Re: [C++ PATCH] Fix constexpr handling of &x->y (PR c++/84463)

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Apr 16, 2018 at 09:28:43PM +0200, Jakub Jelinek wrote:
> On the following new testcase we emit 2 different constexpr errors
> because of premature folding, where the PR44100 hack which is supposed
> to fold expressions like &((S *)0)->f or
> &((S *)24)->f folds all the &x->y expressions if x is TREE_CONSTANT
> into (some type)(x + cst) where what we were actually trying to access
> is lost.
> 
> The following patch limits the offsetof-like expression hack to expressions
> where maybe_constant_value of val's operand is INTEGER_CST, or e.g.
> a cast of INTEGER_CST to some pointer type.  This way we don't regress
> e.g. init/struct2.C, but don't mess up with x is e.g. some constexpr
> variable initialized to address of something.  Or should it avoid
> maybe_constant_value and just handle the literal INTEGER_CST and cast
> thereof?  We wouldn't handle &((S *)(24 + 8))->f that way though...

Or shall we move this folding to cp_fold instead of cp_build_addr_expr_1
(while keeping it limited to INTEGER_CST pointers)?

	Jakub