There is some controversy about enabling -Wunused-const-variable for all
unused static const variables because some feel there are too many errors
exposed in header files. Create two levels for -Wunused-const-variable.
One level to only check for unused static const variables in the main
compilation file. Which is enabled by -Wunused-variable. And a second
level that also checks for unused static const variables in included
header files. Which must be explicitly enabled.
gcc/ChangeLog
PR c/28901
* cgraphunit.c (check_global_declaration): Check level of
warn_unused_const_variable and main_input_filename.
* doc/invoke.texi (Warning Options): Add -Wunused-const-variable=.
(-Wunused-variable): For C implies -Wunused-const-variable=1.
(-Wunused-const-variable): Explain levels 1 and 2.
gcc/c-family/ChangeLog
PR c/28901
* c.opt (Wunused-const-variable): Turn into Alias for...
(Wunused-const-variable=): New option.
gcc/testsuite/ChangeLog
PR c/28901
* gcc.dg/unused-variable-3.c: New test.
---
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 638e9c2..7c5f6c7 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -949,7 +949,11 @@ C ObjC C++ ObjC++ LangEnabledBy(C ObjC C++ ObjC++,Wunused)
; documented in common.opt
Wunused-const-variable
-C ObjC C++ ObjC++ Var(warn_unused_const_variable) Warning LangEnabledBy(C
ObjC,Wunused-variable)
+C ObjC C++ ObjC++ Warning Alias(Wunused-const-variable=, 2, 0)
+Warn when a const variable is unused.
+
+Wunused-const-variable=
+C ObjC C++ ObjC++ Joined RejectNegative UInteger
Var(warn_unused_const_variable) Warning LangEnabledBy(C ObjC,Wunused-variable,
1, 0)
Warn when a const variable is unused.
Wvariadic-macros
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 0a745f0..27a073a 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -942,7 +942,10 @@ check_global_declaration (symtab_node *snode)
/* Warn about static fns or vars defined but not used. */
if (((warn_unused_function && TREE_CODE (decl) == FUNCTION_DECL)
|| (((warn_unused_variable && ! TREE_READONLY (decl))
- || (warn_unused_const_variable && TREE_READONLY (decl)))
+ || (warn_unused_const_variable > 0 && TREE_READONLY (decl)
+ && (warn_unused_const_variable == 2
+ || filename_cmp (main_input_filename,
+ DECL_SOURCE_FILE (decl)) == 0)))
&& TREE_CODE (decl) == VAR_DECL))
&& ! DECL_IN_SYSTEM_HEADER (decl)
&& ! snode->referred_to_p (/*include_self=*/false)
@@ -971,7 +974,7 @@ check_global_declaration (symtab_node *snode)
(TREE_CODE (decl) == FUNCTION_DECL)
? OPT_Wunused_function
: (TREE_READONLY (decl)
- ? OPT_Wunused_const_variable
+ ? OPT_Wunused_const_variable_
: OPT_Wunused_variable),
"%qD defined but not used", decl);
}
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c1ab788..490df93 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -303,7 +303,7 @@ Objective-C and Objective-C++ Dialects}.
-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
-Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol
-Wno-unused-result -Wunused-value @gol -Wunused-variable @gol
--Wunused-const-variable @gol
+-Wunused-const-variable -Wunused-const-variable=@var{n} @gol
-Wunused-but-set-parameter -Wunused-but-set-variable @gol
-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
-Wvla -Wvolatile-register-var -Wwrite-strings @gol
@@ -4231,23 +4231,39 @@ its return value. The default is
@option{-Wunused-result}.
@opindex Wunused-variable
@opindex Wno-unused-variable
Warn whenever a local or static variable is unused aside from its
-declaration. This option implies @option{-Wunused-const-variable} for C,
+declaration. This option implies @option{-Wunused-const-variable=1} for C,
but not for C++. This warning is enabled by @option{-Wall}.
To suppress this warning use the @code{unused} attribute
(@pxref{Variable Attributes}).
@item -Wunused-const-variable
+@itemx -Wunused-const-variable=@var{n}
@opindex Wunused-const-variable
@opindex Wno-unused-const-variable
Warn whenever a constant static variable is unused aside from its declaration.
-This warning is enabled by @option{-Wunused-variable} for C, but not for C++.
-In C++ this is normally not an error since const variables take the place of
-@code{#define}s in C++.
+@option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable}
+for C, but not for C++. In C this declares variable storage, but in C++ this
+is not an error since const variables take the place of @code{#define}s.
To suppress this warning use the @code{unused} attribute
(@pxref{Variable Attributes}).
+@table @gcctabopt
+@item -Wunused-const-variable=1
+This is the warning level that is enabled by @option{-Wunused-variable} for
+C. It warns only about unused static const variables defined in the main
+compilation unit, but not about static const variables declared in any
+header included.
+
+@item -Wunused-const-variable=2
+This warning level also warns for unused constant static variables in
+headers (excluding system headers). This is the warning level of
+@option{-Wunused-const-variable} and must be explicitly requested since
+in C++ this isn't an error and in C it might be harder to clean up all
+headers included.
+@end table
+
@item -Wunused-value
@opindex Wunused-value
@opindex Wno-unused-value
diff --git a/gcc/testsuite/gcc.dg/unused-variable-3.c
b/gcc/testsuite/gcc.dg/unused-variable-3.c
new file mode 100644
index 0000000..6aca958
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/unused-variable-3.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-Wunused-variable" } */
+
+static const int cmain = 42; /* { dg-warning "defined but not used" } */
+
+/* Don't warn for unused static consts in headers,
+ unless -Wunused-const-variable=2. */
+#line 1 "header.h"
+static const int cheader = 42;
--
1.8.3.1
