[C++ PATCH] c++: is unnecessarily redundant, you can just write [PATCH].
On 1/24/20 6:20 PM, Marek Polacek wrote:> I neglected to add a proper
diagnostic for the reference dynamic_cast> case when the operand of a
dynamic_cast doesn't refer to a public base> of Derived, resulting in
suboptimal error message>
error: call to non-'constexpr' function 'void* __cxa_bad_cast()'
Tested x86_64-linux, ok for trunk?
OK.
2020-01-24 Marek Polacek <pola...@redhat.com>
PR c++/93414 - poor diagnostic for dynamic_cast in constexpr context.
* constexpr.c (cxx_eval_dynamic_cast_fn): Add a reference
dynamic_cast diagnostic.
* g++.dg/cpp2a/constexpr-dynamic18.C: New test.
---
gcc/cp/constexpr.c | 15 ++++++++++++-
.../g++.dg/cpp2a/constexpr-dynamic18.C | 22 +++++++++++++++++++
2 files changed, 36 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic18.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 8e8806345c1..577022e9b9a 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1888,7 +1888,20 @@ cxx_eval_dynamic_cast_fn (const constexpr_ctx *ctx, tree
call,
if (tree t = (TREE_CODE (obj) == COMPONENT_REF
? TREE_OPERAND (obj, 1) : obj))
if (TREE_CODE (t) != FIELD_DECL || !DECL_FIELD_IS_BASE (t))
- return integer_zero_node;
+ {
+ if (reference_p)
+ {
+ if (!ctx->quiet)
+ {
+ error_at (loc, "reference %<dynamic_cast%> failed");
+ inform (loc, "dynamic type %qT of its operand does "
+ "not have a base class of type %qT",
+ objtype, type);
+ }
+ *non_constant_p = true;
+ }
+ return integer_zero_node;
+ }
/* [class.cdtor] When a dynamic_cast is used in a constructor ...
or in a destructor ... if the operand of the dynamic_cast refers
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic18.C
b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic18.C
new file mode 100644
index 00000000000..346f9f56470
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic18.C
@@ -0,0 +1,22 @@
+// PR c++/93414 - poor diagnostic for dynamic_cast in constexpr context.
+// { dg-do compile { target c++2a } }
+// Here 'b' doesn't point/refer to a public base of Derived.
+
+struct Base {
+ constexpr virtual ~Base(){}
+};
+
+struct Derived: Base {
+ constexpr ~Derived(){}
+};
+
+constexpr const Derived& cast(const Base& b) {
+ return dynamic_cast<const Derived&>(b); // { dg-error "reference .dynamic_cast.
failed" }
+// { dg-message "dynamic type .const Base. of its operand does not have a base class of type
.Derived." "" { target *-*-* } .-1 }
+}
+
+auto test() {
+ static constexpr Base b;
+ constexpr auto res = cast(b);
+ return res;
+}
base-commit: 55dd44535d2e4e5703c0103c26e7c51ab8c502c4
