https://gcc.gnu.org/g:a82583e43eaacab9a111d1fca14c7d272aa3e039
commit r13-9294-ga82583e43eaacab9a111d1fca14c7d272aa3e039
Author: Marek Polacek <pola...@redhat.com>
Date: Fri Jul 21 17:48:37 2023 -0400
c++: fix ICE with constexpr ARRAY_REF [PR110382]
This code in cxx_eval_array_reference has been hard to get right.
In r12-2304 I added some code; in r13-5693 I removed some of it.
Here the problematic line is "S s = arr[0];" which causes a crash
on the assert in verify_ctor_sanity:
gcc_assert (!ctx->object || !DECL_P (ctx->object)
|| ctx->global->get_value (ctx->object) == ctx->ctor);
ctx->object is the VAR_DECL 's', which is correct here. The second
line points to the problem: we replaced ctx->ctor in
cxx_eval_array_reference:
new_ctx.ctor = build_constructor (elem_type, NULL); // #1
which I think we shouldn't have; the CONSTRUCTOR we created in
cxx_eval_constant_expression/DECL_EXPR
new_ctx.ctor = build_constructor (TREE_TYPE (r), NULL);
had the right type.
We still need #1 though. E.g., in constexpr-96241.C, we never
set ctx.ctor/object before calling cxx_eval_array_reference, so
we have to build a CONSTRUCTOR there. And in constexpr-101371-2.C
we have a ctx.ctor, but it has the wrong type, so we need a new one.
We can fix the problem by always clearing the object, and, as an
optimization, only create/free a new ctor when actually needed.
PR c++/110382
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_array_reference): Create a new constructor
only when we don't already have a matching one. Clear the object
when the type is non-scalar.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-110382.C: New test.
(cherry picked from commit 6e424febfbcb27c21a7fe3a137e614765f9cf9d2)
Diff:
---
gcc/cp/constexpr.cc | 13 +++++++++++--
gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C | 17 +++++++++++++++++
2 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index f885a806c0a2..d34b8bdbd166 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -4301,15 +4301,24 @@ cxx_eval_array_reference (const constexpr_ctx *ctx,
tree t,
else
val = build_value_init (elem_type, tf_warning_or_error);
- if (!SCALAR_TYPE_P (elem_type))
+ /* Create a new constructor only if we don't already have a suitable one. */
+ const bool new_ctor = (!SCALAR_TYPE_P (elem_type)
+ && (!ctx->ctor
+ || !same_type_ignoring_top_level_qualifiers_p
+ (elem_type, TREE_TYPE (ctx->ctor))));
+ if (new_ctor)
{
new_ctx = *ctx;
+ /* We clear the object here. We used to replace it with T, but that
+ caused problems (101371, 108158); and anyway, T is the initializer,
+ not the target object. */
+ new_ctx.object = NULL_TREE;
new_ctx.ctor = build_constructor (elem_type, NULL);
ctx = &new_ctx;
}
t = cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
overflow_p);
- if (!SCALAR_TYPE_P (elem_type) && t != ctx->ctor)
+ if (new_ctor && t != ctx->ctor)
free_constructor (ctx->ctor);
return t;
}
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C
new file mode 100644
index 000000000000..317c5ecfcd52
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C
@@ -0,0 +1,17 @@
+// PR c++/110382
+// { dg-do compile { target c++14 } }
+
+struct S {
+ double a = 0;
+};
+
+constexpr double
+g ()
+{
+ S arr[1];
+ S s = arr[0];
+ (void) arr[0];
+ return s.a;
+}
+
+int main() { return g (); }
