Re: [C++ PATCH] Avoid -Wreturn-type warnings if a switch has default label, no breaks inside of it, but is followed by a break (PR sanitizer/81275)

[Nathan Sidwell <nathan@acm.org>]

On 11/25/2017 07:22 PM, Jakub Jelinek wrote:
> On Sat, Nov 25, 2017 at 10:01:22AM +0100, Jakub Jelinek wrote:
>> Actually, thinking about it some more, maybe it would be more efficient
>> to gather this information during construction of the SWITCH_STMT in some
>> new flag on the tree, so cxx_block_may_fallthru would just:
> 
> Here it is implemented, bootstrapped/regtested on x86_64-linux and
> i686-linux, ok for trunk?

nice.

> --- gcc/cp/cp-tree.h.jj	2017-11-17 08:40:32.000000000 +0100
> +++ gcc/cp/cp-tree.h	2017-11-25 21:25:48.277897180 +0100

> +/* Set if the body of a switch stmt contains a default: case label
> +   and does not contain any break; stmts, thus if SWITCH_STMT_BODY
> +   is not empty and doesn't fallthru, then the whole SWITCH_STMT
> +   can't fallthru either.  */
> +#define SWITCH_STMT_CANNOT_FALLTHRU_P(NODE) \
> +  TREE_LANG_FLAG_0 (SWITCH_STMT_CHECK (NODE))

The macro name isn't quite right.  As the comment says, it's not 
sufficient that this flag is set for the switch to not fall through -- 
the switch body must be non-empty (which I presume it cannot be as there 
must be a default label), and it cannot fall through in its own right.

The semantics of this flag are more like SWITCH_STMT_COVERS_ALL_CASES, 
perhaps something of that ilk would be a clearer name?

nathan

-- 
Nathan Sidwell