c++: ICE when mangling operator name [PR98545]

r11-6301 added some asserts in mangle.c, and now we trip over one of
them.  In particular, it's the one asserting that we didn't get
IDENTIFIER_ANY_OP_P when mangling an expression with a dependent name.

As this testcase shows, it's possible to get that, so turn the assert
into an if and write "on".  That changes the mangling in the following
way:

With this patch:

$ c++filt _ZN1i1hIJ1adS1_EEEDTcldtdefpTonclspcvT__EEEDpS2_
decltype (((*this).(operator()))((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)

G++10:
$ c++filt _ZN1i1hIJ1adS1_EEEDTcldtdefpTclspcvT__EEEDpS2_
decltype (((*this).(operator()))((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)

clang++/icc:
$ c++filt _ZN1i1hIJ1adS1_EEEDTclonclspcvT__EEEDpS2_
decltype ((operator())((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)

This is now tracked in PR98756.

gcc/cp/ChangeLog:

	PR c++/98545
	* mangle.c (write_member_name): Emit abi_warn_or_compat_version_crosses
	warnings regardless of abi_version_at_least.
	(write_expression): When the expression is a dependent name
	and an operator name, write "on" before writing its name.

gcc/ChangeLog:

	PR c++/98545
	* doc/invoke.texi: Update C++ ABI Version 15 description.

gcc/testsuite/ChangeLog:

	PR c++/98545
	* g++.dg/abi/mangle76.C: New test.

1 files changed, 10 insertions, 3 deletions

diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 11eb896..0a9e5aa 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2868,9 +2868,10 @@ write_member_name (tree member)
 {
   if (identifier_p (member))
     {
-      if (abi_version_at_least (11) && IDENTIFIER_ANY_OP_P (member))
+      if (IDENTIFIER_ANY_OP_P (member))
 	{
-	  write_string ("on");
+	  if (abi_version_at_least (11))
+	    write_string ("on");
 	  if (abi_warn_or_compat_version_crosses (11))
 	    G.need_abi_warning = 1;
 	}
@@ -3349,7 +3350,13 @@ write_expression (tree expr)
   else if (dependent_name (expr))
     {
       tree name = dependent_name (expr);
-      gcc_assert (!IDENTIFIER_ANY_OP_P (name));
+      if (IDENTIFIER_ANY_OP_P (name))
+	{
+	  if (abi_version_at_least (15))
+	    write_string ("on");
+	  if (abi_warn_or_compat_version_crosses (15))
+	    G.need_abi_warning = 1;
+	}
       write_unqualified_id (name);
     }
   else