This patch resolves PR114915 by replacing the logic that fills in the missing
levels in do_auto_deduction in cp/pt.cc.
The new approach now trims targs if the depth of targs is deeper than desired
(this will only happen in specific contexts), and still fills targs with empty
layers if it has fewer depths than expected.
---
gcc/cp/pt.cc | 20 ++++++++---
.../g++.dg/cpp2a/concepts-placeholder14.C | 19 +++++++++++
.../g++.dg/cpp2a/concepts-placeholder15.C | 15 +++++++++
.../g++.dg/cpp2a/concepts-placeholder16.C | 33 +++++++++++++++++++
4 files changed, 83 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-placeholder14.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-placeholder15.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-placeholder16.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 3b2106dd3..479b2a5bd 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -31253,6 +31253,19 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
full_targs = add_outermost_template_args (tmpl, full_targs);
full_targs = add_to_template_args (full_targs, targs);
+ int want = TEMPLATE_TYPE_ORIG_LEVEL (auto_node);
+ int have = TMPL_ARGS_DEPTH (full_targs);
+
+ if (want < have)
+ {
+ // if a constrained auto is declared in an explicit specialization
+ gcc_assert (context == adc_variable_type || context == adc_return_type
+ || context == adc_decomp_type);
+ tree trimmed_full_args = get_innermost_template_args
+ (full_targs, want);
+ full_targs = trimmed_full_args;
+ }
+
/* HACK: Compensate for callers not always communicating all levels of
outer template arguments by filling in the outermost missing levels
with dummy levels before checking satisfaction. We'll still crash
@@ -31260,11 +31273,10 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
these missing levels, but this hack otherwise allows us to handle a
large subset of possible constraints (including all non-dependent
constraints). */
- if (int missing_levels = (TEMPLATE_TYPE_ORIG_LEVEL (auto_node)
- - TMPL_ARGS_DEPTH (full_targs)))
+ if (want > have)
{
- tree dummy_levels = make_tree_vec (missing_levels);
- for (int i = 0; i < missing_levels; ++i)
+ tree dummy_levels = make_tree_vec (want - have);
+ for (int i = 0; i < want - have; ++i)
TREE_VEC_ELT (dummy_levels, i) = make_tree_vec (0);
full_targs = add_to_template_args (dummy_levels, full_targs);
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder14.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder14.C
new file mode 100644
index 000000000..fcdbd7608
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder14.C
@@ -0,0 +1,19 @@
+// PR c++/114915
+// { dg-do compile { target c++20 } }
+
+template<typename T>
+concept C = __is_same(T, int);
+
+template<typename T>
+void f() {
+}
+
+template<>
+void f<int>() {
+ C auto x = 1;
+}
+
+int main() {
+ f<int>();
+ return 0;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder15.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder15.C
new file mode 100644
index 000000000..b4f73f407
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder15.C
@@ -0,0 +1,15 @@
+// PR c++/114915
+// { dg-do compile { target c++20 } }
+
+template<typename T, typename U>
+concept C = __is_same(T, U);
+
+template<typename T>
+int x = 0;
+
+template<>
+C<double> auto x<double> = 1.0;
+
+int main() {
+ return 0;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder16.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder16.C
new file mode 100644
index 000000000..f808ef1b6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder16.C
@@ -0,0 +1,33 @@
+// PR c++/114915
+// { dg-do compile { target c++20 } }
+
+template<typename T, typename U>
+concept C = __is_same(T, U);
+
+template<typename T>
+struct A
+{
+ template<typename U>
+ void f() {
+ }
+};
+
+template<>
+template<>
+void A<int>::f<int>() {
+ C<int> auto x = 1;
+}
+
+template<>
+template<typename U>
+void A<bool>::f() {
+ C<int> auto x = 1;
+}
+
+int main() {
+ A<bool> a;
+ a.f<char>();
+ A<int> b;
+ b.f<int>();
+ return 0;
+}
--
2.45.0
