PR tree-optimization/83671 - Fix for false positive reported by…

PR tree-optimization/83671 - Fix for false positive reported by -Wstringop-overflow does not work with inlining

gcc/testsuite/ChangeLog:

	PR tree-optimization/83671
	* gcc.dg/strlenopt-40.c: New test.
	* gcc.dg/strlenopt-41.c: New test.

gcc/ChangeLog:

	PR tree-optimization/83671
	* builtins.c (c_strlen): Unconditionally return zero for the empty
	string.
	Use -Warray-bounds for warnings.
	* gimple-fold.c (get_range_strlen): Handle non-constant lengths
	for non-constant array indices with COMPONENT_REF, arrays of
	arrays, and pointers to arrays.
	(gimple_fold_builtin_strlen): Determine and set length range for
	non-constant character arrays.

From-SVN: r256457

gcc/ChangeLog

+2018-01-10  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/83671
+	* builtins.c (c_strlen): Unconditionally return zero for the empty
+	string.
+	Use -Warray-bounds for warnings.
+	* gimple-fold.c (get_range_strlen): Handle non-constant lengths
+	for non-constant array indices with COMPONENT_REF, arrays of
+	arrays, and pointers to arrays.
+	(gimple_fold_builtin_strlen): Determine and set length range for
+	non-constant character arrays.
+
 2018-01-10  Aldy Hernandez  <aldyh@redhat.com>
 
 	PR middle-end/81897

gcc/builtins.c

@@ -621,6 +621,9 @@ c_strlen (tree src, int only_value)
 	  return NULL_TREE;
 	}
 
+      if (!maxelts)
+	return ssize_int (0);
+
       /* We don't know the starting offset, but we do know that the string
 	 has no internal zero bytes.  We can assume that the offset falls
 	 within the bounds of the string; otherwise, the programmer deserves
@@ -651,7 +654,8 @@ c_strlen (tree src, int only_value)
       if (only_value != 2
 	  && !TREE_NO_WARNING (src))
         {
-	  warning_at (loc, 0, "offset %qwi outside bounds of constant string",
+	  warning_at (loc, OPT_Warray_bounds,
+		      "offset %qwi outside bounds of constant string",
 		      eltoff);
           TREE_NO_WARNING (src) = 1;
         }

gcc/gimple-fold.c

@@ -1299,7 +1299,7 @@ static bool
 get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
 		  bool fuzzy, bool *flexp)
 {
-  tree var, val;
+  tree var, val = NULL_TREE;
   gimple *def_stmt;
 
   /* The minimum and maximum length.  The MAXLEN pointer stays unchanged
@@ -1311,15 +1311,34 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
     {
       /* We can end up with &(*iftmp_1)[0] here as well, so handle it.  */
       if (TREE_CODE (arg) == ADDR_EXPR
-	  && TREE_CODE (TREE_OPERAND (arg, 0)) == ARRAY_REF
-	  && integer_zerop (TREE_OPERAND (TREE_OPERAND (arg, 0), 1)))
+	  && TREE_CODE (TREE_OPERAND (arg, 0)) == ARRAY_REF)
 	{
-	  tree aop0 = TREE_OPERAND (TREE_OPERAND (arg, 0), 0);
+	  tree op = TREE_OPERAND (arg, 0);
+	  if (integer_zerop (TREE_OPERAND (op, 1)))
+	    {
+	      tree aop0 = TREE_OPERAND (op, 0);
 	      if (TREE_CODE (aop0) == INDIRECT_REF
 		  && TREE_CODE (TREE_OPERAND (aop0, 0)) == SSA_NAME)
 		return get_range_strlen (TREE_OPERAND (aop0, 0),
 					 length, visited, type, fuzzy, flexp);
 	    }
+	  else if (TREE_CODE (TREE_OPERAND (op, 0)) == COMPONENT_REF && fuzzy)
+	    {
+	      /* Fail if an array is the last member of a struct object
+		 since it could be treated as a (fake) flexible array
+		 member.  */
+	      tree idx = TREE_OPERAND (op, 1);
+
+	      arg = TREE_OPERAND (op, 0);
+	      tree optype = TREE_TYPE (arg);
+	      if (tree dom = TYPE_DOMAIN (optype))
+		if (tree bound = TYPE_MAX_VALUE (dom))
+		  if (TREE_CODE (bound) == INTEGER_CST
+		      && TREE_CODE (idx) == INTEGER_CST
+		      && tree_int_cst_lt (bound, idx))
+		    return false;
+	    }
+	}
 
       if (type == 2)
 	{
@@ -1337,21 +1356,48 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
 	    return get_range_strlen (TREE_OPERAND (arg, 0), length,
 				     visited, type, fuzzy, flexp);
 
-	  if (TREE_CODE (arg) == COMPONENT_REF
+	  if (TREE_CODE (arg) == ARRAY_REF)
+	    {
+	      tree type = TREE_TYPE (TREE_OPERAND (arg, 0));
+
+	      while (TREE_CODE (type) == ARRAY_TYPE
+		     && TREE_CODE (TREE_TYPE (type)) == ARRAY_TYPE)
+		type = TREE_TYPE (type);
+
+	      val = TYPE_SIZE_UNIT (type);
+	      if (!val || integer_zerop (val))
+		return false;
+
+	      val = fold_build2 (MINUS_EXPR, TREE_TYPE (val), val,
+				 integer_one_node);
+	      /* Set the minimum size to zero since the string in
+		 the array could have zero length.  */
+	      *minlen = ssize_int (0);
+	    }
+	  else if (TREE_CODE (arg) == COMPONENT_REF
 	      && TREE_CODE (TREE_TYPE (TREE_OPERAND (arg, 1))) == ARRAY_TYPE)
 	    {
 	      /* Use the type of the member array to determine the upper
 		 bound on the length of the array.  This may be overly
 		 optimistic if the array itself isn't NUL-terminated and
 		 the caller relies on the subsequent member to contain
-		 the NUL.
+		 the NUL but that would only be considered valid if
+		 the array were the last member of a struct.
 		 Set *FLEXP to true if the array whose bound is being
 		 used is at the end of a struct.  */
 	      if (array_at_struct_end_p (arg))
 		*flexp = true;
 
 	      arg = TREE_OPERAND (arg, 1);
-	      val = TYPE_SIZE_UNIT (TREE_TYPE (arg));
+
+	      tree type = TREE_TYPE (arg);
+
+	      while (TREE_CODE (type) == ARRAY_TYPE
+		     && TREE_CODE (TREE_TYPE (type)) == ARRAY_TYPE)
+		type = TREE_TYPE (type);
+
+	      /* Fail when the array bound is unknown or zero.  */
+	      val = TYPE_SIZE_UNIT (type);
 	      if (!val || integer_zerop (val))
 		return false;
 	      val = fold_build2 (MINUS_EXPR, TREE_TYPE (val), val,
@@ -1361,11 +1407,18 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
 	      *minlen = ssize_int (0);
 	    }
 
-	  if (VAR_P (arg) 
-	      && TREE_CODE (TREE_TYPE (arg)) == ARRAY_TYPE)
+	  if (VAR_P (arg))
 	    {
-	      val = TYPE_SIZE_UNIT (TREE_TYPE (arg));
-	      if (!val || TREE_CODE (val) != INTEGER_CST || integer_zerop (val))
+	      tree type = TREE_TYPE (arg);
+	      if (POINTER_TYPE_P (type))
+		type = TREE_TYPE (type);
+
+	      if (TREE_CODE (type) == ARRAY_TYPE)
+		{
+		  val = TYPE_SIZE_UNIT (type);
+		  if (!val
+		      || TREE_CODE (val) != INTEGER_CST
+		      || integer_zerop (val))
 		    return false;
 		  val = wide_int_to_tree (TREE_TYPE (val),
 					  wi::sub(wi::to_wide (val), 1));
@@ -1374,6 +1427,7 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
 		  *minlen = ssize_int (0);
 		}
 	    }
+	}
 
       if (!val)
 	return false;
@@ -3462,12 +3516,44 @@ static bool
 gimple_fold_builtin_strlen (gimple_stmt_iterator *gsi)
 {
   gimple *stmt = gsi_stmt (*gsi);
-  tree len = get_maxval_strlen (gimple_call_arg (stmt, 0), 0);
-  if (!len)
-    return false;
-  len = force_gimple_operand_gsi (gsi, len, true, NULL, true, GSI_SAME_STMT);
-  replace_call_with_value (gsi, len);
+
+  wide_int minlen;
+  wide_int maxlen;
+
+  tree lenrange[2];
+  if (!get_range_strlen (gimple_call_arg (stmt, 0), lenrange)
+      && lenrange[0] && TREE_CODE (lenrange[0]) == INTEGER_CST
+      && lenrange[1] && TREE_CODE (lenrange[1]) == INTEGER_CST)
+    {
+      /* The range of lengths refers to either a single constant
+	 string or to the longest and shortest constant string
+	 referenced by the argument of the strlen() call, or to
+	 the strings that can possibly be stored in the arrays
+	 the argument refers to.  */
+      minlen = wi::to_wide (lenrange[0]);
+      maxlen = wi::to_wide (lenrange[1]);
+    }
+  else
+    {
+      unsigned prec = TYPE_PRECISION (sizetype);
+
+      minlen = wi::shwi (0, prec);
+      maxlen = wi::to_wide (max_object_size (), prec) - 2;
+    }
+
+  if (minlen == maxlen)
+    {
+      lenrange[0] = force_gimple_operand_gsi (gsi, lenrange[0], true, NULL,
+					      true, GSI_SAME_STMT);
+      replace_call_with_value (gsi, lenrange[0]);
       return true;
+    }
+
+  tree lhs = gimple_call_lhs (stmt);
+  if (lhs && TREE_CODE (lhs) == SSA_NAME)
+    set_range_info (lhs, VR_RANGE, minlen, maxlen);
+
+  return false;
 }
 
 /* Fold a call to __builtin_acc_on_device.  */

gcc/testsuite/ChangeLog

+2018-01-10  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/83671
+	* gcc.dg/strlenopt-40.c: New test.
+	* gcc.dg/strlenopt-41.c: New test.
+
 2018-01-10  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/83093

gcc/testsuite/g++.dg/warn/string1.C

 // PR c++/35652
-// { dg-options "-O" }
+// { dg-options "-O -Wall" }
 
 #include <string>
 int test() {

gcc/testsuite/gcc.dg/strlenopt-41.c

+/* PR tree-optimization/83671 - fix for false positive reported by
+   -Wstringop-overflow does not work with inlining
+   Verify that the length the empty string is folded to zero even at -O1
+   regardless of offset into it.
+   Also verify that the length of a non-empty string isn't folded given
+   a variable offset.
+   { dg-do compile }
+   { dg-options "-O1 -fdump-tree-optimized" } */
+
+#include "strlenopt.h"
+
+inline unsigned length (const char *s)
+{
+  return __builtin_strlen (s);
+}
+
+void check_length_cst (int i)
+{
+  unsigned len = length (&""[i]);
+
+  if (len)
+    __builtin_abort ();
+}
+
+void check_length_var (int i)
+{
+  unsigned len = length (&"1"[i]);
+
+  if (len != 1)
+    __builtin_abort ();
+}
+
+/* { dg-final { scan-tree-dump-times "abort" 1 "optimized" } }
+   { dg-final { scan-tree-dump-times "strlen" 1 "optimized" } } */