re PR middle-end/32135 (bogus array-ref fold triggering array overflow warning)

	PR middle-end/32135
	* tree-ssa-ccp.c (maybe_fold_offset_to_array_ref): Do not construct
	references above array bounds.  This might trigger bounds checks for
	pointers to arrays.

From-SVN: r131502

4 files changed, 45 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 045118a..6cd0af8 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2008-01-12  Jan Hubicka  <jh@suse.cz>
+
+	PR middle-end/32135
+	* tree-ssa-ccp.c (maybe_fold_offset_to_array_ref): Do not construct
+	references above array bounds.  This might trigger bounds checks for
+	pointers to arrays.
+
 2008-01-12  Sebastian Pop  <sebastian.pop@amd.com>
 
 	* tree-ssa-ter.c (free_temp_expr_table): Free num_in_part and
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 34b4ec1..b067970 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2008-01-13  Jan Hubicka  <jh@suse.cz>
+
+	PR middle-end/32135
+	* gcc.dg/pr32135.c: new.
+
 2008-01-12  Doug Kwan  <dougkwan@google.com>
 
 	* gcc.dg/qual-return-1.c: Add -Wignored-qualifiers.
diff --git a/gcc/testsuite/gcc.dg/pr32135.c b/gcc/testsuite/gcc.dg/pr32135.c
new file mode 100644
index 0000000..4459656
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr32135.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-Warray-bounds -O2" } */
+struct PhaseEntryType
+{
+  char raw_field[50 + 1];
+};
+int
+ParsePhase (char in_cols[15][250], struct PhaseEntryType *P)
+{
+  __builtin_strncpy (P->raw_field, in_cols[2], 50);
+}
diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index 15f14c4..f9f1217 100644
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -1588,6 +1588,7 @@ maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type)
 {
   tree min_idx, idx, idx_type, elt_offset = integer_zero_node;
   tree array_type, elt_type, elt_size;
+  tree domain_type;
 
   /* If BASE is an ARRAY_REF, we can pick up another offset (this time
      measured in units of the size of elements type) from that ARRAY_REF).
@@ -1659,9 +1660,10 @@ maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type)
      low bound, if any, convert the index into that type, and add the
      low bound.  */
   min_idx = build_int_cst (idx_type, 0);
-  if (TYPE_DOMAIN (array_type))
+  domain_type = TYPE_DOMAIN (array_type);
+  if (domain_type)
     {
-      idx_type = TYPE_DOMAIN (array_type);
+      idx_type = domain_type;
       if (TYPE_MIN_VALUE (idx_type))
 	min_idx = TYPE_MIN_VALUE (idx_type);
       else
@@ -1681,6 +1683,24 @@ maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type)
   /* Make sure to possibly truncate late after offsetting.  */
   idx = fold_convert (idx_type, idx);
 
+  /* We don't want to construct access past array bounds. For example
+     char *(c[4]);
+
+     c[3][2]; should not be simplified into (*c)[14] or tree-vrp will give false
+     warning.  */
+  if (domain_type && TYPE_MAX_VALUE (domain_type) 
+      && TREE_CODE (TYPE_MAX_VALUE (domain_type)) == INTEGER_CST)
+    {
+      tree up_bound = TYPE_MAX_VALUE (domain_type);
+
+      if (tree_int_cst_lt (up_bound, idx)
+	  /* Accesses after the end of arrays of size 0 (gcc
+	     extension) and 1 are likely intentional ("struct
+	     hack").  */
+	  && compare_tree_int (up_bound, 1) > 0)
+	return NULL_TREE;
+    }
+
   return build4 (ARRAY_REF, elt_type, base, idx, NULL_TREE, NULL_TREE);
 }