From 0f876f22887f239cedca64ff170b71e5f1daaf54 Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Mon, 14 Sep 2015 09:49:47 +0000 Subject: [PATCH] PR28901 -Wunused-variable ignores unused const initialised variables in C 12 years ago it was decided that -Wunused-variable shouldn't warn about static const variables because some code used const static char rcsid[] strings which were never used but wanted in the code anyway. But as the bug points out this hides some real bugs. These days the usage of rcsids is not very popular anymore. So this patch changes the default to warn about unused static const variables in C with -Wunused-variable. And it adds a new option -Wno-unused-const-variable to turn this warning off. For C++ this new warning is off by default, since const variables can be used as #defines in C++. New testcases for the new defaults in C and C++ are included testing the new warning and suppressing it with an unused attribute or using -Wno-unused-const-variable. gcc/ChangeLog PR c/28901 * toplev.c (check_global_declaration): Check and use warn_unused_const_variable. * doc/invoke.texi (Warning Options): Add -Wunused-const-variable. (-Wunused-variable): Remove non-constant. For C implies -Wunused-const-variable. (-Wunused-const-variable): New. gcc/c-family/ChangeLog PR c/28901 * c.opt (Wunused-variable): Option from common.opt. (Wunused-const-variable): New option. gcc/cp/ChangeLog PR c/28901 * cp-objcp-common.c (cxx_warn_unused_global_decl): Remove hard-coded VAR_P TREE_READONLY override. gcc/testsuite/ChangeLog PR c/28901 * g++.dg/warn/unused-variable-1.C: New test. * g++.dg/warn/unused-variable-2.C: Likewise. * gcc.dg/unused-4.c: Adjust warning for static const. * gcc.dg/unused-variable-1.c: New test. * gcc.dg/unused-variable-2.c: Likewise. From-SVN: r227742 --- gcc/ChangeLog | 10 ++++++++++ gcc/c-family/ChangeLog | 6 ++++++ gcc/c-family/c.opt | 8 ++++++++ gcc/cp/ChangeLog | 6 ++++++ gcc/cp/cp-objcp-common.c | 4 ---- gcc/doc/invoke.texi | 18 +++++++++++++++--- gcc/testsuite/ChangeLog | 9 +++++++++ gcc/testsuite/g++.dg/warn/unused-variable-1.C | 7 +++++++ gcc/testsuite/g++.dg/warn/unused-variable-2.C | 7 +++++++ gcc/testsuite/gcc.dg/unused-4.c | 2 +- gcc/testsuite/gcc.dg/unused-variable-1.c | 7 +++++++ gcc/testsuite/gcc.dg/unused-variable-2.c | 7 +++++++ gcc/toplev.c | 11 ++++++----- 13 files changed, 89 insertions(+), 13 deletions(-) create mode 100644 gcc/testsuite/g++.dg/warn/unused-variable-1.C create mode 100644 gcc/testsuite/g++.dg/warn/unused-variable-2.C create mode 100644 gcc/testsuite/gcc.dg/unused-variable-1.c create mode 100644 gcc/testsuite/gcc.dg/unused-variable-2.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 9059ffa23e8..0aa46d05150 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,13 @@ +2015-09-11 Mark Wielaard + + PR c/28901 + * toplev.c (check_global_declaration): Check and use + warn_unused_const_variable. + * doc/invoke.texi (Warning Options): Add -Wunused-const-variable. + (-Wunused-variable): Remove non-constant. For C implies + -Wunused-const-variable. + (-Wunused-const-variable): New. + 2015-09-14 Richard Biener * doc/match-and-simplify.texi: Update for changed syntax diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog index 3acc84f433b..0163b1593dd 100644 --- a/gcc/c-family/ChangeLog +++ b/gcc/c-family/ChangeLog @@ -1,3 +1,9 @@ +2015-09-11 Mark Wielaard + + PR c/28901 + * c.opt (Wunused-variable): Option from common.opt. + (Wunused-const-variable): New option. + 2015-09-09 Paolo Carlini PR c++/53184 diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index d519d7a000b..47ba0704da8 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -912,6 +912,14 @@ Wunused-result C ObjC C++ ObjC++ Var(warn_unused_result) Init(1) Warning Warn if a caller of a function, marked with attribute warn_unused_result, does not use its return value +Wunused-variable +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) +Warn when a const variable is unused + Wvariadic-macros C ObjC C++ ObjC++ CPP(warn_variadic_macros) CppReason(CPP_W_VARIADIC_MACROS) Var(cpp_warn_variadic_macros) Init(0) Warning LangEnabledBy(C ObjC C++ ObjC++,Wpedantic || Wtraditional) Warn about using variadic macros diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index a9952fcae75..4101a2e123e 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,9 @@ +2015-09-11 Mark Wielaard + + PR c/28901 + * cp-objcp-common.c (cxx_warn_unused_global_decl): Remove hard-coded + VAR_P TREE_READONLY override. + 2015-09-10 Paolo Carlini PR c++/67318 diff --git a/gcc/cp/cp-objcp-common.c b/gcc/cp/cp-objcp-common.c index 2cab89c1552..808defdb986 100644 --- a/gcc/cp/cp-objcp-common.c +++ b/gcc/cp/cp-objcp-common.c @@ -62,10 +62,6 @@ cxx_warn_unused_global_decl (const_tree decl) if (DECL_IN_SYSTEM_HEADER (decl)) return false; - /* Const variables take the place of #defines in C++. */ - if (VAR_P (decl) && TREE_READONLY (decl)) - return false; - return true; } diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 518d68933c9..7b5e44e0881 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -290,6 +290,7 @@ 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-but-set-parameter -Wunused-but-set-variable @gol -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol -Wvla -Wvolatile-register-var -Wwrite-strings @gol @@ -4143,9 +4144,20 @@ its return value. The default is @option{-Wunused-result}. @item -Wunused-variable @opindex Wunused-variable @opindex Wno-unused-variable -Warn whenever a local variable or non-constant static variable is unused -aside from its declaration. -This warning is enabled by @option{-Wall}. +Warn whenever a local or static variable is unused aside from its +declaration. This option implies @option{-Wunused-const-variable} 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 +@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++. To suppress this warning use the @code{unused} attribute (@pxref{Variable Attributes}). diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 65dde8ccc7b..a285ee22b90 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,12 @@ +2015-09-11 Mark Wielaard + + PR c/28901 + * g++.dg/warn/unused-variable-1.C: New test. + * g++.dg/warn/unused-variable-2.C: Likewise. + * gcc.dg/unused-4.c: Adjust warning for static const. + * gcc.dg/unused-variable-1.c: New test. + * gcc.dg/unused-variable-2.c: Likewise. + 2015-09-13 David Edelsohn * gfortran.dg/private_type_3.f90: Require visibility. diff --git a/gcc/testsuite/g++.dg/warn/unused-variable-1.C b/gcc/testsuite/g++.dg/warn/unused-variable-1.C new file mode 100644 index 00000000000..cf531c01f18 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/unused-variable-1.C @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-Wunused-variable" } */ + +static int a = 0; /* { dg-warning "defined but not used" } */ +static const int b = 0; /* Unlike C, this doesn't cause a warning in C++. */ +static int c __attribute__ ((unused)) = 0; +static const char rcsid[] = "version-string"; /* Likewise. */ diff --git a/gcc/testsuite/g++.dg/warn/unused-variable-2.C b/gcc/testsuite/g++.dg/warn/unused-variable-2.C new file mode 100644 index 00000000000..b608fbce038 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/unused-variable-2.C @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-Wunused-variable -Wunused-const-variable" } */ + +static int a = 0; /* { dg-warning "defined but not used" } */ +static const int b = 0; /* { dg-warning "defined but not used" } */ +static int c __attribute__ ((unused)) = 0; +static const char rcsid[] __attribute__ ((unused)) = "version-string"; diff --git a/gcc/testsuite/gcc.dg/unused-4.c b/gcc/testsuite/gcc.dg/unused-4.c index 99e845f45a3..53236008007 100644 --- a/gcc/testsuite/gcc.dg/unused-4.c +++ b/gcc/testsuite/gcc.dg/unused-4.c @@ -1,6 +1,6 @@ /* { dg-do compile } */ /* { dg-options "-Wunused -O3" } */ -static const int i = 0; +static const int i = 0; /* { dg-warning "defined but not used" } */ static void f() { } /* { dg-warning "defined but not used" } */ static inline void g() { } diff --git a/gcc/testsuite/gcc.dg/unused-variable-1.c b/gcc/testsuite/gcc.dg/unused-variable-1.c new file mode 100644 index 00000000000..cb86c3bc8d2 --- /dev/null +++ b/gcc/testsuite/gcc.dg/unused-variable-1.c @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-Wunused-variable" } */ + +static int a = 0; /* { dg-warning "defined but not used" } */ +static const int b = 0; /* { dg-warning "defined but not used" } */ +static int c __attribute__ ((unused)) = 0; +static const char rcsid[] __attribute__ ((unused)) = "version-string"; diff --git a/gcc/testsuite/gcc.dg/unused-variable-2.c b/gcc/testsuite/gcc.dg/unused-variable-2.c new file mode 100644 index 00000000000..0496466a45f --- /dev/null +++ b/gcc/testsuite/gcc.dg/unused-variable-2.c @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-Wunused-variable -Wno-unused-const-variable" } */ + +static int a = 0; /* { dg-warning "defined but not used" } */ +static const int b = 0; +static int c __attribute__ ((unused)) = 0; +static const char rcsid[] = "version-string"; diff --git a/gcc/toplev.c b/gcc/toplev.c index 926224a4c20..95e4c522e4a 100644 --- a/gcc/toplev.c +++ b/gcc/toplev.c @@ -497,10 +497,9 @@ check_global_declaration (tree decl) /* Warn about static fns or vars defined but not used. */ if (((warn_unused_function && TREE_CODE (decl) == FUNCTION_DECL) - /* We don't warn about "static const" variables because the - "rcs_id" idiom uses that construction. */ - || (warn_unused_variable - && TREE_CODE (decl) == VAR_DECL && ! TREE_READONLY (decl))) + || (((warn_unused_variable && ! TREE_READONLY (decl)) + || (warn_unused_const_variable && TREE_READONLY (decl))) + && TREE_CODE (decl) == VAR_DECL)) && ! DECL_IN_SYSTEM_HEADER (decl) && ! snode->referred_to_p (/*include_self=*/false) /* This TREE_USED check is needed in addition to referred_to_p @@ -527,7 +526,9 @@ check_global_declaration (tree decl) warning_at (DECL_SOURCE_LOCATION (decl), (TREE_CODE (decl) == FUNCTION_DECL) ? OPT_Wunused_function - : OPT_Wunused_variable, + : (TREE_READONLY (decl) + ? OPT_Wunused_const_variable + : OPT_Wunused_variable), "%qD defined but not used", decl); } -- 2.30.2