re PR middle-end/81782 (Yet another -Wmaybe-uninitialized false positive with empty array)

2017-12-08  Richard Biener  <rguenther@suse.de>

	PR middle-end/81782
	* tree-ssa-uninit.c (warn_uninitialized_vars): Properly
	handle accesses outside of zero-sized vars.

	* gcc.dg/uninit-pr81782.c: New testcase.

From-SVN: r255512

gcc/ChangeLog

+2017-12-08  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81782
+	* tree-ssa-uninit.c (warn_uninitialized_vars): Properly
+	handle accesses outside of zero-sized vars.
+
 2017-12-08  Martin Jambor  <mjambor@suse.cz>
 
 	PR tree-optimization/83141

gcc/testsuite/ChangeLog

+2017-12-08  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81782
+	* gcc.dg/uninit-pr81782.c: New testcase.
+
 2017-12-08  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* g++.dg/opt/pr83252.C: Add -mclear-hwcap on *-*-solaris*.

gcc/testsuite/gcc.dg/uninit-pr81782.c

+/* { dg-do compile } */
+/* { dg-options "-Wmaybe-uninitialized" } */
+
+int
+foo (void)
+{
+  char empty_array[] = { };
+  int i, ret = 0;
+
+  for (i = 0; i < (int) (sizeof (empty_array) / sizeof (empty_array[0])); i++)
+    ret = empty_array[i]; /* { dg-bogus "uninitialized" } */
+
+  return ret;
+}

gcc/tree-ssa-uninit.c

@@ -296,8 +296,8 @@ warn_uninitialized_vars (bool warn_possibly_uninitialized)
 	         variable.  */
 	      if (DECL_P (base)
 		  && ref.size != -1
-		  && ref.max_size == ref.size
-		  && (ref.offset + ref.size <= 0
+		  && ((ref.max_size == ref.size
+		       && ref.offset + ref.size <= 0)
 		      || (ref.offset >= 0
 			  && DECL_SIZE (base)
 			  && TREE_CODE (DECL_SIZE (base)) == INTEGER_CST