On Mon, 15 Jan 2024, Jason Merrill wrote:
> On 1/5/24 11:50, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> > for trunk and perhaps 13?
> >
> > -- >8 --
> >
> > invalid_tparm_referent_p was rejecting using the address of a class NTTP
> > object as a template argument, but this should be fine.
>
> Hmm, I suppose so; https://eel.is/c++draft/temp#param-8 saying "No two
> template parameter objects are template-argument-equivalent" suggests there
> can be only one. And clang/msvc allow it.
>
> > PR c++/113242
> >
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (invalid_tparm_referent_p) <case ADDR_EXPR>: Suppress
> > DECL_ARTIFICIAL rejection test for class NTTP objects.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/nontype-class61.C: New test.
> > ---
> > gcc/cp/pt.cc | 3 ++-
> > gcc/testsuite/g++.dg/cpp2a/nontype-class61.C | 27 ++++++++++++++++++++
> > 2 files changed, 29 insertions(+), 1 deletion(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class61.C
> >
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 154ac76cb65..8c7d178328d 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -7219,7 +7219,8 @@ invalid_tparm_referent_p (tree type, tree expr,
> > tsubst_flags_t complain)
> > * a string literal (5.13.5),
> > * the result of a typeid expression (8.2.8), or
> > * a predefined __func__ variable (11.4.1). */
> > - else if (VAR_P (decl) && DECL_ARTIFICIAL (decl))
> > + else if (VAR_P (decl) && !DECL_NTTP_OBJECT_P (decl)
> > + && DECL_ARTIFICIAL (decl))
>
> If now some artificial variables are OK and others are not, perhaps we should
> enumerate them either way and abort if it's one we haven't specifically
> considered.
Sounds good, like so? Shall we backport this patch or the original
patch to the 13 branch?
-- >8 --
Subject: [PATCH] c++: address of class NTTP object as targ [PR113242]
invalid_tparm_referent_p was rejecting using the address of a class NTTP
object as a template argument, but this should be fine.
This patch fixes this by refining the DECL_ARTIFICIAL rejection test to
check specifically for the kinds of artificial variables we want to
exclude.
PR c++/113242
gcc/cp/ChangeLog:
* pt.cc (invalid_tparm_referent_p) <case ADDR_EXPR>: Refine
DECL_ARTIFICIAL rejection test. Assert that C++20 template
parameter objects are the only artificial variables we accept.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/nontype-class61.C: New test.
---
gcc/cp/pt.cc | 13 +++++++---
gcc/testsuite/g++.dg/cpp2a/nontype-class61.C | 27 ++++++++++++++++++++
2 files changed, 37 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class61.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index b6117231de1..885c297450e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7212,12 +7212,14 @@ invalid_tparm_referent_p (tree type, tree expr,
tsubst_flags_t complain)
/* C++17: For a non-type template-parameter of reference or pointer
type, the value of the constant expression shall not refer to (or
for a pointer type, shall not be the address of):
- * a subobject (4.5),
+ * a subobject (4.5), (relaxed in C++20)
* a temporary object (15.2),
- * a string literal (5.13.5),
+ * a string literal (5.13.5), (we diagnose this early in
+ convert_nontype_argument)
* the result of a typeid expression (8.2.8), or
* a predefined __func__ variable (11.4.1). */
- else if (VAR_P (decl) && DECL_ARTIFICIAL (decl))
+ else if (VAR_P (decl)
+ && (DECL_TINFO_P (decl) || DECL_FNAME_P (decl)))
{
if (complain & tf_error)
error ("the address of %qD is not a valid template argument",
@@ -7242,6 +7244,11 @@ invalid_tparm_referent_p (tree type, tree expr,
tsubst_flags_t complain)
decl);
return true;
}
+
+ /* The only artificial variables we do accept are C++20
+ template parameter objects. */
+ if (VAR_P (decl) && DECL_ARTIFICIAL (decl))
+ gcc_checking_assert (DECL_NTTP_OBJECT_P (decl));
}
break;
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class61.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class61.C
new file mode 100644
index 00000000000..90805a05ecf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class61.C
@@ -0,0 +1,27 @@
+// PR c++/113242
+// { dg-do compile { target c++20 } }
+
+struct wrapper {
+ int n;
+};
+
+template<const wrapper& X>
+void f1() {
+ static_assert(X.n == 42);
+}
+
+template<const wrapper* X>
+void f2() {
+ static_assert(X->n == 42);
+}
+
+template<wrapper X>
+void g() {
+ f1<X>();
+ f2<&X>();
+}
+
+int main() {
+ constexpr wrapper X = {42};
+ g<X>();
+}
--
2.43.0.367.g186b115d30
