c++: ICE with -Wduplicated-branches in template [PR117880]

In a template, for things like void() we'll create a CAST_EXPR with
a null operand.  That causes a crash with -Wduplicated-branches on:

  false ? void() : void();

because we do

  if (warn_duplicated_branches
      && (complain & tf_warning)
      && (arg2 == arg3 || operand_equal_p (arg2, arg3,
                                           OEP_ADDRESS_OF_SAME_FIELD)))

even in a template.  So one way to fix the ICE would be to check
!processing_template_decl.  But we can also do the following and
continue warning even in templates.

This ICE appeared with the removal of NON_DEPENDENT_EXPR; before,
operand_equal_p would bail on this code so there was no problem.

	PR c++/117880

gcc/ChangeLog:

	* fold-const.cc (operand_compare::operand_equal_p) <case tcc_unary>:
	Use OP_SAME_WITH_NULL instead of OP_SAME.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wduplicated-branches8.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

2 files changed, 18 insertions, 1 deletions

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 2e18553..af2851e 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -3470,7 +3470,7 @@ operand_compare::operand_equal_p (const_tree arg0, const_tree arg1,
 	  break;
 	}
 
-      return OP_SAME (0);
+      return OP_SAME_WITH_NULL (0);
 
 
     case tcc_comparison:
diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-branches8.C b/gcc/testsuite/g++.dg/warn/Wduplicated-branches8.C
new file mode 100644
index 0000000..f03c92a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wduplicated-branches8.C
@@ -0,0 +1,17 @@
+// PR c++/117880
+// { dg-do compile }
+// { dg-options "-Wduplicated-branches" }
+
+struct X {};
+
+template<typename>
+struct S {
+  void g1 () { false ? void() : void(); }   // { dg-warning "this condition has identical branches" }
+  void g2 () { false ? int() : int(); }	    // { dg-warning "this condition has identical branches" }
+  void g3 () { int() ? : int(); }	    // { dg-warning "this condition has identical branches" }
+  void g4 () { false ? int() : double(); }
+  void g5 () { false ? unsigned() : int(); }
+  void g6 () { false ? signed() : int(); }  // { dg-warning "this condition has identical branches" }
+  // Two different TARGET_EXPRs.
+  void g7 () { false ? X() : X(); }
+};