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* [gcc r9-10154] c++: Fix deduction with reference NTTP [PR83476]
@ 2022-05-11 14:59 Patrick Palka
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From: Patrick Palka @ 2022-05-11 14:59 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:c6432e17960799509c48df6b500a8d069110980b
commit r9-10154-gc6432e17960799509c48df6b500a8d069110980b
Author: Patrick Palka <ppalka@redhat.com>
Date: Wed Apr 14 08:54:30 2021 -0400
c++: Fix deduction with reference NTTP [PR83476]
In the testcase ref11.C below, during deduction for the call f(a),
uses_deducible_template_parms returns false for the dependent
specialization A<V> because the generic template argument V here is
wrapped in an implicit INDIRECT_REF (formed from template_parm_to_arg).
Since uses_deducible_template_parms returns false, unify_one_argument
exits early without ever attempting to deduce 'n' for 'V'. This patch
fixes this by making deducible_expression look through such implicit
INDIRECT_REFs.
gcc/cp/ChangeLog:
PR c++/83476
PR c++/99885
* pt.c (deducible_expression): Look through implicit
INDIRECT_REFs as well.
gcc/testsuite/ChangeLog:
PR c++/83476
PR c++/99885
* g++.dg/cpp1z/class-deduction85.C: New test.
* g++.dg/template/ref11.C: New test.
(cherry picked from commit 2ccc05a5141506fde0e20dec702c717fd67bf6ee)
Diff:
---
gcc/cp/pt.c | 6 ++++--
gcc/testsuite/g++.dg/cpp1z/class-deduction85.C | 16 ++++++++++++++++
gcc/testsuite/g++.dg/template/ref11.C | 9 +++++++++
3 files changed, 29 insertions(+), 2 deletions(-)
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 612557bb717..08909e2c863 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -20824,8 +20824,10 @@ static bool uses_deducible_template_parms (tree type);
static bool
deducible_expression (tree expr)
{
- /* Strip implicit conversions. */
- while (CONVERT_EXPR_P (expr) || TREE_CODE (expr) == VIEW_CONVERT_EXPR)
+ /* Strip implicit conversions and implicit INDIRECT_REFs. */
+ while (CONVERT_EXPR_P (expr)
+ || TREE_CODE (expr) == VIEW_CONVERT_EXPR
+ || REFERENCE_REF_P (expr))
expr = TREE_OPERAND (expr, 0);
return (TREE_CODE (expr) == TEMPLATE_PARM_INDEX);
}
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction85.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction85.C
new file mode 100644
index 00000000000..0b22f8eb982
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction85.C
@@ -0,0 +1,16 @@
+// PR c++/99885
+// { dg-do compile { target c++17 } }
+
+template <auto const& A>
+struct Foo {};
+
+template <auto const& A>
+struct Bar {
+ constexpr auto foo() const -> Foo<A> {
+ return {};
+ }
+};
+
+constexpr int a = 1;
+constexpr Bar<a> bar;
+Foo foo = bar.foo(); // <-- CTAD failure
diff --git a/gcc/testsuite/g++.dg/template/ref11.C b/gcc/testsuite/g++.dg/template/ref11.C
new file mode 100644
index 00000000000..c43c67edf70
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ref11.C
@@ -0,0 +1,9 @@
+// PR c++/83476
+
+int n;
+template <int& V> struct A {};
+template <int& V> void f(A<V>);
+int main() {
+ A<n> a;
+ f(a);
+}
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