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Thu, 19 Oct 2023 17:07:55 -0400 X-MC-Unique: MH-ziq0VNYKMupnDi9BJfg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 43AD71C05137 for ; Thu, 19 Oct 2023 21:07:55 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.64]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 938E62026D4C for ; Thu, 19 Oct 2023 21:07:54 +0000 (UTC) From: Florian Weimer To: gcc-patches@gcc.gnu.org Subject: [PATCH] c: Add -Wreturn-mismatch warning, split from -Wreturn-type Date: Thu, 19 Oct 2023 23:07:53 +0200 Message-ID: <87fs26pbh2.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-10.8 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org The existing -Wreturn-type option covers both constraint violations (which are mandatory to diagnose) and warnings that have known false positives. The new -Wreturn-mismatch warning is only about the constraint violations (missing or extra return expressions), and should eventually be turned into a permerror. The -std=gnu89 test cases show that by default, we do not warn for return; in a function not returning void. This matches previous practice for -Wreturn-type. gcc/c-family/ * c.opt (Wreturn-mismatch): New. gcc/c/ * c-typeck.cc (c_finish_return): Use pedwarn with OPT_Wreturn_mismatch for missing/extra return expressions. gcc/ * doc/invoke.texi (Warning Options): Document -Wreturn-mismatch. Update -Wreturn-type documentation. gcc/testsuite/ * gcc.dg/Wreturn-mismatch-1.c: New. * gcc.dg/Wreturn-mismatch-2.c: New. * gcc.dg/Wreturn-mismatch-3.c: New. * gcc.dg/Wreturn-mismatch-4.c: New. * gcc.dg/Wreturn-mismatch-5.c: New. * gcc.dg/noncompile/pr55976-1.c: Change -Werror=return-type to -Werror=return-mismatch. * gcc.dg/noncompile/pr55976-2.c: Likewise. --- gcc/c-family/c.opt | 4 +++ gcc/c/c-typeck.cc | 15 +++-------- gcc/doc/invoke.texi | 35 +++++++++++++++--------- gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c | 40 ++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c | 41 +++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/Wreturn-mismatch-3.c | 40 ++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/Wreturn-mismatch-4.c | 40 ++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/Wreturn-mismatch-5.c | 40 ++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/noncompile/pr55976-1.c | 2 +- gcc/testsuite/gcc.dg/noncompile/pr55976-2.c | 2 +- 10 files changed, 234 insertions(+), 25 deletions(-) base-commit: 8f4bbdc28df6e87a7ad5ec5ca191a7a836a4f016 diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index 44b9c862c14..4c2ebd08af5 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -1263,6 +1263,10 @@ Wreorder C++ ObjC++ Var(warn_reorder) Warning LangEnabledBy(C++ ObjC++,Wall) Warn when the compiler reorders code. +Wreturn-mismatch +C ObjC Var(warn_return_mismatch) Warning Init(1) +Warn whenever void-returning functions return a non-void expressions, or a return expression is missing in a function not returning void. + Wreturn-type C ObjC C++ ObjC++ Var(warn_return_type) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall) Init(-1) Warn whenever a function's return type defaults to \"int\" (C), or about inconsistent return types (C++). diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc index 6e044b4afbc..1da622160a3 100644 --- a/gcc/c/c-typeck.cc +++ b/gcc/c/c-typeck.cc @@ -11281,17 +11281,10 @@ c_finish_return (location_t loc, tree retval, tree origtype) if ((warn_return_type >= 0 || flag_isoc99) && valtype != NULL_TREE && TREE_CODE (valtype) != VOID_TYPE) { - bool warned_here; - if (flag_isoc99) - warned_here = pedwarn - (loc, warn_return_type >= 0 ? OPT_Wreturn_type : 0, - "% with no value, in function returning non-void"); - else - warned_here = warning_at - (loc, OPT_Wreturn_type, - "% with no value, in function returning non-void"); no_warning = true; - if (warned_here) + if (pedwarn (loc, OPT_Wreturn_mismatch, + "% with no value," + " in function returning non-void")) inform (DECL_SOURCE_LOCATION (current_function_decl), "declared here"); } @@ -11302,7 +11295,7 @@ c_finish_return (location_t loc, tree retval, tree origtype) bool warned_here; if (TREE_CODE (TREE_TYPE (retval)) != VOID_TYPE) warned_here = pedwarn - (xloc, warn_return_type >= 0 ? OPT_Wreturn_type : 0, + (xloc, OPT_Wreturn_mismatch, "% with a value, in function returning void"); else warned_here = pedwarn diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 9b5ff457027..c0c155af7cd 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -7338,22 +7338,33 @@ This warning is enabled by @option{-Wall} for C and C++. Do not warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope after the function returns. +@opindex Wreturn-mismatch +@opindex Wno-return-mismatch +@item -Wreturn-mismatch +Warn about return statements without an expressions in functions which +do not return @code{void}. Also warn about a @code{return} statement +with an expression in a function whose return type is @code{void}, +unless the expression type is also @code{void}. As a GNU extension, the +latter case is accepted without a warning unless @option{-Wpedantic} is +used. + +Attempting to use the return value of a non-@code{void} function other +than @code{main} that flows off the end by reaching the closing curly +brace that terminates the function is undefined. + +This warning is specific to C and enabled by default. + @opindex Wreturn-type @opindex Wno-return-type @item -Wreturn-type -Warn whenever a function is defined with a return type that defaults -to @code{int}. Also warn about any @code{return} statement with no -return value in a function whose return type is not @code{void} -(falling off the end of the function body is considered returning -without a value). +Warn whenever a function is defined with a return type that defaults to +@code{int} (unless @option{-Wimplicit-int} is active, which takes +precedence). Also warn if execution may reach the end of the function +body, or if the function does not contain any return statement at all. -For C only, warn about a @code{return} statement with an expression in a -function whose return type is @code{void}, unless the expression type is -also @code{void}. As a GNU extension, the latter case is accepted -without a warning unless @option{-Wpedantic} is used. Attempting -to use the return value of a non-@code{void} function other than @code{main} -that flows off the end by reaching the closing curly brace that terminates -the function is undefined. +Attempting to use the return value of a non-@code{void} function other +than @code{main} that flows off the end by reaching the closing curly +brace that terminates the function is undefined. Unlike in C, in C++, flowing off the end of a non-@code{void} function other than @code{main} results in undefined behavior even when the value of diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c new file mode 100644 index 00000000000..3bad847ecf7 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c @@ -0,0 +1,40 @@ +/* { dg-do compile } */ +/* { dg-options "" } */ + +void f1 (void); + +int +f2 (void) +{ + f1 (); +} + +static inline int +f3 (void) +{ + f1 (); +} + +void +f4 (void) +{ + return 1; /* { dg-warning "'return' with a value\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); /* { dg-bogus "ISO C" } */ +} + +int +f6 (void) +{ + return; /* { dg-warning "'return' with no value\[^\n\r\]*-Wreturn-mismatch" } */ +} + +int +f7 (void) +{ + return f1 (); /* { dg-error "void value not ignored as it ought to be" } */ +} diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c new file mode 100644 index 00000000000..49eb5a5a95c --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c @@ -0,0 +1,41 @@ +/* { dg-do compile } */ +/* { dg-options "-Wall" } */ + +void f1 (void); + +int +f2 (void) +{ + f1 (); +} /* { dg-warning "control reaches end of non-void\[^\n\r\]*-Wreturn-type" } */ + +static inline int +f3 (void) +{ + f1 (); +} /* { dg-warning "no return statement in function\[^\n\r\]*-Wreturn-type" } */ + +void +f4 (void) +{ + return 1; /* { dg-warning "with a value,\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); +} + +int +f6 (void) +{ + return; /* { dg-warning "with no value,\[^\n\r\]*Wreturn-mismatch" } */ +} + +int +f7 (void) +{ + return f1 (); /* { dg-error "void value not ignored as it ought to be" } */ +} /* { dg-warning "control reaches end of non-void\[^\n\r\]*-Wreturn-type" } */ + diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-3.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-3.c new file mode 100644 index 00000000000..ee77ec6a769 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-3.c @@ -0,0 +1,40 @@ +/* { dg-do compile } */ +/* { dg-options "-pedantic-errors" } */ + +void f1 (void); + +int +f2 (void) +{ + f1 (); +} + +static inline int +f3 (void) +{ + f1 (); +} + +void +f4 (void) +{ + return 1; /* { dg-error "with a value,\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); /* { dg-error "with expression, in function\[^\n\r\]*-Wpedantic" } */ +} + +int +f6 (void) +{ + return; /* { dg-error "with no value,\[^\n\r\]*Wreturn-mismatch" } */ +} + +int +f7 (void) +{ + return f1 (); /* { dg-error "void value not ignored as it ought to be" } */ +} diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-4.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-4.c new file mode 100644 index 00000000000..f73e8a05dc6 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-4.c @@ -0,0 +1,40 @@ +/* { dg-do compile } */ +/* { dg-options "-std=gnu89" } */ + +void f1 (void); + +int +f2 (void) +{ + f1 (); +} + +static inline int +f3 (void) +{ + f1 (); +} + +void +f4 (void) +{ + return 1; /* { dg-warning "with a value,\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); +} + +int +f6 (void) +{ + return; /* { dg-bogus "with no value" } */ +} + +int +f7 (void) +{ + return f1 (); /* { dg-error "void value not ignored as it ought to be" } */ +} diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-5.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-5.c new file mode 100644 index 00000000000..f2fd3294b7b --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-5.c @@ -0,0 +1,40 @@ +/* { dg-do compile } */ +/* { dg-options "-std=gnu89 -pedantic-errors" } */ + +void f1 (void); + +int +f2 (void) +{ + f1 (); +} + +static inline int +f3 (void) +{ + f1 (); +} + +void +f4 (void) +{ + return 1; /* { dg-error "with a value,\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); /* { dg-error "with expression\[^\n\r\]*-Wpedantic" } */ +} + +int +f6 (void) +{ + return; +} + +int +f7 (void) +{ + return f1 (); /* { dg-error "void value not ignored as it ought to be" } */ +} diff --git a/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c b/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c index d078990bd88..d348b03ad94 100644 --- a/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c +++ b/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c @@ -1,6 +1,6 @@ /* PR c/55976 */ /* { dg-do compile } */ -/* { dg-options "-Werror=return-type" } */ +/* { dg-options "-Werror=return-mismatch" } */ /* { dg-prune-output "some warnings being treated as errors" } */ /* Verify warnings for return type become errors. */ diff --git a/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c b/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c index 0e493d0e8af..a9494255369 100644 --- a/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c +++ b/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c @@ -1,6 +1,6 @@ /* PR c/55976 */ /* { dg-do compile } */ -/* { dg-options "-Wno-return-type" } */ +/* { dg-options "-Wno-return-mismatch" } */ /* Verify that -Wno-return-type turns off warnings about function return type. */