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* [gcc r12-1224] c++: top-level cv-quals on type of NTTP [PR100893]
@ 2021-06-04 18:10 Patrick Palka
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From: Patrick Palka @ 2021-06-04 18:10 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:6f8c9691495ad5a307db98dc19c3296ee4e6de64
commit r12-1224-g6f8c9691495ad5a307db98dc19c3296ee4e6de64
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Jun 4 14:08:26 2021 -0400
c++: top-level cv-quals on type of NTTP [PR100893]
Here, we're rejecting the specialization of g<T,F> with T=A, F=&f in
param4.C below due to a spurious constness mismatch between the type of
the template argument &f and the substituted type of the parm F (the
latter has a top-level const). Note that this mismatch doesn't occur
with object pointers because in that case a call to
perform_qualification_conversions from convert_nontype_argument
implicitly adds a top-level const to the argument (via a cast) to match.
This however seems to be a manifestation of a more general conformance
issue: we're not dropping top-level cv-quals on the substituted
type of an NTTP as per [temp.param]/6 (we only do so at parse time in
process_template_parm). So this patch makes convert_template_argument
drop top-level cv-quals accordingly.
PR c++/100893
gcc/cp/ChangeLog:
* pt.c (convert_template_argument): Strip top-level cv-quals
on the substituted type of a non-type template parameter.
gcc/testsuite/ChangeLog:
* g++.dg/template/param4.C: New test.
* g++.dg/template/param5.C: New test.
* g++.dg/cpp1z/nontype-auto19.C: New test.
* g++.dg/cpp2a/concepts-decltype.C: Don't expect that the
deduced type of a decltype(auto) NTTP has top-level cv-quals.
Diff:
---
gcc/cp/pt.c | 4 ++++
gcc/testsuite/g++.dg/cpp1z/nontype-auto19.C | 8 ++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-decltype.C | 2 +-
gcc/testsuite/g++.dg/template/param4.C | 10 ++++++++++
gcc/testsuite/g++.dg/template/param5.C | 7 +++++++
5 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 744461ed8cb..2ae886d3a39 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8499,6 +8499,10 @@ convert_template_argument (tree parm,
if (invalid_nontype_parm_type_p (t, complain))
return error_mark_node;
+ /* Drop top-level cv-qualifiers on the substituted/deduced type of
+ this non-type template parameter, as per [temp.param]/6. */
+ t = cv_unqualified (t);
+
if (t != TREE_TYPE (parm))
t = canonicalize_type_argument (t, complain);
diff --git a/gcc/testsuite/g++.dg/cpp1z/nontype-auto19.C b/gcc/testsuite/g++.dg/cpp1z/nontype-auto19.C
new file mode 100644
index 00000000000..d6b904fd19c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nontype-auto19.C
@@ -0,0 +1,8 @@
+// Verify top-level cv-qualifiers are dropped from the deduced
+// type of a non-type template parameter, as per [temp.param]/6.
+// { dg-do compile { target c++17 } }
+
+constexpr int x = 42;
+template<decltype(auto) V> decltype(V)& f();
+using type = decltype(f<x>());
+using type = int&;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-decltype.C b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype.C
index 13733c645f3..b375f74eb8a 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-decltype.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype.C
@@ -61,7 +61,7 @@ constexpr int Z = 10;
static_assert(deduced_as<0, int>);
static_assert(deduced_as<0, int&>); // { dg-error "invalid variable template" }
-static_assert(deduced_as<Z, const int>);
+static_assert(deduced_as<Z, int>);
static_assert(deduced_as<(Z), const int>); // { dg-error "invalid variable template" }
static_assert(deduced_as<(Z), const int&>);
diff --git a/gcc/testsuite/g++.dg/template/param4.C b/gcc/testsuite/g++.dg/template/param4.C
new file mode 100644
index 00000000000..8061ff72ba2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/param4.C
@@ -0,0 +1,10 @@
+// PR c++/100893
+
+template<class T, typename T::type F> void g() { }
+
+struct A { typedef void (*const type)(); };
+void f();
+template void g<A, &f>();
+
+struct B { typedef void (B::*const type)(); void f(); };
+template void g<B, &B::f>();
diff --git a/gcc/testsuite/g++.dg/template/param5.C b/gcc/testsuite/g++.dg/template/param5.C
new file mode 100644
index 00000000000..89a5c04c09c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/param5.C
@@ -0,0 +1,7 @@
+// Verify top-level cv-qualifiers are dropped when determining the substituted
+// type of a non-type template parameter, as per [temp.param]/6.
+// { dg-do compile { target c++11 } }
+
+template<class T, T V> decltype(V)& f();
+using type = decltype(f<const volatile int, 0>());
+using type = int&;
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