re PR tree-optimization/83444 (missing strlen optimization on a member array of a local struct)

	PR tree-optimization/83444
	* tree-ssa-strlen.c (strlen_check_and_optimize_stmt): For the
	character load case, if get_stridx on MEM_REF's operand doesn't
	look usable, retry with get_addr_stridx.

	* gcc.dg/strlenopt-38.c: New test.

From-SVN: r255835

gcc/ChangeLog

+2017-12-19  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/83444
+	* tree-ssa-strlen.c (strlen_check_and_optimize_stmt): For the
+	character load case, if get_stridx on MEM_REF's operand doesn't
+	look usable, retry with get_addr_stridx.
+
 2017-12-19  Alexandre Oliva <aoliva@redhat.com>
 
 	PR debug/83422

gcc/testsuite/ChangeLog

@@ -5,6 +5,9 @@
 
 2017-12-19  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/83444
+	* gcc.dg/strlenopt-38.c: New test.
+
 	PR testsuite/83454
 	* gcc.dg/tree-ssa/cswtch-4.c: Require nonpic effective target.
 	* gcc.dg/tree-ssa/cswtch-5.c: Likewise.

gcc/testsuite/gcc.dg/strlenopt-38.c

@@ -36,3 +36,14 @@ baz (void)
   if (s.b[0] != 0)
     abort ();
 }
+
+void
+boo (void)
+{
+  struct S s;
+  strcpy (s.b, "012");
+  strcpy (s.c, "");
+  strcpy (s.b, s.c);
+  if (strlen (s.b) != 0)
+    abort ();
+}

gcc/tree-ssa-strlen.c

@@ -3155,14 +3155,27 @@ strlen_check_and_optimize_stmt (gimple_stmt_iterator *gsi)
 	  {
 	    tree off = integer_zero_node;
 	    unsigned HOST_WIDE_INT coff = 0;
-	    int idx = -1;
+	    int idx = 0;
 	    tree rhs1 = gimple_assign_rhs1 (stmt);
 	    if (code == MEM_REF)
 	      {
 		idx = get_stridx (TREE_OPERAND (rhs1, 0));
-		off = TREE_OPERAND (rhs1, 1);
+		if (idx > 0)
+		  {
+		    strinfo *si = get_strinfo (idx);
+		    if (si
+			&& si->nonzero_chars
+			&& TREE_CODE (si->nonzero_chars) == INTEGER_CST
+			&& (wi::to_widest (si->nonzero_chars)
+			    >= wi::to_widest (off)))
+		      off = TREE_OPERAND (rhs1, 1);
+		    else
+		      /* This case is not useful.  See if get_addr_stridx
+			 returns something usable.  */
+		      idx = 0;
+		  }
 	      }
-	    else
+	    if (idx <= 0)
 	      idx = get_addr_stridx (rhs1, NULL_TREE, &coff);
 	    if (idx > 0)
 	      {