On Thu, Jul 08, 2021 at 09:35:02AM -0400, Marek Polacek wrote:
> On Thu, Jul 08, 2021 at 09:30:27AM -0400, Jason Merrill wrote:
> > On 7/7/21 9:40 PM, Marek Polacek wrote:
> > > It sounds plausible that this assert
> > >
> > > int f();
> > > static_assert(noexcept(sizeof(f())));
> > >
> > > should pass: sizeof produces a std::size_t and its operand is not
> > > evaluated, so it can't throw. noexcept should only evaluate to
> > > false for potentially evaluated operands. Therefore I think that
> > > check_noexcept_r shouldn't walk into operands of sizeof/decltype/
> > > alignof/typeof. Only checking cp_unevaluated_operand therein does
> > > not work, because expr_noexcept_p can be called in an unevaluated
> > > context, so I resorted to the following cp_evaluated hack. Does
> > > that seem acceptable?
> >
> > I suppose, but why not check for SIZEOF_EXPR/ALIGNOF_EXPR/NOEXCEPT_EXPR
> > directly?
>
> I thought I would, but then it occurred to me that it might be better to
> rely on cp_walk_subtrees which ++/--s cp_unevaluated_operand for those
> codes. I'd be happy to change the patch to check those codes directly;
> maybe I'm overthinking things here.
So here's v2 which checks the codes directly, via a new inline:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
It sounds plausible that this assert
int f();
static_assert(noexcept(sizeof(f())));
should pass: sizeof produces a std::size_t and its operand is not
evaluated, so it can't throw. noexcept should only evaluate to
false for potentially evaluated operands. Therefore I think that
check_noexcept_r shouldn't walk into operands of sizeof/decltype/
alignof/typeof.
PR c++/101087
gcc/cp/ChangeLog:
* cp-tree.h (unevaluated_p): New.
* except.c (check_noexcept_r): Use it. Don't walk into
unevaluated operands.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/noexcept70.C: New test.
---
gcc/cp/cp-tree.h | 13 +++++++++++++
gcc/cp/except.c | 9 ++++++---
gcc/testsuite/g++.dg/cpp0x/noexcept70.C | 5 +++++
3 files changed, 24 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept70.C
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index b4501576b26..d4810c0c986 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8465,6 +8465,19 @@ is_constrained_auto (const_tree t)
return is_auto (t) && PLACEHOLDER_TYPE_CONSTRAINTS_INFO (t);
}
+/* True if CODE, a tree code, denotes a tree whose operand is not evaluated
+ as per [expr.context], i.e., an operand to sizeof, typeof, decltype, or
+ alignof. */
+
+inline bool
+unevaluated_p (tree_code code)
+{
+ return (code == DECLTYPE_TYPE
+ || code == ALIGNOF_EXPR
+ || code == SIZEOF_EXPR
+ || code == NOEXCEPT_EXPR);
+}
+
/* RAII class to push/pop the access scope for T. */
struct push_access_scope_guard
diff --git a/gcc/cp/except.c b/gcc/cp/except.c
index a8cea53cf91..a8acbc4b7b2 100644
--- a/gcc/cp/except.c
+++ b/gcc/cp/except.c
@@ -1033,12 +1033,15 @@ check_handlers (tree handlers)
expression whose type is a polymorphic class type (10.3). */
static tree
-check_noexcept_r (tree *tp, int * /*walk_subtrees*/, void * /*data*/)
+check_noexcept_r (tree *tp, int *walk_subtrees, void *)
{
tree t = *tp;
enum tree_code code = TREE_CODE (t);
- if ((code == CALL_EXPR && CALL_EXPR_FN (t))
- || code == AGGR_INIT_EXPR)
+
+ if (unevaluated_p (code))
+ *walk_subtrees = false;
+ else if ((code == CALL_EXPR && CALL_EXPR_FN (t))
+ || code == AGGR_INIT_EXPR)
{
/* We can only use the exception specification of the called function
for determining the value of a noexcept expression; we can't use
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept70.C
b/gcc/testsuite/g++.dg/cpp0x/noexcept70.C
new file mode 100644
index 00000000000..45a6137dd6f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept70.C
@@ -0,0 +1,5 @@
+// PR c++/101087
+// { dg-do compile { target c++11 } }
+
+int f();
+static_assert(noexcept(sizeof(f())), "");
base-commit: 763121ccd908f52bc666f277ea2cf42110b3aad9
--
2.31.1
