On 7/30/24 4:59 PM, Marek Polacek wrote:
On Mon, Jul 29, 2024 at 06:34:40PM -0400, Jason Merrill wrote:
On 7/29/24 4:18 PM, Marek Polacek wrote:
On Tue, Jul 23, 2024 at 05:18:52PM -0400, Jason Merrill wrote:
On 7/17/24 5:33 PM, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
Hmm, I thought I had replied to this already.
-- >8 --
Unfortunately, my r15-1946 fix broke the attached testcase. In it,
we no longer go into the
/* P1009: Array size deduction in new-expressions. */
block, and instead generate an operator new [] call along with a loop
in build_new_1, which we can't constexpr-evaluate. So this patch
reverts r15-1946 and uses CONSTRUCTOR_IS_PAREN_INIT to distinguish
between () and {} to fix the original testcase (anew7.C).
PR c++/115645
gcc/cp/ChangeLog:
* call.cc (convert_like_internal) <case ck_user>: Don't report errors
about calling an explicit constructor when the constructor was marked
CONSTRUCTOR_IS_PAREN_INIT.
* init.cc (build_new): Revert r15-1946. Set CONSTRUCTOR_IS_PAREN_INIT.
(build_vec_init): Maybe set CONSTRUCTOR_IS_PAREN_INIT.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/constexpr-new23.C: New test.
---
gcc/cp/call.cc | 2 ++
gcc/cp/init.cc | 17 ++++-----
gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C | 38 ++++++++++++++++++++
3 files changed, 49 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index a5d3426b70c..2d94d5e0d07 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -8592,6 +8592,8 @@ convert_like_internal (conversion *convs, tree expr, tree
fn, int argnum,
&& BRACE_ENCLOSED_INITIALIZER_P (expr)
/* Unless this is for direct-list-initialization. */
&& (!CONSTRUCTOR_IS_DIRECT_INIT (expr) || convs->need_temporary_p)
+ /* And it wasn't a ()-init. */
+ && !CONSTRUCTOR_IS_PAREN_INIT (expr)
/* And in C++98 a default constructor can't be explicit. */
&& cxx_dialect >= cxx11)
{
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index e9561c146d7..4138a6077dd 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4005,20 +4005,17 @@ build_new (location_t loc, vec<tree, va_gc>
**placement, tree type,
/* P1009: Array size deduction in new-expressions. */
const bool array_p = TREE_CODE (type) == ARRAY_TYPE;
if (*init
- /* If the array didn't specify its bound, we have to deduce it. */
- && ((array_p && !TYPE_DOMAIN (type))
- /* For C++20 array with parenthesized-init, we have to process
- the parenthesized-list. But don't do it for (), which is
- value-initialization, and INIT should stay empty. */
- || (cxx_dialect >= cxx20
- && (array_p || nelts)
- && !(*init)->is_empty ())))
+ /* If ARRAY_P, we have to deduce the array bound. For C++20 paren-init,
+ we have to process the parenthesized-list. But don't do it for (),
+ which is value-initialization, and INIT should stay empty. */
+ && (array_p || (cxx_dialect >= cxx20 && nelts && !(*init)->is_empty ())))
{
/* This means we have 'new T[]()'. */
if ((*init)->is_empty ())
{
tree ctor = build_constructor (init_list_type_node, NULL);
CONSTRUCTOR_IS_DIRECT_INIT (ctor) = true;
+ CONSTRUCTOR_IS_PAREN_INIT (ctor) = true;
vec_safe_push (*init, ctor);
}
tree &elt = (**init)[0];
@@ -4735,6 +4732,9 @@ build_vec_init (tree base, tree maxindex, tree init,
bool do_static_init = (DECL_P (obase) && TREE_STATIC (obase));
bool empty_list = false;
+ const bool paren_init_p = (init
+ && TREE_CODE (init) == CONSTRUCTOR
+ && CONSTRUCTOR_IS_PAREN_INIT (init));
I think rather than recognizing paren-init in general, we want to recognize
() specifically, and set explicit_value_init_p...
if (init && BRACE_ENCLOSED_INITIALIZER_P (init)
&& CONSTRUCTOR_NELTS (init) == 0)
/* Skip over the handling of non-empty init lists. */
@@ -4927,6 +4927,7 @@ build_vec_init (tree base, tree maxindex, tree init,
|| TREE_CODE (type) == ARRAY_TYPE))
{
init = build_constructor (init_list_type_node, NULL);
+ CONSTRUCTOR_IS_PAREN_INIT (init) = paren_init_p;
}
else
{
...by taking the else branch here. Then we shouldn't need the convert_like
change.
Unfortunately that then breaks Jon's test (constexpr-new23.C which this
patch is adding). The problem is that if we do *not* create a new {}, and
do explicit_value_init_p, we end up with
int[1] * D.2643;
<<< Unknown tree: expr_stmt
(void) (D.2643 = (int[1] *) D.2642) >>>;
int[1] * D.2644;
<<< Unknown tree: expr_stmt
(void) (D.2644 = D.2643) >>>;
TARGET_EXPR <D.2645, 0>;
<<< Unknown tree: for_stmt
D.2645 > -1
<<cleanup_point <<< Unknown tree: expr_stmt
*(int[1] &) int * D.2646;
<<< Unknown tree: expr_stmt
(void) (D.2646 = (int *) D.2644) >>>;
int * D.2647;
<<< Unknown tree: expr_stmt
(void) (D.2647 = D.2646) >>>;
TARGET_EXPR <D.2648, 0>;
<<< Unknown tree: for_stmt
D.2648 > -1
<<cleanup_point <<< Unknown tree: expr_stmt
*D.2647 = 0, --D.2648 >>>>>;
<<< Unknown tree: expr_stmt
(void) ++D.2647 >>>;
>>>;
D.2646, --D.2645 >>>>>;
<<< Unknown tree: expr_stmt
(void) ++D.2644 >>>;
>>>;
D.2643
rather than:
int[1] * D.2643;
<<< Unknown tree: expr_stmt
(void) (D.2643 = (int[1] *) D.2642) >>>;
int[1] * D.2644;
<<< Unknown tree: expr_stmt
(void) (D.2644 = D.2643) >>>;
TARGET_EXPR <D.2645, 0>;
<<< Unknown tree: for_stmt
D.2645 > -1
<<cleanup_point <<< Unknown tree: expr_stmt
*D.2644 = {}, --D.2645 >>>>>;
<<< Unknown tree: expr_stmt
(void) ++D.2644 >>>;
>>>;
D.2643
In the former, the "*D.2647 = 0" assignment is what breaks constexpr,
which then complains:
constexpr-new23.C:16:16: error: accessing 'test_array()::U::arr' member instead
of initialized 'test_array()::U::x' member in constant expression
16 | return ::new((void*)p) T[1]();
| ^~~~~~~~~~~~~~~~~~~~~~
constexpr-new23.C:31:9: note: initializing 'test_array()::U::arr' requires a
member access expression as the left operand of the assignment
31 | int arr[4];
If there is no bug in constexpr, then it looks like we need to
initialize using a {} rather than a loop that assigns 0 to each
element.
Ah, thanks.
It looks like the first bug is that build_vec_init wrongly leaves try_const
false for this case (without your patch) because int doesn't have a
constexpr default constructor, failing to consider that value-initialization
of scalars is constexpr.
Oh wow, I should have noticed that.
Then, once we're into the looping initialization, we aren't expressing it in
a way that will satisfy the strict checking in constexpr evaluation; it
needs to initialize the array, not just its elements.
I expect we could fix that with something like
/* Start array lifetime before accessing elements. */
if (TREE_CODE (atype) == ARRAY_TYPE)
{
elt_init = build_constructor (atype, nullptr);
CONSTRUCTOR_NO_CLEARING (elt_init) = true;
for_stmt = build2 (INIT_EXPR, atype, obase, elt_init);
finish_expr_stmt (for_stmt);
}
but if we're only concerned about constexpr, fixing the first bug ought to
be enough; in constant evaluation if we don't get a constant initializer
we're failing anyway.
This patch fixes the first bug. Thanks!
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Unfortunately, my r15-1946 fix broke the attached testcase; the
constexpr evaluation reported an error about not being able to
evaluate the code emitted by build_vec_init. Jason figured out
it's because we were wrongly setting try_const to false, where
in fact it should have been true. Value-initialization of scalars
is constexpr, so we should check that alongside of
type_has_constexpr_default_constructor.
PR c++/115645
gcc/cp/ChangeLog:
* init.cc (build_vec_init): When initializing a scalar type, try to
create a constant initializer.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/constexpr-new23.C: New test.
---
gcc/cp/init.cc | 4 ++-
gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C | 38 ++++++++++++++++++++
2 files changed, 41 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index e9561c146d7..a3a97e2c128 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4724,7 +4724,9 @@ build_vec_init (tree base, tree maxindex, tree init,
&& TREE_CONSTANT (maxindex)
&& (init ? TREE_CODE (init) == CONSTRUCTOR
: (type_has_constexpr_default_constructor
- (inner_elt_type)))
+ (inner_elt_type)
+ /* Value-initialization of scalars is constexpr. */
+ || SCALAR_TYPE_P (inner_elt_type)))
I think we also want to check explicit_value_init_p, since default-init
of scalars is not constexpr.
I don't think we'd actually get here in that case, as callers like
build_new_1 avoid calling build_vec_init at all, but I'd still like to
be correct.
Jason
