On Wed, 10 Feb 2021, Jason Merrill wrote:
> On 2/9/21 5:12 PM, Patrick Palka wrote:
> > On Tue, 2 Feb 2021, Jason Merrill wrote:
> >
> > > On 2/2/21 12:19 AM, Patrick Palka wrote:
> > > > In this testcase, we're crashing because the lookup of operator+ from
> > > > within the generic lambda via lookup_name finds multiple bindings
> > > > (namely C1::operator+ and C2::operator+) and returns a TREE_LIST
> > > > thereof, something which maybe_save_operator_binding isn't prepared to
> > > > handle.
> > > >
> > > > Since we already discard the result of lookup_name when it returns a
> > > > class-scope binding here, it seems cleaner (and equivalent) to instead
> > > > communicate to lookup_name that we don't want such bindings in the first
> > > > place. While this change seems like an improvement on its own, it also
> > > > fixes the mentioned PR, because the call to lookup_name now returns
> > > > NULL_TREE rather than a TREE_LIST of (unwanted) class-scope bindings.
> > > >
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > > > trunk/9/10?
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > PR c++/97582
> > > > * name-lookup.c (op_unqualified_lookup): Pass BLOCK_NAMESPACE to
> > > > lookup_name in order to ignore class-scope bindings, rather
> > > > than discarding them after the fact.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > PR c++/97582
> > > > * g++.dg/cpp0x/lambda/lambda-template17.C: New test.
> > > > ---
> > > > gcc/cp/name-lookup.c | 11
> > > > +++--------
> > > > gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C | 8 ++++++++
> > > > 2 files changed, 11 insertions(+), 8 deletions(-)
> > > > create mode 100644
> > > > gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
> > > >
> > > > diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
> > > > index 52e4a630e25..46d6cc0dfa4 100644
> > > > --- a/gcc/cp/name-lookup.c
> > > > +++ b/gcc/cp/name-lookup.c
> > > > @@ -9213,17 +9213,12 @@ op_unqualified_lookup (tree fnname)
> > > > return NULL_TREE;
> > > > }
> > > > - tree fns = lookup_name (fnname);
> > > > + /* We don't need to remember class-scope functions or declarations,
> > > > + normal unqualified lookup will find them again. */
> > > > + tree fns = lookup_name (fnname, LOOK_where::BLOCK_NAMESPACE);
> > >
> > > Hmm, I'd expect this to look past class-scope declarations to find
> > > namespace-scope declarations, but we want class decls to hide decls in an
> > > outer scope.
> >
> > D'oh, good point. But IIUC, even if we did return (and later inject at
> > instantiation time) namespace-scope declarations that were hidden by
> > class-scope declarations, wouldn't the lookup at instantiation time
> > still find and prefer the class-scope bindings (as desired)? It seems
> > to me that the end result might be the same, but I'm not sure.
>
> The injection happens in the function parameter binding level, so I'd expect
> it to be found before class bindings.
Oops, I didn't look at push_operator_bindings closely enough. Never
mind about that idea then.
>
> > Alternatively, would it be safe to assume that if lookup_name returns an
> > ambiguous result, then the result must consist of class-scope
> > declarations and so we can discard it?
>
> That isn't true in general:
>
> inline namespace A { int i; }
> inline namespace B { int i; }
> int main() { return i; } // ambiguous lookup
>
> though I think it is true for functions. But if the result is ambiguous, you
> can look at the first element to see if it's from class scope.
I see, that's good to know. So something like this?
-- >8 --
Subject: [PATCH] c++: Fix ICE from op_unqualified_lookup [PR97582]
In this testcase, we're crashing because the lookup of operator+ from
within the generic lambda via lookup_name finds multiple bindings
(namely C1::operator+ and C2::operator+) and returns a TREE_LIST
thereof, something which op_unqualified_lookup (and
push_operator_bindings) isn't prepared to handle.
This patch makes op_unqualified_lookup and push_operator_bindings handle
an ambiguous lookup result appropriately.
gcc/cp/ChangeLog:
PR c++/97582
* name-lookup.c (op_unqualified_lookup): Handle an ambiguous
lookup result by discarding it if the first element is
a class-scope declaration, otherwise return it.
(push_operator_bindings): Handle an ambiguous lookup result by
doing push_local_binding on each element in the list.
gcc/testsuite/ChangeLog:
PR c++/97582
* g++.dg/cpp0x/lambda/lambda-template17.C: New test.
---
gcc/cp/name-lookup.c | 16 ++++++++++++----
.../g++.dg/cpp0x/lambda/lambda-template17.C | 8 ++++++++
2 files changed, 20 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index 1f4a7ac1d0c..27af21d9ac9 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -9219,11 +9219,15 @@ op_unqualified_lookup (tree fnname)
/* Remember we found nothing! */
return error_mark_node;
- tree d = is_overloaded_fn (fns) ? get_first_fn (fns) : fns;
- if (DECL_CLASS_SCOPE_P (d))
+ tree fn = fns;
+ if (TREE_CODE (fn) == TREE_LIST)
+ fn = TREE_VALUE (fn);
+ if (is_overloaded_fn (fn))
+ fn = get_first_fn (fn);
+ if (DECL_CLASS_SCOPE_P (fn))
/* We don't need to remember class-scope functions or declarations,
normal unqualified lookup will find them again. */
- fns = NULL_TREE;
+ return NULL_TREE;
return fns;
}
@@ -9302,7 +9306,11 @@ push_operator_bindings ()
if (tree val = TREE_VALUE (binds))
{
tree name = TREE_PURPOSE (binds);
- push_local_binding (name, val, /*using*/true);
+ if (TREE_CODE (val) == TREE_LIST)
+ for (tree v = val; v; v = TREE_CHAIN (v))
+ push_local_binding (name, TREE_VALUE (v), /*using*/true);
+ else
+ push_local_binding (name, val, /*using*/true);
}
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
new file mode 100644
index 00000000000..6cafbab8cb0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
@@ -0,0 +1,8 @@
+// PR c++/97582
+// { dg-do compile { target c++11 } }
+
+struct C1 { void operator+(); };
+struct C2 { void operator+(); };
+struct C3 : C1, C2 {
+ template <class T> void get() { [] (T x) { +x; }; }
+};
--
2.30.0.452.gfb7fa4a1fd
