On Thu, Sep 20, 2018 at 12:20:08PM -0400, Jason Merrill wrote:
> On Thu, Sep 20, 2018 at 11:53 AM, Marek Polacek <pola...@redhat.com> wrote:
> > On Thu, Sep 20, 2018 at 11:25:38AM -0400, Jason Merrill wrote:
> >> On Wed, Sep 19, 2018 at 9:50 PM, Marek Polacek <pola...@redhat.com> wrote:
> >> > Aaaand this addresses
> >> > <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87150#c11>,
> >> > as I promised earlier. I hope I got it right.
> >> >
> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >> >
> >> > 2018-09-19 Marek Polacek <pola...@redhat.com>
> >> >
> >> > PR c++/87109 - wrong ctor with maybe-rvalue semantics.
> >> > * call.c (build_user_type_conversion_1): Refine the maybe-rvalue
> >> > check to only return if we're converting from a base class.
> >> >
> >> > * g++.dg/cpp0x/ref-qual19.C: Adjust the expected results.
> >> > * g++.dg/cpp0x/ref-qual20.C: New test.
> >> >
> >> > diff --git gcc/cp/call.c gcc/cp/call.c
> >> > index ddf0ed044a0..4bbd77b9cef 100644
> >> > --- gcc/cp/call.c
> >> > +++ gcc/cp/call.c
> >> > @@ -4034,9 +4034,13 @@ build_user_type_conversion_1 (tree totype, tree
> >> > expr, int flags,
> >> > conv->bad_p = true;
> >> >
> >> > /* We're performing the maybe-rvalue overload resolution and
> >> > - a conversion function is in play. This isn't going to work
> >> > - because we would not end up with a suitable constructor. */
> >> > - if ((flags & LOOKUP_PREFER_RVALUE) && !DECL_CONSTRUCTOR_P (cand->fn))
> >> > + a conversion function is in play. If we're converting from
> >> > + a base class to a derived class, reject the conversion. */
> >> > + if ((flags & LOOKUP_PREFER_RVALUE)
> >> > + && !DECL_CONSTRUCTOR_P (cand->fn)
> >> > + && CLASS_TYPE_P (fromtype)
> >> > + && CLASS_TYPE_P (totype)
> >> > + && DERIVED_FROM_P (fromtype, totype))
> >>
> >> Here fromtype is the type we're converting from, and what we want to
> >> reject is converting the return value of the conversion op to a base
> >> class. CLASS_TYPE_P (fromtype) will always be true, since it has a
> >> conversion op. And I think we also want to handle the case of totype
> >> being a reference.
> >
> > I think I totally misunderstood what this was about. It's actually about
> > this case
> >
> > struct Y { int y; };
> > struct X : public Y { int x; };
> >
> > struct A {
> > operator X();
> > };
> >
> > Y
> > fn (A a)
> > {
> > return a;
> > }
> >
> > where we want to avoid slicing of X when converting X to Y, yes?
>
> Yes.
Got it. So I think the following is the real fix then:
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2018-09-20 Marek Polacek <pola...@redhat.com>
PR c++/87109 - wrong ctor with maybe-rvalue semantics.
* call.c (build_user_type_conversion_1): Refine the maybe-rvalue
check to only return if we're converting the return value to a base
class.
* g++.dg/cpp0x/ref-qual19.C: Adjust the expected results.
* g++.dg/cpp0x/ref-qual20.C: New test.
diff --git gcc/cp/call.c gcc/cp/call.c
index ddf0ed044a0..b2ca667c8b4 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -4034,10 +4034,12 @@ build_user_type_conversion_1 (tree totype, tree expr,
int flags,
conv->bad_p = true;
/* We're performing the maybe-rvalue overload resolution and
- a conversion function is in play. This isn't going to work
- because we would not end up with a suitable constructor. */
+ a conversion function is in play. Reject converting the return
+ value of the conversion function to a base class. */
if ((flags & LOOKUP_PREFER_RVALUE) && !DECL_CONSTRUCTOR_P (cand->fn))
- return NULL;
+ for (conversion *t = cand->second_conv; t; t = next_conversion (t))
+ if (t->kind == ck_base)
+ return NULL;
/* Remember that this was a list-initialization. */
if (flags & LOOKUP_NO_NARROWING)
diff --git gcc/testsuite/g++.dg/cpp0x/ref-qual19.C
gcc/testsuite/g++.dg/cpp0x/ref-qual19.C
index 8494b83e5b0..50f92977c49 100644
--- gcc/testsuite/g++.dg/cpp0x/ref-qual19.C
+++ gcc/testsuite/g++.dg/cpp0x/ref-qual19.C
@@ -85,13 +85,13 @@ int
main ()
{
C c1 = f (A());
- if (c1.i != 1)
+ if (c1.i != 2)
__builtin_abort ();
C c2 = f2 (A());
if (c2.i != 2)
__builtin_abort ();
C c3 = f3 ();
- if (c3.i != 1)
+ if (c3.i != 2)
__builtin_abort ();
C c4 = f4 ();
if (c4.i != 2)
@@ -100,13 +100,13 @@ main ()
if (c5.i != 2)
__builtin_abort ();
D c6 = f6 (B());
- if (c6.i != 3)
+ if (c6.i != 4)
__builtin_abort ();
D c7 = f7 (B());
if (c7.i != 4)
__builtin_abort ();
D c8 = f8 ();
- if (c8.i != 3)
+ if (c8.i != 4)
__builtin_abort ();
D c9 = f9 ();
if (c9.i != 4)
diff --git gcc/testsuite/g++.dg/cpp0x/ref-qual20.C
gcc/testsuite/g++.dg/cpp0x/ref-qual20.C
index e69de29bb2d..c8bd43643af 100644
--- gcc/testsuite/g++.dg/cpp0x/ref-qual20.C
+++ gcc/testsuite/g++.dg/cpp0x/ref-qual20.C
@@ -0,0 +1,70 @@
+// PR c++/87109
+// { dg-do run { target c++11 } }
+
+#include <utility>
+
+struct Y {
+ int y;
+ Y(int y_) : y(y_) { }
+};
+struct X : public Y {
+ int x;
+ X(int x_, int y_) : x(x_), Y(y_) { }
+};
+
+struct A {
+ operator X() & { return { 0, 2 }; }
+ operator X() && { return { 0, -1 }; }
+};
+
+Y
+f (A a)
+{
+ return a;
+}
+
+Y
+f2 (A a)
+{
+ return std::move (a);
+}
+
+Y
+f3 ()
+{
+ A a;
+ return a;
+}
+
+Y
+f4 ()
+{
+ A a;
+ return std::move (a);
+}
+
+Y
+f5 ()
+{
+ return A();
+}
+
+int
+main ()
+{
+ Y y1 = f (A());
+ if (y1.y != 2)
+ __builtin_abort ();
+ Y y2 = f2 (A());
+ if (y2.y != -1)
+ __builtin_abort ();
+ Y y3 = f3 ();
+ if (y3.y != 2)
+ __builtin_abort ();
+ Y y4 = f4 ();
+ if (y4.y != -1)
+ __builtin_abort ();
+ Y y5 = f5 ();
+ if (y5.y != -1)
+ __builtin_abort ();
+}
