PR c++/80767 - unnecessary instantiation of generic lambda

	* call.c (convert_like_real): Call build_user_type_conversion_1 if
	cand is null.
	(add_conv_candidate): Build a ck_user conversion with no candidate.

From-SVN: r251427

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 1e68776..a60f2ad 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,10 @@
 2017-08-29  Jason Merrill  <jason@redhat.com>
 
+       PR c++/80767 - unnecessary instantiation of generic lambda
+       * call.c (convert_like_real): Call build_user_type_conversion_1 if
+       cand is null.
+       (add_conv_candidate): Build a ck_user conversion with no candidate.
+
        Fix lambdas in template default argument of inherited ctor.
        * method.c (synthesized_method_base_walk): Replace an inherited
        template with its specialization.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index cfedd30..f7f9297 100644 (file)
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -2278,8 +2278,10 @@ add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
 
       if (i == 0)
        {
-         t = implicit_conversion (totype, argtype, arg, /*c_cast_p=*/false,
-                                  flags, complain);
+         t = build_identity_conv (argtype, NULL_TREE);
+         t = build_conv (ck_user, totype, t);
+         /* Leave the 'cand' field null; we'll figure out the conversion in
+            convert_like_real if this candidate is chosen.  */
          convert_type = totype;
        }
       else if (parmnode == void_list_node)
@@ -6692,6 +6694,13 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
     case ck_user:
       {
        struct z_candidate *cand = convs->cand;
+
+       if (cand == NULL)
+         /* We chose the surrogate function from add_conv_candidate, now we
+            actually need to build the conversion.  */
+         cand = build_user_type_conversion_1 (totype, expr,
+                                              LOOKUP_NO_CONVERSION, complain);
+
        tree convfn = cand->fn;
 
        /* When converting from an init list we consider explicit

diff --git a/gcc/testsuite/g++.dg/cpp1z/lambda-inherit1.C b/gcc/testsuite/g++.dg/cpp1z/lambda-inherit1.C
new file mode 100644 (file)
index 0000000..75ef586
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/lambda-inherit1.C
@@ -0,0 +1,23 @@
+// PR c++/80767
+// { dg-options -std=c++17 }
+
+template <typename... Fs> 
+struct overloader : Fs...
+{
+    overloader(Fs... fs) 
+        : Fs(fs)...
+    { } 
+
+    using Fs::operator()...;
+};
+
+struct a { void foo() { } };
+struct b { void bar() { } };
+struct c { void bar() { } };
+
+int main() {
+    overloader{
+        [](a x) { x.foo(); },
+        [](auto x) { x.bar(); }
+    }(a{});
+}