOPE (b);
}
+/* Returns the symbol associated with an identifier ID. Currently, this
+ is used only in c_do_switch_warnings so that we can obtain the CONST_DECL
+ associated with an enumerator identifier. */
+
+tree
+get_decl_for_identifier (tree id)
+{
+ return I_SYMBOL_DECL (id);
+}
+
#include "gt-c-c-decl.h"
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 979728027ed..13852dc6446 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -6138,6 +6138,14 @@ maybe_adjust_arg_pos_for_attribute (const_tree fndecl)
return n > 0 ? n - 1 : 0;
}
+/* Stub for c-common. Currently this has no use in the C++ front end. */
+
+tree
+get_decl_for_identifier (tree)
+{
+ gcc_unreachable ();
+}
+
/* Release memory we no longer need after parsing. */
void
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: 0c723bb4be2a67657828b692997855afcdc5d286
--
2.35.1
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