Re: C++ PATCH for c++/91962 - ICE with reference binding and qualification conversion

[Jason Merrill]

On 10/24/19 3:24 PM, Marek Polacek wrote:
When fixing c++/91889 (r276251) I was assuming that we couldn't have a ck_qual
under a ck_ref_bind, and I was introducing it in the patch and so this
+   if (next_conversion (convs)->kind == ck_qual)
+     {
+       gcc_assert (same_type_p (TREE_TYPE (expr),
+                    next_conversion (convs)->type));
+       /* Strip the cast created by the ck_qual; cp_build_addr_expr
+          below expects an lvalue.  */
+       STRIP_NOPS (expr);
+     }
in convert_like_real was supposed to handle it.  But that assumption was wrong
as this test shows; here we have "(int *)f" where f is of type long int, and
we're converting it to "const int *const &", so we have both ck_ref_bind and
ck_qual.  That means that the new STRIP_NOPS strips an expression it shouldn't
have, and that then breaks when creating a TARGET_EXPR.

Are there two conversions in that case, such that stripping only one 
would also fix the problem?

So we want to limit
the stripping to the new case only.  This I do by checking need_temporary_p,
which will be 0 in the new case.  Yes, we can set need_temporary_p when
binding a reference directly, but then we won't have a qualification
conversion.  It is possible to have a bit-field, convert it to a pointer,
and then convert that pointer to a more-qualified pointer, but in that case
we're not dealing with an lvalue, so gl_kind is 0, so we won't enter this
block in reference_binding:
  1747   if ((related_p || compatible_p) && gl_kind)

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

OK.

2019-10-24  Marek Polacek  <pola...@redhat.com>

        PR c++/91962 - ICE with reference binding and qualification conversion.
        * call.c (convert_like_real) <case ck_ref_bind>: Check need_temporary_p.

        * g++.dg/cpp0x/ref-bind7.C: New test.

diff --git gcc/cp/call.c gcc/cp/call.c
index 55d2abaaddd..d4674a77078 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -7386,7 +7386,8 @@ convert_like_real (conversion *convs, tree expr, tree fn, 
int argnum,
        /* direct_reference_binding might have inserted a ck_qual under
           this ck_ref_bind for the benefit of conversion sequence ranking.
           Ignore the conversion; we'll create our own below.  */
-       if (next_conversion (convs)->kind == ck_qual)
+       if (next_conversion (convs)->kind == ck_qual
+           && !convs->need_temporary_p)
          {
            gcc_assert (same_type_p (TREE_TYPE (expr),
                                     next_conversion (convs)->type));
diff --git gcc/testsuite/g++.dg/cpp0x/ref-bind7.C 
gcc/testsuite/g++.dg/cpp0x/ref-bind7.C
new file mode 100644
index 00000000000..e3675bc560d
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/ref-bind7.C
@@ -0,0 +1,13 @@
+// PR c++/91962 - ICE with reference binding and qualification conversion.
+// { dg-do compile { target c++11 } }
+
+template <typename a> class b {
+public:
+  void c(const a &);
+};
+class B {
+  void d();
+  b<const int *> e;
+};
+long f;
+void B::d() { e.c((const int *)f); }