In the testcase below, template argument deduction for the call
g(id<int>) goes wrong because the functions in the overload set id<int>
each have a yet-undeduced auto return type, and this undeduced return
type makes try_one_overload fail to match up any of these functions with
g's parameter type, leading to g's template parameter going undeduced
and to the overload set going unresolved.
This patch fixes this issue by performing return type deduction via
instantiation before doing try_one_overload, in a manner similar to what
resolve_address_of_overloaded_function does.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK to
commit?
gcc/cp/ChangeLog:
PR c++/64194
* pt.c (resolve_overloaded_unification): If the function
template specialization has a placeholder return type,
then instantiate it before attempting unification.
gcc/testsuite/ChangeLog:
PR c++/64194
* g++.dg/cpp1y/auto-fn60.C: New test.
---
gcc/cp/pt.c | 11 ++++++++++-
gcc/testsuite/g++.dg/cpp1y/auto-fn60.C | 11 +++++++++++
2 files changed, 21 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn60.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 4d955c555dc..abb74520fc9 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -22118,7 +22118,16 @@ resolve_overloaded_unification (tree tparms,
if (subargs != error_mark_node
&& !any_dependent_template_arguments_p (subargs))
{
- elem = TREE_TYPE (instantiate_template (fn, subargs, tf_none));
+ fn = instantiate_template (fn, subargs, tf_none);
+ if (undeduced_auto_decl (fn))
+ {
+ /* Instantiate the function to deduce its return type. */
+ ++function_depth;
+ instantiate_decl (fn, /*defer*/false, /*class*/false);
+ --function_depth;
+ }
+
+ elem = TREE_TYPE (fn);
if (try_one_overload (tparms, targs, tempargs, parm,
elem, strict, sub_strict, addr_p, explain_p)
&& (!goodfn || !same_type_p (goodfn, elem)))
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn60.C
b/gcc/testsuite/g++.dg/cpp1y/auto-fn60.C
new file mode 100644
index 00000000000..237868c076b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn60.C
@@ -0,0 +1,11 @@
+// PR c++/64194
+// { dg-do compile { target c++14 } }
+
+template <typename T> void g(void (*)(T)) { }
+
+template <typename T> auto id(int) { }
+template <typename T> auto id(char) { return 0; }
+
+int main() {
+ g(id<void>);
+}
--
2.28.0.rc1
