On Fri, Dec 06, 2019 at 02:31:55PM -0500, Jason Merrill wrote:
> > Note, just to double check g++ doesn't ICE on expr1 ? : expr2 GNU extension,
> > I also wrote the attached testcase, but unlike the testcase included in the
> > patch which behaves the same with patched g++ as does recent clang++, the
> > testcase with expr1 ? : expr2 (omitted second operand) actually never
> > extends the lifetime of any temporary (that is the baz function), unlike
> > clang++ which extends the lifetime of expr2 if expr1 is false, and doesn't
> > extend lifetime of anything if expr1 is true. This is outside of the scope
> > of the standard, so no idea what is correct, so I'm just asking how it
> > should behave.
>
> I would expect one or the other to be extended. I imagine that clang not
> extending expr1 is a bug due to however they avoid evaluating it twice.
>
> > extend_ref_init_temps_1 is never called in that case when the expression is
> > COND_EXPR.
>
> I think the problem is in build_conditional_expr_1, which needs to treat
> xvalues properly in the handling of this extension, i.e.
>
> > - if (lvalue_p (arg1))
> > + if (glvalue_p (arg1))
> > arg2 = arg1 = cp_stabilize_reference (arg1);
Indeed, that fixes it and you've preapproved a patch doing that on IRC, which
I've
committed to trunk now that it successfully bootstrapped/regtested on
x86_64-linux and i686-linux. Thanks.
2019-12-07 Jason Merrill <ja...@redhat.com>
Jakub Jelinek <ja...@redhat.com>
PR c++/92831
* call.c (build_conditional_expr_1): For ?: with omitted middle
operand use cp_stabilize_reference if arg1 is glvalue_p rather than
just if it is lvalue_p.
* g++.dg/ext/temp-extend1.C: New test.
--- gcc/cp/call.c.jj 2019-12-06 21:15:48.842199643 +0100
+++ gcc/cp/call.c 2019-12-06 22:01:18.737636630 +0100
@@ -5077,7 +5077,7 @@ build_conditional_expr_1 (const op_locat
warn_for_omitted_condop (loc, arg1);
/* Make sure that lvalues remain lvalues. See g++.oliva/ext1.C. */
- if (lvalue_p (arg1))
+ if (glvalue_p (arg1))
arg2 = arg1 = cp_stabilize_reference (arg1);
else
arg2 = arg1 = cp_save_expr (arg1);
--- gcc/testsuite/g++.dg/ext/temp-extend1.C.jj 2019-12-06 22:10:45.489814074
+0100
+++ gcc/testsuite/g++.dg/ext/temp-extend1.C 2019-12-06 22:10:09.495374051
+0100
@@ -0,0 +1,43 @@
+// PR c++/92831
+// { dg-do run { target c++11 } }
+// { dg-options "" }
+
+template<typename T> using id = T;
+struct S { S () : s (false) { ++c; } S (bool x) : s (x) { ++c; } ~S () { --c;
}; bool s; static int c; };
+int S::c = 0;
+
+void
+foo (int i)
+{
+ const bool&& a
+ = id<S[3]>{false, true, false}[i].s
+ ? id<S[2]>{true, false}[i].s : id<S[4]>{true, false, true, false}[i].s;
+ if (S::c != (i ? 2 : 4))
+ __builtin_abort ();
+}
+
+void
+baz (int i)
+{
+ const bool&& a = id<S[3]>{false, true, false}[i].s
+ ? : id<S[4]>{true, false, true, false}[i].s;
+ if (S::c != (i ? 3 : 4))
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ foo (0);
+ if (S::c != 0)
+ __builtin_abort ();
+ foo (1);
+ if (S::c != 0)
+ __builtin_abort ();
+ baz (0);
+ if (S::c != 0)
+ __builtin_abort ();
+ baz (1);
+ if (S::c != 0)
+ __builtin_abort ();
+}
Jakub
