From: Florian Weimer Date: Thu, 9 Nov 2023 08:50:54 +0000 (+0100) Subject: c: Add -Wreturn-mismatch warning, split from -Wreturn-type X-Git-Tag: basepoints/gcc-15~4867 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6e312b2b864bf923a9d772429f014375bf9dabc8;p=thirdparty%2Fgcc.git c: Add -Wreturn-mismatch warning, split from -Wreturn-type 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/Wreturn-mismatch-6.c: New. * gcc.dg/noncompile/pr55976-1.c: Change -Werror=return-type to -Werror=return-mismatch. * gcc.dg/noncompile/pr55976-2.c: Change -Wreturn-type to -Wreturn-mismatch. --- diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index d81177f38001..b10c6057cd15 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -1271,6 +1271,10 @@ 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 4580ff0576bd..dd5016ab3b9d 100644 --- a/gcc/c/c-typeck.cc +++ b/gcc/c/c-typeck.cc @@ -11311,17 +11311,11 @@ 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 (emit_diagnostic (flag_isoc99 ? DK_PEDWARN : DK_WARNING, + loc, OPT_Wreturn_mismatch, + "% with no value," + " in function returning non-void")) inform (DECL_SOURCE_LOCATION (current_function_decl), "declared here"); } @@ -11332,7 +11326,7 @@ 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 d0b55fb106f9..1bf71ce47a8a 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -7350,22 +7350,33 @@ 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). - -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. +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. + +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 000000000000..3bad847ecf7a --- /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 000000000000..49eb5a5a95c5 --- /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 000000000000..ee77ec6a7694 --- /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 000000000000..f73e8a05dc63 --- /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 000000000000..f2fd3294b7b3 --- /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/Wreturn-mismatch-6.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-6.c new file mode 100644 index 000000000000..51543fb71411 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-6.c @@ -0,0 +1,40 @@ +/* { dg-do compile } */ +/* { dg-options "-std=c90 -pedantic-errors -Wreturn-type" } */ + +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-error "with a value,\[^\n\r\]*-Wreturn-mismatch" } */ +} + +void +f5 (void) +{ + return f1 (); /* { dg-error "with expression\[^\n\r\]*-Wpedantic" } */ +} + +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" } */ +} /* { dg-warning "control reaches end of non-void\[^\n\r\]*-Wreturn-type" } */ diff --git a/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c b/gcc/testsuite/gcc.dg/noncompile/pr55976-1.c index d078990bd88f..d348b03ad944 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 0e493d0e8af5..d6f07a9572cb 100644 --- a/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c +++ b/gcc/testsuite/gcc.dg/noncompile/pr55976-2.c @@ -1,8 +1,8 @@ /* 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 +/* Verify that -Wno-return-mismatch turns off warnings about function return type. */ void t () { return 1; } /* normally generates function returning void */