DR 976 affects conversion operator deduction, swapping reference stripping and
cv-qual removal. This allows 'Y::operator P const & ()' to deduce T against a
call wanting plain A (previously that would fail as 'P const' cannot be deduced
from 'A').
It also affects deductions for array- or function-producing conversions, which I
suspect is rarer.
pushed to trunk
nathan
--
Nathan Sidwell
From 80f075b410125bddb31459428760645baba1a69f Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nat...@acm.org>
Date: Sat, 10 Jun 2023 12:42:17 -0400
Subject: [PATCH] c++: Adjust conversion deduction [PR61663][DR976]
Drop the return type's reference before doing cvqual and related decays.
gcc/cp/
PR c++/61663
* pt.cc (maybe_adjust_types_for_deduction): Implement DR976.
gcc/testsuite/
* g++.dg/template/pr61663.C: New.
---
gcc/cp/pt.cc | 11 +++--
gcc/testsuite/g++.dg/template/pr61663.C | 63 +++++++++++++++++++++++++
2 files changed, 69 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/pr61663.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 6b20c58ce66..6a2cf2c123f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22725,10 +22725,16 @@ maybe_adjust_types_for_deduction (tree tparms,
break;
case DEDUCE_CONV:
+ /* [temp.deduct.conv] First remove a reference type on parm.
+ DRs 322 & 976 affected this. */
+ if (TYPE_REF_P (*parm))
+ *parm = TREE_TYPE (*parm);
+
/* Swap PARM and ARG throughout the remainder of this
function; the handling is precisely symmetric since PARM
will initialize ARG rather than vice versa. */
std::swap (parm, arg);
+
break;
case DEDUCE_EXACT:
@@ -22795,11 +22801,6 @@ maybe_adjust_types_for_deduction (tree tparms,
result |= UNIFY_ALLOW_OUTER_MORE_CV_QUAL;
}
- /* DR 322. For conversion deduction, remove a reference type on parm
- too (which has been swapped into ARG). */
- if (strict == DEDUCE_CONV && TYPE_REF_P (*arg))
- *arg = TREE_TYPE (*arg);
-
return result;
}
diff --git a/gcc/testsuite/g++.dg/template/pr61663.C b/gcc/testsuite/g++.dg/template/pr61663.C
new file mode 100644
index 00000000000..2964fa6c309
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr61663.C
@@ -0,0 +1,63 @@
+// { dg-do compile { target c++11 } }
+// PR c++/61663
+// DR 976, strip ref from conv op return type before doing
+// fn and ary decay or CV qual removal
+
+struct F
+{
+ template<class T>
+ operator const T&();
+};
+
+void Foo ()
+{
+ F f;
+ int i = f;
+}
+
+template<typename T> struct X {};
+
+struct Y
+{
+ template<typename T> operator X<T> () &&; // #3
+ template<typename T> operator X<T> const & () const &; // #4
+};
+
+void Use (X<void>);
+Y Val ();
+Y const &Ref ();
+
+// { dg-final { scan-assembler "_Z5Frob3v:.*_ZNO1Ycv1XIT_EIvEEv.*_Z3Use1XIvE" } }
+void Frob3 ()
+{
+ Use (Val ()); // #3
+}
+
+// { dg-final { scan-assembler "_Z5Frob4v:.*_ZNKR1YcvRK1XIT_EIvEEv.*_Z3Use1XIvE" } }
+void Frob4 ()
+{
+ Use (Ref ()); // #4
+}
+
+struct Z
+{
+ template<typename T> using FnRef = void (&) (T);
+ template<typename T> using AryRef = T (&)[];
+
+ template<typename T> operator FnRef<T> ();
+ template<typename T> operator AryRef<T> ();
+};
+
+// { dg-final { scan-assembler "_Z5Frob5R1Z:.*_ZN1ZcvRFvT_EIiEEv.*_ZN1ZcvRA_T_IiEEv" } }
+void Frob5 (Z &z)
+{
+ void (*fnptr)(int) = z;
+ int *iptr = z;
+}
+
+// { dg-final { scan-assembler "_Z5Frob6R1Z:.*_ZN1ZcvRFvT_EIfEEv.*_ZN1ZcvRA_T_IfEEv" } }
+void Frob6 (Z &z)
+{
+ void (&fnref)(float) = z;
+ float (&aryref)[] = z;
+}
--
2.40.1
