c++: Mangling of dependent conversions [PR91377]

We skip over other conversion codes when mangling expressions, we should do
the same with IMPLICIT_CONV_EXPR.

gcc/cp/ChangeLog
2020-04-04  Jason Merrill  <jason@redhat.com>

	PR c++/91377
	* mangle.c (write_expression): Skip IMPLICIT_CONV_EXPR.

gcc/cp/ChangeLog

+2020-04-04  Jason Merrill  <jason@redhat.com>
+
+	PR c++/91377
+	* mangle.c (write_expression): Skip IMPLICIT_CONV_EXPR.
+
 2020-04-04  Patrick Palka  <ppalka@redhat.com>
 
 	PR c++/94205

gcc/cp/mangle.c

@@ -2875,6 +2875,7 @@ write_expression (tree expr)
   /* Skip NOP_EXPR and CONVERT_EXPR.  They can occur when (say) a pointer
      argument is converted (via qualification conversions) to another type.  */
   while (CONVERT_EXPR_CODE_P (code)
+	 || code == IMPLICIT_CONV_EXPR
 	 || location_wrapper_p (expr)
 	 /* Parentheses aren't mangled.  */
 	 || code == PAREN_EXPR

gcc/testsuite/g++.dg/abi/mangle75.C

+// PR c++/91377
+// { dg-do compile { target c++11 } }
+
+struct f {
+  static constexpr int d = 3;
+  typedef int e;
+};
+template <int a> struct x { };
+template <typename g, g j, g m> using n = x<j + m>;
+template <typename ac> auto v() -> n<typename ac::e, 0, ac::d>;
+void af() { v<f>(); }
+
+// { dg-final { scan-assembler "_Z1vI1fE1xIXplLi0EsrT_1dEEv" } }