On 11/20/20 2:41 PM, Jakub Jelinek wrote:
On Fri, Nov 20, 2020 at 02:30:43PM -0700, Martin Sebor wrote:
VLA parameter bounds can involve any other expressions, including
function calls. It's those rather than other parameters that also
trigger the problem (at least in the test cases I've seen).
When/how would the unsharing cause the expression to be evaluated
multiple times? And if/when it did, would simply wrapping the whole
expression in a SAVE_EXPR be the right way to avoid it or would it
need to be more involved than that?
Well, unshare_expr just doesn't unshare SAVE_EXPRs, it only ensures that
the trees inside of them aren't shared with something else (aka unshares the
subtrees the first time it sees the SAVE_EXPR), but doesn't unshare the
SAVE_EXPR node itself and doesn't walk children the second and following
time.
So, the question is whether you are creating the attributes before the
SAVE_EXPRs are added to the bounds or after it, and whether when evaluating
the (unshared) expressions in there you always place it after something
initialized those SAVE_EXPRs first.
The SAVE_EXPRs are essential, so that the functions aren't called multiple
times.
At the point the attribute is created there is no SAVE_EXPR. So for
something like:
int f (void);
void g (int a[f () + 1]) { }
the bound is a PLUS_EXPR (CALL_EXPR (f), 1).
I don't do anything with the expression except put them on the chain
of arguments to the two attributes and print them in warnings.
Martin
