Re: C PATCH to add -Wswitch-unreachable (PR c/49859)

[Sandra Loosemore <sandra at codesourcery dot com>]

On 05/20/2016 10:36 AM, Marek Polacek wrote:
> diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
> index f3d087f..5909b9d 100644
> --- gcc/doc/invoke.texi
> +++ gcc/doc/invoke.texi
> @@ -297,7 +297,8 @@ Objective-C and Objective-C++ Dialects}.
>   -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
>   -Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
>   -Wmissing-format-attribute -Wsubobject-linkage @gol
> --Wswitch  -Wswitch-default  -Wswitch-enum -Wswitch-bool -Wsync-nand @gol
> +-Wswitch  -Wswitch-default  -Wswitch-enum -Wswitch-bool @gol
> +-Wswitch-unreachable  -Wsync-nand @gol
>   -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
>   -Wtype-limits  -Wundef @gol
>   -Wuninitialized  -Wunknown-pragmas  -Wunsafe-loop-optimizations @gol

I think this list is supposed to be alphabetized except with respect to 
-Wno-foo being sorted as if it were -Wfoo.  I realize there are other 
inconsistencies, but can you at least keep the -Wswitch* entries in 
proper order?

> @@ -4144,6 +4145,39 @@ switch ((int) (a == 4))
>   @end smallexample
>   This warning is enabled by default for C and C++ programs.
>
> +@item -Wswitch-unreachable
> +@opindex Wswitch-unreachable
> +@opindex Wno-switch-unreachable
> +Warn whenever a @code{switch} statement contains statements between the
> +controlling expression and the first case label, which will never be
> +executed.  For example:
> +@smallexample
> +@group
> +switch (cond)
> +  @{
> +   i = 15;
> +  @dots{}
> +   case 5:
> +  @dots{}
> +  @}
> +@end group
> +@end smallexample
> +@option{-Wswitch-unreachable} will not warn if the statement between the

s/will/does/

> +controlling expression and the first case label is just a declaration:
> +@smallexample
> +@group
> +switch (cond)
> +  @{
> +   int i;
> +  @dots{}
> +   case 5:
> +   i = 5;
> +  @dots{}
> +  @}
> +@end group
> +@end smallexample
> +This warning is enabled by default for C and C++ programs.
> +
>   @item -Wsync-nand @r{(C and C++ only)}
>   @opindex Wsync-nand
>   @opindex Wno-sync-nand

The doc part of the patch is OK with those things fixed.

-Sandra