Re: double gimplification in C++ FE

[Jason Merrill <jason at redhat dot com>]

Aldy Hernandez wrote:
> I'm in the process of converting the C++ FE to tuples.  In doing so I
> have noticed that the C++ FE will frequently gimplify bits of a tree,
> and then expect gimplify_expr() to gimplify the rest.  This seems
> redundant, as gimplify_expr() more often than not will gimplify the
> entire tree structure, without regard to what parts the C++ FE already
> gimplified.

Yes, the gimplifier often makes several passes over the same trees to 
get them completely lowered.  cp_gimplify_expr is a subroutine of the 
gimplifier.

> This behavior is common throughout C++.  The C++ FE calls gimplify_stmt
> on bits of trees, but then gimplify_expr() has to gimplify again.

> It seems to me that a better approach would be to pass the
> tree structure as generic as we can (without calls to gimplify_stmt in
> the C++ FE), and then let gimplify_expr do its job.

Sure.  Another alternative would be to leave the calls to gimplify_stmt 
(or probably change them to gimplify_to_stmt_list) and return 
GS_ALL_DONE from cp_gimplify_expr.

Jason