On 11/23/20 10:30 AM, Jakub Jelinek wrote:
On Mon, Nov 23, 2020 at 10:03:44AM -0700, Martin Sebor wrote:
If the most significant bound is lost, why don't you save in the attribute
early only the most significant bound before it is lost
The other bounds are a part of the type so saving them in the attribute
isn't essential. I save all of them because it simplifies their lookup.
With only the most significant bound in the attribute argument, looking
up the other bounds (e.g., when checking function redeclarations for
mismatches) will, in addition to doing what's done for the most
significant bound, involve scanning the declarations' argument lists,
extracting the bounds from the SAVE_EXPRs, before comparing them.
As an example, in
void f (int A[m][n]);
the attribute has the chain (VAR_DECL(m), VAR_DECL(n)) as arguments
and comparing them with another declaration of f is as simple as
traversing the chain and comparing each node value.
With the change you suggest, the attribute will only have VAR_DECL(m)
and the least significant bound will have to be extracted from A[m]'s
type's size which is:
MULT (NOP (bitsizetype, NOP (sizetype, SAVE (VAR (n)))), 32)
It's possible to do but not without some additional complexity and
cost.
I don't think it would be significant complication, on the other side you
avoid wasting compile time memory on that (GC one, which means it will be
wasted until GC collection if there is one ever). Plus all the issues from
having the same information in multiple different places.
So just to make sure I understand correctly (and answer the question
I asked): unsharing the expression as in the proposed patch won't
cause any correctness issues. You just find rewriting the code to
use the existing SAVE_EXPRs instead preferable for the reasons above.
Please correct me if I misunderstood something.
Thanks
Martin
