[PATCH v2] c++: ICE with invalid structured bindings [PR107276]

[Marek Polacek <polacek@redhat.com>]

On Mon, Oct 24, 2022 at 10:31:50AM -0400, Jason Merrill wrote:
> On 10/21/22 19:29, Marek Polacek wrote:
> > This test ICEs in C++23 because we reach the new code in do_auto_deduction:
> > 
> > 30468   if (cxx_dialect >= cxx23
> > 30469       && context == adc_return_type
> > 30470       && (!AUTO_IS_DECLTYPE (auto_node)
> > 30471           || !unparenthesized_id_or_class_member_access_p (init))
> > 30472       && (r = treat_lvalue_as_rvalue_p (maybe_undo_parenthesized_ref (init),
> > 30473                                         /*return*/true)))
> > 
> > where 'init' is "VIEW_CONVERT_EXPR<<<< error >>>>(y)", and then the move
> > in treat_lvalue_as_rvalue_p returns error_mark_node whereupon
> > set_implicit_rvalue_p crashes.
> > 
> > I don't think such V_C_Es are useful so let's not create them.  But that
> > won't fix the ICE so I'm checking the return value of move.  A structured
> > bindings decl can have an error type, that is set in cp_finish_decomp:
> > 
> >   8908           TREE_TYPE (first) = error_mark_node;
> > 
> > therefore I think treat_lvalue_as_rvalue_p just needs to cope.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > 	PR c++/107276
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* typeck.cc (treat_lvalue_as_rvalue_p): Check the return value of move.
> > 
> > gcc/ChangeLog:
> > 
> > 	* tree.cc (maybe_wrap_with_location): Don't create a location wrapper
> > 	when the type is erroneous.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/cpp2a/decomp4.C: New test.
> > ---
> >   gcc/cp/typeck.cc                     | 7 ++++++-
> >   gcc/testsuite/g++.dg/cpp2a/decomp4.C | 8 ++++++++
> >   gcc/tree.cc                          | 3 ++-
> >   3 files changed, 16 insertions(+), 2 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/cpp2a/decomp4.C
> > 
> > diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> > index 16e7d85793d..5ca191759f6 100644
> > --- a/gcc/cp/typeck.cc
> > +++ b/gcc/cp/typeck.cc
> > @@ -10726,7 +10726,12 @@ treat_lvalue_as_rvalue_p (tree expr, bool return_p)
> >     if (DECL_CONTEXT (retval) != current_function_decl)
> >       return NULL_TREE;
> >     if (return_p)
> > -    return set_implicit_rvalue_p (move (expr));
> > +    {
> > +      expr = move (expr);
> > +      if (expr == error_mark_node)
> > +	return NULL_TREE;
> > +      return set_implicit_rvalue_p (expr);
> > +    }
> >     /* if the operand of a throw-expression is a (possibly parenthesized)
> >        id-expression that names an implicitly movable entity whose scope does not
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/decomp4.C b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
> > new file mode 100644
> > index 00000000000..28b3f172b53
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
> > @@ -0,0 +1,8 @@
> > +// PR c++/107276
> > +// { dg-do run { target c++20 } }
> > +
> > +auto f(auto x) {
> > +  auto [y] = x; // { dg-error "cannot decompose" }
> > +  return y;
> > +}
> > +int i = f(0);
> > diff --git a/gcc/tree.cc b/gcc/tree.cc
> > index 81a6ceaf181..4e5b1df4d85 100644
> > --- a/gcc/tree.cc
> > +++ b/gcc/tree.cc
> > @@ -14352,7 +14352,8 @@ maybe_wrap_with_location (tree expr, location_t loc)
> >     /* For now, don't add wrappers to exceptional tree nodes, to minimize
> >        any impact of the wrapper nodes.  */
> > -  if (EXCEPTIONAL_CLASS_P (expr))
> > +  if (EXCEPTIONAL_CLASS_P (expr)
> > +      || (TREE_TYPE (expr) && EXCEPTIONAL_CLASS_P (TREE_TYPE (expr))))
> 
> I think check error_operand_p instead; I don't think it makes sense to look
> for other exceptional nodes in TREE_TYPE.

Makes sense.  I don't suppose you want to replace the whole condition with
error_operand_p, only what comes after ||.  Updated patch below, thanks.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
This test ICEs in C++23 because we reach the new code in do_auto_deduction:

30468   if (cxx_dialect >= cxx23
30469       && context == adc_return_type
30470       && (!AUTO_IS_DECLTYPE (auto_node)
30471           || !unparenthesized_id_or_class_member_access_p (init))
30472       && (r = treat_lvalue_as_rvalue_p (maybe_undo_parenthesized_ref (init),
30473                                         /*return*/true)))

where 'init' is "VIEW_CONVERT_EXPR<<<< error >>>>(y)", and then the move
in treat_lvalue_as_rvalue_p returns error_mark_node whereupon
set_implicit_rvalue_p crashes.

I don't think such V_C_Es are useful so let's not create them.  But that
won't fix the ICE so I'm checking the return value of move.  A structured
bindings decl can have an error type, that is set in cp_finish_decomp:

 8908           TREE_TYPE (first) = error_mark_node;

therefore I think treat_lvalue_as_rvalue_p just needs to cope.

	PR c++/107276

gcc/cp/ChangeLog:

	* typeck.cc (treat_lvalue_as_rvalue_p): Check the return value of move.

gcc/ChangeLog:

	* tree.cc (maybe_wrap_with_location): Don't create a location wrapper
	when the type is erroneous.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/decomp4.C: New test.
---
 gcc/cp/typeck.cc                     | 7 ++++++-
 gcc/testsuite/g++.dg/cpp2a/decomp4.C | 8 ++++++++
 gcc/tree.cc                          | 2 +-
 3 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/decomp4.C

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 16e7d85793d..5ca191759f6 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -10726,7 +10726,12 @@ treat_lvalue_as_rvalue_p (tree expr, bool return_p)
   if (DECL_CONTEXT (retval) != current_function_decl)
     return NULL_TREE;
   if (return_p)
-    return set_implicit_rvalue_p (move (expr));
+    {
+      expr = move (expr);
+      if (expr == error_mark_node)
+	return NULL_TREE;
+      return set_implicit_rvalue_p (expr);
+    }
 
   /* if the operand of a throw-expression is a (possibly parenthesized)
      id-expression that names an implicitly movable entity whose scope does not
diff --git a/gcc/testsuite/g++.dg/cpp2a/decomp4.C b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
new file mode 100644
index 00000000000..d1b0c90ee26
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/decomp4.C
@@ -0,0 +1,8 @@
+// PR c++/107276
+// { dg-do compile { target c++20 } }
+
+auto f(auto x) {
+  auto [y] = x; // { dg-error "cannot decompose" }
+  return y;
+}
+int i = f(0);
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 81a6ceaf181..04603c8c902 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -14352,7 +14352,7 @@ maybe_wrap_with_location (tree expr, location_t loc)
 
   /* For now, don't add wrappers to exceptional tree nodes, to minimize
      any impact of the wrapper nodes.  */
-  if (EXCEPTIONAL_CLASS_P (expr))
+  if (EXCEPTIONAL_CLASS_P (expr) || error_operand_p (expr))
     return expr;
 
   /* Compiler-generated temporary variables don't need a wrapper.  */

base-commit: 131d18e928a3ea1ab2d3bf61aa92d68a8a254609
-- 
2.37.3