[PATCH] c, c++: Implement -Wsizeof-array-div [PR91741]

[Joseph Myers]

On Mon, 14 Sep 2020, Marek Polacek via Gcc-patches wrote:

> so I followed suit.  In the C++ FE this was rather easy, because
> finish_parenthesized_expr already set TREE_NO_WARNING.  In the C FE
> it was trickier; I've added a NOP_EXPR to discern between the non-()
> and () versions.

This sort of thing is normally handled for C via original_code in c_expr.  
I suppose that doesn't work in this case because the code dealing with 
parenthesized expressions has a special case for sizeof:

          if (expr.original_code != C_MAYBE_CONST_EXPR
              && expr.original_code != SIZEOF_EXPR)
            expr.original_code = ERROR_MARK;

Handling this in some way via c_expr seems better to me than generating 
NOP_EXPR.  I suppose you could invent a PAREN_SIZEOF_EXPR used by (sizeof 
foo) and ((sizeof foo)) etc. as an original_code setting (and handled the 
same as SIZEOF_EXPR by whatever other warnings look for SIZEOF_EXPR 
there), or else add fields to c_expr to allow more such information to be 
tracked there.

-- 
Joseph S. Myers
joseph@codesourcery.com