re PR tree-optimization/35468 (LHS of assignment can be folded to a constant causing ICE)

	PR tree-optimization/35468
	* tree-ssa-ccp.c (fold_stmt_r): Don't fold reads from constant
	string on LHS.

	* gcc.dg/pr35468.c: New test.
	* gcc.c-torture/compile/pr35468.c: New test.

From-SVN: r142598

gcc/ChangeLog

+2008-12-09  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/35468
+	* tree-ssa-ccp.c (fold_stmt_r): Don't fold reads from constant
+	string on LHS.
+
 2008-12-09  Richard Guenther  <rguenther@suse.de>
 
 	PR tree-optimization/38445

gcc/testsuite/ChangeLog

+2008-12-09  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/35468
+	* gcc.dg/pr35468.c: New test.
+	* gcc.c-torture/compile/pr35468.c: New test.
+
 2008-12-08  Jason Merrill  <jason@redhat.com>
 
 	PR c++/38410

gcc/testsuite/gcc.c-torture/compile/pr35468.c

+/* PR tree-optimization/35468 */
+
+void
+foo (void)
+{
+  *(char *) "c" = 'x';
+}

gcc/testsuite/gcc.dg/pr35468.c

+/* PR tree-optimization/35468 */
+/* { dg-do compile  }*/
+/* { dg-options "-O2 -fno-tree-dce" } */
+
+char *const f(void)
+{
+  char *const line = "/dev/ptyXX";
+  line[8] = 1;
+  return line;
+}

gcc/tree-ssa-ccp.c

@@ -2191,6 +2191,9 @@ fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data)
 
       t = maybe_fold_stmt_indirect (expr, TREE_OPERAND (expr, 0),
 				    integer_zero_node);
+      /* Avoid folding *"abc" = 5 into 'a' = 5.  */
+      if (wi->is_lhs && t && TREE_CODE (t) == INTEGER_CST)
+	t = NULL_TREE;
       if (!t
 	  && TREE_CODE (TREE_OPERAND (expr, 0)) == ADDR_EXPR)
 	/* If we had a good reason for propagating the address here,
@@ -2219,8 +2222,10 @@ fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data)
 	 Otherwise we'd be wasting time.  */
     case ARRAY_REF:
       /* If we are not processing expressions found within an
-	 ADDR_EXPR, then we can fold constant array references.  */
-      if (!*inside_addr_expr_p)
+	 ADDR_EXPR, then we can fold constant array references.
+	 Don't fold on LHS either, to avoid folding "abc"[0] = 5
+	 into 'a' = 5.  */
+      if (!*inside_addr_expr_p && !wi->is_lhs)
 	t = fold_read_from_constant_string (expr);
       else
 	t = NULL;