re PR c++/84171 (ICE with -Wsign-compare)

	PR c++/84171
	* c-warn.c (warn_for_sign_compare): Bail out if any of the operands
	is erroneous.

	* g++.dg/warn/Wsign-compare-8.C: New test.

From-SVN: r258147

gcc/c-family/ChangeLog

+2018-03-02  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/84171
+	* c-warn.c (warn_for_sign_compare): Bail out if any of the operands
+	is erroneous.
+
 2018-03-02  Thomas Schwinge  <thomas@codesourcery.com>
 
 	* c-attribs.c (c_common_attribute_table): Remove "cilk simd

gcc/c-family/c-warn.c

@@ -1931,6 +1931,9 @@ warn_for_sign_compare (location_t location,
 		       tree op0, tree op1,
 		       tree result_type, enum tree_code resultcode)
 {
+  if (error_operand_p (orig_op0) || error_operand_p (orig_op1))
+    return;
+
   int op0_signed = !TYPE_UNSIGNED (TREE_TYPE (orig_op0));
   int op1_signed = !TYPE_UNSIGNED (TREE_TYPE (orig_op1));
   int unsignedp0, unsignedp1;

gcc/testsuite/ChangeLog

+2018-03-02  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/84171
+	* g++.dg/warn/Wsign-compare-8.C: New test.
+
 2018-03-02  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/84662

gcc/testsuite/g++.dg/warn/Wsign-compare-8.C

+// PR c++/84171
+// { dg-options "-Wsign-compare" }
+
+bool foo (char c)
+{
+  const int i = 0 = 0; // { dg-error "lvalue" }
+  return c = i;
+} // { dg-warning "control reaches" }