On Thu, Oct 19, 2023 at 5:08 PM Florian Weimer <fwei...@redhat.com> wrote:
>
> 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(-)
>
> 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,
> - "%<return%> with no value, in function returning non-void");
> - else
> - warned_here = warning_at
> - (loc, OPT_Wreturn_type,
> - "%<return%> with no value, in function returning non-void");
> no_warning = true;
> - if (warned_here)
> + if (pedwarn (loc, OPT_Wreturn_mismatch,
> + "%<return%> 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,
> "%<return%> 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. */
Comment here should be updated to match the flag being used.
>
> base-commit: 8f4bbdc28df6e87a7ad5ec5ca191a7a836a4f016
>
