C++ PATCH to fix bogus warning with a non-type argument (PR c++/82541)

[Marek Polacek]

This PR complains about a bogus -Wduplicated-branches warning with a non-type
template argument.  That can be easily fixed with a new sentinel.  I also
noticed a missing tf_warning warning check, so I added it for good measure.

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

2018-01-02  Marek Polacek  <polacek@redhat.com>

	PR c++/82541
	* call.c (build_conditional_expr_1): Check complain before warning.
	* pt.c (tsubst_copy_and_build) <case COND_EXPR>: Suppress
	-Wduplicated-branches.

	* g++.dg/warn/Wduplicated-branches4.C: New test.

diff --git gcc/cp/call.c gcc/cp/call.c
index bd7666d72bb..c23a733978e 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -5343,6 +5343,7 @@ build_conditional_expr_1 (location_t loc, tree arg1, tree arg2, tree arg3,
   /* If the ARG2 and ARG3 are the same and don't have side-effects,
      warn here, because the COND_EXPR will be turned into ARG2.  */
   if (warn_duplicated_branches
+      && (complain & tf_warning)
       && (arg2 == arg3 || operand_equal_p (arg2, arg3, 0)))
     warning_at (EXPR_LOCATION (result), OPT_Wduplicated_branches,
 		"this condition has identical branches");
diff --git gcc/cp/pt.c gcc/cp/pt.c
index a8144e85a39..2c216eaebbe 100644
--- gcc/cp/pt.c
+++ gcc/cp/pt.c
@@ -17846,6 +17846,7 @@ tsubst_copy_and_build (tree t,
 	    exp2 = RECUR (TREE_OPERAND (t, 2));
 	  }
 
+	warning_sentinel s(warn_duplicated_branches);
 	RETURN (build_x_conditional_expr (EXPR_LOCATION (t),
 					 cond, exp1, exp2, complain));
       }
diff --git gcc/testsuite/g++.dg/warn/Wduplicated-branches4.C gcc/testsuite/g++.dg/warn/Wduplicated-branches4.C
index e69de29bb2d..7963c9e8ab5 100644
--- gcc/testsuite/g++.dg/warn/Wduplicated-branches4.C
+++ gcc/testsuite/g++.dg/warn/Wduplicated-branches4.C
@@ -0,0 +1,16 @@
+// PR c++/82541
+// { dg-do compile }
+// { dg-options "-Wduplicated-branches" }
+
+template<int N>
+struct AR
+{
+    char a1[N > 0 ? N : 1]; // { dg-bogus "this condition has identical branches" }
+    char a2[N > 0 ? 1 : 1]; // { dg-warning "this condition has identical branches" }
+};
+
+int
+main ()
+{
+    AR<1> w;
+}

	Marek